L I E> RARY OF THE UNIVERSITY OF ILLINOIS S3O.7 U V c c VH 1 -vOC> OM/5^-Of, fCM-^C'OO *C Ov Ov f (N >/) fS *t OC OC 00 CC 00 OCOCOOOCOCOCOCOCOOOO 00 00 00 00 00 vC>c!c>cr- r-- t^ i^. 12 S oc oo oo oo oooooooo oooooooo TCOO O vOOOO . ec -00 -~ "COOO M ^ 4j isi ^1.1 r^Sb sfl 1SS .SJL o o a - 8^ *j o c .2_ o Q-0 O EJj B -S3 w'o wws 1958] CHANGES IN POPCORN KERNELS AND COBS 11 | 1$ s ggss:: KS- CN) V 1 IM o T3 H 3 * 11 n Q 'Sti t"Of^ CN CN^^CN 10 O'OO'') O't ,J O) CNCN CN & w > si C o C t) O J3 to U ^ es when liar a ill aoooroooo oo oo oo oo oo oo oo oo oo oo oooooooo oooooooo CNOO^O OO*O-"O* > *^J'ONU^ON OOONO^* ^ON^IO Is j percentag If OOOt^-O t- t- t^ 00 00 < 00 00 00 00 OOOOOOOO OCtt^.t-- Jj<3 .si to U _e "3 in .0 w l p o CN -re -ONOCN roO^m w5-*Ot~ (A > 11 IV ved from 1 CO "3 00 -T)< -OONO OOrJI<> OOTfOOcN -M PM c V -CN -OOCN ~ W5tO f^flOt^ c re when rei M c c s o fN . -ON -0 -ON -" CN W>rO WjTCOt^ w l> :ent moi 2 r< c ^ u 1 1 OO ^* ~* O CN CN PO f> fO ^f O t^. c o rt txo -C a cent, to 13 perce were filled. fi (J S|| *4> CO 1 i hen harve "3 c co a o o 2 s D 2; 4; 1 ' J - f V i oisture adjus id cob moistt content at tt Date samplt *Jt-ON *1"OOO ^f*^lOOOOCNIO4 > ^'*" t^^^-00 *OCNONNO i "-& "j'l ESj; 3 "3 3 ill 12 BULLETIN NO. 625 [March, Bureau standards, and when completely filled with corn, had a capacity of 4 bushel baskets of lopop 6 and 4.5 baskets of Purdue 202. Two cribs were filled with each hybrid September 24, and two more were filled October 3. Because of dry weather, the moisture losses from the popcorn in the field and that in the cribs were practically the same until October 17. After October 17 the cribbed popcorn picked up moisture at practically the same rate as that left on the stalk in the field. Judging from these results, it is doubtful whether popcorn should be stored for long periods in outdoor cribs. Maturation in relation to the weather The rainfall during the actual harvests of 1954 and 1956 is shown in Tables 1 and 2 respectively. A three-year summary appears in Table 4. The 1956 season was the driest of the three under consideration, with September temperatures nearly normal and October temperatures much above normal. The 1954 season was characterized by one of the driest Septembers on record and above-normal rainfall in October. The temperatures were much above normal. The 1955 season was warm, with an extremely wet October. As might be expected, the drying rates per day were most rapid in 1956 and slowest in 1955. The belief commonly exists that heavy rains cause an increase in moisture content in the kernels and cobs of popcorn. While the plant is still actively developing and the vascular system functioning, this is probably true; but during all three harvest years the plants were definitely dying when harvest started. There is slight evidence in 1954 I Table 1) that the heavy rainfall of October 11 and 13 caused a nom- inal increase in kernel and cob moisture. In contrast, the extremely heavy rains October 5 and 6, 1955, totaling 5.97 inches, failed to have the slightest effect on kernel and cob moistures (Fig. 1). The moisture loss per day from kernels and cobs was most rapid in 1956 and slowest in 1955 (Table 4). However, consideration must be given to the initial and final moisture contents. In 1955 the initial moistures in the kernels of upper and lower ears of lopop 6 were 44 and 45 percent respectively (Fig. 1) and 45 percent for Purdue 202. The final moisture contents in the same order were 18, 19, and 16 percent. The total kernel moistures lost in 1955 were 26 and 26 percent for lopop 6 (Fig. 1), and 29 percent for Purdue 202. In 1956 the initial and final moisture contents in the kernels of both hybrids were much lower. lopop 6 and Purdue 202 lost kernel moistures totaling 25.2 and 25.9 percent respectively between September 14 and October 17, 1956 (Tables 2 and 3). Thus in 1955, 53 days were re- 1958] CHANGES IN POPCORN KERNELS AND COBS 13 a; J3 4J a v c o JS c OH T3 I u g 03 bD C '& Q ^0) H E"o 0.4) ES <1P 3 E i p 1 -" SN 00 t~-(S 1 + 1 1 ++ 1 1 1 + >/> -OtNUI tMTi' 00 +++ ++ 1 1 + 1 + 14 BULLETIN NO. 625 [March, 65 60 55 50 45 40 35 30 25 20 15 10 j^ /- COBS LOWER EARS t/V IOPOP 6-1955 V- KERNELS LOWER EARS 4.00 3.50 3.00 IJ 15 2.50 2.00. .50 1.00 .50 14 16 1921 23 262830 SEPTEMBER 3 57 10 12 14 17 19 21 24 2628 31 2 4 OCTOBER HARVEST DATES NOVEMBER Percent moisture in kernels and cobs of upper and lower ears of lopop 6 at successive harvest dates with rainfall records interpolated (averages of 5 ears, 1955). (Fig. 1) 7958] CHANGES IN POPCORN KERNELS AND COBS 15 quired for the popcorn to lose about the same percentage of moisture that was lost in 28 days in 1956 (Table 4). The mean temperatures in Table 4 fail to account for these differ- ences. In 1955, both September and October temperatures were above normal; but in 1956, September was below normal and October much above normal. The differences in drying rate must have been due to the heavy rainfall in 1955 as contrasted with the lack of rainfall in 1956. The curves in Fig. 1 do not show any increase in moisture in the kernels or cobs following a rain, but rain rather than low temperature lengthens the drying period. In 1956 popcorn was harvested to December 26, and the moisture content of both cobs and kernels increased gradually after October 17 (Tables 2 and 3) because of high humidity and above normal rainfall (Table 4). Fifteen foggy days between November 1 and December 22 would account for the increases in moisture content of the corn both outdoors and in cribs. Maturation of upper and lower ears compared The observations with respect to upper and lower ears were con- fined to lopop 6, which, under favorable conditions, develops a second ear. The harvest moistures for lopop 6 in 1955 (Fig. 1) show that the kernels of both upper and lower ears had about the same moisture content at the 45-percent stage; but as maturity advanced, the kernels from the upper ears lost moisture slightly faster until within the 30 to 35 percent range. Beyond this point the kernels matured at about the same rate. With a few exceptions, the cobs of the upper ears had less moisture than the cobs of the lower ears. The exceptions were prob- ably due to errors in sampling. Because the 1955 kernel moistures were recorded by single ears, each ear could be classified according to its respective cob moisture. The number of ears falling into each class varied from 1 to 15. New curves were then calculated, those for lopop 6 appearing in Fig. 2. These curves closely resemble the results obtained in 1954 by Bemis and Huelsen (4), who found that the cobs lost practically no moisture until the kernel moisture had decreased to 30 percent. Their data were based only on Purdue 202 and upper ears of lopop 6. The curve for upper ears of lopop 6 in Fig. 2 tends to follow this pattern; but the cobs of lower ears, which contain considerably more moisture, start to dry out rapidly when the kernel moisture reaches 35 percent. When both upper and lower ears were combined on a 50:50 basis, which would assume that all plants bore two ears (Fig. 2), the sharp drop in cob moisture occurred between 30 and 35 percent kernel moisture. 16 BULLETIN NO. 625 [March, 15 20 25 30 35 PERCENT KERNEL MOISTURE 40 45 Calculated curves showing relationship between upper and lower ears of lopop 6 at harvest (averages of 5 ears, 1955). (Fig- 2) ?958] CHANGES IN POPCORN KERNELS AND COBS 17 In Fig. 3 the 1952, 1953, and 1954 kernel-cob relationships based only on upper ears have been combined into a single curve and com- pared with the results obtained in 1955. The two curves for upper ears are so much alike that it may be assumed that the cobs of lopop 6 lose no moisture until the kernel moisture falls below 35 percent. The curve representing both upper and lower ears in a 50:50 ratio shows substantially the same trend. The lower ears alone also show a similar trend (Fig. 2). The kernel-cob moisture relationships of Purdue 202 in 1955 were also plotted on a single-ear basis, and the results were practically identical with those of lopop 6. Practical application of kernel-cob moisture relationships The moisture differences between upper and lower ears and be- tween kernels and cobs have a practical bearing at harvest. Unless the ears are artificially dried, very little popcorn is harvested at kernel moistures higher than 20 percent. At harvest the kernels of lower ears contain slightly more moisture than the kernels of upper ears, and the cobs of both upper and lower ears contain considerably more moisture than the kernels. The following summary shows the rela- tionship. Cob moisture at 20-percent kernel moisture (percent} 1952, '53, '54 lopop 6, upper ears 31.5 1953, '54 Purdue 202 33.0 1955 lopop 6, upper ears 28.5 1955 lopop 6, lower ears 31.5 1955 Purdue 202 31.5 1956 lopop 6, upper ears 35.0 1956 Purdue 202 29.0 Although variable from year to year, lopop 6 cobs contain 8.5 to 15 percent more moisture than the kernels at 20-percent kernel mois- ture. In Purdue 202 the range is from 9 to 13 percent. Thus, if popcorn containing 20-percent kernel moisture is placed in a crib, the kernels will absorb moisture from the cobs as shown by Huelsen and Thomp- son (11), and damage may result if weather conditions are unfavorable for drying. Relation between butt, center, and tip sections of ear At harvest. Huelsen and Thompson (11) and Huelsen and Bemis (13) found that artificial drying of popcorn on the ear was responsible for varying losses in popping expansion. When popcorn was 18 BULLETIN NO. 625 (March, 1955 UPPER AND LOWER 50=50 1952,1953,1954 AVERAGE UPPER EARS 20 25 30 PERCENT KERNEL MOISTURE Calculated curves showing relationship between kernel and cob moistures in lopop 6 at harvest. The combined averages of 5 upper ears for 1952, 1953, and 1954 are compared with the average of 5 ears in 1955. (Fig. 3) 7958] CHANGES IN POPCORN KERNELS AND COBS 19 dried in open mesh bags at room temperatures, popping was not ad- versely affected unless the kernel moisture exceeded 33 percent. Below 25-percent kernel moisture, the popping expansion of artificially dried popcorn was only slightly affected; but as the moistures increased above 25 percent, the losses in popping expansion became more severe. Out- door controls popped better than either room-dried corn or corn dried at 110 F. This fact led to the conclusion that speed of drying had something to do with the adverse effects, especially since the controls had the slowest rate of drying, and the rate was most rapid at 110 F. Shelled corn dried more rapidly than ear corn at equivalent tempera- tures, and popping quality was even more adversely affected. No reason could be assigned for these decreases in popping expan- sion, since both commercial dent and sweet corn seed are dried at 110 F. without injury to the germination. The theory was advanced that the various sections of the ear did not lose moisture at the same rate. Under slow drying conditions no damage would result, but rapid drying at 110 F. might impair popping expansion. Thus the kernels of an ear might average 25-percent moisture, but one ear section could be higher and another lower than this amount. All the damage might then be confined to one section of the ear. In 1955 the ears were divided into three sections, butt, center, and tip, in order to test this hypothesis. The ears were sectioned and shelled within two hours of harvest, thus eliminating the factor of absorption of moisture from the cobs by the kernels. A typical set of curves showing the kernel moisture relationships by ear section at harvest appears in Fig. 4 and the equivalent cob mois- tures in Fig. 5. The method used in calculating these curves was to assume that the regressions for the butt sections would be a straight line. If the tip and center sections dried at a uniform rate in relation to the butt sections, their respective regressions would also consist of straight lines. The data for the kernels of the upper ears of lopop 6 in Fig. 4 indicate that the tip and center sections deviated somewhat from a straight-line regression. Above 30-percent butt kernel moisture, the tip sections contained slightly more moisture than the butt and center sections. Below 22-percent butt kernel moisture, the center sec- tions tended to maintain a slightly higher moisture level than either the butt or tip sections. The lower ears of lopop 6 showed the same trends. In contrast, the tip sections of Purdue 202 contained slightly less moisture than the butt and center sections at all stages. For all 20 BULLETIN NO. 625 [March, 50 45 P 40 35 30 25 20 KERNELS FROM // TIP SECTIONS // W^ KERNELS FROM BUTT SECTIONS KERNELS FROM CENTER SECTION 20 25 30 35 40 PERCENT BUTT KERNEL MOISTURE 45 50 Calculated curves showing percent moisture at harvest in lopop 6 kernels from butt, center, and tip sections of upper ears. The center and tip sec- tions are plotted in relation to the butt section (averages of 5 ears, 1955). (Fig. 4) practical purposes, however, it may be assumed that the kernels of both hybrids dried at the same rate in all three parts of the ear. The cob moistures of lopop 6 upper ear sections (Fig. 5) differed widely enough to have some practical significance. The tip sections contained considerably less moisture than the butt and center sections at all stages below 50- to 47-percent butt moisture. Above 30-percent butt moisture, the center sections maintained a consistently lower moisture content than the butts. The lower ears of lopop 6 showed somewhat similar trends. Below 54-percent butt moisture, the tip sec- tions contained considerably less moisture than the butts. The center sections contained less moisture than the butt sections above 40-per butt moisture. Below this point the moistures were practical!} same. 7958] CHANGES IN POPCORN KERNELS AND COBS 21 The tip sections of lopop 6 and Purdue 202 showed similar trends, except that the Purdue 202 tip sections contained less moisture than the butt sections at all stages. Below 44-percent butt moisture, the tip sections of Purdue 202 contained less moisture than the center sections. Below 37-percent butt moisture, the butt and center sections contained about the same amount of moisture. In general, the differences in kernel moisture of the butt, center, and tip sections of both hybrids were too small to be worth consider- ing; but it is worth noting that the cob moistures of the tip and center sections of lopop 6 were lower than the butts. In Purdue 202 only the tip sections tended to maintain a consistently lower moisture than the butt sections. 55 50 40 35 30 25 20 BUTT SECTIONS- 25 30 35 40 45 PERCENT BUTT COB MOISTURE 50 55 C& ulated curves showing percent moisture at harvest in lopop 6 cobs fr butt, center, and tip sections of upper ears. The center and tip sec- t are plotted in relation to the butt section (averages of 5 ears, 1955). (Fig. 5) 22 BULLETIN NO. 625 [March, During drying at room temperatures. It may be assumed from these differences in initial cob moistures that the drying rates of the butt, center, and tip sections of the ears might differ under the en- vironmental conditions of an unheated attic room. The entire ears were placed in mesh bags and were sampled and sectioned as shown in Table 5. The total moisture losses were divided by the number of drying days to give the daily moisture loss. The kernels and cobs of the butt and tip sections lost moisture at a more rapid daily rate than the center sections of both lopop 6 and Purdue 202. And with one excep- tion, the center sections of the kernels and cobs contained more mois- ture at the end of the drying period than the butt and tip sections. The kernels from the butt sections of lopop 6 maintained a slightly lower moisture content than the tip and center sections during most of the drying period. In Purdue 202 the relationship between the ear sections varied, but the differences were small. All the data in Table 5 were calculated as curves, but only the cob moistures of lopop 6 upper ears are shown in Fig. 6. The butt and tip sections of the cobs maintained practically the same moisture content during the entire drying period. The moistures in the center sections were more variable. Above 40-percent cob moisture in lopop 6 (Fig. 6), and above 36 percent in Purdue 202, the center sections contained less moisture than the butt sections. Below 35-percent moisture, the center sections of the cobs of both hybrids contained more moisture than either butts or tips. Since the daily moisture losses of the center sections of the cobs were consistently lower than those of the butt and tip sections (Table 5), it is possible that some of the moisture in the centers of the cobs was transported to the two ends during the drying process. This possibility seemed to be confirmed by the final moistures in Table 5, where the center sections contained more moisture than the butt and tip sections. Relation Between Kernel Moistures, Cob Moistures, and Shelling Percentages At harvest Date of harvest had a considerable effect on shelling percentages. In 1955 lopop 6 and Purdue 202 were harvested at three different moisture levels. Each harvest was stored in mesh sacks hung in an unheated attic. The corn was sampled on Monday, Wednesday, and Friday of each week. The kernel and cob moistures, together with the shelling percentages, were recorded. The data were calculated as curves (Figs. 7 and 8). All three harvests dried at about the same rate J958] CHANGES IN POPCORN KERNELS AND COBS 23 8 O ) 2 3 A | " > 3 VO -t \r> D 0> i i Purdue 202 J o U 1 H 3 a 6 U a n 1 H C i ^- * * rj ro cs ts ro t*> 00 >O ui t^ 00 >O 00 * f*) ro r^ ^"f f*5 W fN CS -> PO O-< O^OOt'*5rs < O cs UJVOlOTffO CN * 00 l^ ^t o\ >o *t r> O ^C TC cs (N<-i * n fo cs ts ir< - -i w> ts * 00 10 10 * 00 ro rr> -H fT fO wj ro cs (N cs <->-. ro 8 t~- Tf O 00 00 O Tj" * t^ (S >O- Tf^rOfOfOCSCSCSCS^CS CS * >C ^ 00 Tf >O ^ CS O to t- - TJ-xtf, rOPOCSrtCSCS -H fO >o 10 O-r^fO vOvO'Oi^'fui **O CS CS CSCSCS -. rt 00 * O 00 "5 ro cs O\ 00 ! <-- ~C t~- (SO a : 5 i-. 3 3 "I rt 8 U en 00 vO O >O lO fO >C >O (^ wj 3 Ot^rorsOoOOtO'OrO'* v<5 O 5 S l H V ^ 'li - o 3 p 3 -M 3 CB u * *O > i"c ^ JS U CG H E V U 3 * V ^H r^iooo oot^ ro -*f< "5 "1 Tjl f> tS tN -H T(< U V ,0 6 ^ j. MMinesu>t > O "O Tf M O ro ^O fO i*) VO ^ ts 00 * ^ So O r fo t -H ui TJI to ^< to r~ -H >O t to ") !N to ID CS CS rt ro U V & cs 6 " JT! 00>C >O O TC roOOvOO 00 JJJ TJI TJ> to fO to - 'O Ov O 00 t^- \O Ov 00 Tt< O* -M Purdue 202 E (Averages o I o "5 BQ Q. H i TJ V CO rq w t-. > 10-H-.TJ-00 uir<5^-. U rC T)< 5 (N CN x -H ~ ro n K 5 o T3 V 1 8 > f-400 Ot~OCS\COOI^10 t~O U ro cs cscs cs cs cs < CO ffi "> T3 * c * rt i; vo 1 d D * rots cs-N H cs vE> PO CS CN C4 cs fO CSCSCS CS -< i-H rt i i i 4 I 3 5 3 o :::::::: :g : 3 >, g o ::::::::::: g : 3 >, 3 * Q !JI;Mli;1 CS'f^Oa rO'OOOO Pfc -.^-.-.cscscstsro _^ g, *j Cfl w *J X I :2^ Mi!i!i:ii!lf O M- 10 ^ O CS Tf t O * Eg r^ ^^^^rtCSCS C Q, J . (3 en IS s2J 24 BULLETIN NO. 625 [March, 55 50 40 35 I- UJ o o < 30 25 20 10 20 25 30 35 40 PERCENT BUTT MOISTURE 45 5O 55 Calculated curves showing percent moisture in lopop 6 cobs from butt, center, and tip sections of upper ears. The center and tip sections are plotted in relation to the butt section. The sections were sampled three times weekly while drying at room temperatures (averages of 3 ears, 1955). (Fig. 6) but the shelling percentages of the first series, harvested at 44- to 45- percent kernel moisture, were consistently the lowest. The second series, harvested at 30- to 33-percent kernel moisture, had shelling percentages as high as those from the final series, harvested at 19- to 21 -percent kernel moisture. Thus, from the standpoint of shelling percentage, nothing is gained by delaying harvest after the kernels reach 30- percent kernel moisture. Miles and Remmenga (16) discuss in detail the relationships of kernel to cob moistures in dent corn and the effect of their variation on shelling percentages. Following their lead, an attempt was made to utilize the kernel-cob moisture relationships which have just been discussed. 1958] CHANGES IN POPCORN KERNELS AND COBS 25 Kernel and cob moistures in lopop 6 were recorded for the five crop years 1952-1956, and in Purdue 202 for the four crop years 1953-1956. Using three years' data (1952-1954) on lopop 6 and two years' data (1953-1954) on Purdue 202, Bemis and Huelsen (3) com- puted a table showing the kernel-cob moisture relationships of these hybrids and estimated the shelling percentages within the kernel moisture range of 13 to 33 percent. They assumed that by the time the kernel moisture reached 33 percent both kernels and cobs would be fully mature, and the shelling percentages computed on a dry-weight basis would not change. From the data available they found that the 85 80 75 70 65 60 55 50 45 LOT C (ACTUAL)- LOT B (ACTUAL) SHELLING PERCENTAGES OF THREE LOTS OF IOPOP6 ACTUAL, AND ADJUSTED TO 13-PERCENT KERNEL MOISTURE -LOT A (ADJUSTED) 40 35 30 25 20 PERCENT KERNEL MOISTURE 15 10 Shelling percentages of lopop 6 harvested at three successive maturities and sampled three times weekly while drying at room temperatures, 1955. (Fig. 7) 26 BULLETIN NO. 625 [March, dry-weight shelling percentage was 83.7 percent for lopop 6 and 80.5 percent for Purdue 202. These shelling percentages were checked again in 1956. From the first 23 successive harvests of lopop 6, beginning September 19 in Table 2, the average dry-weight shelling percentage checked exactly at 83.7 percent. A similar check on Purdue 202, starting with the harvest of September 19 in Table 3, showed that the 23 85 80 75 70 65 o z 60 55 50 45 40 LOT C (ACTUAL) - LOT B (ACTUAL K LOT A (ACTUAL) SHELLING PERCENTAGES OF THREE LOTS OF PURDUE 202- ACTUAL,AND ADJUSTED TO 13- PERCENT KERNEL MOISTURE 45 40 35 30 25 PERCENT KERNEL MOISTURE 20 15 10 Shelling percentages of Purdue 202 harvested at three successive maturities and sampled three times weekly while drying at room temperatures, 1955. (Fig. 8) - K)] 1958] CHANGES IN POPCORN KERNELS AND COBS 27 harvests averaged 81.1 dry- weight shelling percent, only slightly higher than the 80.5 percent used by Bemis and Huelsen (3). The formula used by Bemis and Huelsen follows: Shelling percentage = 100 A [ 100 x (100 JK)"-^ X (C A is the average dry-weight shelling percentage 83.7 for lopop 6 and 80.5 for Purdue 202. C is the cob moisture. K is the kernel moisture. The values calculated by Bemis and Huelsen are reproduced in Table 6 under the headings "Calculated." To use the above formula, assume that a given lot of lopop 6 contains 25-percent kernel moisture. From Table 6 the cob moisture is 44.3 percent. Substituting, the formula now becomes: Shelling percentage = 1 on v * 7 f _ 100 44.3 _ ~| _ [lOO X (100 - 25.0) - 83.7 X (44.3 - 25.0) J ~ The calculated shelling percentage at harvest shown in Table 6 is 79.1 percent. The slight discrepancy of 0.2 percent is due to the fact that the calculations from the formula were plotted on a curve that had been smoothed. The calculated values in Table 6 were taken from the curve. The calculated shelling percentages were checked against actual shelling percentages from the 1955 and 1956 crops. The two percentages were close enough to justify using the calculated values to predict the probable shelling percentages of lopop 6 and Purdue 202. It is not difficult to compute shelling percentage tables for any hybrid if the kernel and cob moistures are obtained from six to ten harvests at various moistures between 33 and 13 percent. Smoothed curves may be drawn and the shelling percentages calculated from the formula shown above. The shelling percentages in Table 6 will prove useful in finding the shelling percentage at 13-percent kernel moisture for corn with kernel moistures up to 33 percent. For example, a lot of lopop 6 that tests 22-percent kernel moisture in the field has a calculated cob moisture of 39.9 percent and a shelling percentage of 79.7, or 71.5 at 13-percent kernel moisture. The conversion to 13-percent kernel mois- ture is as follows: A 100-pound lot of lopop 6 containing 22-percent kernel moisture will shell out 79.7 pounds of kernels. These kernels will contain 17.53 pounds of water (79.7 times 22 percent). The number of pounds of moisture-free kernels in 100 pounds of ear corn at harvest equals 79.7 28 BULLETIN NO. 625 [March, TJ 5 C w 3 6 w C 0) 1) bfl o rt I* O CO fc^ 1 A O C/3 3-8 w CO c s^ .2 ^ O 03 T3 CO DQ H ro H o *f r}< Tt t-. esOooooo f^O^f^Ov^O Tj*C"l^t-l/3f5 O IN Tj< 1O t~ 00 !> CS r^t^t^t^t^ oo ^> O PO to r* - O cs r^ cs'OOfjOt 0000000000 OOoOOOvO l^OvOO-^-" CSCSr^tOPOf 1958] CHANGES IN POPCORN KERNELS AND COBS 29 minus 17.53 or 62.17 pounds. To convert to kernels at 13-percent moisture, divide 62.17 by 100 minus 13 (62.17 divided by 87), which equals 0.715. To find the number of pounds of kernels containing 13- percent moisture, multiply 0.715 by 100, which equals 71.5 pounds. Table 6 shows that the shelling percentage of lopop 6 harvested at 22-percent kernel moisture and adjusted to 13-percent kernel moisture is 71.5. Hybrids like Purdue 202, which produce only one ear, present no problem. In contrast, lopop 6 produces a variable number of second ears. Eldredge and Thomas (10) show that Purdue 202 produced an average of 101 ears per 100 stalks in 1953, 1954, and 1955, and lopop 6 produced an average of 135 ears per 100 stalks during the same period. Since lower ears are usually smaller than upper ears, it is often assumed that their shelling percentage is lower. The calculated curves in Fig. 9 show that this assumption was true only when the kernel moisture exceeded 40 percent. When the shelling percentages were adjusted to 13-percent kernel moisture, the lower ears had the same or a slightly better shelling percentage at all kernel moistures than the upper ears. From corn cribs Miles and Remmenga (16) observed that the curve showing the relationship between kernel and cob moistures in dent corn taken directly from the field differed from the curve showing the relationship after two weeks' storage in a corn crib. The cribbed corn had a lower cob moisture at between 22- and 11 -percent kernel moisture than the corn harvested from the field. There were similar differences in kernel moisture. It follows that dent corn harvested from the field at any- where between 22- and 11-percent kernel moisture will have a different shelling percentage than corn with equivalent kernel moisture removed from the crib. In order to determine whether this hypothesis applies to popcorn, lopop 6 and Purdue 202 were each harvested twice at different mois- ture levels and placed in four outdoor cribs as previously described. Weekly samples were taken from the cribs between October 3 and December 26, 1956. These were checked against controls harvested from the field. The results (Tables 2 and 3) show that during the dry period between September 24 and October 10 the cribbed corn lost moisture at a more rapid rate than the standing corn; but by October 17 they were alike. Moderate rains started October 25, followed by numerous fogs. This weather increased both kernel and cob moistures, but there were no consistent differences between the cribbed corn and 30 BULLETIN NO. 625 [March, the corn remaining in the field (Tables 2 and 3). Consequently, shelling percentages were alike. Unlike corn in the field, ear corn stored under shelter is not subject to the wide variations of late fall weather. There- fore, corn standing in the field would have a higher kernel and cob moisture content because popcorn absorbs moisture from the air at a relatively rapid rate (12). 85 80 75 70 65 o 3 60 in 55 50 45 40 ACTUAL LOWER EARS- UPPER AND LOWER EARS COMBINED 50 UPPER EARS UPPER AND LOWER EARS COMBINED LOWER EARS SHELLING PERCENTAGES OF UPPER AND LOWER EARS OF KDPOP 6- ACTUAL, AND ADJUSTED TO 13-PERCENT KERNEL MOISTURE 45 40 35 30 PERCENT KERNEL MOISTURE 25 20 15 Shelling percentages of upper and lower ears of lopop 6 at harvest, 1955: (1) calculated on the actual kernel-moisture basis; and (2) adjusted to 13- percent kernel moisture. (Fig. 9) 1958] CHANGES IN POPCORN KERNELS AND COBS 31 FACTORS AFFECTING POPPING EXPANSION In addition to the actual moisture content of the kernels when popped, the morphological development or maturity of the kernels seems to have an important effect on popping expansion. In preliminary work Bemis and Huelsen (4) found that since the dry weights of cobs remained constant, the cobs were fully mature on the basis of constant dry weight by the time the kernels had reached 50-percent moisture content. The cobs did not lose moisture until the kernel moistures fell below 30 percent. The kernels accumulated dry matter until they reached 30-percent moisture, after which the cobs lost moisture more rapidly than the kernels. Dry matter or dry weights of the kernels were closely related to popping expansion, the pooled correlation coefficient being 0.976. Effect of Harvest Moisture During the experiments previously discussed it became apparent that popcorn reached its maximum popping expansion at a relatively early stage of maturity. Thus Huelsen and Bemis (13) found that lopop 6 and Purdue 202 could be considered fully mature on the basis of maximum popping expansion when the kernels reached 35- to 30- percent moisture. This conclusion is consistent with the results obtained by Kiesselbach (15) with dent corn. He found that translocation from the plant to the kernels had been completed 50 days after silking, at which time the kernels were too hard to be readily dented with the thumbnail and the kernel and cob moistures had reached 34 and 53 percent respectively. The 1954 harvests showed that maximum popping expansion was reached between 35- and 30-percent kernel moisture at harvest. A slight decline in expansion occurred in subsequent harvests, but no adequate explanation for this trend was found. In 1955 the ears were harvested in the same way except that separate records were kept on butt, center, and tip sections of the ears. The ears were dried at room temperatures and at 110 F. The curves for both lopop 6 and Purdue 202 were calculated, but only those for Purdue 202 are shown in Fig. 10. The maximum popping expansions of both hybrids coincided with the 30- to 25-percent moisture range, after which they decreased slightly as in 1954. In general, the center sections of the ears had the highest popping expansions and the tip sections the lowest. The butt sections were intermediate except when the kernel harvest moistures exceeded 38 percent. 32 BULLETIN NO. 625 [March, 40 35 30 25 20 40 35 30 25 20 15 i CD Z Q. Q. O Q. CENTERS TIPS 7 DRIED AT ROOM TEMPERATURE CENTERS DRIED AT 110 F. 45 40 35 30 25 20 PERCENT KERNEL MOISTURE AT HARVEST Popping expansion of Purdue 202 in relation to butt, center, and tip sections, p cent kernel moisture at harvest, and method of drying, 1955. (Fig- 1' J958] CHANGES IN POPCORN KERNELS AND COBS 33 The 1954 experiments were repeated in 1956, but neither the dry weights per kernel nor the popping expansions in Table 7 show any trend. The 1956 harvest season was almost completely rain-free and lasted only 28 days as compared with 52 days and 53 days in 1954 and 1955 respectively. Although the moisture loss per day from the ears was highest in 1956 (Table 4), the average popping expansion for the harvests below 30-percent kernel moisture were practically the same as in 1954 and 1955 (Table 8). The 1956 results (Table 7) again showed that harvesting popcorn at about 30-percent kernel moisture had no adverse effect on popping expansion. The principal respect in which the 1956 results differ from those obtained in 1954 and 1955 is in the absence of a decline in pop- ping expansion following a peak that varied from 33- to about 25- percent kernel moisture at harvest. Table 7. Popping Expansion and Dry Weights per Kernel as Related to Kernel Moisture at Harvest, 1956 lopop 6 Purdue 202 Percent kernel moisture at harvest Dry weight per kernel (mg.) Popping expansion (volumes) Percent kernel moisture at harvest Dry weight per kernel (mg.) Popping expansion (volumes)" 35.3 95.0 36.8 36.1 139.2 36.3 33.2 96.9 34.6 32.6 138.0 37.2 32.9 101.0 37.2 31.5 144.3 36.3 32.6 95.6 35.0 29.4 139.1 36.8 27.8 98.3 35.5 28.3 145.8 36.3 26.2 104.3 36.3 24.1 138.8 35.5 23.8 98.1 37.2 21.5 142.3 35.5 20.3 97.7 35.9 18.0 141.1 37.2 20.2 102.6 37.2 17.5 141.8 38.5 17.7 102.2 36.8 16.8 145.3 37.6 17.1 107.4 36.8 15.4 144.8 37.2 16.8 101.5 35.9 14.0 142.8 37.6 14.0 99.9 36.3 13.7 141.5 37.6 12.1 102.0 36.8 13.0 143.5 37.6 10.1 104.1 37.2 10.2 142.0 38.0 Average* 1 101.6 36.5 142.4 37.1 S.E.i" .82 .03 .41 .07 All samples were reconstituted with water to 12.5-percent kernel moisture. b For kernels below 30-percent harvest moisture. The correlation coefficients for the 1955 data were computed inde- pendently for butt, center, and tip sections, and were separated into three kernel moisture groups (Table 9). For popcorn dried at room temperatures, the correlations between popping expansion and kernel moistures 34 percent or above were very high. Between 33- and 30- percent kernel moisture the coefficients varied widely, and only one was significant at the 5-percent level. This coefficient of 0.967 would indicate a significant relation between increased kernel moisture and increased popping expansion in lopop 6 butt sections, except that it was based on only four degrees of freedom. Under these circumstances, 34 BULLETIN NO. 625 [March, Table 8. Average Dry Weight per Kernel and Popping Expansion of lopop 6 and Purdue 202 Below 30-Percent Kernel Moisture at Harvest (Dry Weights per cob are for entire moisture range at harvest) Dry weights Popping expansion Part of ear tested Per kernel (mg.) Per cob (grn.) Total volumes Cu. in. per 100 mg. 1954 Average lopop 6 Entire upper ear 104 .5+ . 56 14 .7 + .14 35 .5 + .17 .261 Butts Centers Tips Entire lower ear Purdue 202 Entire ear 153 .6+. 94 22 .8 + .16 38 .5 + .17 .284 Butts Centers Tips 1955 Average lopop 6 Entire upper ear 94 .7. 60 14 .9 + .10 35 .6 + .24 .264 Butts 106 .6+. 73 6 .1 + .09 35 .5 + .30 .261 Centers 95 .8+. 59 5 .1 + .04 35 .4 + .30 .261 Tips 79 .1. 62 3 .7 .06 33 .5 .25 .247 Entire lower ear 93 .2 + 1 .11 9 .5 .20 34 .2 .69 .254 Purdue 202 Entire ear 138 .8+. 79 21 .3 + .10 37 ,8 + .23 .281 Butts 150 .4+. 85 9 .1 .07 37 ,8 + .20 .279 Centers 142 .0+. 72 6 ,9 + .05 37 ,9 + .22 .279 Tips 122 ,2. 85 5 .3 + .06 34 .7 .22 .256 1956 Average lopop 6 Entire upper ear 100 .4+ . 91 14 .4 .28 36 ,5 .17 .269 Butts Centers Tips Entire lower ear Purdue 202 Entire ear 142, 4+ . 64 20. .26 37. 1 + .26 .273 Butts Centers Tips * Popping volume in cubic inches per 100 mg. of kernels, water-free basis. All samples were reconstituted with water to 12.5-percent kernel moisture. significance at the 5-percent level was open to question. Below 30- percent kernel moisture none of the coefficients was significant. The coefficients in Table 9 indicate that popping volumes increase signifi- cantly down to 34-percent kernel moisture at harvest. Later maturities did not have any significant effect. The lower or second ears of lopop 6 showed the same relationships between kernel moisture at harvest and popping expansion as the upper ears and the ears of Purdue 202 (Fig. 10). The only difference seemed to be in the slightly later stage of maturity at which the kernels of the lopop 6 lower ears gave the greatest popping expansion. Both upper and lower ears were characterized by decreased popping expan- sions as the kernel moistures dropped below 25 percent. 3958] CHANGES IN POPCORN KERNELS AND COBS 35 Effect of Artificial Drying Huelsen and Thompson (11) dried popcorn at 100, 110, 120, and 130 F. and found that none of these four drying temperatures had a definitely adverse effect on popping expansion. Huelsen and Bemis (13) showed definite reductions in popping expansion when Table 9. Correlations Among the Three Variables Kernel Moisture at Harvest, Popping Volume, and Dry Weight per Kernel, 1955 Correlation coefficients Correlated variables Butt sections Center sections Tip sections A. lopop 6 dried at room temperature Percent moisture at harvest X popping volume 1. 34% and above kernel moisture at harvest .900* 2. 30-33% kernel moisture at harvest 967* 3. Below 30% kernel moisture at harvest 388 Dry weight per kernel X popping volume 4. 34% and above kernel moisture at harvest 982* 5. 30-33% kernel moisture at harvest . 575 6. Below 30% kernel moisture at harvest 325 Percent moisture at harvest X dry weight per kernel 7. 34% and above kernel moisture .937* 8. 30-33% kernel moisture at harvest .364 9. Below 30% kernel moisture at harvest 572* B. Purdue 202 dried at room temperature Percent moisture at harvest X popping volume 1. 34% and above kernel moisture at harvest .959* 2. 30-33% kernel moisture at harvest 367 3. Below 30% kernel moisture at harvest . 186 Dry weight per kernel X popping volume 4. 34% and above kernel moisture at harvest 975* 5. 30-33% kernel moisture at harvest - .283 6. Below 30% kernel moisture at harvest 196 Percent moisture at harvest X dry weight per kernel 7. 34% and above kernel moisture at harvest .946* 8. 30-33% kernel moisture at harvest .996 9. Below 30% kernel moisture at harvest 366 C. lopop 6 dried at 110 F. Percent moisture at harvest X popping volume 1. 30-35% kernel moisture at harvest .894* 2. 25-29% kernel moisture at harvest .567 3. Below 25% kernel moisture at harvest .278 Dry weight per kernel X popping volume 4. 30-35% kernel moisture at harvest 865 5. 25-29% kernel moisture at harvest . 505 6. Below 25% kernel moisture at harvest 118 Percent moisture at harvest X dry weight per kernel 7. 30-35% kernel moisture at harvest . 790 8. 25-29% kernel moisture at harvest 307 9. Below 25% kernel moisture at harvest 564 D. Purdue 202 dried at 110 F. Percent moisture at harvest X popping volume 1. 30-35% kernel moisture at harvest .868 2. 25-29% kernel moisture at harvest .452 3. Below 25% kernel moisture at harvest 077 Dry weight per kernel X popping volume 4. 30-35% kernel moisture at harvest 695 5. 25-29% kernel moisture at harvest 753 6. Below 25% kernel moisture at harvest 601 Percent moisture at harvest X dry weight per kernel 7. 30-35% kernel moisture at harvest . 751 8. 25-29% kernel moisture at harvest .889 9. Below 25% kernel moisture at harvest . 1 78 .981* .388 .281 .986* .837 .298 .992* .174 .388 .956* .240 .297 .983* .142 .253 .948* .995 .349 .918* .779 .376 .873* .615 .352 .875* .192 .483 .794 .303 .265 .658 .411 .325 .639 .301 .032 .978* .156 .384 .983* .824 .438 .978* .672 .618* .944' .971 .035 .897* .813 .303 .935* .650 .488 .963' .882 .957' .092 .421 .847' .215 .298 .679 .556 .046 .468 .894 .227 .642 .830 .161 * Significant. ** Highly significant. 36 BULLETIN NO. 625 [March, popcorn of various maturities was dried at 110 F. However, these reductions became progressively smaller as maturity advanced; and when the kernel moisture dropped below 25 percent, there were no appreciable decreases in popping expansion due to drying with forced air at 110 F. Additional experiments in 1955 with lopop 6 and Purdue 202 showed that the popping expansions of identical lots of popcorn dried at room temperature and at 110 F. increased as maturity advanced. After reaching a peak, the popping expansions declined slightly. The maximum popping expansion of room-dried corn was attained around 30-percent kernel moisture at harvest regardless of ear section. When the corn was dried at 110 F., the maximum varied, depending upon the ear part. Butt and center sections of both hybrids reached a maxi- mum slightly over 25-percent kernel moisture at harvest. The tip sections of Purdue 202 fell within this range, but the tip sections of lopop 6 reached the maximum popping expansion around 23-percent kernel moisture at harvest. Taking into account the necessary moisture differential at harvest, the results for Purdue 202 (Fig. 10) and lopop 6 showed that room- dried popcorn popped slightly better than popcorn dried at 110 F. These results confirmed the feasibility of artificial drying as reported by Huelsen and Bemis (13). In 1956 further experiments were conducted on a somewhat differ- ent plan. Popcorn was harvested at two different dates (Table 10) and treated three different ways: placed in cribs and sampled periodically; dried at room temperatures; and dried at 110 F. The two hybrids were left in the field and sampled periodically (Tables 2 and 3). One of these harvests was selected on November 7 when the corn was fully mature (Table 10). The November 7 field harvests popped about the same as the room-dried samples and those taken from the cribs on the same day. The popping expansions of the lots dried at 110 F. were slightly lower, but exceeded 35 volumes according to the old scale. Effect of Low Temperatures It is generally believed that freezing is highly injurious to popping expansion. Eldredge (7) states that popcorn exposed to temperatures of 20 F. or lower may pop too poorly to be salable. Huelsen and Bemis (13) harvested lopop 6 and Purdue 202 at different kernel moistures and chilled both varieties of husked ears for 24 hours at 35 F. The ears of each variety were divided into two lots. Each lot was dried either at room temperatures or 110 F. Comparisons with controls showed that chilling had no adverse effect on popping. Addi- CHANGES IN POPCORN KERNELS AND COBS 37 S-i. : J2 cs to >o oo 'an' am 3 u = s s s fa fa o a v ^H VH 1-1 *- o (U 2 s rt 3 M JS O * cs 15 1 -a to.S a ^0 t- o El *c E-a B Q -*j ^ /i 4 0> 4-> "H a O f*; to o V j u *c3 c CO O 00 C^ ^2 -* I u "^ ** o 3 O _, O *5 3s i 3 +* K 3 rt if. ~s cs Q Q to O O cs -o v a t-l t? 1 o a^ ll H ^ ^^ .2^ *c u u c -j L) *g C^ o 2 rt t moistur drying jS U Es ^ rt 3 a c S ~ CS O 00 CS S i 3 1 to * 43 _c.2 t 12 IO 1O CS CN ^ kO'C 2 a c a c3 : 3 ^ J H ^ iJ o a c ft, x~- '- a a * C E V ESS ? " o o CO ^ 3 C 3 _2 *10 OMO W -. *J * U >, 'w oo iocs oocs csro csro ^ o i u 3 O 1 O ?^ U * cs * cs en" - ; -o 5 11 * "S CO O t~*O fjto OOtO 3. 3 4-1 2 3 ^ ^^ U CD 1 CS| CS _ 41 l 5 ^^ S u 3*- 3 T3 > a rt X > *}>'>+}> a o tJo a o t!o V c- si c/}/5 Oi& WA OZ. 8 . r/a " I. 3 CM rt ) Ov-r-t S|g ^"o I 4 >, ll ti cs cs !E ^ o o ^ cs cs So a a a = a A ao ^ ^ a h b o o 38 BULLETIN NO. 625 [March, tional harvests made at the same time were exposed to 10 F. for periods of 6 hours and 15 hours respectively, and then dried by forced heated air at 80 F. and 110 F. Freezing reduced popping expansion in two lots harvested at 29.65- and 31.00-percent kernel moisture, but two others with 17.55- and 23.40-percent moisture were not injured. Additional tests showed that when kernel moistures reached 20 percent, injuries due to freezing were either absent or negligible. Since the experiments failed to agree with the statements made by Eldredge (7), additional tests were undertaken in 1956. The data from these tests are summarized in Table 11. The husked ears were placed in open baskets under refrigeration at the temperatures indicated. Only one of the four lots of lopop 6 the lot harvested at 23.8-percent kernel moisture showed any material damage to popping expansion. Compared with the control, the popping expansion of this lot was reduced considerably by 40 below zero and only slightly by 25 F. Purdue 202 was definitely damaged by freezing when harvested at 28.3-percent moisture. At 18.5-percent moisture the damage was very slight, and at 17.5 and 13.7 percent almost no damage occurred. In general, the damage to both hybrids was relatively minor, and even the lowest popping expansion of the lots tested (875 cu. in. per lb., or 30 volumes on the old scale) would be acceptable for commercial use. Table 11. Effect on Popping Expansion of Freezing Popcorn Ears at Various Maturities, Followed by Drying at Room Temperature (Controls also dried at room temperature) Variety and planting Kernel moisture at harvest (percent) Treatment Popping expansion (cu. in. per lb.) m lopop 6, first 27.8 27.8 27.8 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 1038 1025 1050 lopop 6, first 20.3 20.3 20.3 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 1050 1138 1112 lopop 6. second 23.8 23.8 23.8 Control (not frozen) 24 hours at 40 F. 24 hours at +25 F. 1125 938 1050 lopop 6, first 20.2 20.2 20.2 Control (not frozen) 24 hours at 40 F. 24 hours at +25 F. 1088 1075 1100 Purdue 202, first 28.3 28.3 28.3 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 1062 912 962 Purdue 202, first 17.5 17.5 17.5 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 1125 1162 1125 Purdue 202. second 18.5 18.5 18.5 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 962 925 875 Purdue 202, first 13.7 13.7 13.7 Control (not frozen) 24 hours at -40 F. 24 hours at +25 F. 1100 1138 1125 * Divide by 29.24 to convert to volumes. All samples were reconstituted with water to 12.5- percent kernel moisture. J958] CHANGES IN POPCORN KERNELS AND COBS 39 Although the two separate experiments fail to agree with statements made by Eldredge (7), this fact does not mean that he is wrong. Assuming that frost or freezing alone may not be the only factor affecting popping expansion, lopop 6 and Purdue 202 were left in the field and harvested once a week between October 17 and December 26, 1956. The kernel moistures reached 10 percent by October 17, and then gradually increased until they reached 16 to 17 percent by De- cember 26 (Tables 2 and 3). Each harvest was placed in mesh bags and hung in an unheated attic. The controls consisted of two harvests as shown in Table 12. The field-harvested lots reached their peak popping volumes in late October and remained more or less static until late December. lopop 6 showed a greater tendency to decline than Purdue 202. The controls reached their peaks early in November, and tended to decline thereafter. It is obvious that the popcorn left in the field did not deteriorate any more than that stored in cribs, but it should be noted that the rainfall in November and December was fairly light ( see Tables 2 and 3 ) . Table 12. Popping Expansions of Popcorn Left in the Field Compared With Controls Sampled From Corn Cribs, 1956 In field until harvested Popping expansion of controls from corn crib (cu. in. per lb.)* Date harvested Percent kernel moisture at harvest Popping expansion' (cu. in. per Ib.) Harvested Sept. 24, kernel mois- ture high b Harvested Oct. 3, kernel mois- ture low b lopop 6 Oct. 3 17.7 1075 10 17.1 1075 1112 1075 17 10.1 1088 1100 1100 24 11.4 1125 1075 1088 31 12.1 1125 1100 1088 Nov. 7 12.6 1125 1112 1125 14 12.2 1100 1100 1138 21 13.1 1125 1075 1088 28 12.8 1100 1075 1050 Dec. 5 13.0 1125 1075 1062 12 14.5 1050 1088 1100 19 15.9 1012 962 1075 26 16.9 1050 987 1075 Purdue 202 Oct. 3 16.8 1100 10 13.0 1100 1062 1075 17 10.2 1112 1125 1088 24 11.1 1138 1062 1125 31 11.8 1138 1088 1050 Nov. 7 12.5 1162 1112 1138 14 11.9 1150 1125 1162 21 12.6 1150 1088 1100 28 12.6 1175 1088 1125 Dec. 5 13.1 1188 1100 1112 12 14.8 1112 1112 1150 19 15.2 1125 1050 1100 26 16.5 1088 988 1062 a Divide by 29.24 to convert to volumes. All samples were reconstituted with water to 12.5- percent kernel moisture. b September 24 and October 3 harvest moistures of lopop 6 kernels were 27.8 and 17.7 per- cent respectively, and 28.3 and 16.8 percent for Purdue 202. 40 BULLETIN NO. 625 [March, Effect of Alternate Wetting and Drying Since low temperatures alone and moderate rainfall such as pre- vailed in 1956 seemed to have only a slight effect on popping expansion, an experiment was set up to simulate the normal weather conditions in late October and in November. A single harvest of each of the two hybrids, lopop 6 and Purdue 202, was used for the controls as well as for the treatments. The controls were dried in mesh bags in an unheated attic. The treatments consisted of immersing the ears in water for vari- ous periods of time up to two hours. The soaked ears were then placed in boxes, covered with wet burlap sacks, and put in cold storage at 35 F. for 24 hours. They were then placed in the dryer described by Huel- sen and Bemis (13) and dried by means of unheated forced air for the periods shown in Table 13. Samples sufficiently large for moisture testing and popping were shelled after drying and stored in glass jars. The remaining ears were used to complete another cycle of soaking, cold storage, and drying until nine cycles had been completed. All samples were adjusted to 12.5-percent moisture before popping. The popping expansion of lopop 6 was not affected by the treat- ments until the sixth cycle had been completed (Table 13). The be- havior of Purdue 202 was different. Popping expansion decreased after Table 13. Effect on Popping Expansion of Alternately Soaking Ears and Drying Them by Forced Air at Room Temperature, 1956 Percent kernel moisture" Cycle Before After soaking soaking After drying Hours dried Mg. dry weight per kernel Popping expansion (cu. in. per lb.) b Control. First . . . Second. Third... Fourth. Fifth . . . Sixth. . . Seventh. Eighth.. Ninth. . 9.2 9.2 10.0 11.2 12.0 14.4 12.6 10.8 10.0 9.5 lopop 6 12.6 16.8 21.2 22.6 27.6 26.5 27.4 26.4 24.0 10.0 11.2 12.0 14.4 12.6 10.8 10.0 9.5 8.6 23.0 23.2 24.0 25.0 23.0 49.0 65.0 47.2 48.8 Purdue 202 102.2 102.6 102.1 96.8 96.3 99.2 101.2 100.3 101.8 97.8 1075 1050 1062 1075 1044 1050 1025 988 950 850 Control 8.9 145.3 1100 First 8.9 13.5 10.8 23.2 138.2 1050 Second 10.8 18.3 12.7 24.0 144.9 1038 Third 12.7 22.3 14.2 25.0 135.6 969 Fourth 14.2 26.2 16.2 23.0 144.1 1031 Fifth 16.2 30.1 13.0 49.0 138.8 1000 Sixth 13.0 28.9 11.6 65.0 140.5 938 Seventh 11.6 28.6 10.5 47.2 139.6 925 Eighth 10.5 26.0 9.4 48.8 138.6 875 Ninth 9.4 25.2 9.1 117.0 141.3 812 .7 pe 202. Controls came from same lots as the soaked treatments. b Divide by 29.24 to convert to volumes. All samples were reconstituted with water to 12.3- percent kernel moisture. 7958] CHANGES IN POPCORN KERNELS AND COBS 41 each of the first three cycles. For some reason it increased again after the fourth cycle, followed by successive decreases. The wetting fol- lowed by low temperatures and then drying seem to be the factors that reduce popping expansion. It should be noted that freezing was not involved, the treatments merely attempting to simulate the October- November weather frequently occurring at Urbana. After the first few soakings the kernels became discolored and the cobs assumed a soggy, water-soaked appearance. There was no evidence of mold or bacterial breakdown. All of the lopop 6 treatments popped normally; but beginning with the sixth cycle, the Purdue 202 hulls (pericarps) broke loose during popping -a condition that would be highly desirable if it could be attained without impairing popping expansion. Effect of Kernel Development The generally accepted method of determining maturity is by means of kernel moistures at harvest, and the grower assumes that his crop is ripe when the kernel moisture drops below 20 percent. This assump- tion is incorrect in two respects. First, this study has shown that popcorn is mature when the kernel moisture reaches 30 percent, and Kiesselbach (15) has shown that dent corn is mature when the kernel moisture reaches 34 percent. Second, it is false to assume that moisture content of the kernels is the true criterion of maturity when this term is taken to mean full morphological development. Under certain condi- tions the stalk dies prematurely, thus stopping translocation, which. in turn, inhibits full development of the kernels. The moisture content of these kernels may be at the optimum for popping, but popping ex- pansion will be below normal. In extreme cases the kernels are notice- ably smaller, but otherwise their appearance is normal. During the three-year period (1954-1956) covered by these experi- ments, all but one planting of popcorn developed normally. No frost damage occurred in any of the three years. The underdeveloped lot was planted June 14, 1956, on high ground. A combination of dry weather (Table 4) and severe European corn borer damage caused premature drying of the stalks and lack of proper kernel development. This condi- tion was especially noticeable in Purdue 202. Both lopop 6 and Purdue 202 were harvested, and before shelling, the ears were sorted into classes according to kernel development. The better developed ears had a higher kernel moisture content, a higher dry weight per kernel, and a higher popping expansion than the less well-developed ears. The extent of the underdevelopment of the kernels (Table 14) is apparent when the dry weights are compared with 42 BULLETIN NO. 625 [March, Table 14. Kernel Development of lopop 6 and Purdue 202 Popcorn in Relation to Kernel Dry Weight and Popping Expansion, 1956 Moisture Dry weight Popping expansion 1 at harvest (percent) Kernel development per kernel (mg.) Cu. in. per Ib. Volume equivalent 21.9 lopop 6 fair 92.6 1125 38.5 20.1 poor 83.3 1062 36.0 16.4 Purdue 202 poor 108.7 1012 35.0 16.3 100.0 925 32.0 14.0 extremely poor 84.5 788 27.0 a All samples were reconstituted with water to 12.5-percent kernel moisture. those for the more normally developed kernels (Table 8). The surpris- ing part of the data in Table 14 is the fairly high popping expansion of the poorly developed ears. Only the Purdue 202 ears with "extremely poor" kernel development popped below the trade standard of 30 volumes. It is obvious that the popping expansion of poorly developed popcorn can be improved either by sorting out the substandard ears or by rigorous control of the milling process. Effect of Dry Weight per Kernel Proper development of the kernel is usually necessary to insure maximum popping expansion. As mentioned in the previous section, the kernel is fully developed or mature when the storage of nutrients is complete. This point is characterized by no further gains in dry weight. In preliminary work, Bemis and Huelsen (4) showed that no further gains in dry weight occurred after the kernel moisture reached 30 per- cent. A great deal of additional work has been done subsequently on the problem of ear maturity. For all practical purposes there were no changes in dry weight per kernel of lopop 6 when the moisture fell below 27 percent in 1954. At this point the dry weight of 105.0 mg. was equal to the average of 104.5 mg. (Table 15). In Purdue 202 the kernel dry weight reached 153.5 mg. at 28.1-percent moisture, equalling the average of 153.6 mg. When harvesting started in 1954, the cob moistures were 53.8 and 49.0 percent for lopop 6 and Purdue 202 respectively (Table 15). But it should be noted that the changes in dry weight per cob were very minor, indicating that the cobs attained full maturity much sooner than the kernels. More detailed studies in 1955 showed very similar results (Tables 16 and 17). Excluding minor variations, the dry weights per kernel of 7958] CHANGES IN POPCORN KERNELS AND COBS 43 c O '35 a a X w bJO PH o e C 3 rt S . 2 ** OJ 4) 04 U SO) 3 C T) fS i & Ov 00 t- t^- t^- t^ ^O fTf^Tfro rcp^r^f^cs (N PS rs CN cs ~ ^ *-* ^ ^H *-H T-* ^H -N CN CS CN rf) roOoOtT) l-t5O)O^ f: * O -H r*5 O CM fO <-i O t^ >O ^0 )(SOOOO> OOO>0000>O OO tst rO O ^ -O t~ O "TO >c t^f^c OOOOO 44 BULLETIN NO. 625 [March, i sZ, S ! 3-2 S (NOfN O CSOOOOOOtN IO1OOOOOO CS O O O O >O 00 O 00 1 i 1 3 5 3 a-g NNCN PC PCPCPCPCPC PCPCPCP^PC J?PCPCPCPC PCPCPCPC S 3 * X 3 X 3 4 Jin 4 "bif^ cs 9 ~s 8^ PCCN>COM OPCO'OO Os^^O>\O O^'COOI^ Tj"t~rN 5 i- E O^N3\^5aQ >oooo asOvOsc^ov ocQr^r- da\o\f> 1 i,So -. MM 5 1 > _g Q =>; 3 2 U ^a X 3 ** v " 4 t-< b S -O>OOOCSO 't'^^OOO 'tO^'l'W OOOOO't CSCOOTl" q 1 fc.| n \o ' O o* ^o ^ws^or^cN oopcfs^t^ pct^OPC*o ^O*OPC wo > j ~" 2 <- X J3 X 3 ^^ d 4 ^* T5 ^ M c " 3 "" |sj"3 r~^t oo <0 r^oxs ott^oo -*tM >0 J 3 m -a 3 VO *t!s 5S!o! aSSSS aaSSw SwoJ ^ ., O* O . i-i -i-> ?n fl r 13 d QQ. 5 f 8 W ^rt J 3 5 -M Si SS OOCMMO^OO OOOOCOtS -*00000 VOCSCMOOO * * O OO * 2 aj v> ctf ^IJ^PCPC PC SPCPCPC cscN?5cscs Scs2S 2^22 >^ o o OH'O-^ H OH 1- c 3 | 5 u jf_i "! a S" u 'o C H O V as o *" o . l j 3.2? 00^-fl.OOO OOPCOOO^ PCPCOO^OO OO^u,^^ O^PC1 " 1 -> *- i i J 3 D, Q ^c^SpCPC PCP^P^PCPC S^PCPCPC^ PCPC^P^PC PCPOPCPC 5 J4 8 rt |2 P "5 4-> J 'O $ ^^ PC " si ji 20 E ^s-s 2 *f S C 5 - "Sxi 3 1: I^E ^'rs' ''"' "*. ^ "* . "*. ^^^ r "- t>: ^^- t> '. ^ ^^-^3j +l - ^ - 3 c5 > ^ Q Q 2 l^ Ja "* C C s 1 i o O -^ J3 V t. 4- o I. l- h 2i S *OO^OO OO-O^^OO OOCN-^CS O'OCSO^l OOOOOO 3 * ^~ Q PCPCO-HO o\oooo r^inio^pc oom^oo^ O-OPCPC ^ss S ^ 3 j a ('OJ3 E IOl/^tO"5^ ^"*lOtOlO ^t^"Tj''^T^ PCPCPCPCC^J PCPNCSCS 'H_o_o i - 4 " " J l- O O D fl^ (SlOCMO't PCOOr^OOO PCOO")O PCt^PC'*!^ f >O PC ^ > > 4 SJd g oow a^SSSS SSaS;^ S5S3S? o!! if "* C C j ) - ( f M &;'"' i III 4 tS ** V 3 "5 C a* M CNOOOO>O OO^OOOO OOrJifsOO >O O O * ^" OrC^-O ^ <-- 3 > 'tt'fPCPC PCPCPCPCPC CSCSCSCSCS CSCSCSCN-^ rt > J i ft.'IJ ^ 7958] CHANGES IN POPCORN KERNELS AND COBS 45 lopop 6 did not increase after the kernel moisture reached 32.0 percent for upper ears (Table 16) and 28.0 percent for lower ears. The estimated curves for the two hybrids were plotted by ear sec- tion and by entire ear; but since the curves were quite similar, only those for lopop 6 upper ears are shown in Fig. 11. The maximum kernel dry weights for the entire ear were reached between 30- and 25-percent kernel moisture at harvest. These dry weights were prac- tically the same as those for the center section. As might be expected, the dry weight per kernel was highest for the butt sections and lowest for the tip sections, reflecting the larger kernels found at the butts and the smaller kernels at the tips. Each of the three sections showed parallel trends. The correlations between kernel moisture at harvest and dry weight per kernel for room-dried ears of lopop 6 and Purdue 202 were cal- culated by ear section for three moisture groups: above 34 percent; 33 to 30 percent; and below 30 percent (A and B, Table 9). As would be expected from Fig. 11, corn harvested with a moisture content above 34 percent had highly significant correlation coefficients (A-7, B-7, Table 9). Table 17. Relation Between Moisture at Harvest, Dry Weight, and Popping Expansion of Purdue 202 Dried at Room Temperature, 1955 Kernels Cobs Popping expansion (volumes)* Percent moisture at harvest Dry weight per kernel (mg.) Percent moisture at harvest Dry weight per cob (gm.) 44.8 101.6 48.6 21.8 22.8 43.8 108.8 48.8 20.8 25.8 40.4 122.6 46.2 21.0 32.5 36.6 127.2 47.6 21.5 35.3 34.8 128.4 45.4 20.9 36.0 34.8 137.4 47.8 22.0 36.8 31.2 133.9 46.2 21.0 37.8 30.8 137.6 47.8 21.7 39.8 29.6 141.9 47.2 20.5 38.8 28.2 140.6 45.2 21.5 38.3 27.6 141.2 45.4 21.3 37.5 26.8 144.8 42.0 21.8 38.5 25.0 139.7 41.8 20.6 35.8 24.0 137.3 40.8 21.2 37.8 23.6 138.0 39.8 21.5 37.5 22.0 133.3 34.6 20.5 38.8 20.4 137.0 30.2 21.2 37.8 20.2 134.9 32.8 21.8 37.0 19.0 136.1 27.0 21.6 37.8 18.6 137.4 25.0 20.8 37.3 18.2 138.5 25.2 20.9 38.0 17.6 144.5 26.2 21.9 37.8 16.6 137.4 19.2 21.1 37.5 16.4 138.3 20.2 22.1 39.8 Average 138. 8 .79 b 21. 3 .10 37.8.23" a All samples were reconstituted with water to 12.5-percent kernel moisture. b Including only those below 30-percent kernel moisture. c Including only those below 35-percent kernel moisture. 46 BULLETIN NO. 625 [March, 110 105 100 95 90 85 C 80 s I 70 65 60 55 BUTTS 45 40 35 30 25 PERCENT KERNEL MOISTURE AT HARVEST 20 Relation between percent kernel moisture at harvest and dry weight per kernel from butt, center, and tip sections, and from entire upper ears of lopop 6 (averages of 25 ears, 1955). (Fig. 11) 7958] CHANGES IN POPCORN KERNELS AND COBS 47 The lots dried at 110 F. (C-7, D-7, Table 9) showed the same trend, although only two of the six coefficients were significant. None of the coefficients calculated from harvests below 30 percent moisture was significant (C-8, C-9, D-8, D-9). When the corn was harvested below 30-percent moisture and dried at room temperatures, all six of the coefficients were positive, but only two were significant (A-9, B-9, Table 9), indicating a tendency for dry weights to increase in relation to moisture content. In other words, as moisture decreased, the dry weights per kernel also decreased. The artificially dried lopop 6 showed the same tendency (C-9), but coeffi- cients for Purdue 202 (D-9) were too small to show any trend. The correlations between dry weight per kernel and popping ex- pansion for the room-dried lots were all highly significant (A-4, B-4) in Table 9. In contrast, only two of the coefficients for the group har- vested between 30- to 35-percent kernel moisture and dried at 110 F. were significant, and they showed a similar trend (C-4, D-4). In more mature ears (lines 5 and 6, A, B, C, D), the correlations of both the room-dried and artificially dried ears were variable and none was sig- nificant. The relation between dry weights per kernel and popping volumes were plotted as estimated curves for both hybrids; but since the curves are similar, only those for Purdue 202 are shown in Fig. 12. The different behavior of the three ear sections is of interest. 40 35 TIPS 30 25 20 95 100 105 110 115 120 125 130 135 140 145 150 MG. DRY WEIGHT PER KERNEL Relation between popping expansions and dry weight per kernel from butt, center, and tip sections, and from entire ears of Purdue 202 (averages of 25 ears, 1955). (Fig. 12) 48 BULLETIN NO. 625 [March, Assuming that a popping expansion of 30 volumes is the trade standard, the tip, center, and butt sections of lopop 6 harvested in 1955 reached 30 volumes with dry weights per kernel of 69.3, 82.5, and 94.0 mg. respectively. For the entire ear this point coincided with 80 mg. The maximum popping expansion for the tip sections was 35 volumes, but the center and butt sections attained 37 volumes. Purdue 202 showed a similar but more pronounced relationship (Fig. 12). At 118.0 mg. dry weight per kernel for the entire ear, the popping expansion reached 30 volumes. When the tip, center, and butt sections reached a popping expansion of 30 volumes, the dry weights per kernel were 114.8, 123.5, and 131.9 mg. respectively. The maximum expansions for the three ear sections were 36, 40, and 38 volumes for the tip, center, and butt sections respectively, and 40 volumes for the entire ear. Both the average dry weights per kernel by ear section and the corresponding popping expansion of lopop 6 (Table 8) decrease from butt, through center, to the tip. The kernel dry weights of Purdue 202 showed the same trend, but only the tip sections had a decreased pop- ping expansion. The maturity experiments were again repeated in 1956 (Tables 18 and 19), but with certain variations. In the first series, which matured normally (Table 18), the harvests of lopop 6 and Purdue 202 began at 35.3- and 36.1-percent kernel moisture respectively. The dry weight per kernel of lopop 6 changed very little after reaching 32.9-percent harvest moisture. In Purdue 202 there was no trend below 31.5-percent kernel moisture. The harvests from a second planting in 1956 (Table 19) were started at a much higher moisture level ; and since it was impossible to remove the kernels from the early harvested ears, only the ear mois- tures were recorded. After room drying, the ears were shelled and the kernels weighed and counted. The dry weights per kernel increased very rapidly during the early harvest stages (74.4- to 39.8-percent ear moisture). After reaching 29.5-percent kernel moisture, the dry weights per kernel of lopop 6 changed very little and failed to develop as great a dry weight as in the first series (Table 18) by a considerable margin. The trends in Purdue 202 (Table 19) were practically the same as those for lopop 6 except that the dry weights per kernel were much below those in Table 18. This decrease may be attributed to the month- long drouth (Tables 2 and 3) which prevented normal kernel develop- ment. Purdue 202 was planted higher in a sloping field than lopop 6, and consequently was more severely damaged by drouth than the latter. The Purdue 202 corn was also badly infected with European corn borer. CHANGES IN POPCORN KERNELS AND COBS 49 a o & C O 'ta C a a W T3 i C b TO ^J . rt i* J3 a) .SP& OJ .2 3 O T3 2 i c^ a > C ^ n -> u PQ ,0 'C JS "w I 5 (N f3 00 r IN a e * +\ a ?o rs r^tstN CNCN tscs Q S6 C V ' O 3 > 00 'tOf-Ot -._>- r^r^r5(MrscNt 0.0* M E * sl Ti S'3 - -^ P a (3 E n & O * K ^ ii ;; rt u ^ ; o 1 ?- .C LO W d JH 4J 1 O 0> 50 BULLETIN NO. 625 [March, Table 19. Relation Between Moisture at Harvest, Dry Weight, and Popping Expansion of lopop 6 and Purdue 202 Dried at Room Temperature, 1956 a 3 cs u 1 S, NO a o a, o Percent moisture Dry Cobs Percent moisture Dry Cobs at harvest weight Popping at harvest weight Popping :ent Dry weight expansion per Percent Dry weight expansion are at per cob (volumes) Entire Kernels kernel moisture at per cob (volumes) 11 rest (gm.) ear (mg.) harvest (gm.) * to ID IDOtO'DOO O\CS^"O>OOO -OCSOvCS^O ' ID OOlDfOl^fOtO Ov * to vC * -H -H i/> r~ n t & oo cs fcotsct rr> xo 10 ro O r~ -*OOOO> Ov 1^ ?*5^H^iot^iD r^lWOcsO^^ *O^^^"O^Hr^ cs^^cs-^O O CS fO W) ^ >O >O < OOOOOOO OvOOOvOO O O OO^OOIOOCS O W3 O 00 "C D O CS 00 O 00 O ID r~ cs oo <*5 1^ O cs oo *O t- oo oo O oo O t .- cs cs cs fofjfjfjfjfitocototof; ; r~ to t^ O to 00 t r- 00 IO O\ CS I^OO"O" ' O> t^ 00 >/5 ID 00 O rJ-TjD to TC ID IDD O ^ 00 00 ^ IDI Ot^CS'OTj'O O ID t- ^-O ID O >O OM~- ^CS^J'CSO "^ CSCStOt f) >D O t- t^. t>. 00 Ov 00 O\ 00 00 OM> Ov Ov O\ CS O O ^IID OOOOO P-lDOOO CS^OM^-tOtO OOOOfOCS & 8b TfvOt^iDOOO'OO'-OoOrt ; ; a I^r-.D>D -9"1"t * * CO > > < < 1958] CHANGES IN POPCORN KERNELS AND COBS 51 The dry weights per cob in lopop 6 and Purdue 202 did not change materially through the entire range of ear and kernel moistures (Tables 18 and 19). Allowing for the normal variations in size of cob, the average dry weight per cob of lopop 6 above 39.8-percent ear mois- ture was 12.0 gm. as compared with 13.9 gm. between 32.4- and 12.1- percent kernel moisture. Similar comparisons of Purdue 202 showed an average of 15.8 gm. per cob above 34.5-percent ear moisture and 17.1 gm. between 26.8- and 10.4-percent kernel moistures (Table 19). These slight differences indicate that the cobs were fully mature much earlier than the kernels. FACTORS AFFECTING ENDOSPERM FRACTURING Bemis and Huelsen (2) found that, as indicated by highly signifi- cant correlation coefficients, the rate of moisture loss from the kernels during drying by artificial heat was closely related to the number of kernels having fractured endosperms; but the final moisture content was not a factor. In lopop 6 the harvest moisture and fracturing were positively and significantly correlated, but in Purdue 202 there was only a very small negative correlation. The 1955 experiments afforded an excellent opportunity to gain further information on endosperm fracturing, since the records were kept by ear section and the ears were dried at room temperature as well as by heat at 110 F. Both the room-dried and artificially dried ears were not sectioned until just before the counts were made. The fracture counts were made on duplicate 100-kernel samples, and the results in Table 20 are expressed in terms of the number of kernels with fractured endosperms per 100 total kernels. Virtually no fracturing occurred when the corn was dried slowly at room tempera- tures. As indicated by the dry weights in Table 20, the butt sections of the two hybrids had the largest kernels. These kernels were subject to the greatest amount of fracturing. The center and tip sections of lopop 6 averaged about the same number of kernels fractured, but the tip sections of Purdue 202 had more fractured kernels than the center sections. When the corn was dried at 110 F., fracturing of the kernels from the butt sections of lopop 6 decreased in relation to the initial moisture. Since kernels with a high initial moisture content dry much more rap- idly than those with a low initial moisture content, the decreased rate of moisture loss in the dryer was accompanied by a decrease in fracturing. The butt and center sections of Purdue 202 showed the same trends and had similar drying rates. All the lots were dried from 45 to 48 52 BULLETIN NO. 625 [March, g - ,* c/T H v s - o G o 2 Q S CO O 13 r O o j ""5 \o '>^- OJ O Gi S O " ~ " O h CC WJ H rt w "i O O "~. O ") O "5 O O ") "". O "~. O O >/5 O "5 O W;C C O "5 5 10 c O O O O ": "". O >o o ooo u-, o "~. "; c o ooooo>o ooooo c^i 00 CCCCC OOOOiO COOCO "I O "-. O ~. OCCC CSCSO OOCOC OOOCC OOOC C CCCCO OOOOO 00000 CCOO =! aooD^ > <0eooor400iOr>)nf.s coooo ooooo ooooo oooo n "S Q " - _ tC M - 5?*R*S O !>> )> NNtNtStS WeSN N " ^ '" J958] CHANGES IN POPCORN KERNELS AND COBS 53 hours at 110 F., and it is probable that the decreased fracturing was due to the lower kernel moisture at harvest rather than to the decreased drying rate per hour. Since the more mature lots contained a lower initial moisture, the drying rate per hour was naturally less. Drying did not proceed at a uniform rate. Lots with a high initial moisture content, as shown by Huelsen and Bemis (13), lost moisture rapidly upon first entering the dryer. The drying rate slowed down rapidly as the moisture content of the ears decreased. The popping expansions of the respective ear sections of Purdue 202 are shown in Fig. 10. When dried at room temperatures, the kernels from the tip sections of both hybrids did not pop as well as those from the center and butt sections. A similar tendency was noted in the artificially dried lots, with Purdue 202 showing a greater difference than lopop 6. Since the two methods of drying had similar trends, it is doubtful whether increased fracturing was responsible for the lower popping expansion of the tip sections. As indicated in Fig. 10, the artificially dried ears did not pop quite as well as the room-dried ears, but it is doubtful that endosperm frac- turing was responsible for the difference. Practically all of the lots were dried to moistures below the 12.5 percent optimum for popping. These lots were reconstituted with water. Bemis and Huelsen (2) showed that rehydration of kernels with perfect endosperms results in considerable fracturing even when the increases in moisture content are small. / SUMMARY AND CONCLUSIONS Maturity studies were conducted with two popcorn hybrids, lopop 6 and Purdue 202, over a three-year period, 1954-1956. Two plantings of the hybrids were made each year. Samples of at least five ears, except as noted, were harvested three times weekly as part of a much larger sample used for popping. The ears were shelled together and the cobs combined into one sample in order to determine the moisture content. In 1955 the ears were tested individually after division into three nearly equal sections. All samples were dried either at room temperatures or at 110 F. Later they were reconstituted with water to 12.5-percent moisture and popped. In 1956 corn was permitted to stand in the field until Decem- ber 26, long after it had dried sufficiently for cribbing. Two control series were stored in outdoor cribs. Kernel and cob moistures were equal in both hybrids at about 50- percent moisture. The kernel moistures decreased rapidly, but the cob moistures remained static until the kernel moistures reached about 30 54 BULLETIN NO. 625 [March, percent. After that point, both the kernel and cob moistures dropped rapidly, tending to reach equilibrium again in the field when the mois- ture content fell to about 15 percent or slightly lower. During the fall of 1956, corn standing in the field and held in outdoor cribs after harvesting reached a low point of about 10-percent kernel and cob moisture. By December 26 the kernels and cobs of both hybrids had absorbed about 7 percent additional moisture from rain and ground fogs. It is unusual, however, for popcorn to reach 10-percent moisture content in the field. Under ordinary conditions popcorn should be har- vested as early as possible, consistent with keeping qualities in the corn crib. Long exposures under field conditions are not recommended; and since popcorn in the crib absorbed moisture at the same rate as that standing in the field, the question may be raised whether it is advisable to store popcorn for long periods in ordinary outdoor corn cribs. The three-year period covered by the experiments included one of the driest fall seasons on record as well as one that was warm and unusually rainy. There was no evidence that rainfall caused an increase in the kernel and cob moisture during the normal maturity period of September and October, even though the stalks were either definitely dying or entirely dead. However, the average daily moisture loss from kernels and cobs was most rapid during the driest fall and slowest during the wettest. During the wettest fall, even though October temperatures were far above normal, almost twice as much time was required for the popcorn to lose an equivalent percentage of moisture as during the driest fall. Under favorable conditions lopop 6 develops a considerable per- centage of second or lower ears on the stalks. Comparison of the dry- ing rates showed that upper and lower ears contained the same amount of moisture at the 45-percent kernel moisture stage; but as maturity advanced, the upper ears dried slightly faster than the lower ears until within the 35- to 30-percent stage. After that point, maturity pro- ceeded at the same rate. In contrast, the cobs from the lower ears lost moisture at a slower rate than the cobs from the upper ears, but below 20-percent kernel moisture the differences were small. Kernel-cob moisture relationships are important from a practical standpoint because of their effect on shelling percentages. Popcorn is often purchased from the grower at 20-percent kernel moisture, and it is important to know what cob moisture to expect at this time. Moisture tests covering the five-year period 1952-1956 showed that when the kernel moisture reached 20 percent the cobs of lopop 6 con- tained 8.5 to 15 percent more moisture than the kernels and those of Purdue 202 from 9 to 13 percent more. 7958] CHANGES IN POPCORN KERNELS AND COBS 55 Although previous work indicated that rapid drying of popcorn by artificial heat was somehow injurious to popping expansion, these ex- periments revealed that below 25-percent kernel moisture the injurious effects were slight. Drying experiments showed that the kernels dried much faster than the cobs at 110 F. The theory was advanced that the several sections of the ear might differ in moisture content. Al- though the kernel moisture of the entire ear might average 25 percent, one part of the ear could have a higher initial moisture content than another, and therefore the average popping expansion for that part could possibly be damaged when dried at 110 F. Successive harvests three times weekly indicated, however, that the kernels shelled from butt, center, and tip sections of lopop 6 and Purdue 202 all lost moisture at practically the same rate. There were slight differences in the drying rates of the ear sections and between varieties, but these were too small to account for any variations in popping expansion. The cob sections, in contrast, showed considerable differences in moisture content at harvest. The tip sections of the cobs of both upper and lower ears of lopop 6 contained less moisture at all stages below 50- to 47-percent butt moisture. Above 30-percent butt moisture, the center cob sections of the upper ears of lopop 6 also contained con- sistently less moisture than the butt sections. The relationship was similar in the lower ears. In Purdue 202 the tip cob sections contained less moisture than the butts at all stages. The butt and.center sections contained approximately the same amount of moisture below about 35-percent butt moisture. In general, the butt sections of the cobs of both hybrids contained more moisture at harvest than the center and tip sections. Under drying conditions in an unheated attic, both the kernels and cobs of the butt and tip sections of the two hybrids lost moisture at a more rapid rate than the center sections, indicating a gradual transfer of moisture from the center toward the ends of the ears. Almost with- out exception, the kernels and cobs of the center sections contained more moisture than either end of the ear at the close of the drying period. Throughout the entire room-drying period, the tip sections of the cobs of both hybrids contained slightly less moisture than the butt sections. The center sections, on the other hand, contained less moisture than either the butts or tips below 35-percent butt moisture. Above 36- to 40-percent butt moisture, the center sections contained more moisture than either butt or tip sections. Shelling percentages were affected to a considerable extent by the moisture content (maturity) at harvest. lopop 6 and Purdue 202 were 56 BULLETIN NO. 625 [March, harvested periodically at three initial kernel-moisture levels 44 to 45, 30 to 33, and 19 to 21 percent and dried at room temperatures. Both the actual and adjusted (to 13-percent moisture) shelling percentages were reduced in the earliest harvest, but the two later harvests had comparable shelling percentages. Since the kernel-cob moisture relationships below 35-percent kernel moisture appeared to be fairly constant, a table was compiled to show the expected shelling percentages on both an unadjusted and adjusted (to 13-percent moisture content) basis for the 33- to 12-percent kernel- moisture range. The calculated table was found to check closely with the actual shelling percentages obtained over a two-year period. It is sometimes assumed that the lower ears of a multiple-eared hybrid like lopop 6 will have a smaller shelling percentage than the upper ears, especially since the lower ears often weigh less than the upper ears. On an unadjusted moisture basis, the shelling percentages of the lower ears were slightly higher than those of the upper ears. When adjusted to 13-percent kernel moisture, however, the lower ears tended to have the same or a very slightly higher shelling percentage than the upper ears. In dent corn the kernel-cob moisture relationships for ears taken directly from the field differ from those for ears taken from outdoor corn cribs; consequently the shelling percentages of the two also differ. But the moisture relationships between kernels and cobs of popcorn ears taken from the field were identical with those for ears removed at the same time from outdoor cribs. Their shelling percentages were also similar. Popping expansion is conditioned by variety and by moisture con- tent at the time of popping. Morphological and physiological develop- ment, collectively termed "maturity," is also important, but practically nothing is known about its effect on popping expansion. Preliminary work in 1954 showed that the kernels reached maxi- mum popping expansion between 35- and 30-percent kernel moisture, after which there was a slight decrease in expansion. The experiments were repeated in 1955 with similar results, except that the maximum popping expansion fell within the 30- to 25-percent kernel-moisture range. The ears were divided into three sections; in general, the center sections popped the best and the tip sections the poorest. The experi- ments were repeated again in 1956; but owing to prolonged drouth, there were no trends in popping expansion below 35-percent kernel moisture. The results of these experiments over the three-year period 1958] CHANGES IN POPCORN KERNELS AND COBS 57 showed clearly that harvesting at 30-percent moisture had no adverse effects on popping expansion when the ears were slowly dried at room temperature. However, the subsequent decline in popping expansion in later harvests could not be explained. Very similar trends were observed when popcorn was dried by forced hot air at 110 F. The exception was that harvest had to be delayed until the kernel moisture reached 25 percent. The popping expansions of corn handled in four different ways were compared. Corn harvested from the field, taken from outdoor corn cribs, or dried at room temperature popped about the same; but corn dried at 110 F. had a slightly lower popping expansion. lopop 6 and Purdue 202 were harvested at four different times with kernel moistures as high as 28 percent. The ears were husked and stored at two temperatures, 25 F. and 40 F. The results were variable, but none of the cold treatments reduced popping expansion sufficiently to make the corn unmarketable. This experiment was supplemented by another in which the popping expansions of corn stored in outdoor cribs were compared weekly with those for corn remaining on the stalk in the field. This experiment was terminated December 26. Despite low temperatures, the ears in the field popped as well as those in the cribs. It was then believed that weathering (alternate wetting and drying) rather than low temperatures alone might be responsible for damage to popping expansion, and two lots were artificially weathered to test this hypothesis. The ears were soaked up to two hours, held while wet at 35 F. for 24 hours, and then dried by unheated forced air. Five or six of these cycles were required before any serious effects were noted, indicating that lopop 6 and Purdue 202 are well able to resist weather- ing. Underdeveloped ears, as indicated by abnormally low dry weights per kernel, had an adverse effect on popping expansion. Under- development may be caused by prolonged drouth, disease, insect dam- age, or mechanical injury. Dry weights, or moisture-free weights, are an index of kernel de- velopment. These will vary from season to season and from one field to the next, and when they are too low, popping expansion suffers. The three years of experiments showed that maximum kernel dry weights coincided very closely with 30-percent kernel moisture. Below 30 per- cent there was a distinct tendency for the dry weights per kernel to decrease, a trend that could not be explained. Butt, center, and tip sec- tions all showed practically the same trends. The dry weights of the 58 BULLETIN NO. 625 [March, kernels from the butt sections were higher than those from the tip sections, reflecting the differences in sizes of the kernels. Dry weights per kernel and popping expansion were significantly correlated above 34-percent kernel moisture when the ears were dried at room temperatures, but at lower moistures the coefficients were not significant. When analyzed on the basis of ear section, considerable differences were noted in the dry weights when the kernels reached the trade standard of 30 volumes expansion. Tip, center, and butt sec- tions reached 30 volumes in the order given, the tip sections weighing much less than either center or butt sections. However, the maximum popping expansions of the tip sections were less than those of either the center or butt sections. In 1956 harvests were started when the ear moisture reached 74 to 70 percent. Dry weights per kernel increased very rapidly as matu- rity advanced and remained static after the kernel moisture reached approximately 30 percent, proving again that the point where full ' maturity is reached comes much earlier than is generally believed. The cobs reached full maturity as indicated by their constant dry weights at above 70-percent moisture. At this time the kernels had the same or slightly less moisture, but were losing moisture rapidly. The cobs, on the other hand, maintained a fairly constant moisture content. By the time the kernels reached 35- to 30-percent moisture, the cobs also started to lose moisture rapidly, but without any increase in dry i weight. Further experiments on endosperm fracturing indicated that prac- i tically no fracturing occurred when the husked ears were dried in an unheated room. The percentage of kernel moisture at harvest was not a factor. Drying the ears at 110 F. was the cause of severe fractur- ing. Comparing the amount of fracturing by ear section showed that fracturing increased in relation to kernel dry weight. In other words, more kernels from butt sections fractured than tip kernels. Center sections were intermediate. Fracturing of the kernels from the butt sections of lopop 6 and from the butt and center sections of Purdue 202 decreased as maturity advanced. The center and tip sections of lopop 6 and the tip sections of Purdue 202 failed to show a similar trend. Fracturing was confined to the ears dried at 110 F.; and since these popped slightly less than the controls dried at room temperature, it might be assumed that the decrease in popping was due to fracturing. However, evidence proved that this conclusion was erroneous. 7958] CHANGES IN POPCORN KERNELS AND COBS 59 LITERATURE CITED 1. ANDERSON, E., and CUTLER, H. C. Races of Zea Mays: I. Their Recogni- tion and classification. Mo. Bot. Card. Ann. 29, 69-86. 1942. 2. BEMIS, W. P., and HUELSEN, W. A. Dehydration and rehydration in rela- tion to endosperm fracturing of popcorn. Am. Soc. Hort. Sci. Proc. 65, 371-380. 1955. 3. BEMIS, W. P., and HUELSEN, W. A. Estimating the shelling percentage of lopop 6 and Purdue 202 popcorn. Popcorn Merchandiser 10(3), 30-33. 1955. 4. BEMIS, W. P., and HUELSEN, W. A. Maturity in relation to popping expan- sion of popcorn. Amer. Soc. Hort. Sci. Proc. 67, 451-459. 1956. 5. BRUNSON, A. M., and SMITH, G. M. Popcorn. U. S. Dept. Agr. Farmers' Bui. 1679. 1948. 6. ELDREDGE, J. C., and THOMAS, W. I. Popcorn experiments for 1953. Iowa Agr. Exp. Sta. Mimeo. n.d. 7. ELDREDGE, J. C. Factors affecting popping volume. Iowa Agr. Exp. Sta. Mimeo. 1953. 8. ELDREDGE, J. C. Factors affecting popping volume. Popcorn Merchandiser 9(1), 20-33. 1954. 9. ELDREDGE, J. C., and THOMAS, W. I. Popcorn experiments for 1954. Iowa Agr. Exp. Sta. Mimeo. n.d. 10. ELDREDGE, J. C., and THOMAS, W. I. Popcorn experiments for 1955. Iowa Agr. Exp. Sta. Mimeo. n.d. 11. HUELSEN, W. A., and THOMPSON, A. E. Artificial drying of popcorn in relation to popping expansion. Amer. Soc. Hort. Sci. Proc. 60, 341-350. 1952. 12. HUELSEN, W. A., and BEMIS, W. P. Reconstituting moisture in overdried popcorn by blending with wet popcorn. Food Technol. 9, 426-430. 1955. 13. HUELSEN, W. A., and BEMIS, W. P. Artificial drying and rehydration of popcorn and their effects on popping expansion. 111. Agr. Exp. Sta. Bui. 593. 1955. 14. KIESSELBACH, T. A. The structure and reproduction of corn. Neb. Agr. Exp. Sta. Res. Bui. 161. 1949. 15. KIESSELBACH, T. A. Progressive development and seasonal variations of the corn crop. Neb. Agr. Exp. Sta. Res. Bui. 166. 1950. 16. MILES, S. R., and REMMENGA, E. E. Relations of kernel, cob, and ear mois- ture in dent corn. Purdue (Ind.) Agr. Exp. Sta. Bui. 599. 1953. 17. RANDOLPH, L. F. Developmental morphology of the caryopsis in maize. Jour. Agr. Res. 53, 881-916. 1936. 5M 3-59 67331