SF ^ I Issued May SI, 1910. J](,^ U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ANIMAL INDUSTRY.— BULLETIN 123. A. D. MELVIN, Chief of Bureau. THE INFLUENCE OF LACTIC ACID ON THE QUALITY OF CHEESE OF THE CHEDDAR TYPE. BY If^ U.^ C: F. DOANE, Assistant Dairyman, Dairy Division. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1910. Class 'gs F'^7 ( Book • II(o^, Issued May 31, 1910. U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ANIMAL INDUSTRY.— Bulletin 123. A. D. MELVIN, Chief of Bureau. THE INFLUENCE OF LACTIC ACID ON THE QUALITY OF CHEESE OF THE CHEDDAR TYPE. BY C. F. DOANE, Assistant Dairyman, Dairy Division. r WASHINGTON: GOVERNMENT PRINTING OFFICE. 1910. K}.^y--^ ^^ 'S> G^ ^ ' L THE BUREAU OF ANIMAL INDUSTRY. Chkf: A. D. Melvin. Assistant Chief: A. M. Farrington. Chief Clerk: Charles C. Carroll. Animal Ilusbandry Division: George M. Rommel, chief. Biochemic Division: M. Dorset, chief. Dairy Division: B. H. Rawl, chief. Inspection Division: Rice P. Steddom, chief; Morris \Yooden, R. A. Ramsay, and Albert E. Behnke, associate chiefs. Pathological Division: John R. Mohler, chief. Quarantine Division: Richard W. Hickman, chief. Zoological Division: B. H. Ransom, chief. Experiment Station: E. C. Schroeder, superintendent. Editor: James M. Pickens. 9 JUfJ 1 lyio LETTER OE TRANSMITTAL. U. S. Department of Agriculture, Bureau of Animal Industry, Wasliington, D. C, March I4, 1910. Sir: I have the honor to transmit the accompanying manuscript of an article entitled "The Influence of Lactic Acid on the Quality of Cheese of the Cheddar Type/' by C. F. Doane, of the Dairy Divi- sion of this Bureau. Mr. Doane has for some time been stationed at one of the principal cheese-makmg centers of the country, carrying on work connected with the manufacture and storage of cheese under practical conditions. The experiments described in the present paper have resulted in establishing data which are contrary to the usual practice of factories producing the Cheddar type of cheese, and are therefore calculated to be of value to this section of the cheese- making industry. I recommend the publication of the article in the bulletin series of this Bureau. Very respectfully, A. D. Melvin, Chief of Bureau. Hon. James Wilson, Secretary of Agriculture. CONTENTS. Page. Introduction 5 Lactic-acid problems in cheese making 5 Effect of high acidity on quality of storage cheese 11 Experimental work to test effect of acid on flavor 14 Results of experiments contrary to general practice 16 The use of starter in milk 18 Effect of early storage on acid cheese .^ 18 Conclusions 20 ILLUSTRATIONS. Page. Fig. 1. Diagram showing relation of acidity to score of cheese at various periods and temperatures 14 2. Diagram showing relation of acidity to score of high-acid and normal cheese 16 THE INFLUENCE OF LACTIC ACID ON THE QUALITY OF CHEESE OF THE CHEDDAR TYPE. INTRODUCTION. The relation of lactic acid to the science of cheese making, par- ticularly its action under varying conditions, and the necessity, or otherwise, for its development during the process of manufacture, are among the greatest unsolved problems connected with the dairy industry. In the making of the Cheddar type of cheese at the present time the expert cheese maker is chiefly concerned with this development of lactic acid, and his entire ability is exerted to secure a uniformity of cooking with the development of the acid. This is desired because . it is believed that a maximum quantity of acid is necessary for the best results. This maximum development is determined by the amount of acid that the curd will stand in the whey at the time of drawing the latter without subsequent injury to the texture and the color of the cheese. The best cheese makers are agreed, almost without excep- tion, that on this development of acid depends to a great extent the delicate flavor that the best cheese should have, also, the desired closeness of body, as well as some of the qualities of texture found in the best cheese. Under the present conditions, therefore, there is ample opportunity for the exhibition of skill in handling the milk and the curd, since the attainment of even a small degree of success in securing uniformity of the different processes under varying conditions comes only with long practice and keen observation. LACTIC- ACID PROBLEMS IN CHEESE MAKING. There is undoubtedly much yet to be learned concerning the development of lactic acid and its effects in cheese making. One apparent inconsistency lies in the differing effects of the lactic acid which is developed before, as compared with that which is devel- oped after, the whey is drawn. It it well known that the develop- ment of acid in the whey beyond approximately 0.2 per cent will 5 6 INFLUENCE OF LACTIC ACID ON QUALITY OF CHEESE. result in an acid cheese, although a slight variation from this will depend upon whether the milk is working fast or slow. A high- acid condition has a decidedl}^ injurious effect on the texture and the color of the cheese, and the greater the development of acid in the whey beyond the above limit the more pronounced is the injury. On the other hand, after the whey is drawn and the curd is put on the rack, the acid may develop until the expressed whey shows a full 1 per cent, or even more, without any injury to texture or color. This would certainly appear to be inconsistent. In both cases the acid formed is evidently lactic acid. In both cases the acid is formed inside of the curd particles, as the greater part of the bacteria are carried down into the curd after setting the milk and cutting the curd," and the acid is formed in the curd and expelled into the whey. We have, then, in each case a process of acid formation operating under such similar conditions as to be apparently identical, yet the results are radically different. While in the whey a development of 0.3 per cent of lactic acid will practically ruin the commercial value of the cheese, yet in the matted curd more than three times this quantity may develop with what most cheese makers believe to be a benefit, and certainly without apparent injury. In the best present-day practice in cheese making there is an attempt to develop all the acid possible without injury to the texture and color of the product. To begin with, a maximum amount of acid is developed in the whey, and finally the curd is allowed to remain on the rack until all the acid that will develop in a practicable length of time is obtained. But while there are many positive opinions in regard to the good results of this method, there is but little accurate knowledge. The effect of acid on flavor is not known, and, contrary to general opinion, a glance at some of the tables included in this paper will show that a flat or low flavor may be found in a high-acid cheese. Again, the actual effects of a so-called proper development of acid on the closeness or the texture of tlie cheese is not known. The desired characteristics of texture, body, and flavor may be found, and have been found on numberless occasions, when the curd has been worketl through comparatively sweet. However, we know bej'ond doubt that a high acid development in the whey will injure the resulting product. Furthermore, we have very good reason to believe that a high acid development in the curd made from so-called gassy milk is necessary to overcome the gas, and it may at the same time prevent a full development of the undesirable flavors attending gassy curds. « J. L. Sammis. Factors controlling the moisture content of cheese curds. U. S. Department of Agriculture, Bureau of Animal Industry, Bulletin 122. INFERIORITY OF HIGH-ACID CHEESE. +^iriO0O0OO--3 0'rj q-1 O O O loo o OPhcB "=o_j->; .S2 i "S'3 o o ^ I - . JSmcc ^3 s cj.ac o^S tn c y o 65 021-5 T3 J « -^ 'tf iiSVO -^ Oi -^ ":C"-^"iO Tt- CO 'Tf lo >o »o P-i i-H .-H .— I 01 Ol T-H !M (M 0^» Ol C^l C-l C-1 tM C^l '>\ CI C'l -M *M CI C^ C^l C^ C0f^Q0t--cD'*.-t»0C^(>i:DC0T-t(>lC^C^a)WOh-r^O':C>:0(^:!t:00iOC^C0C^O c^c^c^N<^^c^c^^c^cocofocccocoeococccoccroooc'1coccpo^c■^cccccocc^^^ocococofO .g .:::;::::;::;;:::: I ,;.::,:::::::;; : o I ! ; • : 1 ! ' ' 1 ! ■ ! ! ■ ; ! 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CI (M CI o o CI O C^ CI O (M O' (M O CJ o i; CO-^COCO-^COTfCO't'CO-^C I o CI r:) o o CI o c-1 o ca o CI o CI o c 1 o CI o CI o CI o CI o CI o ct o CI o CI o ca o 'CO^CO'^CO'^CO'^CO-t'CO'TCO'^COTt'CO'^CO-^CO'^CO'^CO-^CO-^CO-^CO'^CO-^CO-^COTP --: f^ — : CI '^ -: • cj <^ -, • ci co eg co c^ <^ ■ ■ ci co c^i co ci co ^ • • c^ co rvi eo ci co ^ ■ • ci co m « "^ "^ *■; ->J "^^ ^ ci co "^^ ^^ *,' *-: coco^•^•n^^OlO»o^o■^0'Xlcotc■^:c:c^^t-»r--r^^-^-•^-.^^ooc»c»(»ccocooQOc^asalClOiaio;olOOCoooo ClCICJCIClC^ClClCJCIClClCJC?CIC5CJCJCJC3ClClC^ClClCldClCJClClC3CldCJC)CJdClClCJCOCOCOCOCOCOCOCOCOCO 35824— Bull. 123—10- 10 INFLUEJS'CE OF LACTIC ACID ON QUALITY OF CHEESE. ■K >--° >> o -0000000-r;00 ■3 ■o xs T! T3 -c x; g-o-c C3 ■^Xi 53 ^ . . ;^ :^ :^ : ; : :^^ : ;e ie : :^ : : : :h ■^&§?? B^ p X . oooooooooooooooooooooooooooooo : lo u* ic »o if^ lo » "MOOOrOM'^'MO'MOC;- I^i0iC'^»f5i0b-irei0i0'^'^CCC0"^iC(MC'ICCtDCCC0r-^l^;0h-O1 C^ C^ (N C-1 CS C^l (Tl (N C-1 CS W I>1 C-l C^l C'l C-1 (N W CS C<) ^CCCOjptC-t'OI-^I^OOiDiOOt^OOiO'-t'tr^-jDcO-l'C'leC^'— 'OOiCCOC CO J C^l ro ?C CC CC C*5 'M ?S "M ?s?^ EE ccggcgggggcc f: C C SEEE oooooooooooooooooooooooooooooo ooocooooooooooooocoooooooooooo CI O CI O C-l C "I O C~l O C-l O -1 O C'l O M O C-1 C Ol ! M O M O Ol O C^) o ?' ." N M N " .; „' <^1 « (M « N M -,• ^ N M N TO IM » • • W M N M N M cocccoccroccrororcrccoccccrocccccccc^?:*rrorcccccfcfcccffcfcffc •OT3 ■2.3 §5 •So 26 ■S 3 0) o EFFECT OF HIGH ACIDITY. 11 EFFECT OF HIGH ACIDITY ON QUALITY OF STORAGE CHEESE. The attention of the writer was called to one phase of this acid question at the time of scoring the cheese in the storage experiments made in the summer of 1906. A representative of the Dairy Division visited a number of cheese factories near Plj-mouth, Wis., that were having trouble with their product, and secured a quantity of cheese for storage. Most of these lots of cheese turned out to be high acid, and it was noted that where this was the case the qualit}^ was so very low as to make it appear that the acid was responsible in part at least for the poor flavor, as well as for the other undesirable characteristics always found in a high-acid cheese. The cheese in question was obtained for the purpose of determining the effect of storage on different kinds of poor cheese. It was pur- chased in July and August and was scored in January. The scores are given in Table 1 . Because of the large proportion of this cheese that turned out to be high acid the work as planned was not satis- factory, but it did show the tendency to make high-acid cheese when troubles with bad milk are experienced, and it illustrated very well the probable effect of high acid on the quality of the product. There were 34 lots of the cheese, each consisting of 8 cheeses, one-half of which were stored in the 32° F. room at various periods ranging up to two weeks, the other half being similarly placed in the 40° F. room. The average score on flavor for the high-acid cheese was 27, while the average on the normal acid cheese was 31. The comparatively poor flavor of ail the high-acid cheese was so marked that all who were connected with the scoring of this cheese noticed it and commented upon it. The Dairy Division made some high-acid cheese in the summer of 1906 to determine the effects of storage on this quality of product. The cheese was made from exceptionally good milk, and the flavor should have been, in some of the lots at least, above criticism. Nine lots of cheese were made with varying amounts of acid. Quite a wide variation in the percentages of acid was sought, especially at the time the whej was drawn, as the degree of acidit}" at this period influences the quality of the cheese more than the acidity shown at any other period of its manufacture. The acid at the time of setting was regulated to suit the percentage desired at the time of drawing the whey. The percentages of acid at different stages of manufac- ture are shown in Table 3. Eight cheeses were made in each lot. These were stored two at a time — one at 32° F. and the other at 40° F. — at each of the following periods: Fresh from the press, four days old, one week old, and two weeks old. All the cheese was scored by three judges working inde- pendently, and Table 2 gives the average scores. Table 4, abstracted 12 INFLUE^'CE OF LACTIC ACID ON QUALITY OF CHEESE. £^- -3 •6666666666666666666666660 ?~V J!-c ?: ^ 2i =3 Si&Cg W E OJ p. li Q o/ Orf 'r^ Si.'tiO^^^O^C/^^0"0>'0>i ' •OU3O"u3u3?'t/305^'t'3'*"'S^ ■a- t3 0) to I 3 C3 oj *"^ ® -■" 5 •- 3 '3 '3 "3 ._ - 1 »ii H 2 (M C-l C^l n n CI C^ CI CI CI ^ C-1 ^^ --H C^ ^ ^ ^H ^ C^l C^ CS C^l C^l C^l M (N C^ (N c^ c» js«l ^^Ooc^-«occi^:oco.*'^cceo»-Hw:)CicioooooeDic«DiDOt^t^..^co»o..So?;>o?:£:o>?:oS:o c3 rt -^ .^ f-H ^ Cl C) oi r-H Cl c3 r-< Cl c3 ^ Cl rt CI c3 ^ ci c3 — » ci rt ^ Cl air 0/ OJ ^ C' c^ O te EEEESccScEGcScEcESEESEESEEEEEES ooooooooooooooooooococooocooooo oooooooooooooooooooooooooooooop IQCIQCIQOOCI Cl O Cl Cl O Cl Cl Q Cl C Cl CI O Cl Cl O CI c: 1 Q Cl Cl g "^ CO re ^ '^l c^ ^1' pX '^1 ec w e^ c^ c^j cc M c^ CO t>J c^ M c^ cc c^i Cl c^ c^i (TJ <^ c^i C"i CO (>i c^ CO ,-.rtrtT-(^,-t,^^c^)c^j^)forocO"^'^"!fiJOio<^'^«ci^t^t'»ooooooojosoi EFFECT OF HIGH ACIDITY, 13 from Table 2, and figure 1 are arranged to show more clearly the rela- tion of the numerical score to the acidity. Not all the scores are given, but those omitted are in line with those given. Enough are given to show conclusively the effect of the high acid on the cheese. Table 3. -Acidity at stated periods of high-acid cheese used in storage experiments and scored in Table 2. No. of lot. Acidity when set. Acidity when cut. Acidity when drawn. 1 2 3 4 5 6 7 8 9 Per cent. 0.175 .175 .185 .195 .260 .200 .175 .182 .170 Per cent. 0.120 Per cent. 0.207 .229 .240 .215 .303 .225 .220 .211- .220 .184 .145 '.m Table 4. — Relation of the numerical score to the acidity of cheese described in Table 2. Num- ber of lot. Acid- ity. 32° room, at once. 32° room, one week. 40° room, two weeks. Flavor. Tex- ture. Total. Flavor. Tex- ture. Total. Flavor. 1^. Total. 1 8 4 7 9 6 2 3 5 Per ct. 0.207 .211 .215 .220 .220 .225 .229 .240 .303 311 271 25 26§ 26J 28i 23| 20 26J 22J 25 24 25i 24J 22J 14 82 71S 67 72J 71 74i 721 67 49i 26§ 27 22§ 25J 25J 26 24^ 23J. 23§ 24 18 23 22 24 23* isl 72i VIJ 58i m 66J 70 68J OIJ 26§ 241 22 20J 24§ 25 26i 21* 18J 25 18J 22J 211 21§ 18J 17 14J 75J 67S 58J 681 65 C5J 63§ 56 47§ It has already been stated that the above cheese was made as far as could be judged from perfect milk and that the curds worked through in excellent shape. At least a few cheeses should have been of excel- lent quality; but it appears that the quality was injured in about the same proportion as the amount of acid developed. The cheese in lot 1 was made with acid very slightly in excess of normal, and the cheese from this lot that was placed in the 32° room at once scored 82, while the similarly treated cheese in lot 5 was made with much too high a development of acid and scored a fraction less than 50. It is prob- able that cheese made from good milk would never score as low as 50 points or as low as 20 points in flavor if it had been treated nor- mally in all stages of making and curing. Hence it would appear very probable that the high-acid development was responsible in part, at least, for the poor flavor. These results were so contrary to all belief and teaching; that it was thought desirable to make some 14 INFLUENCE OF LACTIC ACID ON QUALITY OF CHEESE. accurate comparative tests that would settle the question be3'ond controversy. For this purpose the author spent some time at a factor}^ near Plymouth, Wis., and carried out the experiments described in the followino; pages. EXPERIMENTAL WORK TO TEST EFFECT OF ACID ON FLAVOR. Sixteen lots of cheese were made for these experiments. Two lots were made each day from vats of divided milk so as to have identical conditions as regards quality of milk. One of these lots was worked up with just sufficient acid in the whey to make a light-acid cheese, the other lot being worked up on the same day in the regular way for that factory. The cheese maker in charge of this factory set his as 80 7S so 4-S I or Af(/AfBeff 'a4-7 96Z3S \ \ ^ \ V ~ ■^ . ^ ^ — X \ \ "^ ./ ^--:: ^ --~. ^-''' '" — ^ \. \ \ > / — \. \ •^ ^y \ \ ffOOM AT 0/VC£. /fooAt oA/er ivecH. ffOOAf TiVO WSSHS. .-\s 32' ^0' X. ^0.30 \o.2S \0.P0 y y ■ ^ 1 Fig. 1.— Diagram showing relation of acidity to score of cheese at various periods and temperatures. milk and drew tlie whey somewhat sweeter than is customary among the best cheese makers; but the curd was allowed to develop the acid on the rack until all danger of gas had passed. Table 5 shows some of the details of the manufacture of each lot. The cheese was made during the first half of September, 1907, and each lot was held in the factory curing room one week before being placed in storage. The storage room was held at about 33° F. The cheese was scored in the middle of January, 1908, by J. W. Moore and Robert McAdam, of the Dairy Division, both experienced cheese makers and judges. The average score of each cheese is shown in Tal)le 6, and the relation of the numerical score to the acidity is graphicall}' shown in figure 2. EFFECT OF HIGH ACIDITY ON FLAVOR. 15 Table 5. — Details of manufactvre of cheese for test of high acid oyi flavor. Lot. Time set. Acidity wtien set. Time cut. Time drawn. Acidity when drawn. Curd ground. Curd salted. Remarks. a. m. Per cent. a. m. a. m. Per cent. p. m. p. m. 1, acid 7.52 0.17 8.25 11.00 0.23 1.15 1.40 Curd firm; few pin holes flavor. ; bad 1, sweet.. 7.45 .17 8.25 10.00 .17 12.30 2.15 Numerous pin holes; bad same as acid vat. flavor, 2, acid.... 8.30 .20 8.50 9.55 .20 12.20 1.30 Oood curd. 2, sweet. - 7.20 .17 7.55 9.15 .15 12.30 1.30 Do. 3, acid.... 8.10 .20 8.30 9.55 .20 11.45 12.30 Good curd; slight taint. 3, sweet.. 7.40 .175 8.20 9.45 .16 12.00 12.30 Few pin holes; slight taint. 4, acid 7.50 .20 8.20 9.35 .21 12.05 1.00 Gassy. 4, sweet.. 7.40 .17 8.20 9.45 .18 12.45 1.30 Do. 5, acid 10.00 .20 10.20 11.55 .21 2.20 3.30 Slight taint; pin holes. 5, sweet.. 8.50 .17 8.45 10.40 .16 1.00 2.30 Do. 6, acid 8.40 .20 9.02 10.45 .20 1.00 2.15 Do. 6, sweet.. 8.00 .19 8.30 10.30 .16 12.40 2.00 Do. 7, acid 8.52 .20 9.15 10.45 .20 1.00 2.00 Shght taint. 7, sweet.. 8.10 .18 8.50 ia.50 .18 2.00 3.00 Slight taint; few pin holes. 8, acid.... 9.20 .145 9.40 11.30 .19 1.30 2.30 Slight taint; pin holes. 8, sweet.. 7.45 .175 8.32 10.45 .16 1.15 2.00 Do. Table 6. — Average scores of cheese described in Table 5. Numerical score. Per ct. 0.23 .17 .20 .15 .20 .16 .21 .18 .21 .16 .20 .16 .20 .18 .19 .16 Descriptive score. Flavor. Sour whey, sweet. . . Sweet Sour, bitter, unclean. Unclean Very unclean, sweet, sour whey. Trifle sweet Unclean, sweet Sweet Sour whey, bitter, sweet. Slightly sweet Sour whey, bitter, sweet. Sweet Fermented, sour whey, bitter, sweet. Tainted, sweet Sour, bitter, sweet.. . Coarse, mealy, stiff. Mechanical holes . . . Short, pasty, mealy. Mechanical holes. . . Crumbly, mealy Coarse Short, mealy Coarse " Crumbly, mealy, salvy. Uneven Mealy, soggy Uneven Short, mealy. Weak Crumbly, mealy... Acid cut. Straight. Acid cut. Straight. Acid cut. Straight. Acid cut, slightly. Straight. Acid cut. Straight. Acid cut. Slightly faded. Acid cut. Straight. .\cid cut. Straight. Average score on flavor of cheese made with normal acid, 39. .\verage score on flavor of cheese made with high acid, 35.5. As will be noted from Table 6, the milk was not perfect at any time during which the experimental cheese was made, neither was it very bad, and there was no difficulty in making a cheese that commanded full market price. There was a slight taint, also a few pin holes that worked out easily in the matted curd. It was perhaps unfortunate in some respects that the milk was not perfect for a few of the lots. 16 INFLUENCE OF LACTIC ACID ON QUALITY OF CHEESE. But the results of the experiment are so positive that it can not be consitlered otherwise than conchisive. A study of the numerical and descriptive scores in Table 6 shows that high acid has a markedly injurious influence on the flavor. The bad flavors in the cheese made up sweet were in ever}' case less pronounced than in that of the same lot which was made up acid. In addition other bad flavors appeared in the acid cheese that were not apparent in the cheese made normallv. The sweet or fruity flavor that was noticed in all the cheese was more pronounced in the high acid than in the normal cheese of the same day. In five out of the eight lots a bitter flavor in the acid cheese appeared that was not noticeable in the normal cheese of the same day. A sour or old whey flavor appeared in most of the high-acid cheese. LOT /V(/AfS£ff r 1 0.2S 1 \ 1 \ / \ / / \ \ 1 \ y^ / 1 / / \ \ \ \ 1 1 1 \ \ \ / / / \ \ \ / / \ \ \ / / / \ \ \ 1 / 1 \/ / 1 \ \ 1 1 \ \ \ / / \ / \ / Sv y >» \ y \ / \ A X y \ / \ / \ Fig. 2.— Diagram showing relation of acidity to score of liigli-acid and normal cheese. RESULTS OF EXPERIMENTS CONTRARY TO GENERAL PRACTICE. These results are certainly very radical in view of the belief of cheese makers and the teaching of experts to the contraiy. The great majority of cheese makers believe that a high development of acid is an antidotie for bad flavors of all kinds, and that it is about the only means they have of fighting bad flavors as well as gas. Whenever a period of bad milk comes and the product is off flavored or gassy, the effort has always been made to develop a maximum of acid in the whey as a preventive of the trouble. It has, in fact, usually been considered advisable, where the trouble has been pro- nounced, to make a slightly high-acid cheese, as the high acid has been considered the less of the tw^o evils. This practice is taught by dairy instructors and recommended by many cheese dealers who act as advisers to the cheese makers from whom they buy. The result has usually been that after a few lots of })()or cheese were made at a factory a period of high-acid cheese followed. The foregoing experi- EESULTS OF TESTS WITH HIGH-ACID CHEESE. 17 ments prove that this tendency to develop excessive acid is poor poHcy. In fact, instead of minimizing the faults it makes them more pronounced, as well as adding new faults to the product. It is universally believed and taught that a maximum development of acid in the whey is necessary for a satisfactory and maximum development of acid in the matted curd. Dean,'^ in some of his work, seemed to show that the curd was ready for grinding and for the press at the same time regardless of the percentage of acidity at which the milk was set or the whey drawn, vats of divided milk being used for the experiments. In view of the fact that the bacteria are held within the curd particles and the acid is consequently developed in the curd, we have no reason to believe that this development would not go on as fast in the matted curd as in the whey. This would appear to be much more reasonable than the old idea that a maxi- mum development of acid in the whey was necessary to hurry the process. While a high acidity is needed to exclude undesirable forms of bacteria and give the cheese its desired characteristics, this high acidity can develop in the matted curd. That there is no virtue in a high development of acid in the whey can be seen from Table 5. The taint and the gas were as bad in the curd allowed to remain in the whey until a high acid was developed as they were in the curds from the comparatively sweet whey. The development of high acid in the whey did not have any effect on the growth of injurious bac- teria, as far as could be judged from the product. The maximum amount of acid in the whey at time of drawing is about 0.2 per cent, and this is generally considered to be insufficient to check most of the injurious bacteria. It is the comparatively high-acid develop- ment which takes place in the matted curd that holds these bacteria in check. From all this evidence there is but one conclusion to be drawn, namely, that the teaching which led to a maximum development of acid in the whey was wrong. The high acid developed in the whey is likely to cause much injury, and from the evidence at hand it does no good. With our present knowledge, however, it can hardly be advised to go to the other extreme and run the whey as sweet as pos- sible, but it is certamly evident that the whey should be run suffi- ciently sweet to leave no possibility of making a high-acid cheese. An interesting feature of the results of the experiments shown in Tables 1 and 2 is seen in the lots where only part of the cheese turned out to be high acid. The cheeses in those lots that were placed in storage direct from the press showed no evidence of high acid, while those that remained in the factory curing room for a time before going o Twenty-second Annual Report, Ontario Agricultural College, 1896, p. 54. 18 INFLUENCE OF LACTIC ACID ON QUALITY OF CHEESE. into storage were injured in texture and color. The point in this connection lies in the fact that the cheese that was injured in texture and color was likewise injured in flavor. Whether the low score on flavor was simply coincident with the low score on texture and color and due to the longer time that the cheese was held out of stor- age, or whether there is some vmexplained connection between the injury in texture and the injury to flavor, might seem open to question. It would appear that the former was the case in part. If the latter be true it must be considered that the point in acidity which injures the texture also injures the flavor. There are reasons to believe that this is true, or at least that the point of acidity at which the flavor is injured and the point at which the texture is injured are not very far apart. There is therefore a question in connection with this which may be investigated with profit. Whey can be drawn with 0.2 per cent of acid without injury to the texture of the curd. Any acid above this evidently injures both texture and flavor. Does the injury to tex- ture and to flavor begin at the same point in acidity, or does injury to flavor begin with a lower acidity than 0.2 per cent ? THE USE OF STARTER IN MILK. Nothing in this discussion should be interpreted as being opposed to the use of a good starter in the milk before setting. The develop- ment of acid is, according to our present knowledge on the subject, necessary to overcome the growth of gas-producing and other unde- sirable forms of bacteria. Bacteriological investigations have shown that if there is a sufficient number of lactic-acid bacteria as compared with the other kinds, the lactic-acid bacteria increase to the partial exclusion of many other kinds. When the lactic acid has developed to a relatively higli degree it makes the milk or the curd an unfavor- able place for many kinds of bacteria to grow. The starter can be added usually without any danger of increasing the acidity to a point where it will be difficult to cook to a proper degree of firmness before too high acidity has developed in tlie whey. EFFECT OF EARLY STORAGE ON ACID CHEESE. This work may be considered a continuation of previous work carried on by the Dairy Division at Plymouth during the summer of 1905." It was planned to determine definitely some of the results which showed incidentally in the previous work. The main point which it was desired to cover was the effect of low storage tempera- tures on high-acid cheese. o Bureau of Animal Industry Bulletin 85. EFFECTS OF EARLY STORAGE ON ACID CHEESE. 19 In the report on the previous storage work at Plymouth atten- tion was called to the fact that in two or three lots of cheese used in the tests the cheese which was left in the factory curing room for from one to two weeks at a temperature of from 55° to 70° F. showed decidedly too much acid, almost a so-called ''dead sour" in one case. The ones from the same lots (including the dead-sour lot) which went directly from the hoop into the rooms held at 32° and 40° F. were very slightly acid, in fact showed so little evidence of too much acid that the selling price was not affected in the least. This was a decidedly interesting point, and as practically all cheese dealers held entirely opposite views, a thorough demonstration of the results obtained would be of economic importance as well as of scientific value. At the present time most of the cheese dealers protest against receiving a cheese under one week of age, because in a young cheese too much acid can not be readily detected. If it can be satisfactorily shown that a cheese which does not show too much acid at the time it goes into storage will come out of storage in good condition the objection on the part of the dealers to receiving very fresh goods would be entirely overcome, so far as high acid is concerned. A reference to Tables 2 and 3, which give details of experiments intended to cover this point, shows that the sooner a high-acid cheese is placed in cold storage the better it is for the cheese. This is borne out by the scoring of the cheese in lot 1. The cheese that was left in the factory curing room for a week before going into storage showed decidedly acid and was badly injured, while that which went directly into storage was not injured in either texture or color. In all the other lots the scores show that the effect of the high acid was minimized by early storage. The favorable effect that immediate storage has on high-acid cheese was very clearly demonstrated also in Table 1. Lots 4, 12, 14, 15, 16, 19, 20, 22, 26, and 31 described in this table were evidently made up with too much acid. The portions of these lots that remained in the factory curing rooms for aiiy length of time after making showed defects in texture and color, while those that went directly into storage were not injured in the least. The average score on the high-acid lots of the cheese just referred to that went into storage at once was 78, while the average score of the lots that went into storage in one week was 74. Similarly the scores of the lots in Table 2 were 72.5 and 67.2, respectively. In so-called dead-sour cheese early storage will minimize the damage, but it is not a cure, as is evidenced by lot 5 in Table 3. How- ever, the buyers can usually detect these very sour cheeses at an early age, and there is no danger of deception. From these experiments 20 INFLUENCE OF LACTIC ACID ON QUALITY OF CHEESE. it would appear that the objection on the part of the buyers to handhng a cheese direct from the press is not well founded. CONCLUSIONS. 1. In the process of making Clieddar cheese a too high develop- ment of whey acid injures the flavor as well as the. texture of the curd. 2. The development of acid in the matted curd overcomes gas and bad taints and does not injure the flavor and texture. 3. Cheese with high acid should be. put into cold storage as early as possible to minimize the bad effect of the acid. o k LIBRARY OF CONGRESS OODDfl^lEbEE 0: