■SC'-' 
 
 [eh] ^talauft fltpartmtnt of g^grituUnrt. "^^^ J^e-CL-t) / 
 
 ■' --^ 7/ 
 
 JOHN D. RITCHIE. Secretary. 
 
 DAIKYING SERVICE. 
 
 PASTEURISATION OF MILK AND CREAM. 
 
 BY 
 
 C. W. SOEBNSEN, 
 
 GOVBBNMENT DAIBY EXPERT. 
 
 Published by the nuilwrity of the Hon. JOHN MoKENZIE, Minister for. Agriculture. 
 
 WELLINGTON. 
 
 BY AUTHOEITY : JOHN MACKAY, GOVERNMENT PRINTER. 
 
 1898. 
 
Cornell University 
 Library 
 
 The original of tiiis bool< is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924003099151 
 
^tbs Mtnlmxts ^ti^nxtmtnt of gigricuUnrt. 
 
 JOHN D. BITOHIE, Secretary. 
 
 DAIEYING SBRYICE. 
 
 PASTEURISATION OF MILK AND CREAM. 
 
 BY 
 
 C. W. 80EENSBN, 
 
 GOVERNMENT DAIRT EXPERT. 
 
 PubUshed hy the wufhority of the Hon. JOHN MeKBNZIE, Minister for Agriculture. 
 
 WELLINGTON. 
 
 BY AUTHORITY : JOHN MACKAY, GOVERNMENT PRINTER.- 
 1898. 
 
 ^ 
 
 1 I 
 

 e /^X A 
 
THE PASTEURISATION OE MILK AND CREAM. 
 
 So many inquiries are constantly being received on the subject of pasteur- 
 isation, both from butter-makers and milk-dealers, that it is evident that 
 a leaflet dealing with the theory and practice of the process, and its 
 application in New Zealand dairying, will prove acceptable to managers 
 and directors of co-operative companies, as well as to town dairymen, who 
 are at present considering the expediency of adopting the system. 
 
 Benefits op Pastbueisation. 
 
 Pasteurisation of milk and cream affords, without doubt, one of the 
 best means that we have at our command for improving the quality of 
 our butter. The commercial value of butter depends mainly on its 
 flavour. Now, flavou r is just the point wherein much of the New Zea- 
 land butter is defective, and the consequence is a serious depreciation in 
 value, ranging from 2s. to 10s. per hundredweight. This is for the most 
 part due to lack of care in the handling of the milk on the part of the 
 producers; also to faulty treatment (including feeding and watering) of 
 the cows. As a result of this careless handling, undesirable ferments are 
 introduced into the milk, which injure the flavour, and make it impossible, 
 without special means, to manufacture good butter. Bank pastures, the 
 prevalence of vr ee ds, and such foods as turnips, &c., irSpart charactenslic 
 taints to the iniS, which, 'being volatfTSTTQiay-toTt great extent be got rid 
 of by thoroughly cooling the milk. As a rule, however, the milk is 
 delivered at the factories in a more or less defective condition, especially 
 in warm weather, and in consequence the butter cannot fail to be of 
 inferior quality. Pasteurisation expels these taints, if not altogether, at 
 least to a very large degree, and stops the undesired fermentations. The 
 process enables the butter-maker to produce an article of uniform flavour 
 under conditions which would otherwise render such uniformity im- 
 possible. 
 
 In Danish factories pasteurisation is almost universal, 97J per cent. 
 of the output of Danish butter during 1897 having been made from 
 pasteurised milk or cream ; in America and in Australia satisfactory results 
 have been attained wherever the system has been intelligently applied; 
 and in New Zealand the one butter-factory which has adopted the pro- 
 cess as part of its daily routine has had a markedly improved output as a 
 result. Numerous experiments have been made by several other factories 
 during the past season, and in nearly every case the pasteurised butter 
 has shown improvement over the unpasteurised from the same factory, 
 more or less, according to the maker's knowledge of the principles of the 
 process and the efficiency of the appliances used. Perhaps nowhere was 
 the value of pasteurisation so convincingly proved as at the dairy schools 
 held under the auspices of the Department of Agriculture during the last 
 three winters, when milk three days' _ old, smelling strongly of turnips 
 and other taints, was by the aid of pasteurisation manufactured into fairly 
 good butter. Equally beneficial has the system been in districts where 
 strong feed taints characterize the bulk of the milk, though naturally, 
 where really fine butter is made without pasteurisation, the effects have 
 been less noticeable. 
 
It may be asked whether the improvement in quality is sufficiently 
 marked to result in the realisation of a price which will repay the 
 expense of pasteurisation. On this point we may refer inquirers to 
 the experience of the Euroa Butter-factory, in Victoria, where part of 
 the output of the past season was pasteurised, the rest being made in 
 the ordinary way. The directors state that the pasteurised butter 
 showed a clear gain of 4s. per hundredweight over the unpasteurised ; 
 as high as £5 12s. having been realised for the pasteurised portion. 
 
 Pasteurisation of milk for human consumption has been much dis- 
 cussed of late, and the public, scared by reports of dirty dairies and of 
 infectiou s di3easesbeinjg_transmitted by milk, has jumped at the idea of 
 pasteurisation as aTpanacealor alltEe ills that milk is heir to. There is 
 no doubt that pasteurisation, properly carried" out on the lines indicated 
 further on, is a wise precaution under the existing condition of affairs 
 in the town milk trade. But, as prevention is better than cure, and 
 pasteurisation is, after all, simply a cure for dirt and disease, the 
 authorities should go to the root of the matter, and remove the dirt 
 and disease altogether. Milk drawn from healthy cows, milked and 
 handled by clean and healthy people, needs no pasteurisation, and any 
 efforts of the public to secure better milk should be in the direction of 
 a stricter veterinary inspection of all cows, better sanitary conditions 
 in their byres, and greater cleanliness on the part of all those con- 
 nected with the production, handling, and delivery of the milk itself. 
 
 In the meantime, however, the pasteurisation of milk intended for 
 human consumption may be regarded as a temporary remedy for existing 
 evils, provided always that the 'process is carried out on the lines hereinafter 
 laid down. The public and milk-vendors should bear in mind that 
 there is pasteurisation and pasteurisation, and that merely to label milk 
 "pasteurised" is not to say that it is necessarily the least degree more 
 wholesome than ordinary milk. 
 
 About Bacteeia. 
 
 In the course of our visits amongst the factories we hear such curious 
 ideas expressed as to the effect of pasteurisation upon milk or cream, that 
 it may be well to explain a few facts about these small organisms, the 
 study of whch is termed "bacteriology," and which are of such importance 
 in all dairy work. Without at least an elementary acquaintance wich this 
 science, factory-managers cannot do full justice to a process which is really 
 a bacteriological operation. 
 
 All fermentation, putrefaction, or decomposition is caused by microbes. 
 Microbes (micro-organisms, or bacteria) are small organized living bodies, 
 of the lowest known form of life, which are absolutely invisible unless by 
 means of powerful microscopes. They are present in the air, in the soil, 
 in water — everywhere on earth. Some are beneficial in their action, such 
 as those which ripen cream for churning or impart special flavours to the 
 different kinds of cheese ; others are injurious, and are associated with dis- 
 ease ; while the remainder are neutral, and, so far as we know, exercise 
 neither injurious nor beneficial effects. 
 
 Microbes reproduce themselves, or multiply, either by dividing in two, 
 each half taking on the functions of a complete organism, or by shedding 
 seed-like bodies, termed " spores," of greater resisting-capaeity, which 
 ultimately develop into full-grown organisms. Certain microbes, how- 
 ever,, have the power of reproduction by both methods. Microbes, as a 
 rule, are easily killed, but the spores are capable of existing under very 
 unfavourable conditions, such as extreme heat or cold. 
 
Amongst the most common bacteria which propagate by division (or 
 fission) only, are the jactic- acid or milk-souriug bacteria, and the more im- 
 portant pathogenic oFdiseas^prSdllCin^ germs. It is this class of bacteria 
 which may be killed by the application of a comparatively low heat, such 
 as is employed in pasteurisation. The spores of such bacteria as produce 
 spores are not killed by this low heat, unless applied for a very long time 
 (several days). It is possibly due to the recollection of having read some- 
 thing to this effect that some people are impressed with the erroneous 
 idea that pasteurisation destroys the good germs and leaves the injurious 
 ones unharmed. 
 
 Milk in the udder of a healthy cow contains no bacteria, but the 
 instant it is drawn from the udder it becomes contaminated with these 
 organisms from the air, the teats of the cow, the hands of the milker, and 
 the milking- vessels. Warm milk, fresh from the cow, forms a specially 
 favourable breeding-ground for these microbes, and, as they possess 
 marvellous powers of reproduction, a few of them will in the course of 
 three or four hours multiply into thousands and millions per cubic inch 
 of milk. Their capacity for multiplication, however, is largely con- 
 trolled by temperature, and, as a low temperature retards their growth, 
 the importance of prompt and thorough cooling of all milk immfediately 
 after milking is evident. At 90° to 100° multiplication proceeds fast and 
 furiously ; at 60° it is comparatively slow ; at 50° it almost ceases ; and 
 at 40° or under it may be said to stop altogether. Consequently, the 
 nearer to the last-mentioned temperature we can cool milk, the longer will 
 it keep. 
 
 Tmpoetance of Clean Milking. 
 
 The purer the air and the cleaner the conditions under which a cow is 
 milked the fewer bacteria will get into the milk. The following experiment, 
 made by Soxhlet, shows that this has an important bearing in practice : 
 A cow, kept in a dirty cowshed, was milked without having her udder pre- 
 viously cleaned. The milk, kept at a temperature of 60"Fahr., coagulated, 
 as a result of the action of microbes, in fifty hours. The milk of the same 
 cow, drawn under better conditions — viz., in the fresh air of an orchard, 
 and after the cow's udder and the hands of the milker had been washed — 
 did not coagulate, though kept at the same temperature, until after a lapse 
 of eighty-eight hours. The lesson taught by this experiment is that 
 everything connected with the operation of milking should be scrupulously 
 clean. Unfortunately, milking is too often carried out without sufficient 
 cleanliness, and it is to remove the injurious effects caused by bacteria 
 introduced through dirty and careless handling, that milk requires to be 
 pasteurised. The process, as stated above, kills the bacteria present, but 
 the destruction of the spores of the spore-bearing bacteria requires the 
 application of the process known as " sterilisation." 
 
 Pasteueisation not necessaeilt Stbeilisation. 
 
 These two terms are often used as though they were synonymous, but 
 this is not the case. Sterilisation means the complete destruction of all 
 life, and is usually accomphshed by the continued application of a tem- 
 perature considerably above boiling-point. In other words, sterilisation 
 destroys not only all bacteria, but also their spores, many of which, as 
 already mentioned, possess great vitality. Perfect sterilisation of milk 
 can best be effected by raising the milk to a temperature of 240° for fifteen 
 minutes, or by oft-repeated heating and cooling. In practice this is not 
 attainable without great difficulty ; neither is it necessary nor desirable, 
 
so far as butter-making is concerned, for the physical condition and 
 flavour of the milk are permanently impaired at that temperature. Pas- 
 teurisation, on the other hand, is quite sufficient for all practical purposes, 
 and has the advantage of being fairly easily carried out, while not altering 
 the character of the milk to any extent. 
 
 Definition op Pastbubisation. 
 
 We may define pasteurisation as a process whereby a liquid is raised 
 to, and kept sufficiently long at, that temperature which, while destroying 
 certain undesired micro-organisms, will not impair the flavour or alter 
 the chemical constitution of the liquid ; and thereafter cooled to such a 
 low temperature as will prevent the multiplication of any microbes which 
 may subsequently gain access. The length of time during which the , 
 heat is applied to the liquid is 'of great importance, for the lower the 
 temperature employed the longer must the liquid be subjected to that 
 temperature to insure the destruction of the bacteria. In order to 
 destroy different bacteria it is necessary to employ different degrees of 
 heat, or different periods of application of the same degree of heat — for 
 instance, lactic-acid bacteria are readily killed by subjecting them tcT a 
 temperature of 158° for one minute, whereas it requires 185° maintained 
 for the same period to destroy with certainty the bacteria of tuberculosis. 
 Five minutes at 175°, ten minutes at 165°, twenty minutes at 155°, or 
 even thirty minutes at 150° have proved as effectual in destroying this 
 bacterium as 185° for the shorter period. 
 
 The treatment, therefore, must vary according to the object in view. 
 The question may suggest itself, "If the higher temperatures are more 
 effective than low ones, why not go to boiling-point, and be done with 
 it?" The answer is, "Because milk and cream, when heated beyond a 
 certain point, acquire a cooked taste, which subsequent cooling cannot 
 remove." 
 
 The Limit 6p Heat. 
 
 Duclaux, the great French chemist and bacteriologist, has made 
 several experiments to ascertain the exact temperature at which milk 
 acquires the cooked taste permanently, and found 158° to be the limit of 
 safety. Above this degree, he states, the albumen of the milk coagu- 
 lates, and the milk becomes physically altered. Consequently milk for 
 direct consumption should not be heated above 1S8°. In butter-making 
 we may venture somewhat higher, for the cooked taste, though noticeable 
 in the milk or cream while sweet, disappears during the process of ripen- 
 ing, and cannot be detected in the butter. 
 
 No experiments, so far as I am aware, have yet been instituted to 
 decide the exact limit of heat that may be employed in pasteurising 
 milk or cream for butter-making, but, whereas a few years ago 158° to 
 165° were the temperatures generally employed in the Danish factories, 
 I notice of late a tendency to employ considerably higher degrees of heat, 
 reaching even to 185°. Assuming, for argument's sake, that 158° is the 
 maximum temperature to be employed, the question arises whether this 
 degree of heat-, maintained for the short time milk remains in a pasteuris- 
 ing-machine as at present constructed, is sufficient to destroy all the 
 bacteria we wish to get rid of. In considering this question much 
 depends on the object in view — in other words, upon what particular 
 bacteria one wishes to destroy. For instance, the butter-maker is prac- 
 tically not concerned about pathogenic germs ; all he wants is to compass 
 the death of those bacteria which would otherwise interfere with the 
 flavour of his cream. The milk-supplier, on the other hand, is very 
 
much concerned with the pathogenic germs, for he has to feed his calves 
 and pigs on the skim-milk returned from the factory, and he wishes to be 
 sure that it contains no disease-germs. The town milk-vendor is also con- 
 cerned about the disease-germs, for not only does he desire to enhance the 
 keeping qualities of his milk by killing the lactic-acid bacteria, but to 
 guard against possible contamination from tuberculosis and every other 
 disease that can be conveyed in milk. 
 
 For clearness' sake, we will discuss the question of the best tempera- 
 ture to employ in pasteurisation from each of these three standpoints — 
 the butter-maker's, the factory-supplier's, and the town milk- vendor's. 
 
 The Butter-maker's Standpoint. 
 
 The aim of the butter-maker is to kill all the lactic-acid and other 
 bacteria which influence the flavour of his product, so that he may have 
 a perfectly clean field in which to sow and cultivate the particular bacteria 
 that will produce the flavour he desires. He can effect this in two ways : 
 he can pasteurise the whole milk before separation, putting it through the 
 separator hot and subsequently cooling the cream, or he may pasteurise 
 the cream by itself after separation. If he discards all thought of destroy- 
 ing disease-germs he need have no hesitation as to the best temperature 
 to employ, whether upon milk or cream. The bacteria likely to give him 
 trouble (in the case of milk of average cleanliness) may be killed at 160° 
 to 165°, maintained for about two minutes, which is the time milk remains 
 in any ordinary pasteurising-machine. He will gain nothing by exceeding 
 this point, and he avoids all risk of imparting any cooked taste to the 
 product, provided it is kept in motion whilst being heated, and is after- 
 wards cooled quickly. 
 
 The Factory-supplier's Standpoint. 
 
 It must, however, be borne in mind that this temperature, unless 
 maintained for at least fifteen minutes, will not destroy the germs of 
 tuberculosis. Now, it is with these very germs that the milk-supplier is 
 chiefly concerned. If the butter-maker pasteurises the cream by itself 
 there is no difficulty in treating the skim-milk so as to kill all disease- 
 germs. All that has to be done is to heat it to 190° or over and deliver it 
 to the suppliers either hot or cooled down, according to the facilities avail- 
 able for cooling. Of course, such a high temperature as 190° will impart 
 a cooked taste to the milk, but where it is intended only for calf- and pig-- 
 food this will not signify. If, however, it is decided to adopt the system 
 of pasteurising the whole milk prior to separation, a conflict of interests 
 may arise between the butter-maker and the supplier. The former fears 
 •to exceed 165°, or at most 170°, lest he should thereby injure his butter, 
 while the supplier insists upon the skim-milk being free from the germs 
 of tuberculosis. To meet this difficulty one of two plans may be adopted : 
 the hot milk as it comes from the pasteuriser may be kept for fifteen 
 to twenty minutes (according to the temperature used) in an insulated vat 
 before passing into the separator, or the skim-milk may be further heated 
 to at least 190° by passing it through a second pasteurising-machine as 
 it comes from the separator. Of course, all these precautions against 
 tuberculosis would be obviated by a regular system of veterinary inspec- 
 tion of the cows. 
 
 The Milk-vendor's Standpoint. 
 The milk-vendor employs pasteurisation to kill the lactic-acid and the 
 ordinary pathogenic germs, and while doing this he has to be most care- 
 
ful not to injure the flavour of the milk in the least degree, nor to impair 
 its digestibility by allowing the coagulation of the albumen to take place. 
 Consequently he is limited to 158°, and, if the more resistant pathogenic 
 germs are to be destroyed with certainty, he must submit his milk or 
 cream to this temperature for at least twenty minutes. There is no great 
 difficulty about doing this on a small, nor for that matter on a large, 
 scale, provided one has the apparatus. But it is as well to emphasize the 
 fact that none of the continuous pasteurising-machines yet introduced 
 fulfil the above requirements. Few of them retain the milk for more than 
 one or two minutes, the aim of the makers being to put as much milk 
 through in a given time as possible, and this they effect by shortening the 
 period of the action of the temperature on the milk. In fact, pasteurisa- 
 tion of milk as carried out in any of the ordinary pasteurising-machines 
 is comparatively valueless as a preventive of milk-borne disease. A cor- 
 respondent hit the nail on the head when he wrote, " You may introduce 
 plant, and call the work done by it ' pasteurisation,' and people will be 
 content, even if contentment under the circumstances is foolishness." 
 
 There is only one way for milkmen to secure perfect pasteurisation 
 without injuring the milk in flavour or digestibility, and that is to 
 
 HEAT THE MILK IN GLASS BOTTLES TO 158° FOE HALF AN HOUE ; CLOSE 
 THE BOTTLES WHILE STILL HOT ) THEN COOL TO 45°, AND DELIVEE TO 
 
 THE CONSUMEES IN THESE BOTTLES. All Other methods, and any devia- 
 tion from this method, are open to objections. 
 
 Pasteueisation in Peactice. 
 We may now proceed to the consideration of the practical application 
 of the process in factory-work. First of all, there is the choice of methods 
 mentioned in a previous paragraph — pasteurisation of the whole milk prior 
 to separation, or pasteurisation of the cream by itself and the skim-milk 
 by itself after separation. The former method enables cleaner skimming 
 to be done, and at the same time more thoroughly eliminates the noxious 
 fatty acids from the milk. The first of these considerations is the one 
 that appeals to us most strongly, for the saving that may be efi'ected by 
 the cleaner skimming is no trifle on a large turnover. The usual tem- 
 perature for separating is from 75° to 85°, at which temperature the skim- 
 milk from most separators contains about 0-1 per cent, of butter-fat. 
 When separated at 150° or upwards, the skim-milk seldom contains more 
 than 0-05 per cent. — indeed, we have frequently seen even better results. 
 The difference represented here will amount at any fairly large factory 
 to many thousands of pounds of butter per annum. This affords a very 
 strong argument in favour of pasteurising the whole milk. The only 
 objections that occur to us against this plan are the difficulty of hand- 
 ling the hot skim -milk, and the acidity of the milk in warm weather 
 causing the separator bowl to become clogged, which necessitates the 
 cleansing of the bowl at intervals — say, after 600 or 700 gallons have 
 passed through. The skim-milk trouble arises from the frothiness pre- 
 venting the ordinary pumps to work satisfactorily, and may be got over 
 by utilising gravitation wherever possible to convey the milk from the 
 separator to the supplier, or by cooling it to about 65° before pumping. 
 Possibly the large pumps now being introduced will be able to cope 
 with the froth, but on this point we cannot as yet speak authoritatively. 
 To clean the separator^ bowl of its deposit is not a very serious under- 
 taking, especially if things are arranged with a view to this contingency. 
 We are, on the whole, in favour of pasteurising the milk prior to 
 separation, maintaining a_] temperature of 160° to 170° as nearly as 
 
possible; if tuberculosis is feared it Will be necessary either to keep the 
 heated milk for twenty minutes in an insulated vat before passing it into 
 the separator, or else to lead the skim-milk into a second pasteuriser 
 standing below the level of the separator, where the temperature can be 
 raised to 190° or over. Prom this second pasteuriser the skim-milk 
 would be elevated automatically to the suppliers' tank. 
 
 Pastbueised Skim-milk. 
 
 Pasteurised skim- milk will, of course, keep sweet much longer if 
 cooled immediately than if allowed to cool of itself, but even without 
 artificial cooling it will keep many hours longer than if not pasteurised. 
 Consequently calves thrive better on it — apart altogether from the 
 question of tuberculosis— simply because they do not scour. If not cooled 
 down before being delivered to the suppliers it is advisable, though not 
 absolutely necessary, to first steam the cans used to take it home with. 
 The hot milk practically destroys any germs there may be in the cans. 
 But where the milk is cooled down it is an indispensable part of the 
 process of pasteurisation that both cans and lids be thoroughly steamed 
 before the milk is run into them. Otherwise the germs in the cans will 
 contaminate the milk and undo all the benefits of pasteurising. 
 
 The Skimming-station Factoe. 
 
 At most skimming-stations there is no reason why the whole milk 
 should not be pasteurised before separation, as recommended above. The 
 advantage of cleaner skimming comes in here as much as at the main 
 factory, and, so far as expense goes, the increased recovery of butter-fat 
 will more than compensate for the cost of treatment. But there are 
 skimming-stations where cold water for cooling purposes is scarce, or even 
 unattainable, and in this the diificulty lies. It has been suggested that 
 the cream be carted hot, without any cooling whatever. This has actually 
 been done in some parts of America and Australia, but, so far as we know, 
 only in an experimental fashion. The results were reported to be satis- 
 factory, but, as we have had no opportunity of confirming or refuting these 
 reports first hand, we are not prepared to take the responsibility of re- 
 commending this method. 
 
 Another suggestion is to procure ice from the main factory wherewith 
 to cool the cream. In many cases this is quite feasible, and we know of 
 instances where this plan is now in vogue. Faihng these two methods, the 
 only other way in the case of a skimming-station without water would be 
 to pasteurise the cream on, delivery at the main factory. This course is 
 sometimes adopted, but it stands to reason that as good results cannot be 
 expected from cream in which fermentation is comparatively far advanced 
 as from cream in perfect condition. 
 
 Treatment of the Ceeam. 
 Whatever system be adopted, all those experienced in pasteurisation 
 insist that the cream be cooled immediately and rapidly after heating. 
 The Danes invariably cool to 50°, sometimes to 45°, and reheat to ripen- 
 ing temperature (generally about 65° to 70°, according to the time of the 
 year). They claim that this low cooling is necessary to give the butter 
 "body." Few Danish factories, however, handle the big quantities that 
 our larger concerns do, and labour with them is much cheaper. Wherever 
 possible it is certainly advisable to cool right down, and rewarin to ripen- 
 ing temperature. But this involves considerable labour and expense. 
 2 
 
10 
 
 Probably the case may be met and much extra labour saved by simply 
 cooling to 55°, and ripening at that temperature. 
 
 The chemical composition of the milk-fats varies with the locality and 
 the period of lactation of the cows, and it will be found necessary to cool 
 the cream lower in some districts, and at some seasons, than in others. 
 Experience alone can determine what will best suit the requirements of 
 any particular locality, but it may be laid down as a general rule that, 
 unless the cream be cooled- to at lease 65° as soon as possible after heating, 
 the butter will suffer in " body," and be of a greasy, oily nature. In this 
 connection, the importance of every factory being equipped with ample 
 refrigerating-power cannot be too fully realised. Abundant cold water — 
 say, at 52° — will enable pasteurisation to be. undertaken with fairly satis- 
 factory results ; but only by the aid of refrigeration can the best possible 
 results be achieved. 
 
 ElPENING THE CbBAM. 
 
 Considerable difi&culty has been experienced by disciples of pasteurisa- 
 tion in New Zealand in ripening the cream. To npen pasteurised cream 
 successfully we have to inoculate it with a culture of such bacteria as 
 experience has shown will produce the desired aromatic flavour. There 
 are several ways of doing this — we may add a portion of sour butter-milk 
 from the previous churning ; we may use whole milk ripened naturally — 
 i.e., by simply standing in a warm pure atmosphere ; we may use skim- 
 milk similarly treated, or first pasteurised and then allowed to ripen 
 naturally ; or we may employ a pure culture or lactic ferment, the com- 
 mercial starter now universally used in Denmark. Provided the butter- 
 milk shows no fault, and is carefully watched from day to day, we have 
 no objection to its use as a starter. It is generally preferable, however, 
 to be independent of the butter-milk, and to make one's own starter. 
 New milk taken from healthy well-fed cows, milked with the utmost 
 cleanliness, or pasteurised skim-milk, ripened naturally at suitable tem- 
 peratures, form excellent starters. The commercial starter has gained 
 popularity not because it produces a finer flavour, but because it is more 
 uniform. Its use requires just as much care and cleanliness as the home- 
 made starters. It is necessary, however, that this kind of starter should be 
 freshly imported, as the makers do not guarantee it if more than three 
 months old. That most generally used is Hansen's lactic ferment, which 
 costs £1 10s. per dozen bottles in London. There is no reason why 
 arrangements should not be made for the despatch of 'regular supplies by 
 each mail-boat. 
 
 Making a Staetbe. 
 
 For those who wish to make their own starter the following method 
 is recommended by Professor Eobertson, of Canada, and has been found 
 suitable in this country. It is. based upon the assumption that " the 
 atmosphere of a clean dairy building contains ferments which get into all 
 milk or cream exposed to it, and are capable of imparting to the butter a 
 flavour of high market value." Two quarts of sweet skim-milk are taken 
 and heated to 200°. That temperature is maintained for ten minutes, 
 after which, and while exposed to the atmosphere of the dairy, the milk is 
 cooled down to 80°, placed in a clean glass bottle, closed with a glass 
 stopper, and left for five days in the ordinary temperature of the dairy — say, 
 60° to 70°. It will then be found to have coagulated, and to possess a mild, 
 pure lactic-acid flavour, which will become more distinct after it has been 
 kept for a time at a temperature of 40°. This forms the " culture," and is 
 used in the preparation of the starter proper, which is made as follows : 
 
11 
 
 Calculate the quantity of cream to be ripened, and take a quantity of 
 sweet skim-milk equal to 5 per cent, of this amount ; heat to 165° for ten 
 minutes, and then cool to 80° ; add to it 10 per cent, of its bulk of the 
 culture as described above, and allow it to stand till coagulated. Imme- 
 diately coagulation takes place cool to 40°, and keep at that temperature 
 till required. This starter, if properly made, should possess the same 
 characteristics as the culture from which it is made, and may be used in 
 the cream at the rate of about 5 per cent. It is not necessary to form a 
 new culture every day, for as long as the flavour of the starter retains its 
 purity and mildness, it may be used in the place of the original culture. 
 Sometimes it is not necessary to make a fresh culture for a month or six 
 weeks. In the event of the starter going bad, one must throw it out 
 and make a fresh one, using butter-milk from the previous churning in the 
 meantime. 
 
 WOEKING PaSTEUKISBD BuTTEE. 
 
 Butter made from pasteurised milk or cream requires less working to 
 expel the moisture, and care must be taken not to overwork it or it 
 quickly becomes greasy. At the same time, there must be no streakiness 
 in the butter when made ; consequently the butter-maker must use great 
 judgment and a scientifically constructed butter-worker if he wishes to 
 strike the happy medium. The construction of butter-workers on more 
 scientific lines is a point that might well engage the attention of dairy- 
 implement makers and factory-managers. 
 
 As TO THE Cost. 
 
 The cost of pasteurising is comprised of interest and depreciation on 
 the pasteuriser, plus the steam and cooling-power required. The interest 
 and wear-and-tear on a pasteurising-machine ranges from £2 10s. to £5, 
 according to size. The extra cooling-power in most cases would not be 
 worth reckoning up. Where the exhaust steam from the engine is not 
 utilised the heat may be derived from this source. If otherwise utilised, 
 a small pressure of live steam will suffice. At one factory it was found 
 that less than a cord of firewood extra per week was required to pasteurise 
 1,000 gallons of milk daily. The extra fuel cost about 10s. per week ; 
 but against this the manager recovered 901b. to 1001b. extra butter 
 through the cleaner skimming of the pasteurised milk, besides enhancing 
 the value of his whole output by at least fd. per pound. The proprietor 
 of this factory estimated his net gain by pasteurising at not less than 
 £10 per week, and we are prepared to fully indorse this estimate, being 
 personally acquainted with the conditions. 
 
 Wheeb Pasteueisation fails. 
 It is sometimes said that the adoption of pasteurisation will put a pre- 
 mium on dirty milk. The same thing was said of the centrifugal separator 
 when first introduced ; but no dairyman will, in the light of experience, 
 say that such is the case. The separator removes the solid impurities in 
 the milk, but it cannot expel taints. Similarly, pasteurisation checks 
 fermentation and removes taints that are not too pronounced, but it 
 cannot make bad milk perfect ; it will only make it less bad. Neither the 
 separator nor the pasteuriser will produce perfect butter without perfect 
 milk. In the same way the factory management must be of an intelli- 
 gent and painstaking order if pasteurisation is to succeed. Finally, unless 
 proper appliances are provided, and absolute control is obtained over 
 
12 
 
 temperature at every stage of the proceeding, no one need expect to derive 
 the full benefits of pasteurisation. 
 
 Acknowledgment. 
 
 I am indebted to Mr. J. A. Gilruth, Government Bacteriologist, 
 for having kindly revised and approved this pamphlet from a bacterio- 
 logical standpoint. Statements bearing directly on this science are there- 
 fore entitled to an amount of consideration that could not be expected 
 were they made solely on my own responsibility. — C. W. S. 
 
 By Authority : John Mackay, Government Printer, Wellington.— 1898. 
 
 1750/5/98-2854 
 
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