WASHING DAIRY ITTENSMS It is too often the case that the dairyman is sat isfied with cleaning milk utensils like kitchen dishes. More care is required in cleaning dairy utensils, for the reason that bacteria multiply so readily in the smallest particles of milk which may be left in the corners of dairy utensils. Erf and others have repeatedly called atten tion to the necessity of using a brush, and a good washing powder on every part of the cream separator after each using. All parts should then be rinsed in boiling water, or, still better, steamed and left to dry while hot. The use of wiping cloths is almost sure to contami nate milk utensils, since they are not bacteriologically clean, except in the rarest instances. Erf found that the bacterial contamination of milk was in creased three times by running it through a separator which had merely been flushed and not thoroughly cleansed. Various investigators have found that the separator slime, found in the separa tor after the cream has been removed, contains a relatively large percentage of bacteria, and whenever this is used in feeding pigs, without previous boil ing, tuberculosis develops in a large percentage of cases.
Haecker and others have found it de sirable to use special precautions to prevent the contamination of milk dur ing milking. It is recommended by Haecker that the udder and teats be washed, after which an application of a vaseline ointment containing 5 per cent of carbolic acid is used.
Fermentation of milk The presence of bacteria or other filth in milk leads to rapid fermentation and souring. It is a comparatively simple matter to convince one's self that the exercise of special care in preventing the contam ination of milk will yield milk which will keep much longer than that which has been carelessly handled, and, there fore, contains filth. This is a matter of great importance to the dairyman who sells milk for use as such, since the cus tomer naturally wants milk which will keep fresh as long as possible. If milk is intended for the manufacture of but ter or cheese, harmless bacteria in it simply serve to hasten the ripening proc ess. Some of these bacteria, however, may give a rancid or otherwise disagree able flavor to the butter or cheese. Even when every possible precaution is taken, enough bacteria will gain entrance to the milk to produce a souring and ripen ing of the cream.
More than 200 species of bacteria have been found in milk. Fortunately, however, most of them are harmless, ex cept that they cause the milk to sour. Some produce bitter flavors, others, gas, and still others, color changes. The best results in the souring of milk and ripen ing of cream are obtained when bac teria are excluded as far as possible by cleanly methods of milking and han dling the milk, and when starters are used which are known to produce a de sirable flavor in the butter.
Practical methods of handling milk In dairying as conducted at present, the farmer is primarily interested in the production of fine milk. The technical operations by which butter, cheese or condensed milk and other milk products are manufactured, are chiefly of interest to expert butter or cheese makers in the factories to which the farmer delivers his milk. It is still true, however, that far more than half of the butter pro duced in the United States is made on farms. The price obtained for farm butter is altogether too low, and this is due to the poor quality of such butter, and the many complaints which are made concerning it. It is of much im portance to the farmer, therefore, to adopt improved methods in handling milk and making butter, since otherwise, he cannot obtain remunerative prices for these products. Thus, at present, in the southern states, well made creamery butter readily sells for 30 cents a pound, while average farm butter will bring but 10 to 12 cents. The cost of producing 10-cent butter is about the same as that for 30-cent butter, and the desirability of giving more attention to modern methods in producing butter is, there fore, apparent.
Aerating milk Mention has already been made of the desirability of aerat ing the milk as soon as it has been drawn. This is practiced extensively by dairymen and milk dealers throughout the country. It is only recently, that particular attention has been called to this matter in the United States. The immediate purpose of aerating the milk is to remove the animal odor which is present in warm milk, and which is disagreeable to many persons. As a matter of fact, the animal odor of milk will disappear in the ordinary course of events if the milk is allowed to stand for some time under sanitary conditions, but the process is much hastened by the use of an aerator. The aerators in com mon use are very simple in construction. In fact, the milk may be fairly well aerated by simply dipping it up from the can and pouring it back from some height above the can. Most of the aerators in general use consist essen tially of a tin reservoir supported by legs and perforated with small holes. The milk is poured into the reservoir above and passes out through the small holes into the can below. The milk may also be made to run in a tin sheet over a metal surface which is cooled from be hind with cold water. The milk is thus aerated and cooled off at the same time.
Aeration of milk not only removes the animal odor but improves the keeping quality of the milk. In some compara tive tests, it has been found that un aerated milk keeps as long as that which has been aerated, but this, as a rule, is the case only when the milk is obtained in an unusually clean condition. The use of an aerator appears to have little effect upon the quality of butter or cheese made from the milk. Its chief value consists in the fact that aeration may be accomplished by a cheap tus which cools the milk rapidly at the same time.
Another type of aerator depends upon forcing the air through the milk. The animal odors are thus rapidly removed, but the milk is not thereby cooled and does not keep appreciably longer than unaerated milk. Marshall, in Michigan, found that in aerating milk a consider able per cent of the carbon dioxide was removed and this was considered an un favorable result of aeration. Carbon dioxide is not harmful when taken into the stomach, and its presence in the milk has a tendency to ehe,.k the growth of bacteria and prevent the souring of the milk. In some of Marshall's experi ments, the aerated milk soured more quickly than that which was not aerated. In these tests, however, the milk was in an unusually clean condition, and the results perhaps do not apply to milk which contains a relatively high num ber of bacteria and considerable filth.
Doane suggests that the chief use of the aerator should be in helping the city dealer to remove bad odors which milk may contain, while the farmer should strive to produce milk which does not need the aerator in order to eliminate bad smells.
Pasteurization Of the various meth ods which have been adopted for elim inating bacteria from milk, or greatly reducing their number, pasteurization occupies an important place. It may be assumed as certain that even under the best possible conditions a consid erable number of bacteria will gain en trance to the milk. The possibility cannot be excluded that among these bacteria there are some which belong to harmful species. The simplest and surest means of destroying these bac teria is found in pasteurization. This may be accomplished by exposing the milk for 10 to 15 minutes at a tempera ture of 158° F. This method has a dis tinct advantage, since the milk does not thereby acquire a cooked taste, and its keeping qualities are greatly improved. It is desirable, however, immediately af ter pasteurization that the milk be re duced to a temperature of 50° F. and kept at that point. The recommenda tions made by different dairy experts re garding the length of exposure, and the temperature of pasteurization, vary con siderably. In Michigan, pasteurization was successfully accomplished by heat ing the milk to 155° F. and keeping it at that temperature for 20 minutes. Later experiments in Wisconsin showed that when milk was maintained at 140° F. for 15 or 20 minutes, about 99 per cent of bacteria were killed and the milk kept sweet for six days. On this point, however, opinions vary somewhat, and the results obtained depend upon the skill applied to the process of pasteuriza tion. Thus Harrington estimates that about 75 per cent of ordinary bacteria in milk are destroyed by keeping the milk for one hour at 140° F., for 15 minutes at 150° F., or for 10 minutes at 158° F. If milk is carried above 158° F. it acquire a cooked taste. For practical purposes, therefore, a temperature of about 155° F. for 20 or 30 minutes should be considered satisfactory for pas teurization.
Many physicians claim that the use even of such low temperatures unfavor ably influences the digestibility and nu tritive value of milk for infant feeding, and that, for this reason, preference should be given to raw milk for infant feeding obtained under strict sanitary conditions.
Kober and others, however, call atten tion to the difficulty of obtaining raw milk in such a way as to guarantee its absolute wholesomeness for children, and, therefore, recommend pasteurization as the lesser evil of the two. In fact, many physicians believe that the dangers from the use of pasteurized milk have been greatly exaggerated.
Pasteurization is commonly accom plished by placing the milk in vessels surrounded by hot water. A considerable number of satisfactory pasteurizers have been placed on the market and may be obtained from dealers in dairy products. Detailed directions for their use are fur nished with the apparatus.
Bacteria in milk as related to tern perature The chief purpose for cooling milk immediately after it is drawn is to check the growth of bacteria and thereby lengthen the time during which the milk will remain sweet. It has been found by the extensive investigations of Conn and others that variations in temperature have a striking influence upon the rate of multiplication of bacteria in milk. At a temperature of 50° F. bacteria may multiply only fivefold in 24 hours, while in the same period at 70° F. they may multiply 750 times. It is obvious, there fore, that temperature has a great in fluence upon the keeping property of milk. Milk maintained at F. will curdle in 18 hours, while the same milk kept at 70° F. will not curdle until af ter 48 hours, and at 50° F. may not curdle for two weeks. Conn has, there fore, called attention to the fact that the keeping quality of the milk depends more intimately upon the temperature at which the milk is kept than upon the original contamination of the milk with filth and bacteria. The use of refriger ation, however, should not be allowed as a means of preventing the bad results of filthy habits in milking.
Formalin as a preservative of milk Special attention is called to formalin as a milk preservative for the reason that this chemical has recently been used more extensively than any other for the pur pose of preventing the souring of milk, and the development of bacteria in it. Numerous experiments with it have been carried on by European investigators and by the United States Department of Agriculture and agricultural experi ment stations in the different states. It has been shown by Chester, that bacteria diminish rapidly in milk when it con tains formalin at the rate of one part in 2,000. Even when formalin was added only to the extent of one part in 4,000 the multiplication of bacteria was much less rapid than in the case of untreated milk. Chester believes that the use of 1 teaspoonful of 40 per cent formalin for each 15 gallons of milk will improve the sanitary condition of the milk by pre venting fermentation without causing any marked harm to persons who con sume the milk. As already stated under the discussion of Beef Animals, Klein and others have found that the use of formalin in milk fed to calves may be depended upon to prevent or cure scours. The action of the formalin is obviously the same in this case as when used sim ply for preventing the fermentation of milk. Moreover, Von Behring recom mends the addition of formalin at the rate of one part to 20,000 to 40,000 parts of milk in order to destroy tubercle bacilli in the milk. The whole question of the use of preservatives, however, is at present subject to a bitter controversy and until some of the doubtful points are settled regarding their use, it seems best to recommend against the use of any preservative in milk, for the reason that by the exercise of due care milk can be obtained which will keep long enough for the purposes of the ordinary consumer.
Babcock milk test The only means of knowing the productivity of each cow consists in weighing the milk and testing it from time to time for fat con tent. Reliable spring scales are inex pensive and may be hung in positions so that the time occupied in weighing the milk of each cow is exceeding slight. The percentage of butter fat should also be tested once a month or oftener. The best and simplest apparatus for deter mining the percentage of fat in milk is the Babcock tester. In making the test, the milk to be tested should be thor oughly shaken so as to obtain a fair, average sample. The samples from dif ferent cows are then mixed with strong sulphuric acid in Babcock test bottles and whirled at the rate of 850 to 1,000 revolutions a minute in the Babcock tester for about five minutes. The con tents of each bottle should be well shaken before whirling in the tester and immediately after adding the sulphuric acid. The action of the acid is to digest the protein of the milk and set free the fat, which readily separates from the rest of the milk. After the machine has been whirled for five minutes it is stopped and pure hot water, preferably distilled water, is added so as to fill the bottles up to the neck. The machine is then whirled again for two minutes and hot water again added until the fat rises in the neck of the bottle, where the percentage may be read on a gradu ated scale. The machine is again whirled for a minute to make sure that all the fat is separated, and the tempera ture of the milk at this time should preferably range between 120° and 140° F. If too much acid is used or the milk is too warm at the time when the acid is added, some of the fat may be charred; on the other hand, if too little acid is used, white flocculent material may appear at the lower end of the fat column; again, if the water is impure or hard, there may be a mass of foam at the top of the fat column. The reading of the percentage of fat is a simple mat ter, which may be done very accurately after a little experience has been had.
Creaming of milk After the milk has been somewhat cooled by the use of a cooler, or some other cooling device, it may be set in shallow or deep pans for the separation of the milk by gravity; or the milk may be run through a separator without any preliminary cooling. There are. therefore, two general systems of cream separation, the gravity and cen trifugal systems, both of which depend for their results upon the difference in the specific gravity between the fat and other parts of the milk. There are three modifications of the gravity system in common use, namely, shallow setting, deep setting, and water dilution.