The production and handling of clean milk

Front matter

Class Sfji^a.

Book MXX.-

Copyiight N°

Preface

The writer is a graduate in agricultural science, in veterinary and human medicine, and has been connected with a laboratory in which is examined the milk supply of a large city, and finally has had considerable practical experience in the production and distribution of clean milk.

These facts are simply mentioned to show that the book is written from various points of view.

Much blame is attached to sundry persons engaged in vending milk, but the unfortunate farmer is apt to receive an unjust share because of the commonly unclean and therefore unsanitary condition of most market milk. While city contractors and dealers may have much influence in instructing and requiring the farmer to live up to recognized standards of cleanliness, yet, after all, the chief responsibility lies with the consumer. The essential object in the clean milk crusade should be to awaken the public to the dangers of unclean milk and to emphasize the fact that it is impossible to produce and obtain clean milk except at unusual expense.

When the public is sufficiently aroused to the evils of consuming unclean milk and evinces willingness to pay for clean milk, there will be no difficulty about its production. It is merely a question of supply and demand.

PREFACE

It is not generally known that the farmer sometimes receives but one-quarter of the retail price of milk (frequently but 2 cents a quart), and he can hardly be expected to undertake a considerably increased expenditure for the production of clean milk — this being the case.

There is probably more interest being shown in this and other countries in a pure milk supply than ever before. For this reason it should be a comparatively easy task for any individual desiring to produce clean milk in any considerable community to find a sufficient patronage, particularly if the local medical profession is asked to assist, always providing that the proper standard is constantly and conscientiously maintained. The idea of financial return must be subordinated to this, and yet a reasonable profit can and must be had to sustain the required standard.

The aim of this book is to provide a working guide for those pursuing or wishing to pursue one of the most wholesome, worthy and laudable undertakings — the production of clean milk.

Most of the books at our command either touch the subject in a general manner or else describe special phases of it in detail. The attempt has here been made to cover the whole ground in as small compass as possible. That such an attempt must fall short the author is aware, as the topic of feeding cows alone (accorded but a chapter in this book) can only be fully treated in a large volume devoted wholly to this subject.

Objection may be made to the recommendation of particular apparatus of certain manufacturers. But the

PREFACE

writer has been so desirous of making the book practical that it has been deemed essential to choose special appliances in order to avoid generalities and vagueness.

While endeavoring to select the best, it does not follow that other appliances are not as good, or even better than those advised ; but the author can truthfully affirm that both he and his publisher are entirely free from the remotest financial interest in advertising any special dairy appliances. Such appliances are undergoing the most wonderful and rapid improvement, almost from day to day.

Kenelm Winslow,

Contents

CHAP. PAGE

I. Germs in their General Relation to Milk . . i II. Composition of Milk and Cream and Their Products 23

III. Milk Products 33

Chapter I Germs In Their General Relations

TO MILK

THE object of this book is to show the importance — nay, even necessity — of a clean milk production, and the practical methods by which it may be obtained. Heretofore milk has been regarded much in the same light as other articles of food, but It differs from them in many important respects. It is the only animal food which is commonly eaten in the raw state, and it forms the sole diet for human beings at an immature age, when they are least able to cope with the disorders which contaminated and dirty milk is liable to produce. Again — and this is the chief reason why milk needs especial care in its production — it always contains more or less germs, and, indeed, forms one of the most favorable foods on which germs grow.

The common idea of germs appears to be that they are chiefly important in being the. cause of disease, and while some germs do produce disease — and occasionally those inhabiting milk which has not been properly cared for — yet they mainly interest the farmer on account of their powerful and enormous influence upon milk and its products. The chief aim of this book is to enforce on the farrner and dairyman this one fact, that the One Essential in producing and handling milk is Cleanliness, and cleanliness means in this connection freedom from germs, so far as this is possible.

It would scarce be an exaggeration to say that all the trouble which arises in the endeavor to secure good milk or milk-products results from the contamination of milk with undesirable germs. Thus the proper taste, odor, color, consistency and keeping qualities of milk depend upon its comparative freedom from undesirable germs. Conversely, the souring of milk and faults in odor, color, consistency and taste depend almost wholly upon the presence of one or more varieties of germs.

Moreover, the prevention of contamination of milk with miscellaneous germs is just as important in order to make the best products from milk, as it is to avoid disease in man. Thus the finest cream is only produced from milk in which germs are comparatively absent. Cream laden with miscellaneous germs has bad keeping qualities and often a faulty taste or odor. Most of the so-called faults of butter arise not from improper feeding of cows or from improper making or handling of butter, but from undesirable germs which infest it. Among some of the more common faults of butter are poor flavor, tallowy or oily butter, butter having a bitter, rotten or root-taste like turnips, rancid, mottled and moldy butter, and butter of unusual colors ; all of these faults have been proved to be due to the contamination of butter with germs which existed in the milk.

While germs in milk produce changes in cheese which give rise to its proper consistency and flavor, yet it is only a certain type or types of germs which are desirable, and a general pollution of milk with germs of many kinds may wholly unfit milk for cheese making.

It is essential that milk should be pure when employed for condensing, and, although germs are destroyed in the process, this is much more readily accomplished if the milk is clean in the beginning and the keeping qualities will be much better. Above all, when milk is sold for general consumption it must be pure — comparatively germ-free — to be wholesome, to bring a good price, to keep, and to fall within the legal requirements which will soon become general throughout this country.

Heretofore, when milk was regarded in the same litrht as any other food, the law required simply that it should not be adulterated and that it should contain a quantity of food-constituents equivalent to the minimum standard in force. Now, however, it has come to be realized that of the two the cleanliness of the milk is an hundredfold more important than its food value. While a milk poor in fat may mean a certain loss of nutriment to one using it, the contamination of milk with certain germs may be a matter of life and death to the consumer — particularly if an infant. The sooner the farmer and dairyman realize that the secret of success in the making of milk and milk-products is cleanliness — and by cleanliness we mean essentially methods to prevent the entrance of germs into milk — the better will it be for them and for everyone.

Germs, or, as they are more technically termed, bacteria, are the most minute forms of plant life we know. They occur in various shapes, but chiefly in the form of either rods, round cells or spirals. When seen through the microscope they present somewhat the appearance of minute pencils, billiard balls or cork-screws, according as they belong to one or the other of these three types. In masses of thousands they may be visible to the naked eye as specks like mold, but singly they can only be seen with a compound microscope magnifying more than 500 times. The most common of all varieties of germs in milk are those which cause it to sour — the lactic acid bacilli (the bacilli are the rod or pencil-shaped germs), and these are about 3-25,000 of an inch long and 1-25,000 of an inch broad. Germs grow on vegetable and animal matter, but not in the tissues or cells of living animals or vegetables, althougTi they are found on all parts of them exposed to the air. Germs are, in fact, everywhere — in the air, in water, in soil, on the skin and in the digestive canal of animals and on the surface of plants and in dust. Professor Conn has found as many as 200 different kinds of germs in milk alone. Germs.

Fig. I.

General shape of bacteria, a, spheres ; b, rods ; c, spirals. (After Conn.)

0^0

a O propagate by dividing into two equal parts — more usually — which form new individuals. The time required for a germ to mature and form a new germ may not be more than twenty minutes.

Germs also multiply by spores — that is, small, round or egg-shaped bodies appear within the mature germ and these later break loose and develop, under favorable circumstances, into full-grown germs again. Germs which increase in this manner are much more difficult to kill, for in the spore stage they often defy prolonged heat, even at the boiling temperature, and also cold at or below freezing and dryness, as dust, in v ■ 'ch they may exist for years.-

To show the possibilities in the way of multiplication, it has been calculated that a single germ, under favorable circumstances, may within twenty-four hours produce over sixteen millions of progeny.

Germs, however, depend upon certain conditions for their growth ; otherwise they would crowd all other life off the globe. Besides organic matter to feed on, the chief circumstances limiting their existence are heat and moisture. Germs usually do not grow at a temperature below 39*^ or above 140° F. Freezing does not necessarily destroy germs — as, for instance, the germs of typhoid fever have remained alive in ice for a period of three months — but this temperature checks their growth and many kinds of germs are killed by it. Ice water is therefore comparatively free from germs. The most favorable temperature for the growth of disease germs is that of the animal body — from 98^ F. to 103^ F. — while most other germs multiply most readily between the temperatures of 59^ F. and ']']'^ F.

This knowledge is of the greatest importance in the care of milk and teaches us that the chief essential consists in cooling it immediately to a low temperature — 40^^ F. to, 50^ F. — and keeping it at this temperature thereafter till consumed. The number of germs in milk is always estimated as that number contained in a cubic centimeter of milk. A •cubic centimeter represents a cube holding a quantity of hquid equivalent to about one-quarter of a teaspoonful, or sixteen drops of water. If milk is kept at below 50" F. for 24 hours there is not only not an increase but generally a decrease in the number of germs, and the same usually holds good for milk kept 36 hours below 45*^ F. After 36 hours, when milk is kept at 40° F., there is an increase in the number of germs. Dr. Park found in a sample of milk containing only 3,000 germs in the cubic centimeter, that after 24 hours at 42° F. it contained 2,600 germs ; after 48 hours 3,600 germs ; and after 96 hours 500,000 germs to the cubic centimeter. The number of germs in milk kept at 32*-^ F. lessens from day to day.

When milk is kept at higher temperatures the germs multiply rapidly and it sours and deteriorates correspondingly. It has been shown that very clean milk (containing but 3,000 germs to the cubic centimeter^, if kept for 24 hours at 60*^ F., held 180,000 germs; if kept at 86^ F. for 24 hours it contained 1,400,000 germs; and at 94^ F. the germs multiplied so tremendously that at the end of 24. hours the same milk contained 25 billion germs per cubic centimeter.

All germs require some moisture in order that they may actually grow, but they may exist in large quantities — for a longer or shorter time — in dust. Some require air for their existence, others do not.

Sunlight is one of the most powerful enemies of germs, since few will thrive in sunlight, especially in the presence of plenty of air. This explains the value of sunning dairy utensils and of permitting the sunlight to enter freely into the barn and dairy. Some germs grow more readily in substances having an alkaline or neutral reaction ; others, as those which cause milk to sour, flourish in an acid medium, providing the acidity is not too great.

The most potent factors in destroying germs are intense heat and cold, sunlight and chemicals. A temperature varying from 140*^ to 158° F. will kill most germs — if continued long enough or repeated at frequent intervals. Milk treated by continued, intermittent heating at 140^^ F. has been kept for years without changing, owing to the destruction of germs (and ferments) in it. As the time required for the destruction of germs at this temperature is too great for practical dairy purposes, a temperature of 165^ F. is usually applied for either killing or checking the de\elopment of germs in milk. Heating milk with this object in view is called technically pasteurization, after the great originator of the process. If properly done for twenty minutes, pasteurization kills most of the germs in milk and this is the best way to obviate the dangers of dirty milk for human consumption — more particularly in the case of infants. There are certain drawbacks to the process, however. If the milk has been kept long before heating, poisons may form in it which the heat will not destroy. Many medical authorities believe that milk thus heated is less digestible, but this is an unsettled matter at present. There are certain substances present in cows' milk exactly resembling those which bring about the digestion of food in the stomach and bowels of man and animals. These chemical substances in milk or in the digestive organs are called ferments. They appear to aid the digestibility of milk, particularly in infants, and are destroyed by heating milk over 179° F., or at a lower temperature if the milk is repeatedly heated.

It is generally accepted, however, that babies will not thrive so well on pasteurized milk for long periods, as on clean, unheated milk, and occasionally develop malnutrition, anemia, rickets and scurvy. The last may be prevented by feeding infants a small amount of orange juice daily. The simplest method of home pasteurization consists in pouring a quart of milk into a two-quart glass preserve jar and placing the jar with the milk in it on a flat, thin piece of wood (to prevent breaking of the jar by heat) in an open kettle. Warm water is then poured into the kettle so that it will rise to almost the level of the milk In the jar and the kettle Is set upon a stove. When the water in the kettle begins to boil the kettle is removed to the back or side of the stove — where it will receive but little heat — for twenty minutes, and then the bottle is taken from the kettle and placed in a refrigerator. As I have observed, in pasteurization done on a large scale for market purposes in Seattle, the result has been a farce other than it enabled the milkman to keep the milk for perhaps twenty-four hours longer than it would have otherwise kept sweet. The pasteurization of the market milk was only done for three minutes, possibly because the machine — which permitted of a cpntinuous flow of milk through it — was not competent to do the work properly, but also because thoroughly pasteurized milk has a cooked taste and cream does not rise readily from it, much of the fat remaining in the skim milk. The pasteurizers having a large chamber, in which the milk may be retained for the required time at the proper temperature, are preferable. Short pasteurization prevents milk from souring quickly because the germs which cause milk to sour are those most readily succumbing to heat. The general effect of short pasteurization is simply to check — for a longer or shorter time — the growth of germs. They are retarded in their development, not killed. Disease germs are not destroyed at all in the process. Experiments which 1 have conducted with the pasteurized milk of the general market showed that while containing but 15,000 germs to the cubic centimeter, soon after emerging from the pasteurizer on the delivery wagon, in twenty-four hours the same milk contained several million germs to the cubic centimeter. Drs. Bergey and Pennington found much the same result in Philadelphia ; that raw and recently pasteurized milk con-

GERMS IN RELATION TC MILK 9

tained respectively 1,260 and 12 bacteria, but, at the end of 72 hours, the numbers were 17,000,000 and 148,000,000 ^erms. Also the harmless lactic acid germs of raw milk are killed by heat, and the more dangerous germs from dirty bottles, corks and dust contaminate the improperly pasteurized milk. I have, however, pasteurized fresh, clean milk for twenty minutes and exposed it at mild spring weather temperature for nineteen hours in a sealed bottle with the result that it was absolutely free from germs at the end of that time. If pasteurization is done thoroughly the lactic acid bacilli (sour milk germs) are destroyed and so the milk does not sour but putrefies when it ages.

Pasteurization prevents milk from being properly curdled by rennet and so unfits milk for cheese-making. Pasteurized milk or cream may be used to advantage for buttermaking when the lactic acid germs are added In the form of sour milk, known as a "starter," which will be described later. If we must have dirty milk, pasteurization is the best remedy for this unhappy state of affairs, but it may well prove undesirable to thus remove the incentive to dairymen to produce clean milk. If done at all for the market, it should be done thoroughly by heating the milk for twenty minutes to 1650 F., followed by rapid cooling.* If milk is not cooled down to a low point after pasteurization, spores will develop which have escaped destruction on account of their great resistance to heat, and these will result in germs which, while not souring milk, act on the casein to cause it to curdle and perhaps become poisonous and putrid. In Europe pasteurization of milk is much more common than in this country, since ice is in less common use. In Denmark it is required by law, so that tuberculosis may not be spread when skim milk Is returned from the creameries and

* Pasteurized milk wliich is sold for general consumption should be always marked as such, iu order that infants shall not be harmed by its use.

lO CLEAN MILK

fed to calves. This custom might well be imitated in the United States, since the young stock are not only protected from disease, but the keeping quality of the skim milk is so much improved. A higher temperature than 165° F. gives the milk a boiled taste and alters its composition to some extent. Steam or boiling water are used to destroy germs in or on dairy utensils.

Chemicals find little use as germ-destroyers in a properly conducted dairy or farm. They may be employed to some extent in the barn (as lime scattered on the floor), or in case milk products become faulty through some contamination with special germs in the stable or dairy, when general disinfection is in order. The employment of the various preservatives under the trade names of Freezine, Iceline, Preservaline, Milk Sweet (all containing from two to five per cent, of formaldehyde), and others containing boric acid, as Dry Antiseptic, Preserving Salts, "A" Preservaline, Cream Albuminoid, Patent " M " Preservaline and Ozone Antiseptic Compound, are employed to keep milk from souring without the use of ice or cleanliness by killinor or checkincr the crrowth of crerms in milk. Their use is contrary to law and detrimental to the consumer's health, especially when employed, as they usually are, in a careless way, without regard to what the effect of a considerable amount of the chemical might be. Thus the following instance is related in the Year Book of the Department of Agriculture for 1900 of a case where a preserving fluid was first added to the milk by the farmer, then by the collector of the milk, again by the wholesale dealer, and finally the fourth dose by the retail dealer.

If it were impossible to produce clean milk or to preserve it with ice, and if preservatives could be used properly

GERMS IN RELATION TO MILK ii

in a harmless dose, their employment might be permitted, but such is not the case.

Significance of Gcrnis in Milk

The growth of large numbers of germs in milk causes it to deteriorate because they remove nutriment or alter the milk chemically and thus lessen its food-value. Ordinary market milk, which is overrun with germs, loses much of its value as food after it is twenty-four hours old. The ideal result would be reached if milk could be withdrawn from the cow absolutely free from germs. This might be possible if germs did not enter the udder in the air through the opening in the teat and find their way into the cavity or milk-cistern in the lower part of the udder. As the milking proceeds the germs in the milk-cistern and teat are washed away so that the latter part of the milk withdrawn is often absolutely free from germs until contaminated with the outside air. Occasionally germs may persist in milk throughout milking, and the strippings may contain as many as 500 germs to the cubic centimeter. If the latter part of the milk is withdrawn through an absolutely clean milking tube into an absolutely clean bottle, it will often be wholly without germs, and may keep sweet for months or years if it does not come in contact with the air. Such painstaking cleanliness as is necessary to make this experiment successful, is not of course practicable in actual dairy work, since it is not economically possible to throw away a laro-er part of the milk nor to withdraw milk so that it will not come in contact with air.* Therefore, under any ordinary conditions a certain number of germs must inevitably be present in the cleanest milk — perhaps 200 to 4,000 as the least number to the cubic centimeter.

* Since writing the above the use of the milking machine (see p. 189) makes withdrawal of milk without exposure to air practicable.

Then, if the milk is immediately cooled to 40° F. and retained at this temperature, the number of germs will lessen until it is thirty-six hours old.

The presence of many thousand germs to the cubic centimeter in milk freshly withdrawn indicates filthiness of the cow, milker or surroundings.

The existence of a great variety of germs in milk several hours old signifies contamination of the milk with filth also, because in clean milk only one kind of germs (lactic acid bacilli) are found very numerous after many hours.

While the .mere fact that milk contains a vast number of germs is not a sure proof of its unwholesomeness — because the commonest grerms in milk are harmless and because milk may contain but a few germs and these may be the cause of dangerous disease in man — yet the estimation of the number of germs in milk is to-day the best method we possess for determining its purity.

Ordinary market milk contains as many germs as sewage, and unusually dirty milk contains more germs than sewage was ever known to hold. This is, however, not at all a fair comparison, for while sewage is likely to contain all sorts of germs of disease, the germs in dirty milk are mostly not disease-germs.

We may consider the influence of germs in milk under two heads : i. The effects of germs on milk and its products. 2. The influence of eerms in milk on the consumer.

I. The Effects of Germs on Milk and Its Products. — All fermentation and putrefaction or.rotting, anywhere and of anything, are due to germs.

Germs are the great disintegrating agencies in the world ; they tend to break up complex, natural constituents in milk and Its products int.o simpler bodies. The commonest germs in milk — as we have noted — are those causing sourino- of milk ; they are invariably present and are about the only kind existing in very clean milk. They act to ferment or change the natural sugar of milk into an acid (lactic acid), and if they occur in large numbers a few hours after milking it is a sign that the milk has not been properly cooled and will sour early. Lactic acid germs, or those producing souring of milk, besides being the most common, are of most importance in their influence on milk and its products. They exist in very small numbers in milk soon after leaving the cow, but as they grow more readily than all other germs in milk at favorable temperatures (above 50^ and better over 70° F.), they often constitute almost 50 per cent, of all the germs in twenty-four hours. While, after this time, they gradually crowd out the different varieties of competing germs until they produce so much acid that the milk or cream sours and curdles, and they have multiplied so rapidly and have made the milk so unfavorable for other germs that they form from 90 to 99 per cent, of all the germs present. This is a most favorable occurrence, because the flavor of most butter and cheese is chiefly dependent on the action of the lactic acid germs, and in their growth they protect the milk from the action of miscellaneous germs which would spoil these products.

Even to man the growth of the lactic acid germs is a favorable happening, as they are not harmful to adults in themselves and tend to check the development of other harmful ^erms in the digestive canal.* As we have pointed out, heating milk to 155° or 165^ F. readily kills the lactic acid crerms. Therefore such milk does not sour, but is changed by the action of other harmful germs so that it rots

* Indeed Metchnikoflf, perhaps the most celebrated living authority on the action of germs on the body, beUves that lactic acid germs in buttermilk constitute one of the best agencies for prolonging life.

or putrefies when old. A low temperature (40^ F.) also retards the development of the lactic acid germs and they are killed when the milk or cream becomes very sour by means of the lactic acid they themselves produce. The action of these lactic acid orerms is taken advantage of in the ripening of cream for butter by adding them in great numbers, either by the use of sour cream or milk, or by laboratory methods by which they can be obtained in pure culture — that is, free from admixture with other varieties of germs (see page 39). Lactic acid germs are not found in milk when it leaves the udder, but enter the milk when it is exposed to air. They are thought to reside on the skin of the cow, in dust, in the air or surroundings of the barn. Ordinary market milk at 50^ F. sours in 120 hours; at 60*^ F. it sours in 66 hours; at 98^^ it sours in 16 to 18 hours.

At the Paris exposition of 1900 there was an exhibit of dairy products, under care of Major Alford of the U. S. Department of Agriculture, which consisted of fresh milk and cream shipped from Illinois, New Jersey and New York in hot weather (July). Coming some 3,000 to 4,000 miles, the cream and milk were perfectly sweet a fortnight after being bottled, while the only other competitor was the French with a local supply which did not keep a day after reaching the grounds. Cleanliness and cold were the only methods used in so wonderfully preserving this milk,

If milk is very dirty, however, it is not safe to keep it too long with ice, even if it does not sour and is unaltered in taste, as various sorts of harmful germs may develop at a low temperature. Thus, milk containing, soon after milking, some 800,000 germs to the cubic centimeter, after four days at 41*^ F. contained almost five million germs and became sour. At the end of ten days this same milk contained over 400 million germs, or over ten times the number of germs in the same milk kept the same time at 59^ F.* The milk kept at a higher temperature soured more quickly and the acid destroyed many of the germs in the process.