In the use of the apparatus on the right, increased air pressure is used to hasten the filtering process; the same is accomplished in the apparatus shown in the center by warming the milk by the injection of steam between the walls of the double jacket.
1. Dirt or sediment test. This is made by filtering a pint of the mixed milk through a small disc of absorbent cotton. The insoluble dirt is retained and imparts a color to the cotton, the shade of which is dependent on the amount of dirt (P. 45). Since it is impossible to have dirt without bacteria, it is evident that milks containing a large amount of dirt will be high in bacteria. The reverse, however, is not necessarily true.
A plate culture inoculated with 1/100 of a cubic centimeter of milk containing 67 colonies, which equals 6,700 bacteria per cubic centimeter of milk. Such milk will keep well.
2. Acidity test. The acidity of the milk is also an indication of its bacterial content. If the acidity has increased, above the normal for fresh milk, the bacterial content is certain to be high, and the keeping quality poor. An acidity above 0.2 per cent in market milk is to be avoided, as an increase in acidity is always preceded by a great increase of bacteria.
Whether the acidity is above or below this point can be rapidly and easily determined at the receiving station by a modification of the Farrington acid test. Dissolve one alkaline tablet in an ounce of water. A unit volume of this solution added to a unit volume of milk is equal to 0.1 per cent of acidity. If two measures are provided,—one for the alkaline solution holding just twice as much as that used for the milk, the approximate acidity can be quickly determined by mixing a measure of each in a common white cup. If the acidity is above 0.2 per cent the color will remain white; if a pink color develops, it indicates an acidity less than this amount. This test is also useful in the selection of milk or cream that is to be used for special purposes, such as pasteurization.
A plate culture inoculated with 1/1000 of a cubic centimeter of market milk containing 1,680 colonies, which equals 1,680,000 bacteria per cubic centimeter. Such milk has poor keeping qualities.
3. Alcohol test. A test giving similar information is made by adding two parts of 70 per cent alcohol to one part of milk, and noting whether curdling occurs.
4. Curd test. The curd test described on p. 100 gives no indication of the number of bacteria present, only concerning the types present. It has been proposed to combine the fermentation test with the reduction test referred to below and thus gain some idea of, not only the number, but the kinds of bacteria present.
5. Reduction test. The reduction test is made by adding to twenty cubic centimeters of milk, one-half cubic centimeter of a solution of methylene blue, a coal tar dye. A saturated solution of the dye is made in alcohol, and 2.5 per cent of this solution added to water. The time required for the reduction of the dye or the change of the color from blue to white when the samples are placed in tubes and kept at 98 to 100° F., is dependent upon the number of bacteria present. By allowing the tubes to stand until curdling occurs, and noting the nature of the curd, whether the solid curd of the desirable acid-forming bacteria or the gassy curd of the harmful types is produced, knowledge is gained of the kinds of bacteria present.
According to Barthel, milks that reduce the methylene blue within fifteen minutes contain hundreds of thousands of bacteria per cubic centimeter. Those that require from fifteen minutes to one hour for the disappearance of the color are also high in bacteria, and are to be classed as a poor grade of market milk. If one to three hours is required, the milk is comparatively low in bacteria, and is to be classed as a good grade of market milk. When more than three hours elapse before the disappearance of the blue color, the bacterial content is low and the milk is to be placed in the highest grade.
The time of reduction is only a rough index of the number of bacteria present, but it gives a good idea of the keeping quality of the milk, and of the conditions of production and handling. Of the above tests the sediment and acid tests are more frequently used.
Examination of milk sediments. In the modern municipal laboratory, efforts are made to determine, as far as possible, the conditions of production on the farms, by an examination of the milk in the laboratory. The samples of milk are sedimented in a small centrifuge, and an examination of the sediment made with the microscope. The types of bacteria and the number of body cells found is an indication as to whether any of the animals of the herd are suffering from inflammation of the udder. The test also gives information similar to the dirt test since the insoluble dirt will be thrown down and will impart a color to the sediment.
Pasteurization of market milk..The spread of the pasteurizing process as applied to market milk has been rapid. This has been due to the recognition of the fact that only by this process can a safe milk i.e., one free from pathogenic bacteria, be obtained. As previously mentioned a small proportion of all human beings that have suffered from typhoid fever become bacillus carriers. It is impossible to examine all persons who may be concerned in the handling of milk in order to ascertain whether they belong to this dangerous and unfortunate class of people.
The larger cities have also recognized the impossibility of requiring the tuberculin test of all cattle furnishing milk. Pasteurization remains the only safeguard, and it is probable that within a short time all the larger cities will require the pasteurization of all milk, except that produced under strict supervision.
As previously mentioned heating causes certain changes in milk. In the treatment of market milk it is desirable to use as low temperatures as will suffice to destroy the disease-producing bacteria. It is fortunate that temperatures that will insure this result have little effect on the milk. The temperatures now recommended for pasteurization are as follows:
158 degrees F. for 3 minutes.
155 degrees F. for 5 minutes.
152 degrees F. for 10 minutes.
148 degrees F. for 15 minutes.
145 degrees F. for 18 minutes.
140 degrees F. for 20 minutes.
In actual practice the milk is heated to 145 degrees for 25 to 30 minutes. The acid-forming bacteria are not completely destroyed and the pasteurized milk as a rule will undergo the same type of fermentation as raw milk. It is, however, deemed essential that all pasteurized milk be sold as such; that it be delivered to the consumer within twenty-four hours after pasteurization and that no milk be pasteurized a second time.
The continuous pasteurizing machines have the disadvantage that a small portion of the milk passes through so quickly that all pathogenic bacteria therein might not be destroyed, (p. 131). This has led to the use of the "holding" process in which the milk is heated to the desired temperature and then placed in tanks where it remains at this temperature for any desired time. Every portion is thus treated in a uniform manner.
If the milk is bottled after pasteurization, there remains opportunity for reinfection, possibly with typhoid bacilli. Pasteurization in the final container, the bottle, is being recommended. This is possible only when a special bottle is used with a metal cap lined with paper.
Milk distribution. Until within recent years in the cities and at present in smaller towns, milk is largely retailed from cans which are carried on the wagons or are kept in stores. This exposes the milk to contamination from street dust and from the container furnished by the consumer. It is well recognized that every utensil with which milk is brought in contact adds more or less bacteria to it, and the less milk is handled, the better will be its condition when it reaches the consumer. Milk is now largely retailed in glass bottles which are closed with pulp caps. In some cities the bottling is mainly done in the country at the bottling station to which the milk is brought by the farmers; or it may be shipped by the producer to a distributing company, and all subsequent treatment, as pasteurization and bottling done in the city.
Milk plants are now generally equipped for the rapid and economical handling of large quantities of milk in a most sanitary manner. The bottles as they are returned from the consumer are washed in a continuously-acting automatic washer which washes, rinses and sterilizes the bottles without their being removed from the cases in which they are carried on the wagons. These machines are effective, if not run at too rapid a rate, so that the bottles are not exposed for a sufficiently long period of time to sterilize them. The bottles are then filled and the paper caps inserted by machinery. The caps can now be obtained from the manufacturers in sealed tubes in which they have been sterilized so that the contamination from this source is avoided. The shipping cans are washed and sterilized with live steam, and in many plants are thoroughly dried, by passing hot air into them. Under these conditions they then reach the farmer with none of the musty and disagreeable odor that frequently is present when the can contains a small quantity of water, condensed from steam.
The top of the milk bottle over which the milk is poured is exposed to contamination from the hands of the deliveryman. Trouble from this source can be avoided if the consumer cleans the lip of the bottle before removing the cap. The better grades of milk are dispensed in bottles, the top of which is protected by an additional cover of paper or tin foil which reaches to the neck of the bottle and is held in place by a crimped metal band.
Milk supply of the small cities. It is true that the quality of milk supplied to the large cities by the great milk companies is generally much superior to that sold in the smaller cities and villages. Many of the smaller places are however, attempting in various ways to improve their supply. It is evident that methods will be successful here that can not be employed in the larger places. A detailed and careful farm inspection by a tactful, capable inspector, coupled with proper publicity will do much to improve conditions. The publication of the scores of the different farms, and the demonstration of the sediment test as applied to their product attracts favorable attention to the good dairies and unfavorable attention to the poor. This usually has an effect on the trade sufficient to cause the negligent producer and dealer to improve.
It is also becoming recognized that high grade milk can be produced with very simple equipment. In fact the small farm is often more successful in producing high grade milk than is the large farm on which the work must be done by hired help for here the personality of the owner can not make itself felt as where the producer is doing a portion of the work about the barn and dairy himself. It is becoming more and more evident that the chief factor in the production of clean milk is the personality of the producer; he should be one who gets enjoyment out of his clean stables and cows and his high grade product.
The man who is producing milk for the city market is but one of many and his individual efforts can not make themselves felt. The dairyman who is marketing his own product is in a position where his efforts to produce a fine product should prove of distinct advantage to him in enabling him to sell it for a higher price than that obtained for ordinary milk.
It should be remembered that the production of clean, healthful milk is not a question of equipment, but of methods and of additional work. The cows must be fed, the stables must be cleaned, the cows milked, and the milk delivered to the consumer. If beyond this unavoidable labor a small additional amount is expended, the improvement in the product will be great. It is necessary that the additional work be placed where it will do the most good, in keeping the cows clean both summer and winter so that little need be done in cleaning them before milking, the pails and other utensils kept clean and sterilized, and the milk cooled as soon as possible and kept cold until delivered to the consumer. The delivery should be made within the shortest practicable time after the milk is drawn. In order that the healthfulness of the milk may be beyond question, the herd must be kept free from tuberculosis and some attention should be paid to the health of the men, especially with reference to whether they may be typhoid carriers or not. The necessary labor should not increase the cost of the milk over one cent per quart. It has been shown in many cases that such a product can be marketed at a price that will more than compensate for the additional cost. Clean, fresh, rich milk is being sold in villages and small cities located in the great butter and cheese producing sections of the country for eight to ten cents per quart.
The duty of the consumer. The educational campaign that has been carried on by the health departments with reference to farm conditions and methods of handling has been most effective in improving the milk supply. Many cities are now extending this to the consumer, recognizing that as much harm may be done in the home as on the farm. The importance of keeping the milk cold, of not allowing it to stand exposed in open vessels, of thoroughly cleaning the vessel in which it is kept, or the milk bottle before returning it to the milkman are especially emphasized.
Moreover, it must be impressed upon the consumer that all of these improvements, not only on the farm where the milk is produced, but in the hands of the distributing companies in the cities, involve much expense, and cannot be carried out, unless the consumer is willing to pay their cost. More objection seems to be raised over an increase in the price of milk than any other food stuff. The consumer therefore needs education along the line of higher prices for milk. Dairy products of all types have increased much in value in recent years, so that at present prices milk, sold directly as milk, is relatively cheaper than in any form, when prevailing prices are compared with those that obtained a decade ago.
INDEX.
Abnormal fermentations, overcoming of, 108.
Abortion, contagious, 75.
Acid, amount of formed in milk, 84.
Acidity test, 211.
Actinomycosis, 75.
Aeration of milk, 55.
Aerobic bacteria, 13.
Air, contamination of milk from, 51.
Alcohol test, 213.
Alcoholic fermentation, 96.
Anaerobic bacteria, 13.
Animal, contamination of milk from, 42.
Anthrax, 75.
Antiseptics, 16, 117.
B.
Bacillus Bulgaricus, 89, 101.
Bacillus lactis acidi, 86.
Bacteria, aerobic, 13;
anaerobic, 13;
culture media for, 20;
desirable acid-forming, 86;
determining number of, 22;
distribution of, 18;
effect of cold on, 14;
effect of heat on, 15;
food of, 12;
forms of, 8;
manner of growth of, 9;
movement of, 11;
nature of, 8;
parasitic, 11;
products of, 17;
pure cultures of, 25;
rate of growth of, 13;
relation to air, 13;
relation to chemicals, 16;
relation to drying, 15;
relation to light, 16;
relation to temperature, 12;
size of, 9;
saprophytic, 11;
spores of, 10;
types of acid-forming, 86;
undesirable acid-forming, 90.
Bedding, 47.
Bitter fermentation, 97.
Bleaching powder, 112.
Bloody milk, 99.
Butter, bacteria in, 154;
bacterial defects in, 156;
cowy odor in, 157;
deterioration of, 155;
fishy, 157;
metallic, 157;
molding of, 157;
preservatives in, 155;
putrid, 156;
source of flavor, 140;
turnip flavored, 156;
types of, 137.
Butter-milk, 100.
Butyric fermentation, 93.
Boric acid, 117.
Borax, 117.
C.
Carbolic acid, 111.
Cheese, abnormal fermentations of, 174;
bitter, 177;
Camembert, 186;
Cheddar, 164;
colored, 178;
flavor production in, 172;
gassy, 174;
Gorgonzola, 185;
Limburger, 187;
moldy, 179;
preservation of by acid, 171;
putrid, 178;
quality of milk for, 162;
ripening of, 169;
Roquefort, 184;
Stilton, 185;
Swiss, 180;
temperature of ripening, 173;
types of, 161.
Children, diseases of, 80.
Chloride of lime, 112.
Cholera, 80.
Cleaning utensils, 39.
Clean milk, production of, 53.
Cold, effect of, on bacteria, 14.
Colored milk, 98.
Condensed milk, 135.
Contagious abortion, 75.
Contamination of milk, from milking machine, 50;
in factory, 59.
Cooling of milk, 54.
Corrosive sublimate, 111.
Cream, control of fermentation of, 142;
pasteurization of, 146;
ripening of, 138;
separators, 36.
Cresol, 111.
Curd test, 104.
Cycle of fermentations, 99.
D.
Deodorants, 109.
Digestive fermentation, 93.
Diphtheria, 79.
Dirt, exclusion of, 44;
removal of from milk, 53.
Disinfectants, 16, 109.
Disinfection, 109.
Distribution of bacteria, 18.
Dried milk, 135.
Drugs, excretion of in milk, 58.
Drying, effect of on bacteria, 15.
E.
Emmenthaler cheese, 180.
Evaporated milk, 134.
F.
Factory by-products, 36;
treatment of, 38.
Feeds, effect of on milk, 57.
Fermentation test, 104.
Fermented milks, 100.
Fly, contamination of milk by, 60;
means of spreading typhoid fever, 78.
Foot and mouth disease, 74.
Fore milk, 31; rejection of, 34.
Formalin, 112.
G.
Galactase, 172.
Garget, 75.
Germicidal action of milk, 33.
Gorgonzola cheese, 185.
H.
Hairs, bacteria on, 43.
Heat, effect on bacteria, 15.
Heated milk, detection of, 39.
Hydrogen peroxide, 118.
K.
Kefir, 102.
Koumiss, 102.
L.
Lange Wei, 95.
Light, effect on bacteria, 16.
Limburger cheese, 187.
Lime, 110.
Lumpy jaw, 75.
M.
Malta fever, 75.
Market milk, municipal regulations concerning, 190;
pasteurization of, 214.
Milk, acid fermentation of, 83;
aeration of, 55;
affected by feed, 57;
alcoholic fermentation of, 96;
bacterial standards for, 206;
bitter fermentation of, 93;
certified, 202;
butyric fermentation of, 93;
certified, 202, 208;
clarifying of, 115;
condition of when secreted, 29;
contamination of from animal, 42;
from by-products, 36;
from utensils, 34;
contamination of with tubercle bacilli, 67;
cooling of, 54;
creaming of, 136;
culture medium for bacteria, 28;
cycle of fermentation in, 99;
distribution of, 216;
digestive fermentation of, 93;
dirt in, 44;
effect of heat on, 119;
filtration of, 114;
germicidal action of, 33;
grades of, 201;
guaranteed, 201;
inspected, 202;
miscellaneous fermentations of, 98;
pasteurization of, 120;
pasteurization of in home, 131;
preservation of by antiseptics, 117;
preservation of by cold, 116;
relation to children's diseases, 80;
ropy fermentation, 94;
sediments, examination of, 214;
selected, 203;
slimy, 94;
spontaneous fermentation of, 91;
sterilization of, 134;
straining of, 153;
supply of small cities, 217;
sweet curdling fermentation of, 92;
tainted, 56, 58;
temperature standards for, 208;
tests for quality of, 209.
Milk pails, sanitary, 48;
small topped, 48.
Milker, factor in contamination of milk, 51.
Milking-machines, 36, 50.
Mold on butter, 177;
on cheese, 179.
O.
Odors, absorption of, 56, 58.
Oidium lactis, 186.
Oleomargarine, 152.
P.
Pasteurization, 120;
efficiency of, 133;
purpose of, 123;
methods of, 125.
Pasteurized milk, fermentations in, 124.
Pasteurizing machines, tests of, 130.
Process butter, 152.
Ptomaine poisoning, 81.
Pure cultures, 25.
R.
Rabies, 75.
Reduction test, 213.
Rennet, 170.
Ropy fermentation, 94.
Roquefort cheese, 184.
Rusty spot in cheese, 178.
S.
Salicylic acid, 117.
Scarlet fever, 79.
Score card for dairies, 198.
Sediment test, 210.
Skim milk, heating of, 38.
Slimy fermentation, 94.
Spores of bacteria, 10.
Stalls, 46.
Starters, 143;
for cheese, 167;
propagation of, 146.
Sterilization, 21, 134.
Stilton cheese, 185.
Storch test, 39.
Straining of milk, 33.
Sulphur, 111.
Sweet curdling of milk, 92.
Swiss cheese, 180.
T.
Taints, determination of cause of, 58, 103.
Temperature effect on growth, 12.
Tubercle bacilli, destruction of, 71;
in butter, 70;
in cheese, 70;
in milk, 67.
Tuberculin test, 73.
Tuberculosis, 64;
closed, 70;
distribution of disease in animal, 66;
economic aspects of, 72;
open, 70.
Typhoid fever, 76.
U.
Udder, inflammation, 75;
invasion of by bacteria, 30;
number and kind of bacteria from, 32;
structure of, 30;
washing of, 47;
cleaning of, 39.
Utensils, contamination from, 34.
W.
Water, effect on butter, 153;
supply, 59;
testing of, 60.
Whey, heating of, 38.
Wisconsin curd test, 104.
Y.
Yeast fermentation, 96.
Yoghurt, 101.