Normal development of "eyes" in a Swiss cheese. The eyes are generally as large as a cherry.
The "eye"-forming organisms cannot grow in the presence of any amount of salt, hence, if salt is added directly to the curd, the cheese is likely to be "blind" or free from holes. The eyes are formed not at the time gas holes are produced in a cheddar cheese, i.e., early in the ripening process, but after a lapse of three or four weeks. They are most abundant in the middle of the cheese since the manner of salting is such as to inhibit their formation near the surface. The eye-forming bacteria may have some effect on the flavor of the cheese.
The Swiss maker encounters the same troubles as does the cheddar maker. Gassy cheese is more prevalent in the Swiss than in the cheddar industry, since the maker cannot call to his aid the methods used by the cheddar maker, viz., the addition of a heavy starter, the washing of the curd, etc. It is especially important that the quality of the milk be first class in every respect, and yet customs prevail in the Swiss industry that are directly inimical to the production of good milk. The grossest carelessness prevails at the factories in the matter of handling the whey. It is often kept in individual barrels for each patron. (See Fig. 8.) These are not kept thoroughly clean and the result is that the whey taken back to the farm in the cans that are used to bring the fresh milk is often in an advanced stage of fermentation.
There are many other kinds of hard cheese; but in each, so far as is known, the role of the acid-forming bacteria is identical with that noted in cheddar and Swiss cheese, viz, in preparing conditions favorable for peptic action, and preventing the development of putrefactive bacteria present in the curd.
Roquefort cheese. Among the more important foreign types of cheese that are characterized by the development of mold is Roquefort, so named from the district in France in which it is made. This cheese is made from sheep's milk, in much the same manner as cheddar. The characteristic process in its preparation is the inoculation of the curd, at the time it is put to press, with the spores of a particular kind of mold, a type closely related to the ordinary green mold of bread and cheese. The mold for inoculation is grown on bread, the whole mass being dried so that it can be powdered; then the ground-up material is sprinkled on the curd as it is placed in the press hoops. The first stage in the ripening of Roquefort is probably identical with that of the types of hard cheeses already considered, the breaking-down of the curd being due to the pepsin of the rennet used, which action is made possible by the acid formed by the bacteria.
The second stage in ripening, and one in which the characteristic flavor of the cheese is developed, is due to the growth of the mold with which the cheese is seeded. Molds can grow only in the presence of air, and in order to provide this condition, the cheese are run through a machine having a series of needle-like projections which fills the cheese with fine holes. This allows the air to penetrate the cheese and the mold to grow, the fruiting of which develops the characteristic flavor. The changes produced by the mold are not well understood, but the flavor is evidently connected with its development since in the absence of mold, it does not appear. The cheese must be cured under carefully controlled conditions, as to temperature and moisture; in France these are secured by curing the cheese in limestone caves that are highly saturated with moisture. Attempts have been made to make Roquefort cheese in other parts of the world, but they have never been successful, due undoubtedly to the fact that the proper environment and conditions for the development of the various types of organisms necessary in the ripening process have not been met. This cheese is sold for 50 to 75 cents per pound in the markets of the world.
There are two other kinds of cheese that are closely related to Roquefort, as to the manner of ripening, viz., the Gorgonzola of Italy and the Stilton of England, both of which possess their characteristic flavors by reason of the development of molds. In Stilton cheese the mold is not intentionally added, the maker relying on the contamination that comes from the factory for the usual seeding. If this does not develop, it is sometimes inoculated by exchanging plugs with a well-ripened Stilton. This method is not so certain as in the inoculation of Roquefort.
Camembert cheese. A typical example of soft cheese is one of the French types, known as Camembert. This cheese is prepared from cow's milk which is curdled by rennet. The curd is not cut but is dipped into the forms, which condition, taken with the absence of pressure in forming the cheese, accounts for the large quantity of whey in it. The finished cheese are about one inch in thickness and three inches in diameter. In the ripening, the moisture and temperature of the curing room are very carefully regulated.
The first stage in the ripening is due to the rennet and the lactic bacteria. Later there appears on the surface of the moist cheese, a moldy growth. In this, there are at least two kinds of molds, the ordinary mold that appears on sour milk, Oidium lactis, and another that is related to the bread mold but which has a white instead of a green fruiting stage. These molds are confined to the surface of the cheese but the enzymes which they produce diffuse into the substance, changing the color from a dull, opaque white to a translucent yellow. The acid that has been formed by the lactic bacteria is gradually used up by the growth of the mold, and conditions then become favorable for the growth of putrefactive bacteria which digest the curd. The cheese is ready for use when the action of the mold has penetrated to the center of the cheese, and before any pronounced putrefaction has taken place. The production of the typical flavor is dependent upon there being a definite relation between the growth of the molds and bacteria. This relation is dependent largely upon the moisture and temperature of the curing room. These cannot always be regulated with exactness; and hence, much of this type of cheese is not of first quality, and must be sold for a low price. While such fancy cheeses, as Camembert, bring fifty cents and upward per pound, and the yield from the milk is much greater than with the hard type of cheese, yet the difficulties of successful manufacture are such as to make success less easily attained than with the other types.
There are many other kinds of soft cheese that depend for their ripening upon factors similar to those concerned in the ripening of Camembert; most of them are, however, of small importance from a commercial standpoint.
Limburger cheese. A very famous cheese is one originally made in Germany to which the name Limburger is given. It is classed as a soft cheese although it is much firmer than Camembert. This cheese is made from cow's milk and is pressed very lightly or not at all, which condition accounts for its high per cent (50 per cent) of moisture. The surface is kept moist by repeated washing of the cheese, and by keeping the air of the curing room very moist. A yellowish, slimy, bacterial layer soon develops on the surface under these conditions. The enzymes produced by this external growth gradually diffuse to the center of the cheese, when it is regarded as ripe. The odor of the matured product is somewhat putrefactive, but is not so offensive as is usually supposed.
Definite knowledge concerning the types of organisms concerned in the surface layer is very limited. It is not certain whether the same kinds of organisms must always be present. Limburger is much easier to make than Camembert, due possibly to the fact that there are not needed definite forms of life and that the balance between them is not so delicate.
A cheese known as brick is closely related to Limburger in its method of making and of ripening but is less pronounced in flavor.
In the manufacture of all of these types of cheese, troubles are likely to develop, due to an abnormal bacterial condition of the milk.
It will be seen from what has been said that the bacteria are essential factors in cheese ripening, and that the cheese industry, like the butter industry, may be called a true fermentation industry. Close co-operation must exist between the milk producer, and the maker so that the type of fermentation that goes on in the milk can be controlled. A recognition of the fundamental principles governing these fermentations, both normal as well as abnormal, is now regarded as an essential part of the training of the dairy manufacturer of today.
CHAPTER IX.
BACTERIA IN MARKET MILK.
Within the last decade attention has been especially directed toward the quality of milk that is furnished to the people in the cities. This has come about, in part, in connection with the demands made for better and purer food of every kind. These demands are reflected in the pure-food laws enacted by the federal government, and by the various states and municipalities. Another factor that has focused attention on the milk supplies has been the belief that it plays an important role in the production and distribution of disease, especially among children. The rapid growth of cities in all of the great countries of the world, the higher standard of living, and the greater demand for milk and other dairy products, has, of necessity, widened the zone from which the milk supply of any particular city must be drawn. Milk is now an article of export and of import; some of the great cities draw a portion of their supply from farms hundreds of miles away. This means that a longer time must elapse between the time of production and consumption, necessitating the exercise of greater care in production and handling in order to preserve the milk until it reaches the consumer.
In the past in the cities, as in the smaller towns at present, the supply was largely furnished by the producer directly to the consumer. This direct contact afforded the consumer the opportunity of informing himself of the conditions under which his milk supply was produced if he desired. The advent of the middleman in the business, and the gathering of the milk from many hundreds of farms, and its redistribution to thousands of homes has made it impossible for the individual consumer to learn anything of the conditions surrounding production. When the individual cannot protect himself against fraud and unhealthful conditions, it is the duty of the government to protect him. This is the theory underlying the modern control of food supplies, water supplies, and of living conditions in general. Acting on this basis the cities are seeking to control, to an increasing degree, the healthfulness and cleanliness of the milk supply.
Formerly such control as was given was largely with reference to the composition of the milk, the regulations providing that it should contain not less than a minimum amount of fat and other solids, and be free from preservatives. The more modern regulations are much more complex and touch every phase of production and handling that can, in any way, affect the value of the milk as human food.
Municipal regulations. The different cities vary widely in the methods employed to secure a satisfactory milk supply. Rules and regulations are adopted to which the producer and dealer must conform. In order to ascertain whether the regulations are being obeyed, two types of examinations may be made: first the inspection of the farms and of the plants of the dealers; second the examination of the milk itself with reference to its chemical composition, bacterial content and temperature.
The city of New York is doing more to safeguard and to improve its milk supply than any other large city in this country. A brief summary of its regulations and methods follow. A copy of the rules is furnished to each dairyman and is supposed to be posted in the stable.
The Cows.
1. The cows must be kept clean, and manure must not be permitted to collect upon the tail, sides, udder and belly of any milch cow.
2. The cows should be groomed daily, and all collections of manure, mud or other filth must not be allowed to remain upon their flanks, udders or bellies during milking.
3. The clipping of long hairs from the udder and flanks of the cows is of assistance in preventing the collection of filth which may drop into the milk. The hair on the tails should be cut, so that the brush will be well above the ground.
4. The udders and teats of the cow should be thoroughly cleaned before milking; this to be done by thorough brushing and the use of a cloth and warm water.
5. To prevent the cows from lying down and getting dirty between cleaning and milking, a throat latch of rope or chain should be fastened across the stanchions under the cow's neck.
6. Only feed which is of good quality and only grain and coarse fodders which are free from dirt and mould should be used. Distillery waste or any substance in a state of fermentation or putrefaction must not be fed.
7. Cows which are not in good flesh and condition should be immediately removed and their milk kept separate until their health has been passed upon by a veterinarian.
8. An examination by a veterinary surgeon should be made at least once a year.
The Stable
9. No stagnant water, hog-pen, privy or uncovered cesspool or manure pit should be maintained within 100 feet of the cow stable.
10. The cow stable should be provided with some adequate means of ventilation, either by the construction of sufficient air chutes extending from the room in which the cows are kept to the outside air, or by the installation of muslin stretched over the window openings.
11. Windows should be installed in the cow barn to provide sufficient light (2 sq. feet of window light to each 600 cubic feet of air space the minimum) and the window panes be washed and kept clean.
12. There should be at least 600 cubic feet of air space for each cow.
13. Milch Cows should be kept in a place which is used for no other purpose.
14. Stable floors should be made water-tight, be properly graded and well drained, and be of some non-absorbent material. Cement or brick floors are the best, as they can be more easily kept clean than those of wood or earth.
15. The feeding troughs and platforms should be well lighted and kept clean at all times.
16. The ceiling should be thoroughly swept down and kept free from hanging straw, dirt and cobwebs.
17. The ceiling must be so constructed that dust and dirt therefrom shall not readily fall to the floor or into the milk. If the space over the cows is used for storage of hay, the ceiling should be made tight to prevent chaff and dust from falling through.
18. The walls and ledges should be thoroughly swept down and kept free from dust, dirt, manure or cobwebs, and the floors and premises be kept free from dirt, rubbish and decaying animal or vegetable matter at all times.
19. The cow beds should be so graded and kept that they will be clean and sanitary at all times.
20. Stables should be whitewashed at least twice a year unless the walls are painted or are of smooth cement.
21. Manure must be removed from the stalls and gutters at least twice daily. This must not be done during milking, nor within one hour prior thereto.
22. Manure should be taken from the barn, preferably drawn to the field. When the weather is such that this cannot be done, it should be stored not nearer than 200 ft. from the stable and the manure pile should be so located that the cows cannot get at it.
23. The liquid matter should be absorbed and removed daily and at no time be allowed to overflow or saturate the ground under or around the cow barn.
24. Manure gutters should be from six to eight inches deep, and constructed of concrete, stone or some non-absorbent material.
25. The use of land plaster or lime is recommended upon the floors and gutters.
26. Only bedding which is clean, dry and absorbent should be used, preferably sawdust, shavings, dried leaves or straw. No horse manure should be used as bedding.
27. The flooring where the cows stand should be so constructed that all manure may drop into the gutter and not upon the floor itself.
28. The floor should be swept daily. This must not be done within one hour prior to milking time.
29. If individual drinking basins are used for the cows, they should be frequently drained and cleaned.
30. All live stock other than cows should be excluded from the room in which the milch cows are kept. (Calf or bull pens may be allowed in the same room if kept in the same clean and sanitary manner as the cow beds.)
31. The barnyard should be well drained and dry, and should be as much sheltered as possible from the wind and cold. Manure should not be allowed to collect therein.
32. A suitable place in some separate building should be provided for the use of the cows when sick, and separate quarters must be provided for the cows when calving.
33. There should be no direct opening from any silo or grain pit into the room in which the milch cows are kept.
The Milk House.
34. A milk house must be provided which is separated from the stable and dwelling. It should be located on elevated ground, with no hog-pen, privy or manure pile within 100 feet.
35. It must be kept clean and not used for any purpose except the handling of milk.
36. The milk house should be provided with sufficient light and ventilation, with floors properly graded and made water-tight.
37. It should be provided with adjustable sashes to furnish sufficient light and some proper method of ventilation should be installed.
38. The milk house should be provided with an ample supply of clean water for cooling the milk, and if it is not a running supply, the water should be changed twice daily. Also a supply of clean ice should be provided to be used for cooling the milk to 50 degrees within two hours after milking.
39. Suitable means should be provided within the milk house, to expose the milk pails, cans and utensils to the sun or to live steam.
40. Facilities consisting of wash basins, soap and towel should be provided for the use of milkers before and during milking. During the Summer Months the Milk House should be properly screened to exclude flies.
The Milkers and Milking.
41. Any person having any communicable or infectious disease, or one caring for persons having such disease, must not be allowed to handle the milk or milk utensils.
42. The hands of the milkers must be thoroughly washed with soap and water, and carefully dried on a clean towel before milking.
43. Clean overalls and jumpers should be worn during the milking of the cows. They should be used for no other purpose, and when not in use should be kept in a clean place protected from dust.
44. The hands and teats should be kept dry during milking. The practice of moistening the hands with milk is to be condemned.
45. The milking stools should be at all times kept clean, and iron stools are recommended.
46. The first streams from each teat should be rejected, as this fore milk contains more bacteria than the rest of the milk.
47. All milk drawn from the cows 15 days before, or 5 days after parturition should be rejected.
48. The pails in which the milk is drawn should have as small an opening at the top as can be used in milking; top opening preferably not to exceed 8 inches in diameter. This lessens the contamination by dust and dirt during milking.
49. The milking should be done rapidly and quietly, and the cows should be treated kindly.
50. Dry fodder should not be fed to the cows during or just before milking, as dust therefrom may fall into the milk.
51. All milk utensils, including pails, cans, strainers, and dippers, must be kept thoroughly clean and must be washed and scalded after each using, and all seams in these utensils should be cleaned, scraped and soldered flush.
The Milk.
52. Milk from diseased cows must not be shipped.
53. The milk must not be in any way adulterated.
54. The milk as soon as drawn should be removed to the milk house and immediately strained and cooled to the proper temperature.
55. All milk must be cooled to a temperature below 50 degrees F., within two hours after being drawn, and kept thereafter below that until delivered to the creamery.
56. The milk should be strained into cans which are standing in ice water which reaches the neck of the can. The more rapidly the milk is cooled, the safer it is, and longer it will keep sweet. Ice should be used in cooling milk, as very few springs are cold enough for the purpose.
57. If aerators are used, they should stand where the air is free from dust or odors, and on no account should they be used in the stable or out of doors.
58. Milk strainers should be kept clean; scalded a second time just before using, and if cloth strainers are used, several of them should be provided, in order that they may be frequently changed during the straining of the milk.
59. The use of any preservative or coloring matter is adulteration, and its use by a producer or shipper will be a sufficient cause for the exclusion of his product from the City of New York.
Water Supply.
60. The water supply used in the dairy and for washing utensils should be absolutely free from any contamination, sufficiently abundant for all purposes, and easy to access.
61. This supply should be protected against flood or surface drainage.
62. The privy should be located not nearer than 100 feet of the source of the water supply, or else be provided with a water-tight box that can be readily removed and cleaned, and so constructed that at no time will the contents overflow or saturate the surrounding ground.
63. The source of the water supply should be rendered safe against contamination by having no stable, barnyard, pile of manure or other source of contamination located within 200 feet of it.
In order that the farm inspection shall be as effective as possible, and to make the work of the several inspectors as uniform as may be, the dairies are scored. A copy of the score card follows.
DEPARTMENT OF HEALTH
The City of New York
Division of General
Sanitary Inspection
Dairy Report
Inspection No.___ Time___A. P. M. Date______191__
- Dairyman___________ Owner__________
- P. O. Address___________ P. O. Address______ State____
- County_______ State____ Party Interviewed________
- Milk delivered to Creamery at_____ Formerly at_____
- Operated by________ Address____________
- Distance of farm from Creamery____ Occupied farm since____
- No. Cows____ No. Milking____ No. Qts. Produced____
- All persons in the households of those engaged in producing or handling milk are_____free from all infectious disease. Weekly reports are_____being filed
- Date and nature of last case on farm___________
- WATER SUPPLY for utensils is from a_______located ____feet deep and apparently is______pure and wholesome______ State any possible contamination located within 200 feet of source of water supply or if water supply is not protected against surface drainage
- Water supply on this farm analyzed____191__ Result______
- Style of Cow Barn___Length___ft. Width___ft. Height of ceiling___ft.
- Dairy Rules of the Department of Health are_____posted _______
- Dairy Herd examined by________on _________191__
Report______
Remarks
Equipment 40 per cent. Score ....per cent
Methods 60 per cent. Score ....per cent
Perfect Dairy 100 per cent. Score ....per cent
A copy of the completed report is left with the dairyman.
Before the farm inspection is carried out the creameries to which the milk is delivered by the farmers are inspected at the time the milk is being delivered. The temperature of the milk and its cleanliness are noted. In the creamery the straining, cooling and handling of the milk are observed as well as the washing of the milk cans and other utensils, and the construction and condition of the creamery, the opportunity for the water supply to become contaminated, and the presence of infectious diseases among the employees.
Grades of milk. Three grades of milk have been established. Each dealer is required to state which grade or grades he expects to handle. The specifications for the different grades are as follows.
Grade A. Guaranteed Milk. Guaranteed milk is that produced at farms holding permits therefor from the Department of Health and produced and handled in accordance with the following minimum requirements, rules and regulations:
1. Only such cows shall be admitted to the herd as have not re-acted to a diagnostic injection of tuberculin.
2. All cows shall be annually tested with tuberculin, and all re-acting animals shall be excluded from the herd.
3. No milk from re-acting animals shall be shipped to the City of New York for any purpose whatever.
4. The milk shall not contain more than 30,000 bacteria per c. c. when delivered to the consumer, or at any time prior to such delivery.
5. The milk shall be delivered to the consumer only in sealed bottles, which have been sealed at the dairy.
6. The milk shall be delivered to the consumer within 30 hours of the time at which it was drawn.
Grade A. Certified Milk. Certified milk is milk certified by a milk commission appointed by the Medical Society of the County of New York, or the Medical Society of the County of Kings, as being produced under the supervision and in conformity with the requirements of that commission as laid down for certified milk, and sold under a permit therefor issued by the Board of Health.
No milk shall be held, kept, offered for sale, or sold and delivered as certified milk in the City of New York which is produced under requirements less than those for guaranteed milk.
Grade A. Inspected Milk—Raw. Inspected milk (raw) is milk produced at farms holding permits therefor from the Board of Health, and produced and handled in accordance with the following minimum requirements, rules and regulations:
1. Only such cows shall be admitted to the herd as have not re-acted to a diagnostic injection of tuberculin.
2. All cows shall be tested annually with tuberculin, and all re-acting animals shall be excluded from the herd.
3. No milk from re-acting animals shall be shipped to the City of New York for any purpose whatsoever.
4. The farms at which the milk is produced must obtain at least 75 points in an official score of the Department of Health. These 75 points shall be made up as follows: A minimum of 25 points for equipment, and 50 points for method.
5. The milk shall not contain more than an average of 60,000 bacteria per c. c. when delivered to the consumer, or at any time prior thereto.
6. Unless otherwise specified in the permit, the milk shall be delivered to the consumer only in bottles.
Grade A. Selected Milk—Pasteurized. Selected milk (pasteurized) is milk produced at farms holding permits therefor from the Board of Health, and produced and handled in accordance with the following requirements, rules and regulations:
1. The farms at which the milk is produced must obtain at least 60 points in an official score of the Department of Health. Of these 60 points, a minimum of 20 points shall be required for equipment and a minimum of 40 points for method.
2. All milk of this grade shall be pasteurized, and said pasteurization shall be carried on under a special permit issued therefor by the Board of Health, in addition to the permit for "Selected Milk (Pasteurized.)"
3. The milk shall not contain more than an average of 50,000 bacteria per c. c. when delivered to the consumer, or at any time after pasteurization and prior to such delivery.
4. Unless otherwise specified in the permit, the milk shall be delivered to the consumer only in bottles.
5. All containers in which pasteurized milk is delivered to the consumer shall be plainly labeled "Pasteurized." Labels must also bear the date and hour when pasteurization was completed, the place where pasteurization was performed, and the name of the person, firm or corporation performing the pasteurization.
6. The milk must be delivered to the consumers within 30 hours after the completion of the process of pasteurization.
7. No milk shall be pasteurized more than once.
8. No milk containing in excess of 200,000 bacteria per c. c. shall be pasteurized.
General Regulations for Grade A—
1. The caps of all bottles containing milk of Grade A shall be white, and shall contain the words "Grade A" in black letters, in large type.
2. If cans are used for the delivery of milk for Grade A, the said cans shall have affixed to them white tags, with the words "Grade A" printed thereon in black letters, in large type, together with the designation "Inspected Milk (Raw)" or "Selected Milk (Pasteurized)," as the quality of the contents may require.
Grade B. Selected Milk—Raw. Selected milk (raw) is milk produced at farms holding permits therefor from the Board of Health, and produced and handled in accordance with the following minimum requirements, rules and regulations:
1. Only such cows shall be admitted to the herd as have been physically examined by a regularly qualified veterinarian and declared by him to be healthy, and free from tuberculosis in so far as a physical examination may determine that fact.
2. The farms at which the milk is produced must obtain at least 68 points in an official score of the Department of Health. These 68 points shall be made up as follows: A minimum of 25 points for equipment, and a minimum of 43 points for method.
3. The milk shall not contain an excessive number of bacteria when delivered to the consumer, or at any time prior thereto.
Grade B. Pasteurized Milk. Pasteurized milk (Grade B) is milk produced under a permit issued therefor by the Board of Health, and produced and handled in accordance with the following minimum requirements, rules and regulations and in further accordance with the special rules and regulations relating to the pasteurization of milk.
1. The milk after pasteurization must be at once cooled and placed in sterilized containers, and the containers immediately closed.
2. All containers in which pasteurized milk is delivered to the consumer shall be plainly labeled "Pasteurized". Labels must also bear the date and hour when the pasteurization was completed, the place where pasteurization was performed, and the name of the person, firm or corporation performing the pasteurization.
3. The milk must be delivered to the consumer within 36 hours after the completion of the process of pasteurization.
4. No milk shall be pasteurized more than once.
5. No milk containing an excessive number of bacteria shall be pasteurized.
General Regulations for Grade B—
1. Caps of bottles containing milk of grade B shall be white and marked "Grade B" in bright green letters of large type.
2. The necks and shoulders of cans containing grade B milk shall be painted bright green, and a metal tag shall be attached to each can with the words "Grade B" in large type, and the words of the subdivision to which the quality of the milk in said can conforms.
Grade C. Grade C is to be used for cooking and manufacturing purposes only. It includes all raw milk that does not conform to the requirements of any of the subdivisions of grade A or grade B.
1. The caps of all bottles containing milk of grade C shall be white and shall contain in red the words "Grade C" in large type and "for cooking" in plainly visible type.
2. Cans containing milk of grade C shall be painted red on necks and shoulders and shall have in red the words "Grade C" in large type and the words "for cooking" in plainly visible type affixed to each can.
All creameries handling milk of different grades will be required to demonstrate to the Department of Health that they are capable of keeping the grades separate, and must keep records satisfactory to the Department of Health concerning the amount of milk of each grade handled each day.
It is to be noted that the grades of milk are based on the bacterial content of the milk and on the opportunity for the milk to become contaminated with pathogenic organisms. From the statements made in a previous chapter it is evident that the number of bacteria in any sample of milk is dependent upon (1) the original amount of contamination, (2) the age of the milk, and (3) the temperature at which it has been held. A high bacterial content is indicative of poor milk, while a low bacterial content can be obtained, in the case of raw milk, only where due attention is paid to cleanliness and cooling. This relation between the quality of milk and its bacterial content has led many cities to adopt numerical bacterial standards, even when grades of milk have not been established. Boston requires that the milk shall not contain more than 500,000 bacteria per cubic centimeter. Rochester, N. Y., has a standard of 100,000 per cubic centimeter, while Chicago requires that the milk on arrival in the city shall not contain more than 1,000,000 per cubic centimeter from May first to September thirtieth, and not over 500,000 between October first and April thirtieth. The sale of milk containing more than 3,000,000 bacteria per cubic centimeter is prohibited.
It has been urged that bacterial standards are not of value since the healthfulness of milk depends on the kind of bacteria present rather than on the number. It is well recognized that milk containing millions of acid-forming organisms, butter milk, is a healthful food, while that containing many less bacteria may contain some disease-producing organisms. It has been urged that a qualitative standard should supplant the quantitative. The consumer desires milk that has been produced under clean conditions, and which has good keeping qualities. The harmless forms of bacteria exert the greatest influence on the keeping quality. Experience has shown that the quantitative examination of the milk supply as it comes from the farm is the most feasible method of determining, in the laboratory, whether the farmer has obeyed the rules with reference to cleanliness and cooling of the milk. The bacteriological examination also gives an indication as to whether the large number of bacteria is due to gross contamination of the milk with mud and manure, or actual growth of bacteria as in old milk. In the latter case the ordinary acid-forming bacteria will usually predominate in the milk, while in the former, the number of kinds of bacteria and the proportion between the kinds will be changed. It is of course evident that the quantitative standards should be applied with judgment.
It is also claimed that the delay in securing the results in the quantitative examination of milk is an objection to the bacterial standard, since the milk is consumed before the laboratory findings can be obtained. It is true that it does not protect the community as far as the particular sample is concerned, but it is also true that the examination is not made for the purpose of determining the condition of the particular sample, so much as it is to determine the methods that are employed on any particular farm, and these do not vary widely from day to day. Thus, if a number of samples give high results, it is evident that conditions surrounding production need investigation.
If the milk is well cooled on the farm, and kept cold while being shipped, the growth of bacteria will be slow, and the condition of the milk as far as keeping quality is concerned, much better than if less care is used. Some cities have temperature standards; New York requires that the milk shall be cooled to 50° F. on the farm, and shall not be above 50° F. on arrival in the city. Others require that it shall not be above 50° F. on delivery to the consumer.
Certified milk. In many cities the Medical Societies have appointed Milk Commissions, that adopt rules and regulations, concerning the production of milk that shall receive the certificate of the commission. Producers, who desire to have their milk thus certified, must satisfy the commission that they are able to conform to the rules. The commission appoints a physician to examine the personnel of the farm, a veterinarian to make frequent examinations of the herd, a chemist to examine the milk as to its contents in fat and other solids, and a bacteriologist to determine the bacterial content of the milk. The rules are very stringent and cover every point that may influence, in any way, the value of the milk as human food. In order to conform to these requirements, a heavy expenditure must be incurred, and the business must pay for such expert service; hence, certified milk must be sold at high prices, twelve to twenty-five cents per quart. This price makes it a special product and its use is confined mainly to infant feeding.
The bacterial standard for certified milk is usually 10,000 bacteria per cubic centimeter. It is only by the exercise of the greatest care at every point that the bacterial content can be kept below this maximum.
The term "certified milk" has been registered by Mr. Francisco of New Jersey, who was the first to engage in the production of such milk under the direction of the Medical Milk Commission of Essex County, New Jersey. The use of the term is allowed when the milk is produced under the regulation of any Medical Milk Commission.
Most certified milk is now produced on fancy dairy farms conducted by wealthy men. The barns and other equipment are the best that can be obtained, and the methods employed, as far as cleanliness is concerned, are extreme. In some of the dairies the bacterial content is reduced to a few hundred per cubic centimeter, or to that which is derived from the interior of the udder. Such milk will, when well refrigerated, keep for long periods of time. It is a not uncommon thing for such milk to keep perfectly sweet for ten to fifteen days.
Tests for the quality of milk. At the milk depot and elsewhere, it is frequently desired to determine the bacterial condition of the milk in a less refined manner than by the plate cultures of the bacteriologist, which require a large amount of time for their preparation and do not yield any positive information for at least twenty-four hours. There are a number of such tests that may be applied.