Outlines of Dairy Bacteriology, 8th edition / A Concise Manual for the Use of Students in Dairying

nges its character materially as most bacteria cause the production of more or less pronounced fermentative processes. Under normal conditions, milk sours, i. e., develops lactic acid,

at series of changes prevail or not depends upon the initial seeding, and the conditions under which the milk is kept. Ordinarily, the lactic acid organisms grow so luxuriantly in the milk that they overpower all competitors and so determine the nature of th

it possible to develop in milk

nated as the inert bacteria, it must not be supposed that they have absolutely no effect on milk. It is probably true in most

. These transformations may be such as to affect the taste, as in the sour milk or in the bitter fermentations, or the

d by the decomposition of the milk-sugar. While this change is well nigh universal, it does not occur without a pre-existing cause, and that is the presence of certain living

ous other by-products, as other organic acids (acetic, formic and succinic), different al

bout 0.4 per cent., but the curd becomes more solid with increasing acidity. The rapidity of curdling is also dependent upon the temperature of the milk. Thus milk which at ordinary temperatures might remain fluid often curdles when heated. The growth of the bacteria is continued until about 0.8

larger proportion of its volume is made up of butter-fat globules. This fact must be considered in

the view that a few types are responsible for most of these changes. The most common type found in spontaneously soured milk changes the milk-sugar into lactic acid without the production of any gas. This ty

injections into the milk cistern. They abound, however, on hay, in dust, in the barn air, on the hairy coat of the animal, and from these sources easily gain access to the milk. In this medium they find an exceptio

tis aerogenes. This type forms gas in milk so that the soured milk is torn by th

n and Aikman refer to the fact that over one hundred species capable of producing variable quantities of lactic acid are already known. It is fair to presume, ho

haracteristic they are easily destroyed when milk is pasteurized. They live under aerobic or anaerobic conditions, many of them

elatively wide range in temperature, appreciable quantities of acid

ecially prone to develop in the manufacture of milk into certain types of cheese. Not often is their development so rapid that they appear in the milk while it is yet in the hands of the milk producer, but almost invariably the introduction of the causal organisms takes place while the milk is on the farm. Numerous varieties of bacteria possess this proper

d detonations show no effect on acid development, but the atmospheric conditions usually incident to a thunder storm are such as permit of a more rapid growth of organisms. Ther

e to the splitting up of some of the sugar into gaseous products. This type of germ life does not

se made from

e milk is caused by the action of enzyms of a rennet type that are formed by the growth of various species of bacteria. Later the whey separates more or less perfectly from the curd, producing a "wheyed off" condition. Generally the coagulum

pores. The Tyrothrix type of bacteria (so named by Duclaux on account of the supposed relation to cheese ripening) belongs to this class. The hay and potato forms are

ultures in a relatively pure condition, while Fermi[56]

g and subsequent digestion quite independent of cell development. The quantity of ferment produced by different species differs materially in some cases. In these digestive fermentations

hey are held in abeyance, although this type of bacteria is always present to some extent in milk. When the lactic acid

lk, and for a long time was thought to be a continuation of the lactic fermentation, but it is now believed that these organisms find more favorable condition

ominent, but in addition to this, other organic acids, as lactic, succinic, and acetic, are produced, likewise different alcohols. Concerning the chemical origin of butyric acid there is yet some doubt. Duclaux[58] affirms that

rtance, as this fermentation does not readily

t into long threads, several feet in length, as in Fig. 17. Two sets of conditions are responsible for these ropy or slimy milks. The most common is where the milk is clotted or stringy when drawn, as in some forms of garget. This is gen

7. Rop

bacteria which find their way into the milk after it is drawn. These defects are liable to occur at any season of the year. Their presence in a dairy is a source of

pable of producing these viscid changes,[59] but it is quite probable that

germ repeatedly in water tanks where milk cans are cooled; and under these conditions it is easy to see how infection of the milk might occur. Marshall[62] reports an outbreak which he traced to an external infection of the udder; in another case, the slime-forming organism was abundant in the barn dust. A defect of this character is often

germs. In some cases the slimy material is merely the swollen outer cell membrane of the bacteria themselves as in the case of B. lactis viscosus; in othe

"lange wei" (long or stringy whey) which is employed as a starter in Holland to control the gassy f

Where such changes are produced it is due to yeasts. Several outbreaks attributable to such a cause have been reported.[64] Russell and Hastings[65] have found these mi

addition to the CO2 developed, alcohol, lactic acid, and casein-dissolving ferments are formed. Kephir is made by adding to milk Kephir grains, which are a mass of yeast and bacterial cells. The yeasts produce alcohol and CO2 while the bac

ch as lupines, ragweed and chicory, possess the property of affecting milk when the same are consumed by animals. At

er fermentation of milk was thought to be associated with the butyric fermentation, but Weigmann[67] showed that the two con

milk. Sometimes a bitter condition does not develop in the milk, but may appear later in

a milk-sugar splitting yeast, Torula amara which not only grows rapi

bitter flavor, showing that the optimum temperature for this

ng the bitter substances usually possess endospores, and that while the boiling or sterilizing of milk easily kil

onacei, that they found gained access to the milk in one case from the bedding and in another instance from

as sedges and scouring rushes is also said to cause a bloody condition; madders impart a reddish tinge due to coloring matter absorbed. Defects of this class can be readily disti

pment is usually confined to the surface of the milk as it stands in a vessel. The most important is the well-known B. prodigiosus. Another form found at times in milk possessing low acidity[

later become confluent, the blue color increasing in intensity as the acidity increases. The causal organism, B. cyanogenes, is very resistant toward drying,[75] thus accounting for its persistence. In Meckle

le of cooked milk a peculiar form (Bacillus synxanthus) that produced a citron-yellow appearance which precipitated and finally rendered soluble the casein. Ad

any of the chromogenic bacteria are able to produce their color changes in milk as it is such an excellent food medium. Under ordinary c

the herd, it is necessary to ascertain, first, whether it is a general trouble, or restricted to one or more animals. This can someti

oderately high temperature, the bacteria will develop rapidly. A number of different methods have been devised for this purpose. In Walther's lacto-fermentator samples of milk are simply allowed to stand in bottles or glass jars until they sour. They are examined at intervals of several hours. If the curdled milk is homogeneous and has a pure acid smell, the milk is regarded as all right

and Decker.[77] It was used first in connection with experimental work on the influence of gas-generating bacteria in cheese making, but i

ater, as in a wash tub or some other receptacle. When the milk is about 95° F., about ten drops of rennet extract are added to each sample and mixed thoroughly with the milk. The jars should then remain undisturbed until the milk is completely curdled; th

g.

owing construction of cover; S, sieve to hold back the curd when bottle is i

. Generally, they consist of a special bottle having a full-sized top, thus permitting the easy removal of the curd. The one shown

have failed to cement, as is seen in Fig. 19. If gas-producing bacteria are very prevalent in the milk, the conditions under which the test is made cause such a rapid growth of the same that the evidence of the abnormal fe

d milk. The large irregu

hy" texture and the presence of "off" flavors that are rendered more apparent by keeping them in closed

tations that is often fruitful, is that which rests upon the inability of one kind

anisms that are able to obtain the ascendency over the taint-producing germ. Such a method is commonly followed when a lactic fer

e ragged holes are mechanical; numerous small

" (slimy whey), that is used in the manufacture of Edam chee

ith those tainted milks known as "sweet curdling." The ferment organisms concerned in this change are unable to develop in the presence of lactic a

s. Of course with such diseases as tuberculosis, very stringent measures are required, as they are such a direct menace to human lif

heir use should always be preceded by a thorough cleansing with hot water so th

t as deodorants, i.e., destroy the offensive od

ew moments has little or no effect upon germ life. The effect of sulfur vapor (SO2) alone upon germ life is relatively slight, but if this gas is produced in the presence of moisture, sulfurous acid (H2SO3) is formed, which is much more

may be used as a gas where rooms are to be disinfected, or applied as a liquid where desired. It is much more powerful in its action than sulfur

good disinfectant as well as a deodorant, and if applied as a wash, in the proportion of four to six ounces of the powder t

sinfectant, but it is such an intense poison that its use

ly adapted if made from freshly-burned quick lime. It possesses strong germicidal powers, inc

e excellent disinfectants, cannot well be used o

f copper, iron and zinc) are sometimes used. These are deodorants as well as

s and should not be brought into requisition until a thorough application of hot

TNO

96; Esten, 9 Rept. Storrs Expt. Stat., p. 44, 1896; Dinwiddie, Bull. 45, Ark. Expt. Stat., May,

Inaug. Diss., Ki

ent. f. Bakt.

ll, Science,

. Storrs Expt. St

Arch. f. Hyg

ux, Le Lai

Principes de L

. 808) has studied over a dozen diffe

Expt. Stat., Mch., 1899; als

Landw. Jahr.

Mich. Expt. S

Zeit., 18

terie, p. 60. Heinze and Cohn,

Wis. Expt. Sta

Landw. Jahr. d. S

, Milch Zeit.

. Storrs Expt. St

ch, Fühl. Landw

l. 120 Ont. Agr'l.

ch Zeit.

ll. 146, Mich. Ex

t, Milch Zeit.

kt., 6:596; Keferstein,

. d. Kais. Gesund

Milch Zeit.,

tat., 1895, p. 148; also B