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

ess. The cream may be raised by the gravity process or separated from the milk by centrifugal action. In either case the bacteria that are

hter specific gravity, move toward the surface of the milk or toward the interior of the separator bowl. This filtering action of the fat globules is similar to wh

of the bacteria that are to be found in the cream. The difference in species is largely determined by t

rs especially the development of those forms whose optimum growing-point is near the air temperature. By this method the cream layer is exposed to the air for a longer time than with any other

ll depend largely upon the manner in which the milk is handled previous to setting. If care is used in milking, and the milk is kept so as to exclude outside contamination, the cream will be freer from bacteria than if carelessness prevails in handling

forms that have found their way into the milk during and subsequent to the milking, for the cream is ordinarily separated so soon that ther

he cream so as to check growth, as the milk is generall

n cream. For this same reason, cream will sour sooner when it remains on the milk than it will if it is separated as soon as possible. This fact indic

the characteristic flavor and aroma that are so well known in this article. We are so accustomed to the development of these flavors in butter that they are not generally recognized as being intimately associated with bacteri

hurning. The ripening change occurred spontaneously without the exercise of any especial control. With the development of the creamery system came the necessity of exercising a control of

these qualities. While all three are produced simultaneously in ordinary ripening, it does not necessarily follow that they are produced by the same cause. If the ripening changes are allowed to go too fa

the number of organisms may vary widely in unripened cream, but that the germ content of the ripened product is more uniform. When cream is ready for the churn,

oducing class, but in the process of ripening, these forms seem to thrive still better, so that

anges, this enveloping substance is modified, probably by partial solution, so that the globules cohere when agitated, as in churning. The result is that ripened cream churns more easily, and as it is poss

acterial multiplication is that acid is produced i

ent of flavor, the flavor is not directly produced by the formation of acid. If cream is treated in proper proportions with a commercial acid, as hydrochloric,[154] it assumes the same

endency seems to be to develop somewhat more than formerly, as it is thought that this secures more of the "high, quick" flavor wanted in the market. On the average, cream is ripened to about 0.5 to 0.65 per cent. acidity, a higher percentage than this giving a strong-flavored butter. In the determination of acidity, the most convenient method is to employ the Farrington alkaline tablet, which permits of an accurate and ra

better results have been obtained, it is claimed, where the ripening temperature is increased and the period of ripening lessened. As high a temperature as 70° to 75° F. has been recommended. It should be said that this variation in practice may have a valid scientific foundation, for the temperatur

ure culture was used in pasteurized cream, because here p

t the Ontario Agricultural College, however, show practically no difference in the quality of the butter made by these two methods. The great majority

o qualities is not necessarily dependent on the same organisms. The quality of flavor and aroma in butter is, of course, also affected by other conditions, as, for instance, the presence or absence of salt, as well as the inherent qualities of the milk, that are controlled, to some extent at least, by the character of the feed which is consumed by the animal. The exact source of these desirable but evanescent qualities in butter is

roma. He has shown that both flavor and aroma production are independent of acid; that many good flavor-producing forms belong to that class which renders milk alkaline, or do not change the reaction at all. Some of these species liquefied gelatin and would therefore belong to the casein-dissolving class. Those species that produced bad

at different temperatures, the most pronounced being evolved near the optimum

concerned in the production of undesirable ripening changes. This condition being true, it may seem strange that butter is as good as it is, because so frequently the requisite care is not given to the development of proper ripenin

ter. This is frequently done by the addition of a "starter." While starters have been employed for many years for the purpose mentioned, it is only recently that their nature has been understood. A starter may be se

this purpose, whole milk from a single animal is often used where the same is observed to sour with the production of no gas or other undesirable taint. A skim-milk

y be misled in selecting a starter that is not desirable,

is consisted in the use of pure cultures of specific organisms that were selected on account of their ability to produce a desirable ripening change in cream. The introductio

a temperature sufficiently high to destroy the vegetating organisms. The addition of a properly selected starter will then give the chosen organism such an impetus as will generally enable it to gain the ascendency over any other bacteria and so control the character of the ri

quently produce undesirable flavors. These can almost always be controlled if a culture starter is added, the obnoxious form being repressed by the presence of the added starter. This condition is interpreted as indicating that the addition of a starter to cream which already contains developing bacteria will prevent those

doubtful whether it would gain the supremacy in the ripening cream. The above method of adding a culture to raw cream renders cream-ripening d

tensively used are able to produce a perfectly clean but mild flavor, and a delicate but not pronounced aroma. The "high, quick" flavor and aroma that is so much desired in the American ma

is under more complete control, and herein is the greatest advantage to be derived from their use. Even the

en added will keep much better than the ordinary product, because the diversity of the bacterial flora i

re ferments, it is generally possible to eliminate the abnormal conditions.[164] Taints may also be present in cream due to direct absorption from the cow or through exposure to foul odors.[165] Troubles of this sort may thus be carried over to the butter. This is part

. Certain conditions as the following are d

n milk at ordinary r

s to facilitate churning and

a clean flavor an

od keeping qua

ts flavor-producing qualiti

was generally an evanescent property, and therefore opposed to good keeping quality. Conn has shown that the functions of acid-formation, flavor and aroma p

mpt at mixing selected organisms that have been chosen on account of certain favorable characteristics which they might possess. The difficulty of maintaining such a composite cul

ith some sterile, inert, dry substance. This is the method used in most of the Danish culture

ning process, greater attention has been paid to the carrying out of the details. In the hands of the better operators, the differences in flavor of butter made with a culture or a nat

pasteurizing cream for butter-making, it is not necessary to observe the stringent precautions that are to be noted in the preservation of milk; for the addition of a rapidly developing starter controls at once the fermentative changes that subsequently occur. Then again, the physical requirement as to the production of a cooked taste is not so stri

This tendency can be overcome if the ripened cream is chilled to 48° F. for about two hours before churning.

became necessary to treat all of the skim milk that was returned from the creameries. For this purpose the skim milk is heated to a temperature of 176° F., it having been more recently determined that this degree of heat is sufficien

. In the latter case, it is necessary to heat the skim milk after separation to destroy the disease organisms, but this can be quickly done by the use of steam directly. Much more care must be used in heating the cream in order to prevent injury to the grain of the

f a starter, natural as well as a pure culture, it should be employed in cream in which the bacteria have first been killed out by pas

a high, quick flavor to one that is somewhat milder but of better keeping quality, doubtless pasteurization of the cream will become more and more popular. That such a change is gradually occurring is already evident, although as yet only a small proportion of butter made in this country is now made in this way. Where the cream is unheated, a considerable number of species will be found, and even the addition of a pure culture, if that culture is of the lactic acid-produc

ten arise as to the purity and vigor of the various ferments employed. As there is no way for the factory operator to ascertain the actual conditi

cteria mixed with the selected organism. Molds not infrequently are found in cultures put up in the dry form. Doubtless the effect of these accidental contaminations is considerably less in the case of a starter compose

which acid cannot be formed in abundance. Where the conditions permit of the formation of acid, as would be the case if sugar was present with a lactic acid-producing species, the vitality of the culture

pure-culture ferment. In any event, it is necessary that the starter should be handled in a way so as to prevent the introduction of foreign bacteria as far as possible. It should be remembered at all times that the starter is a liv

If the culture is too old, the larger part of the organisms may have died out before it is trans

ossible the changes that naturally go on in the culture liquid. Be careful that the bottle is not exposed to the influence of

greatest possible care in selecting the milk

iously been well steamed. This can be done easily by setting cans containing skim-milk in a vat filled with water and heating the same to 180° F. or above for one-half hour or more. Steam should not be introduced directly. This process destroys all but a fe

desired culture. Sometimes it is desirable to "build up" the starter by propagating it first

e where a large amount of starter

ure that is suitable for the rapid development of the contained bacter

illed with warm water. The starter cans are often arranged

nd only partially curdled for it is difficult to break up thoroughly the curd particles if the starter is

the curd has been formed some time. The continued formation of lactic acid kills many of the bacteria and thus weake

cold weather checks the growth of grain. It is preferable to dilute the starter, if it cannot be used when ready, with sufficient freshly steril

a new lot of freshly prepared milk. For this purpose two propagating cans should

if, however, no especial care is given, it will soon become infected by the air, and the retention of its purity will depend more upon the ability of the contained organism to choke out foreign growths than upon any other factor. Experience seems to indicate that pure-culture starters "run out" sooner than domestic starters. While it is possible, by bacteriological meth

ter will also contain germ life in varying amounts, but as butter-fat is not well adapted

rotenfelt reports in sweet-cream butter, the so-called "Paris butter," only a few bacter

h organic matter, bacterial growth goes on apace. Melick[170] has made some interesting studies on using pasteurized and sterilized well waters for washing. He found a direct relation to exist between the bacterial content of the

this period of increase is dependent largely upon the condition of the butter. If the buttermilk is well worked out of the butter, the increase is slight and last

mber. The lactic acid group of organisms disappear quite rapidly; the spore-bearing species remaining for a so

involve any bacteriological principles other than those that are incident to cleanliness. The cream, if ripened properly, will contain such enormous numbers of favorable

DEFECTS

length of time. All butters, however, sooner or later undergo a change that renders them worthless for table use. This change is usually a rancidity that is observed in all stale products of this class. The cause of this rancid condition in butter was at first attributed to the formation of butyric acid, but it is now recognized that other changes also enter in.[171] Light and especially air also exert a mar

k by storing butter at low temperature

ut sometimes it is impossible to produce a high flavor. The lack of flavor in this case is due to the absence of

tudied by Jensen.[172] Butter affected by it rapidly acquires a peculiar putrid odor that rui

y of the common feces bacillus, produced this rotten odor and taste in milk in a very short time. Fortunately, this organism was easily killed

rouble is due to feeding, there being in several of these crops, aromatic substances that pass directly into the milk, but in some instances the

mpure gases by the milk as it cools, although the gases and odors naturally present in fresh milk have this peculiar property that is demonstrable by certain methods of aeration.

he trouble; then again, butter exposed to direct sunlight bleaches in color and develops a lardy flavor.[175] In addition to these, cases have been found in which the de

d belongs to the sour-milk bacteria. In twenty-four hours it curdles milk, the curd being solid like that of ordinary sour milk. There is produced, however, i

rived primarily from the bacteria present in the cream or milk. Several of the fermentations of this character in milk are also to be found in butter. In addition to thes

. Mold spores are so widely disseminated that if proper conditions are given for their germination, they are almost sure to develop. In some cases the mold is due to the growth of the ordinary bread mold, Penicillium glaucum; in other cases a black mold develops, due

o be dependent upon the storage temperature at which the butter was kept. When the butter was refrigerated at 15° F. no further difficulty was experienced. It is claimed that the cause of

etermined that this flavor is caused by yeasts (Torula) which produc

TNO

n, Cent. f. Bakt.,

nn, Milch Z

1889, p. 7; 1894, p

nt. Agr. Coll

e, Unders. over Fl

torrs Expt. Sta

torrs Expt. Sta

n, Milch Zeit

lchs?ure Bakterien (Di

Milch Zeit.,

torrs Expt. Sta

p. 122; 1894, p. 284; 1

ll. 32, Iowa Ex

ndw. Woch. f. Schl

ent. f. Bakt., II

employed starters, nearly one-half used commercial cultures. There was practically no difference in the average score of

l. 143, Wis. Expt.

. 138, Kansas Expt

kt., 1900, 6:131; Jensen, L

Cent. f. Bakt.

lch Zeit., 1892,

ll. 21, Iowa Exp

er, Hyg. Ru

ept. Danish Agric.

57, B. A. I. U. S