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

, the subject has received more attention from the scientific point of view and the underlying causes determined to some extent. Since the subject ha

ed on the phenomena of ferment action, and that the application of bacteriological principles and ideas is sure to yield more tha

o make a first-class product depends to a large extent on the quality of the raw material. Cheese contains so large a proportion of ni

TERIA IN NORMAL

ses it, the milk is "ripened" to the proper point. The action of the rennet, which is added to precipitate the casein of the milk, is markedly affected by the amount of acid present, as well as the temperature. Hence it is desirable to have a standard amount of acidity as well as a standard temperature for coagulation, so as to unify conditions. It frequently happens that the milk is abn

hat is extremely sweet, so as to curtail the time necessary to get the chee

been allowed to ferment and sour under carefully controlled conditions. Of course much depends upon the quali

ultures of some desirable lactic-acid form.[178] This has rendered the making of cheese not only more uniform, but

Emmenthaler cheese, has been placed on the market under the name Tyrogen. It is claimed that the use of this starter, which is added directly to the milk and also rubbed

to the formation of white spots that are produced by the bleaching of the col

formation in Edam cheese which is made from practically sweet milk. This fermentation, the essential feature of which is prod

eese is another illustration of the empirical development of starters, althoug

in pasteurizing milk, the soluble lime salts are precipitated by the action of heat, and under these conditions rennet extract does not curdle the casein in a normal manner. This condition can be restored, in part at least, by the addition of soluble lime salts, such as calcium chlorid; but in our experience, desirable results were not obtained where heated milks to which this calciu

are never free from bacteria. Adametz[183] found ten different species and from 640,000 to 900,000 bacteria per cc. in natural rennets. Freudenreich has shown that rennet extract solutions can be used in Swiss cheese-making quite as well as nat

erally the case in cheddar making, the number of ba

which usually predominate, develop very rapidly, producing thereby considerable quantities of acid which change materially the texture of the curds. The lactic acid acts upon the casein in solutions containing salt, causing it to dissolve to some extent, thus forming the initial compounds of digestion.[184]

at of cheddar. In all such varieties, a great deal more trouble is experienced from the production of "gassy" curds, becau

entire process. The cooking or heating of curds to expel the excessive moisture is never so high as to be fatal to germ l

. The curd particles do not mat closely together and "mechanical holes," rough and irregular in outline, occur. Very often, at relatively high temperatures, such cheese begin to "huff," soon after being taken from t

g.

holes due to lack of acid development; P, same cheese four

recipitated casein and fat. In a short time, a deep-seated change occurs. Physically this change is demonstrated in the modification that the curd undergoes. Gradually it breaks down and becomes plastic, the elastic, tough curd being changed into a softened m

ure incorporated with the curd materially affects the physical appearance of the cheese, and the rate of change in the same. The ripening temperature, likewise the moisture content of the surrounding air, also exerts a mark

ed into soluble nitrogenous substances (caseone of Duclaux, or caseogluten of Weigmann). This chemical phenomenon is a breaking-down process that is analogous to the peptonization of proteids, alth

own by Congo red, the lactic acid being converted into salts as fast as formed. In very old cheese, undergoing putre

ns practically unchanged, although the researches of Weigmann and Backe[185] show that fatty acids are formed from the fat. In the green

milk, but a study of cheese shows a peculiar change in the character of the flora. In the first place, fresh cottage cheese, made by the coagulation of the casein throug

rked similarity, as is illustrated by Adametz's work[187] on Emmenthaler or Swiss hard cheese, and Schweitzer Hausk?se, a soft va

cheese. The same general law has also been noted in Canadian[190] and English[191] cheese. At first a marked decrease in numbers is usually noted, lasting for a day or two. This is followed by an enormous increase, caused by the rapid growth of the lactic-acid type. The deve

d by these organisms diffuse toward the interior. That such a condition occurs in the hard type of cheese made with rennet is extremely improbable. Most observers agree that in this type of cheese the ripening progresses throughout the entire mass, although Adametz opposes this view and considers that in Emmenthaler cheese the

tent is maintained for a much longer period of time than at higher temperatures. Under these conditions the lactic-acid type continues in the ascendancy as usual. In cheese cured at high temper

robably in the initial stage of this industry cheese were allowed to ripen without any sort of control, with the inevitable result that during the summer months the temperature generally fluctuated so much as to impair seriously the quality. The effect of high temperatures (70° F. and above

on texture of cheese. Upper row ripened e

nitrogenous products. They have an excellent texture, generally solid and firm, free from all tendency to openness; and, moreover, their flavor is clean and entirely devoid of the sharp, undesirable tang that so frequently appears in old cheese. The keeping quality of such cheese is much supe

y has been given the subject of cheese curing or ripening, in order to

the most marked chemical transformation that occurs is that which has to do with the peptonization or breaking down of the casein. It is true that under ordinary conditions this decomposition process is also accompanied with the formation of certain flavor-producing substances, more or less aromatic in character; but it by no means follows that these two processes are necessaril

ed that if milk was boiled and made into cheese, the casein failed to break down. Adametz[196] added to green cheese various disinfectants, as creolin and thymol, and found that this practically stopped the curing process. From these experiments he drew the concl

turing cheese indicates that the general character of the ri

although concerning the nature of these organisms there has been no unanimity of opinion. The overwhelming development of bacteria in all cheeses naturally gave suppor

y organism must possess the property of dissolving the proteid molecule, casein, and forming therefr

y as ripening agents, but they secrete an enzym or unorganized ferment to which he applies the name casease. This ferment acts upon the casein of milk, converting it into a soluble product known as caseone. These organisms are found in normal milk, and if they function as casein transformers, one would naturally expect them to be present, at least frequently, if not predominating in the ripening cheese; but such

heese a digesting species, one of the Tyrothrix type, which is capable of peptonizing the casein and at the same time producing the characteristic flavor of this class of cheese. This organism, called by him Bacillus nobilis, the Edelpilz of Emmenthaler cheese, has been subjected to co

properties. This has been the stumbling-block to the acceptance of this hypothesis, as an explanation of the breaking down of the casein. Freudenreich has recently carried on experiments which he believes solve the problem. By growing cultures of these organisms in milk, to which sterile, freshly precipitated chalk had been added, he was able to prolong the development of bacteria for a considerable period of time, and as a result finds that an appreciable part of the casein is digested; but this action is so slow compared with what normally occurs in a cheese, that exception may well be taken to this type of experiment alone. Weigmann[200

pt that ammonia is not produced as is the case in old cheese. The cause of the decomposition of the casein, they found to be due to the action of a milk enzym which is inherent to the milk itself. This digestive ferment may be separated from fresh milk by concentrating centrifuge slime extracts by the usual physiological reagents. This ferment, called by them galactas

of pancreatic extracts to cheese accelerated

enzym is now generally accepted as one of the factors concerned in the decomposition of the casein. Freudenreich believes it is able to change case

necessarily destroyed. A brief exposure at 176° F. is sufficient to destroy its activity, and even an exposure at lower temperatures weakens its action considerably, especially if the reaction

that time to be the foundation of the bacterial theory of casein digestion-are now explicable on an entirely different basis. In thes

d in the cheddar process. These two factors undoubtedly account for by far the larger proportion of the changes in the casein; and yet, the formation of ammonia in well ripened cheese is not accounted for by these factors. This by-product is the main end product of proteid digestion by the liquefying bacteria but their apparent infrequency in cheese makes it difficult to understand how they can function prominently in the change, unless the small quantity of digestive enzyms excreted by them in t

he intensity of the same generally increases but at no time should it have any bitter, sour, or otherwise undesirable taste or aroma. Texture registers more accurately the physical nature of the ripening. The cheese should not be curdy and harsh, but should yield quite readil

stics in an optimum degree is to be perfect in

e-be perfectly satisfactory, but the factory management while the curds are in the vat demands great skill and careful attention; and finally, the long period of curing in which variation in temperat

ther. Thus the influence of the acidity developed in the curds is felt throughout the whole life of the cheese, an over-development of lactic-acid bacteria producing a sour condition that leaves its impress not only on flavor but texture. An i

at confer on cheese its peculiar aromatic qualities and taste be thoroughly understood. It is to be regretted that the results obtained so f

ounds that resemble, in some cases, the peculiar flavors and odors that characterize some of the foreign kinds of cheese; but an introduction of these into curd has not resulted in the production of the peculiar variety, even though the methods of manufacture and curing were closely followed. The similarity in germ content in different varieties of cheese made in the

. While the liquefying type of bacteria was very sparse in normal cheddar, they developed luxuriantly in the washed cheese. The flavor at the same time was markedly affected. The control cheddar was of good quality, while that made from the washed curds was decidedly off, and in the course of ripening became vile. It may be these two results are simply coinc

tion of various fungi which grow in the cheese, and there produce certain by-products that flavor the cheese. A

troduce the desired mold, which is the ordinary bread-mold, Penicilliu

is done. These caverns are always very moist and have a temperature ranging from 35° to 44° F., so that the growth of the fungus is retarded considerably. The spread of the mold throughout the ripening mass is also assisted in a mechanical way. The partially-matured cheese a

s followed of rubbing the walls and cellars of the new location with material taken from the old established factory. In this cust

ngland, the desired mold fungus is introduced into the green chees

but is hastened by the development of molds and bacteria on the outside that exert a solvent action on the casein. For this reason, soft cheeses are usually made up in small sizes, so that this action may be hastened.

the appearance of the digesting organisms on the surface is delayed until the acidity of the mass is reduced to the pr

the red slimy coat act upon the casein, producing an alkaline reaction that is unfavorable to the growth of the blue mold. Two sets of organisms are, therefore essential in the ripening process, one preparing the soil for the ferment that later produces the requisite ripening changes. As ordinarily carried on, the p

ERIA IN ABNORMAL

considering the more important of these changes, that not all defective conditions in cheese are attributable to the influence of living organisms. Troubles frequently arise from errors in manufacturing details, as too

le of evolving unpleasant or even putrid odors. Most of them are seeded in the milk before it comes to the factory and are due to careless manipulation of the milk while it is still on the farm. Others gain access to the milk in the factory, owing to unclean conditions of one sort or anoth

izes in the green cheese; often they appear in the curd before it is put to press. Usually in this condition the curds look as if they had been punctured with a pin, and are known as "pin holey" curds. Where the gas holes are larger, they are known as "Swiss holes" from their resemblance to

gas causes the green cheese to "huff" or swell, until it may be considerably distorted as in Fig. 3

ese made fro

on of the year, but the trouble is most com

rd cheese. When acidity is produced, these gassy fermentations are checked, and in go

are formed in abundance (bl?hen), the trouble reaches its maximum. If the gas holes are very numerous and therefore sma

s cheese showing "g

mented whey in which to soak the natural rennets. Freudenreich and Steinegger[209] have shown that a much more unifor

animal gases, etc., but in all these cases it was nothing more than a surmise. Very often the milk does not betray any visible sy

efore, much more widely distributed than it would be if it was caused by a single specific organism. These gas-producing organisms are to be found, sparingly at least, in almost all milks, but are normally held in check by the ordinary lactic species. Among them are a large number of the bacteria, although yeasts and allied germs are often present and are likewise able to set up ferme

rms that are able to produce an infectious inflammation (mastitis

perfectly sweet milk, it is possible to artificially produce t

part within certain limits. These methods of treatment are, as a rule, purely mechanical, as when the curds are piled and turned, and sub

-acid bacteria, the gas-producing species do not readily thrive. Another reason why acid aids in repressing the development of gas is that the curd particles are partially softened or digeste

lt than usual in making the cheese will very often restrain the production of gas. Tendency to form gas in Edam cheese is controlle

as-producing bacteria contained therein. Care must be taken not to carry this too

lopment of gas. At high curing temperatures, gas-producing organisms develop

the early recognition of such milks that are not apparently affected when brought to the factory, fermentation or curd tests (p. 76) are of great value. The use of this tes

in kinds of wine. It has been noted in widely different sections of the country and its presence bears no relation to the other qualities of the cheese. The cause of this trouble has recently been traced[212] to the presence of vario

rennet used than usual. The cause of the defect is obscure, but it has been demonstrated that the same is communicable if a starter is made by grating some of this mottled cheese into milk. The bacteriology of the trouble has

ally where the ripening process is carried on at a low temperature in

er cheese which he connected with udder inflammation

elated to Conn's micrococcus of bitter milk. It develops lactic acid rapidly, coagulating the milk and producing an intensely bitter taste in the course of one to three

at grows in the milk and also in the cheese

ble to produce bitter products in milk do not retain

nterior of the cheese undergoes this slimy decomposition. The soft varieties are more prone toward this fermentation than the hard, although the firm cheeses are by no means exempt from the trouble. The "Verlaufen" or "running" of limburger cheese is a fermentation allied to this. It is where the inside of the cheese breaks down

ored points to be located along the edges of the curd particles. According to Harding,[216] this trouble is most common in spring and fall. The cause of the difficulty has been traced by Connell

ifferent pigments in or on the cheese. More frequently these are merely superficial and affect only the outer layers of the cheese. Generally they are attributable to the development of certain

e inside, increasing rapidly in size until the whole mass is affected. This defect he was able to show was produced by

revail, these spores will always develop. At temperatures in the neighborhood of 40° F. and below, mold growth is exceedingly slow, and often fructification does not occur, the only evidence of the mold being the white, felt-like covering that is made up of the vegetating filaments. The use of paraffin has been suggested as a means of overcoming this growth, the cheese being dipped at an early stage into melted paraffin. Recent experiments have shown that "off" flavors sometimes develop where cheese are paraffined directly from the

ry blue-green bread mold, Penicillium glaucum, is most frequently found, but

oisonous alkaloid which he has isolated, and which he calls tyrotoxicon.[220] This poisonous ptomaine has also been demonstrated in milk and other milk products, and is undoubtedly due to the developmen

they only become manifest in most cases during the later stages of the curing process. The only remedy against future loss is to recognize the conditions

or them he alone is responsible. The development of taints due to the growth of unwelcome bacteria that have gained access to the milk while it is yet on the farm are generally beyond the control of the cheese maker, unless they are so pronounced as to appea

to point out to his patrons the absolute necessity of their handling the mil

TNO

, 1896, p. 112; Campbell, Trans. High. &

ch Zeit. (Hildeshe

No. Brit., Agric

, Milch Zeit.,

h Zeit. (Hildeshe

z, Landw. Ja

rt, Bull. 214, N. Y. E

h Zeit., 1

Technical Myc

z, Landw. Ja

, Landw. Jahr. d.

Rept. Wis. Expt. S

, Rev. gen. du Lait, Nos.

nd West of Eng. Soc

r. d. Schweiz, 1900; Adametz,

897, p. 203. Harrison and Connell, Re

pt. Stat., 1901. Dean, Harrison and Harcour

, Milch Zeit.,

z, Landw. Ja

aux, Le La

st. Molk. Zeit.,

Landw. Jahr. d. Sc

. Bakt., II Abt., 1898,

bs. in Expt. St

ell, 14 Rept. Wis. Exp

ent. f. Bakt.,

Cent. f. Bakt., II

n, Ibid., 1

Wis. Expt. Stat

Landw. Jahr. d

ussell, 18 Rept. Wi

f. Bakt. 1

, Wis. Expt. St

ussell, 18 Rept. Wi

mith, Bull. 183, N. Y. (Gen

au, Landw. Jah

ich, Füehl. Lan

ll. 123 Ont. Agr'l

. Y. (Geneva) Expt

ull. Canadian De

, Milch Zeit.,

Milch Zeit., 188

. physiol. Ch

DE

t of, on ch

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tes

n of mi

c bact

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ic bact

nce of, on mil

l odo

rax,

ptics,

of butt

definiti

lactic

-fuscu

genus

s lacti

aerogen

rythroge

saponac

visco

s, 162

giosu

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ter

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in mil

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re of

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actory, methods

ase,

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ee

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er,

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, 72

thale

r of,

mentation

nzola

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and c

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n of defe

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isinfectan

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of heat

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effect

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a, effect of,

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