Part 10 (2/2)

2 Those that act directly upon the bacteria intheir development The substances most frequently utilized are salicylic acid, formaldehyde and boracic acid These are nearly always sold to the reatly in excess of what the crude cheht for in the open market Formaldehyde has been widely advertised of late, but its use is fraught with the greatest danger, for it practically renders insoluble all albureatly increased in larger doses

These substances are generally used byof their poisonous action, and although it may be possible for adults to withstand their use in dilute foreneral milk supplies that may be used by children is little short of criminal The sale of these preparations for use in milk finds its only outlet with those dairymen who are anxious to escape the exactions that must be met by all who atteton has suggested a simple means for the detection of preservalin (boracic acid)[128] When this substance is added to freshits taste As normal milk tastes sour when it contains about 03 per cent lactic acid, asour has been probably treated with this antiseptic agent

~Physical methods of preservation~ Methods based upon the application of physical forces are less likely to injure the nutritive value of milk, and are consequently more effective, if of any value whatever A nuhly in an experimental way that have not yet been reduced to a practical basis, as electricity, use of a vacuu been used with great success, but in this process the nature of thequality in condensed milk often depends upon the action of another principle, viz, the inhibition of bacterial growth by reason of the concentration of the ar and so increasing the soluble solids, or by driving off the water by evaporation, preferably in a vacuues are, however, of therowth can be brought to a standstill, and under proper conditions thoroughly destroyed

~Use of low te on the keeping quality of milk is well known When the tehborhood of 45 F, the development of bacterial life is so slow as to materially increase the period that milk remains sweet

Within recent years, attempts have beendistances by freezing the product, which in the form of e[130] A modification of this process known as Casse's systeen and in several places in Ger a se cans of milk (one part to about fifty of milk) which may or may not be pasteurized[131] This reduces the teer Such a processdistances with safety but as a matter of fact, the system has not met with especial favor

[Illustration: FIG 22 Microscopic appearance of norated in clusters]

~Use of high teent

Milk has been scalded or cooked to keep it from time immemorial Heat may be used at different te effect, depending upon temperature employed All methods of preservation by heat rest, however, upon the application of the heat under the following conditions:

1 A te-point (105-115 F) and below the therrowth, and consequently fermentative action

2 A temperature above the theres This temperature varies, however, with the condition of the bacteria, and for spores is etative forms

Attempts have beentemperature, but when ed[132] Themost satisfactorily used are known as sterilization and pasteurization, in which a degree of te points respectively

[Illustration: FIG 23 Microscopic appearance of eneous distribution of fat-globules The physical change noted in co 22 causes the diminished consistency of pasteurized cream]

~Effect of heat on milk~ When es in its physical and chemical properties are to be noted

_1 Diminished ”body”_ When milk, but more especially cream, is heated to 140 F or above, it becomes thinner in consistency or ”body,” a condition which is due to a change in the grouping of the fat globules

In normal milk, the butter fat for the22) When exposed to 140 F or above for ten lobules beco 23) A _h as 158-160 may be made without serious effect on the cream lime; but above this the creaives the impression of thinner milk

_2 Cooked Taste_ If milk is heated for some minutes to 160 F, it acquires a cooked taste that becomes more pronounced as the temperature is further raised Milk so heated develops on its surface a pellicle or ”skin” The cause of this change in taste is not well known Usually it has been explained as being produced by changes in the nitrogenous elements in the milk, particularly in the albumen Thoerner[133] has pointed out the coincidence that exists between the appearance of a cooked taste and the loss of certain gases that are expelled by heating

He finds that the as cannot escape has a much less pronounced cooked flavor than if heated in an open vessel The so-called ”skin” on the surface of heated htly-closed receptacle By some[134] it is asserted that this layer is composed of albumen, but there is evidence to show that it is modified casein due to the rapid evaporation of the estibility_ Considerable difference of opinion has existed in the estibility of raw and heated milks A considerable a artificial digestion experiestion experiments with animals, and in a few cases with children The results obtained by different investigators are quite contradictory, although the preponderance of evidence seeestibility ofpoint[135] It has been observed that there is a noteworthy increase in amount of rickets,[136] scurvy and hly-heated milks are employed These objections do not obtain with reference to milk heated to h even this lower teestibility The successful use of pasteurized milks in children's hospitals is evidence of its usefulness

_4 Fere in milk is due to the predoanisms as a class do not possess spores, they are readily killed when heated above the ther cell The destruction of the lactic for types possessors of the field, and consequently the feres in heated milk are not those that usually occur, but are characterized by the curdling of the milk from the action of rennet enzy milk causes the soluble li of ) is dependent upon the presence of these salts, their absence in heated reatly retards the action of rennet This renders it difficult to utilize heatedunless the soluble li solutions of calcium chlorid

~Sterilization~ As ordinarily used in dairying, sterilization , if not exceeding, 212 F It does not necessarily ierm-free; for, on account of the resistance of spores, it is practically impossible to destroy entirely _all_ these hardy for point, as is done where steaerned to keepperiod of time The treateneral favor in this country, although it has been more widely introduced abroad In most cases the process is carried out after the enuity has been exercised in the construction of devices which will per process has been coh a temperature have a more or less pronounced boiled or cooked taste, a condition that does not eneral favor in this country The apparatus suitable for this purpose must, of necessity, be so constructed as to withstand steam pressure, and consequently is considerablyprocess

~Pasteurization~ In this es from 140 to 185 F and the application is th of time The process was first extensively used by Pasteur (fro various maladies of beer and wine Its i quality of o; but therapidly in favor as amilk for coeranisetative condition; but if thequality very materially It is unfortunate that this sa of cream as a preparatory step to the use of pure cultures in crea The objects to be accomplished vary materially and the details of the two processes are also quite different

While pasteurizing can be performed on a small scale by the individual, the process can also be adapted to the coe quantities of milk The apparatus necessary for this purpose is not nearly so expensive as that used in sterilizing, a factor of ies are considered In this country pasteurization hasa ned to serve as children's food, but even for general purposes

~Requirements essential in pasteurization~ While considerable latitude with reference to pasteurizing limits is permitted, yet there are certain conditions which should be observed, and these, in a sense, fix the linated as (1) the _physical_, and (2) the _biological_ requirements

~Physical requirelish and American people are so averse to a scalded or cooked flavor in hly heated product to be sold in competition with ordinary raw milk In pasteurization then, care must be taken not to exceed the temperature at which a permanently cooked flavor is developed As previously observed, this point varies with the period of exposure A momentary exposure to a temperature of about 170 F may be made without any material alteration, but if the heat is maintained for a few minutes (ten minutes or over), a temperature of 158 to 160 F is about the maximu of the milk_ It is especially desirable that a sharp and definite cream line be evident on the milk soon after pasteurization If this fails to appear, the natural inference of the consumer is that the milk is skih to cause the fat-globule clusters to disintegrate (see Figs 22 and 23), the globules do not rise to the surface as readily as before and the cream line remains indistinct

Where the exposure is made for a considerable period of time (10 minutes or more), thethis change is about 140 F; if the exposure is made for a very brief time, a minute or less, theproperty