Part 11 (1/2)

_3 No die which takes place in the creae in body or consistency which is noted where creah a teiven under (2) cream heated above these temperatures is reduced in apparent thickness and appears to contain less butter-fat Of course the pasteurizing process does not change the fat content, but its ”body” is apparently so affected Thus a 25 per cent cream may seem to be no thicker or heavier than an 18 per cent raw cream This real reduction in consistency naturally affects the readiness hich the creaical require quality_ In coical require quality of the pasteurized er process The i quality depends upon the temperature and time of exposure, but fully as much also on the way in which the pasteurized product is handled after heating The lowest temperature which can be used with success to kill the active, vegetative bacteria is about 140 F, at which point it requires about ten minutes exposure If this period is curtailed the tely An exposure to a temperature of 175 F for a ree of heat for the longer tiical studies as to the effect which a variation in temperature exerts on bacterial life inthe foundation for the selection of the proper li table the exposures were made for a uniform period (20 minutes):

_The bacterial content of milk heated at different temperatures_

Number of bacteria per cc in milk

45 C 50 C 55 C 60 C 65 C 70 C

Unheated 113 F 122 F 131 F 140 F 149 F 158 F

Series I 2,895,000 ---- 1,260,000 798,000 32,000 5,770 3,900 Series II 750,000 665,000 262,400 201,000 950 700 705 Series III 1,350,000 1,100,000 260,000 215,000 575 610 650 Series IV 1,750,000 ---- 87,360 ---- 4,000 3,500 3,600

It appears from these results that the most marked decrease in temperature occurs at 140 F (60 C) It should also be observed that an increase in heat above this teanis were in a spore or resistant condition It was noted, however, that the developing colonies grew hly heated reater extent even though not killed

_2 Destruction of disease bacteria_ While milk should be pasteurized so as to destroy all active,bacteria, it is particularly iht find their way into the sa in milk before or after it is drawn from the animal are not able to form spores and hence succumb to proper pasteurization Such is the case with the diphtheria, cholera and typhoid organisanism that is invested with most interest in this connection is the tubercle bacillus On account of its h powers of resistance, it

~Ther the exact teerm is destroyed there is considerable difference of opinion Part of this arises froanisrow readily on artificial media), and part from the lack of uniform conditions of exposure The standards that previously have been enerally accepted are those of De Man,[137] who found that thirty minutes exposure at 149 F, fifteen minutes at 155 F, or ten erm

More recently it has been demonstrated,[138] and these results confirmed,[139] that if tuberculous milk is heated in closed receptacles where the surface pellicle does not forerm is destroyed at 140 F in 10-15 minutes, while an exposure at 160 F requires only about oneare such that the surface of the reatly increased When heated in open vessels Sanism was not killed in some cases where the exposure was s[141] have shown an instance where the thermal death-point of a micrococcus isolated fro it under conditions that permitted of the formation of the scalded layer

It is therefore apparent that apparatus used for pasteurization should be constructed so as to avoid this defect

~Methods of treatrown up in the treatienic or sanitary aspect of the problem and is used more particularly in the treatment of cream and relatively small milk supplies The other system has been developed prie amount of milk must be treated in the minier period of time, about fifteen minutes at a relatively low temperature from 140-155 F; in the other, the milk is exposed to the source of heat only while it is passing rapidly through the apparatus Naturally, the exposure under such conditions her tehborhood of 160 F

The types of apparatus used in these respective processes naturally varies Where the heating is prolonged, the apparatus employed is built on the principle of a _tank_ or _reservoir_ in which a given voluiven period of time

When the heat is applied for a much shorter period of tih the machine Naturally the capacity of a continuous-flow apparatus is reater than a machine that operates on the intere supplies, as in city distribution, this systee The question as to relative efficiency is however one which should be givenapparatus~ The problened for direct consumption are so materially different fro that the type of machinery for each purpose is quite different The equipeneral classes:

1 Apparatus of lined for family use

2 Apparatus of sufficient capacity to pasteurize on a co milk for individual use, it is not desirable to treat at one time more than will be consu a few bottles will suffice In this case the treatment can best be perforer of infection Several different types of pasteurizers are on the market; but special apparatus is by no means necessary for the purpose The process can be efficiently performed by any one with the addition of an ordinary dairy ther 24 indicates a sied for this purpose

The following suggestions indicate the different steps of the process:

1 Use only fresh milk

2 Placeto a uniforhtly with a cork or cover If pint and quart cans are used at the same time, an inverted boill equalize the level Set these in a flat-bottomed tin pail and fill ater to same level as milk An inverted pie tin punched with holes will serve as a stand on which to place the bottles during the heating process

3 Heat water in pail until the temperature of same reaches 155 to 160 F; then remove from source of direct heat, cover with a cloth or tin cover, and allow the whole to stand for half an hour In the preparation of milk for children, it is not advisable to use the low-temperature treatment (140 F) that is recommended for commercial city delivery

[Illustration: FIG 24 A home-made pasteurizer]

4 Remove bottles of er to bottles and store in a refrigerator

~Commercial pasteurizers~ The two methods of pasteurization practiced commercially for the preservation of milk and cream have been developed because of the two types of machinery now in use Apparatus constructed on the reservoir or tank principle permits of the retention of the milk for any desired period of time Therefore, a lower temperature can be employed in the treath the heater in a more or less continuous stream, the period of exposure is necessarily curtailed, thereby necessitating a higher temperature

~Reservoir pasteurizers~ The si on this principle is where the un cans and immersed in water heated by steam Ordinary tanks surrounded ater spaces can also be used successfully The Boyd crea vat has also been tried In this the h which hot water circulates

In 1894 the writer[142] constructed a tank pasteurizer which consisted of a long, narrow vat surrounded by a steam-heated water chamber Both the itators having a to-and-fro movement