PASTEURIZATION OF MILK FOR CHEESEMAKING.

New Zealand Journal of Agriculture, Volume XII, Issue 6, 20 June 1916, Page 440

PASTEURIZATION OF MILK FOR CHEESEMAKING.

C. STEVENSON and W. GRANT,

Dairy Instructors, Taranaki.

Since the pasteurization of cream for buttermaking resulted in such a marked improvement in the quality of butter considerable interest has been taken in the possibility of applying similar treatment to milk used for cheesemaking. For some time this was considered almost impracticable, owing, firstly, to the very large quantities of milk to be dealt with in the limited time available for this purpose —in most factories from two to two and a half hours; and, secondly, to the high cost of heating such large quantities of milk by the methods adopted in butter-factories for dealing with cream.

The - advent of the regenerative heaters now on the market has, however, completely overcome both the difficulties indicated. These machines are capable of treating up to 1,800 gallons of milk per hour, while heating to a temperature of from 165° to 170° F., and at the same time regenerating up to forty degrees. Thus, a duplicate plant of this capacity running, for two and a half hours would in that time be capable of- dealing with 9,000 gallons of milk a capacity sufficient for practically any . of the largest cheese-factories in the Dominion. Moreover, there appears to be no reason why the capacity of these machines could not be increased to, say, 2,000 gallons per hour.

A complete plant of 1,800-gallon capacity can be installed for £3OO. As few cheese-factories have yet carried on this pasteurizingwork for a complete season, no reliable figures are available regarding the cost of running. It is, of course, evident .to any one conversant with the business of cheesemaking that heating the milk to a temperature of 165° must cause an increase in the amount of fuel consumed, but this increase is actually not nearly so great as would at first appear to be the case. When pasteurizing is carried out there is obviously . no necessity to heat the milk in the vats, as is the case under the old system of cheesemaking. This latter method of heating is a most extravagant one, whereas the system of regenerative heating is as economical a one as it is possible to obtain, the heaters in use being so constructed that they utilize to the fullest possible extent every unit of heat applied.

From information at present available it would appear that the increase in fuel-consumption when pasteurizing with live steam is from 15 to 20 per cent. A saving, however, may be effected in this direction by having exhaust steam from the engine connected to the heater.

Some dairy companies contemplating the ' installation of a pasteurizing plant may be inclined to delay on account of the scarcity of water available for cooling purposes; but as the regenerative heater delivers the milk to the cooler at a temperature of 125 0 , and it requires only to be further cooled to setting-tempera-ture— to 90 0 -it will be seen that no very great quantity of water is required. Where water is somewhat scarce a saving can be effected by installing a small pump, and pumping the waste water from the cooler to overhead tanks. This water is, of . course, perfectly clean, though slightly warm.

In the manufacture of cheese from pasteurized milk practically the same treatment should be applied as in dealing with nonpasteurized milk under normal conditions. Extreme care must be taken to guard against the possibility of the milk becoming in any way contaminated during the process of pasteurization. Only the best-quality drawn brass piping should be used where piping is required. In order to facilitate cleaning, the piping should be joined by brass unions in fairly short lengths. Every part of ■ the plant with which the milk comes in contact should be thoroughly' cleaned as soon as possible after the machine is stopped.

A good starter is, of course, essential in either case; but in working with pasteurized milk, which is practically free from bacteria, the influence of the starter is naturally much more prominent. Consequently, in the manufacture of cheese from pasteurized milk only the best-quality starters should be used.

The best pasteurizing-temperature to aim at is from 160 0 to 168 0 F. In the very late autumn it will be found advisable to fix the maximum temperature at 160°. A temperature lower than i6o°iis not sufficient to destroy all the injurious germs, while, on the other hand, the curds obtained from milk heated to i7s°-iBo° are always more or less broken, and, in addition, usually develop a slightly scorched flavour.

The use of a quantity of hydrochloric acid for acidulating the milk before adding the rennet has been tried in some cases; but, except when the milk was heated to high temperatures, practically no difference in the nature of the curds was observed. When heating the milk to temperatures of 175 0 or over, the addition of

1 oz. to i| oz. of hydrochloric acid per 100 gallons of milk will be found to be an advantage.

There are many benefits to be derived from the pasteurization of milk . for cheesemaking, chief of which is the great improvement in the quality of the cheese. Some very striking instances of this have been observed in Taranaki during the past season. One particular factory while working under the old method always produced a large percentage of second-grade cheese, but • since pasteurization was adopted not a single second-grade cheese has been manufactured, and, in addition, the factory’s average grade has risen from 89 points to 92.

Another important factor from the dairy-farmer’s point of view is whether or not the expenditure incurred in installing a pasteurizing plant is going to be a good investment. From . information now available there can be no doubt that the investment is an excellent one. ' . . “• '

There are many ways in which the farmers’ returns, will be increased with the assistance of a pasteurizing plant. To begin with, “ fast - working ” vats, which are due to slightly overripe milk, are never experienced when pasteurizing is followed. All factory managers and directors are. well aware of the enormous losses which take place while working with this class of milk, especially in a season such as the one just past, when the weather was for a long time exceptionally warm. The saving effected in this direction alone, by means of the pasteurizer, must be very material.

Again, we have the fact that there is a considerable increase in, the amount of ■ butter-fat incorporated in cheese made from pasteurized milk. This is proved by the small percentage of fat left in the whey, and also by the-fact that no fat is found floating on the milk or in the cheese-presses. The presence of extra solids in the cheese indicates, of course, that the moisture-content can be increased without injury to. the body, thus producing a direct increase in the amount of cheese made per pound of butter-fat contained in the milk. -

The improvement in the quality of the cheese . also means a direct increased'return to the dairy-farmer. By working with milk which has been delivered to the factory in good condition and afterwards pasteurized, and by giving careful attention to the manufacture, second-grade cheese can be almost entirely eliminated. As practically all cheese sales are made on a basis of |d. per pound deduction for second-grade, the saving thus effected must also be credited for the most part to the pasteurizer.

Taking all these factors and the saving thereby effected into consideration, it is perfectly safe to assume that the total increased return of a cheese-factory working with pasteurized milk will be equal to at least a 3-per-cent. increase in yield. On this basis a very simple calculation will show the amount of net profit, after allowing for interest and depreciation on plant, extra fuel required, and also a reduction of approximately .20 per cent, in the amount of butter manufactured from the fat in the whey.

Regarding the quality of the milk supplied, it would be a fatal mistake for the dairy-farmer to assume that the installation of a

pasteurizing plant at the factory in any way lessens his responsibilities with regard to the care of the milk on the farm. The quality of the milk supplied will always be the chief factor in determining the quality of the cheese made, whatever method of manufacture may be adopted. For instance, an experience in Taranaki during the past season with milk strongly tainted with turnip flavour proved conclusively that pasteurization would not entirely eliminate this flavour. The latter was easily detected in

the cheese, notwithstanding the fact that the milk had been heated to a temperature of 190°. During the season 1914-15 seven pasteurizing plants were installed in cheese-factories in Taranaki, while at the present time thirty-two plants are in operation there. This large increase in the number of plants installed proves that the factory managers and directors in this district are fully convinced of the benefits

of pasteurization. From all the facts now available, it is quite evident that the pasteurization of milk for cheesemaking has been in all respects an unqualified success. There is no doubt whatever that the general adoption of the system of pasteurization in the cheese-factories throughout the Dominion will cause as great a revolution in the manufacture of cheese as it has already effected in relation to butter.