Bacteriophage infection of the starter streptococci, which commonly causes ‘slowness’ in cheese manufacture, may arise from whey infection of milk cans used for the cartage of cheese whey from factory to farm. Thus ‘slowness’ can occur even when the starter itself and all the factory utensils are free from infection. The pasteurizing treatment which the cheese milk receives is not sufficient to destroy the traces of phage derived from infection of the milk cans.

Three methods for eliminating this trouble were investigated:

(i) Pasteurization of the whey at 190° F. for a few seconds immediately after removal from the cheese vat.

(ii) Treatment of the whey with chloride of lime.

(iii) The use of a series of single-strain starters in daily rotation in the cheese factory.

All three methods proved practicable, although some mechanical difficulties were encountered in the particular pasteurization system which was tried. The third method is at present undergoing an extensive trial on a commercial scale. It is preferred in the first place because it is costless, whereas the first two methods would involve a regular additional cost in steam of chloride of lime.