Action of bacteriophage is one of the principal causes for failure in the production of lactic acid during the manufacture of certain dairy products, especially cheddar and cottage cheese. Rotation of cultures, strict sanitization of equipment and the use of procedures which minimize the nmnber of bacteriophage particles that may gain entrance into milk and milk products from the air have been emphasized as means of keeping down the concentration of bacteriophage However, the level to which contamination with bacteriophage nmst be reduced to permit a given amount of lactic starter to coagulate milk normally has not been established. Whitehead and IIunter (11) observed that increasing the inoeulum to about 1.0 to 1.6 per cent permitted one additional propagation of some cultures before evident bacteriophage action. Anderson and Meanwell (2) indicated that retarded development of acid frequently could be overcome by using 4 :per cent starter. Ilowever, Turner (10) added about 10 particles per milliliter of bacteriophage ]68 to eonc'entrations of about 1,000, t0,000 and ],000,000 Streptococcus lactis IP5 bacteria per milliliter and found that the larger munbers of bacteria decreased the time required for mass lysis.
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E.B. Collins (1951) studied this question.