Factors Influencing Acid Production by Cheese Cultures. II. Influence of Bacteriophage on Acid Production in the Manufacture of Cheddar and Cottage Cheese

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Abstract
Slow acid production, due to the presence of bacteriophage, in the manufacture of cheddar cheese usually was first noticed at the time of draining the whey or shortly thereafter. The rapid increase in acidity of the whey, soon after draining, with normal vats was not apparent when bacteriophage was present. The presence of bacteriophage, active against the lactic acid-producing culture employed, resulted in almost complete cessation of acid production in the manufacture of cheddar cheese when either single-strain or multiple-strain cultures were employed. An increase in the time of cheddaring did not result in an appreciable increase in acidity when acid production was slow because of bacteriophage action. The presence of bacteriophage could be demonstrated in bacteria-free filtrates of whey, cultures, etc., by adding a small amount of the filtrate to pure cultures of Streptococcus lactis isolated from the culture used in the manufacturing process and also by the production of bacteriophage plaques on a solid medium. When a vat of skim milk intended for cottage cheese was contaminated slightly with bacteriophage active against the culture employed, acid formation was very slow for about 24 hours after setting. During this period the bacteria count showed a slight increase, then a large decrease, and finally a large increase. The bacteriophage titer increased for 7 to 12 hrs. following setting and then remained practically constant. When secondary growth occurred (usually after 24 hrs.) acid production proceeded normally.