Behavior of Listeria monocytogenes During the Manufacture and Storage of Colby Cheese

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Abstract
Colby cheese was made from pasteurized whole milk to which Listeria monocytogenes (strain V7 or California) was added. Cheese was stored for 140 d at 4°C. Numbers of L. monocytogenes in newly-made cheese were 1.27 orders of magnitude (average) higher than in milk from which cheese was made. This indicates the bacterium did not grow to any appreciable extent during the manufacture of cheese. A minor portion (2.4%) of the population of Listeria in the cheese vat escaped in the whey and the rest was entrapped in the curd. Early during storage, numbers of Listeria in the cheese remained relatively constant for a time that depended on the strain used. Numbers of Listeria in cheese decreased steadily thereafter at a rate that depended mainly on composition of the cheese. After 140 d of storage, higher numbers of Listeria remained in cheese when (a) a higher rather than lower concentration of the microorganism was present in milk, (b)cheese with a higher rather than lower moisture content was produced, and (c) strain V7 rather than California was added to milk.