Growth of Pseudomonas or Flavobacterium in Milk Reduced Yield of Cheddar Cheese

Cheddar cheese was manufactured from milk which was artificially contaminated with proteolytic species of Pseudomonas or Flavobacterium and stored at 7°C. Cheese was analyzed for moisture content and yield was determined on a dry matter basis. Bacterial counts were made during 7 d of milk storage. Pseudomonas isolates grew to larger populations and faster than did Flavobacterium isolates. Yield of cheese decreased as time of storage was extended beyond 3 d and psychrotrophic populations increased. Greatest losses were observed after 5-7 d of storage with psychrotrophic bacterial counts of 10⁶-10⁸/ml. Overall average decreases in yield of cheese caused by Pseudomonas spp. or by Flavorbacterium spp. were 0.53% and 0.39% per day, respectively, when divided equally over a 7-day period. However, losses generally were not evident until milk was held for 5 d. Numbers of and kind of psychrotrophic bacteria, and multiplication and metabolic activity of these bacteria, when present in milk, are among the factors important in causing a reduction of cheese yield.