Samples of Canadian Cheddar and Oka cheeses which exhibited gas formation and fissure defects were examined microbiologically. Analyses revealed that lactobacilli, especially heterofermentative types, as well as organisms capable of using citrate were more numerous in defective cheeses than in high quality products. Higher numbers of viable lactobacilli were obtained in assays where APT or MRS media were used than when MRS adjusted to pH 5.5 or Rogosa agar were used, especially when younger cheeses were sampled. The number of lactic streptococci did not differ between good quality Cheddar or rejected aged cheese. Coliforms, staphylococci, yeasts, molds and Clostridia appeared to have no relationship with the formation of gas in cheeses late in the maturation process.
2Agriculture Canada, St.-Hyacinthe.
3Agriculture Canada, Ottawa.