Emmental cheese: a complex microbial ecosystem. Consequences on selection and use of starters.

Two fermentations usually take place in emmental cheese, lactic acid fermentation, followed by propionic acid fermentation. Unfortunately, an undesirable fermentation sometimes occurs during cheese ripening: the butyric acid fermentation. Numerous microorganisms cooperate and interact in these fermentations: lactococci, thermophilic streptococci and lactobacilli, heterofermentative lactobacilli and pediococci, propionic acid bacteria. Thus, the cheese is a microbial ecosystem which, in addition to bacteriophages, has other parasites. The properties and the role of each species, the effects of various strains (and the interactions between them) on curd acidification, proteolysis during ripening, eye formation and sensorial characteristics of emmental cheese is demonstrated using examples. Such properties should be taken into account during the selection of lactic and propionic acid bacteria for use as starters.