Leuconostoc species are important flavour producers in some fermented dairy products. There is general agreement that two species, Leuconostoc mesenteroides subsp. cremoris and Lecon. lactis are important in starter cultures. Unlike lactococci, leuconostocs grow on Rogosa agar (see Billie et al., 1992; Mullan, 2000) and are hetrofermentative producing carbon dioxide from glucose and usually fructose. While the carbon dioxide production is undesirable in Cheddar cheese gas production is desirable in some varieties e.g. Emmental.