Acetaldehyde is considered as the major flavour component of yogurt (Pette and Lolkema, 1950c; Dumont and Adda, 1973; Law, 1981) while high concentrations of this compound in other dairy products (cheese or cream) lead to flavour defects described as "green" or "yogurt-Iike" (Lindsay et al, 1965). Bottazzi and Vescovo (1969), however, underlined the importance of the acetaldehyde to acetone ratio.