Various strains of lactobacilli isolated from Cheddar cheese were added to the milk employed in cheese manufacture. Different strains of these organisms were found to impart specifically characteristic flavours to the cheese. The range of flavours developed included both desirable and objectionable types, many of which are commonly encountered in commercial cheese, e.g. “pleasant aromatic”, “diacetyl-like”, “metallic”, “bitter”, “unclean” and “fermented”.

The inoculation of cheese-milk with natural mixtures of lactobacilli from mature cheeses led almost always to the development of unclean “fermented” flavours. The causative strains of lactobacilli were isolated and shown to be of frequent occurrence in normal mature cheeses but under ordinary circumstances the actual numbers of these bacilli present in most cheeses were too small to spoil the flavour.