Inhibition of certain lactic acid bacteria by free and bound sulphur dioxide

Growth of two heterofermentative lactic acid bacteria (Lactobacillus hilgardii and Leuconostoc mesenteroides) isolated from wine, was inhibited in a medium to which sulphurous acid and an excess of acetaldehyde had been added. It was found that the bacteria rapidly attacked the aldehyde and liberated sufficient free sulphur dioxide to prevent further growth. A homofermentative bacterium (Lactobacillus arabinosus) consumed much less aldehyde than the two heterofermentative organisms, but nevertheless failed to grow in the presence of 100 p.p.m. of bound sulphur dioxide. The significance of these results in relation to the malo‐lactic fermentation in wines is discussed.