Growth of two heterofermentative lactic acid bacteria (Lactobacillus hilgardii and Leuconostoc nzesenteroides) 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 t o the malo-lactic fermentation in wines is discussed.

The influence of various yeasts on the growth of lactic acid bacteria in wine was tested by inoculating Lactobacillus hilgardii, L. brevis and two strains of Leuconostoc mesenteroides into experimental wines made with twelve different yeasts of the genus Saccharomyces. Wines made from juice which had been infected with several spoilage yeasts and then fermented with a wine yeast were also tested in this way. It was found that the yeasts differed considerably in their effects on bacterial growth. In some of the experimental wines bacterial growth was delayed or failed altogether. Generally, the unfavourable influence of any yeast on bacterial growth was much reduced if the wines were left in contact with the yeast cells for some weeks after the fermentation. The significance of these results in relation to the occurrence of malo‐lactic fermentation in commercial wineries is discussed.

Malo‐lactic fermentation occurred in 62% of 466 Australian dry red wines of 1968 vintage at 6 months of age. In a further 9 % of wines the fermentation was still in progress. Wines which had undergone the fermentation were less acid than those which had not. The difference was greater in wines made from Cabernet Sauvignon than from Shiraz or Grenache grapes. The winery in which the wine was made strongly influenced the occurrence of malo‐lactic fermentation in a particular wine‐growing area, and was the most important factor involved. Incidence of malo‐lactic fermentation was closely correlated with the presence of Leuconostoc and Coccus in the wine, but less so with Lactobacillus. Leuconostoc, Lactobacillus and sometimes Coccus occurred together, but no wines contained both Lactobacillus and Coccus. Diacetyl content of the wines ranged from 0 to 7.5 ppm. In wines which had undergone malo‐lactic fermentation the mean diacetyl content was 2.8 ppm, compared with 1.3 ppm for wines which had not undergone this. Diacetyl content of wines made from Grenache was not significantly different, with respect to the occurrence or absence of malo‐lactic fermentation. The statistical significances of the various inter‐relationships between malo‐lactic fermentation, type of bacteria present and certain wine constituents are assessed. Estimates of variance components of II constituents of Australian dry red wines are given, and these may be used in designing future sampling surveys.

Wines which have undergone malo‐lactic fermentation contain significantly more diacetyl and acetoin than wines which have not. The amounts of diacetyl and acetoin formed depend on the type of bacterium present and on the composition of the wine. Leuconostoc mesenteroides is the chief organism forming these products in Australian wines while pyruvic acid and citric acid are the chief substrates from which they are formed. The presence of a few g. per litre of glucose interferes with the formation of these products in wine. The heterofermentative rods, Lact. hilgardii and Lact. brevis, which are responsible for malo‐lactic fermentation in some Australian wines, produce diacetyl and acetoin only under conditions unlikely to occur in wines. Homofermentative lactobacilli have not yet been isolated from Australian wines.

No abstract