Lactic bacteria, spoilage caused

This chapter deals exclusively with organoleptic defects that develop during aging. Some are of chemical origin (oxidation, reduction and contact with certain materials), but microbiological processes are often involved, even in the development of cork taint and spoilage due to sulfur derivatives. The various problems caused by anaerobic lactic bacteria are described, as well as the role of acetic bacteria. The mycodermic yeasts responsible for/tor are included in Section 8.3. 

Bacterial spoilage at various stages in the brewing process The spoilage caused by bacteria at the various stages of the brewing process are outlined in Table 21.2. The infection of sweet-wort by thermophilic lactic acid bacteria has already been mentioned. Because these bacteria are sensitive to isohumulones, they do not survive in hopped wort. 

Early research by Krumperman and Vaughn (1966) reported five species of Lactobacillus, including L. brevis and L. plantarum, that can utihze tartaric acid. Apparently, pathways to metabohze tartaric acid differ between heterofermentative and homofermentative bacteria. As described by Radler and Yaimissis (1972), L. brevis (heterofermentative) converts tartaric to oxaloacetic acid and through a series of intermediates, succinic acid, acetic acid, and GO2. By comparison, L. plantarum (homofermentative) decarboxylates oxaloacetic acid to pyruvic acid, which is subsequently reduced to lactic acid or decarboxylated to acetic acid and GOj. More recently, a novel species of Candida has been isolated from wine lees that can degrade tartaric acid (Fonseca et al., 2000), but it remains unknown if this yeast causes spoilage in wines. 

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