Other Spoilage Yeasts

The only species recognized by Lodder (1970) is S, ludwigii. It has (rarely) been reported growing in both cellar aging and bottled wine (Thomas, 1993). In addition to formation of high levels of acetaldehyde, the organism is also relatively resistant to sorbic acid and sulfur dioxide (Boulton, et al., 1995). 

Schizosaccharomyces pombe is another yeast that is infrequently isolated from juice/wine. Since the yeast utilizes L-malic acid as a carbon source in formation of ethanol (Temperli et al., 1965), S. pombe has been proposed as an alternative to LAB or carbonates for deacidification of high acid musts. However, over-deacidification may result from sole utilization. Be- 

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O Neill, M. Lebrun, S. Rapid, low-cost assay for detecting Brettanomyces and other spoilage yeast in... 

The analytical methods used by the industry to evaluate yeasts present in drinks are still, generally, laborious and provide poor information. The most common microbial indicator is still the yeasts and molds , resulting from the utilization of a rich culture medium (supplemented with antibiotics to prevent bacterial growth) to enumerate yeasts and molds. However, this indicator does not distinguish between the dangerous spoilage yeasts and others. 

Several methods have been developed for the differentiation of yeasts. Traditional platting techniques may be adapted using selective and/or differential platting media. Such media have been developed for Zygosaccharomyces bailii, the most important of all food spoilage yeasts. However, yeast differentiation by differential media is poorly developed when compared with similar works applied to bacteria. Other phenotyping methods include conventional yeast identification by means of assimilation or fermentation tests and the use of morphological characteristics. Conventional methods are not suited to industrial laboratories even when these procedures are automated and computerized. 

In laboratory studies using model systems for juice and wine, control of several spoilage yeasts was examined. At inoculum levels of 10-20 X 10 CFU/mL, Brettanomyces and Hansenula were controlled by exposure to 90 mg/L CO compared with Dekkera which required 120 mg/L and Kloeckera at 240 mg/L. Zygosaccharomyces bailii in the juice system was controlled at treatment levels of 480 mg/L, whereas in wine at 7.5% and 10% ethanol, activity was delayed for 14 days. By comparison to the spoilage yeast, Sac-charomyces was not affected at CO levels of 1000 mg/L. Our work is currently being extended to include other species of spoilage yeast and bacteria. Scale-up pilot plant studies are planed for fall of 1996. 

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