Spoilage yeasts: characteristics

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. 

Some winemakers and coimnentators believe that the ambient yeast population in the vineyard and winery constitnte part of the characteristics of a natural wine (Lewin, 2010). They believe that the uniqne contributions of diverse yeast species -including non-Saccharomyces species - confer a complexity upon wine not seen in inoculated ferments. This might be tme (Varela et al., 2009), but it comes with the risk of spoilage. There is also an increased risk that the fermentation will become stuck (Martini, 1993) - i.e. the ferment will stop and be difficult to restart. In addition. 

Cultural characteristics of Pectimtus species have been studied in peptone yeast extract fructose (PYF) medium (http //culturecollection.vtt.fi) and MRS medium. The beer-spoilage species form circular, entire, glistening and opaque colonies on PYF... 

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