Growth and effects in beer

Factors controlling the growth of P. Aa/torae have not been studied. To our knowledge, this species has only spoiled low-alcohol products (Juvonen, 2009 Voetz et al., 2010). 

Itgrows in typicalpH values ofbeer. P. haikarae appears to be better adapted to the brewing environment compared to its closest relative, P. cerevisiiphilus. It grows at lower temperatures and produces a catalase enzyme protecting the cells from toxic oxygen radicals. The isolation of P haikarae from air samples indicates that it can survive in the air at least for short periods of time (Henriksson Haikara, 1991). 

There is a lack of data about beer-spoilage properties of the other species. M. sueciensis has been found as a spoilage microbe in low-alcohol beer, whereas M. paucivorans was found in spoiled product with an ethanol content of 3.9% (w/v). The pH of the beers spoiled by these species varied from 4.3 to 4.9 (Juvonen Suitako, 2006). 

Propionispira raffinosivorans is considered to be a potential beer spoiler owing to its ability to grow in beer at pH 5.0 but not at pH 4.6. P paucivorans was able to grow in beer at pH 6.0 bnt not at pH 5.0 and appears to be a harmless brewery contaminant (Seidel-Riifer, 1990). There is a lack of data about other beer-spoilage properties of the Propionispira species. 

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Yeast flocculation, an essential phenomenon in beer fermentation, is influenced by the medium composition, especially by the glucose concentration, and is delayed by the mixing effect of CO2 production. The time variation of the suspended yeast concentration is thus taken as the difference between the growth and flocculation rate as ... 

All of these factors, individually or more often in combination with one another, permit the definition of the requirements of an acceptable brewer s yeast strain (Stewart Russell, 2009). To achieve beer of high quality, not only the yeast must be effective in receiving the required nutrients from the growth/fermentation medium (the wort), able to tolerate the prevailing environmental conditions (e.g. osmotic, temperature and ethanol tolerance) and impart the desired flavour to the beer, but the microorganisms themselves must be effectively removed from the fermented wort by flocculation, centrifugation and/or filtration after they have fulfilled their metabolic role. 

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