Low-temperature environments in the brewery
In S. cerevisiae (ale and wheat strains), cold shock occurs at temperatures below 20°C (Kondo and Inouye, 1991; Kondo et al., 1992; Kowalski et al., 1995; Abramova et al., 2001b). It is therefore no surprise that ale fermentations are typically conducted at higher temperatures, between 18°C and 25°C. In contrast, lager fermentations are conducted at much lower temperatures and indeed lager strains are better able to grow at 10°C relative to ale strain counterparts. Interestingly, the cold tolerance of lager strains is hybrid group specific. The Saaz strains display greater cold tolerance than the Frohberg strains (Gibson et al., 2013). Of the two yeast hybrids used for lager brewing, the Frohberg group has predominantly retained DNA of the S. cerevisiae parent, while the Saaz group has retained proportionally more of the S. eubayanus DNA (Dunn and Sherlock, 2008). These genetic differences appear to reflect functional differences, with the Saaz strain apparently inheriting a relatively greater cold tolerance from the characteristically cryotolerant S. eubayanus parent.
Temperatures used for yeast storage between successive fermentations typically range from 2°C to 11°C and, where applied, acid washing is also conducted at 4°C. Yeast handling, therefore, consists of a series of low-temperature environments, which may lead to the yeast slurry experiencing cold shock, a phenomenon that is well documented in other organisms (Phadtare et al., 1998; Rodriguez- Vargas et al., 2002), but has not been extensively studied in yeast.