  During beer production, yeast generate ethanol that is exported to the
extracellular environment where it accumulates. Depending on the initial
carbohydrate concentration in the wort a high concentration of ethanol can be
achieved in beer, often higher than 20% (v/v). It is noteworthy that the
effects of elevated ethanol concentrations generated during beer fermentation
resemble those of heat shock stress, with similar responses observed in both
situations, such as the activation of proteostasis and protein quality control
mechanisms in different cell compartments, including endoplasmic reticulum
(ER), mitochondria, and cytosol. Despite the extensive published molecular and
biochemical data regarding the roles of proteostasis in different organelles of
yeast cells, little is known about how this mechanism impacts beer fermentation
and how different proteostasis mechanisms found in ER, mitochondria, and
cytosol communicate with each other during ethanol/fermentative stress.
Supporting this integrative view, transcriptome data analysis was applied using
publicly available information for a lager yeast strain grown under in beer
production conditions. The transcriptome data indicated upregulation of genes
that encode chaperones, co-chaperones, unfolded protein response elements in ER
and mitochondria, ubiquitin ligases, proteasome components, N-glycosylation
quality control pathway proteins, and components of processing bodies
(p-bodies) and stress granules (SGs) during lager beer fermentation. Thus, the
main purpose of this hypothesis and theory manuscript is to provide a concise
picture of how inter-organellar proteostasis mechanisms are connected with one
another and with biological processes that may modulate the viability and/or
vitality of yeast populations during HG/VHG beer fermentation and serial
repitching.
