The robustness of industrial grain whisky fermentation is influenced by environmental stresses that affect the performance of distiller's yeast, and have an effect on its sugar usage and ethanol. production. Among changes that occur during ferinentation is an increase in temperature and ethanol concentrations, which both are known to cause a stress response in. yeast. In order to understand the yeast response, I used proteomics technology to quantify levels of identified proteins during industrial fermentations. Increased levels of stress proteins and proteases were among the significant changes in the soluble proteome of distiller's yeast, as the fermentations progressed. The proteomic data set was complemented with an expression analysis of-selected yeast genes, which included a detailed analysis of genes and proteins involved in sugar uptake and metabolism. Proteomics technology was also used to study molecular differences in distiller's yeast that occurred when changing the volumetric scale from industrial (400,000 1) to laboratory (0.5 1), and in a second series of experiments, increasing the yeast pitching rate from 1 g- L to 4 g L. The results showed that up-regulation of proteases was not observed at laboratory scale, and increasing pitching rate led to a significant:increase in . the levels of heat shock proteins during fermentation. The mitochondrial proteome of distiller's yeast was also investigated at 30 min and 48 h of laboratory fermentations, leading to quantification of mitochondria-associated proteins that may be important for metabolism and/or yeast survival under fermentative conditions. Gene deletion of the HSP26 gene in distiller's yeast revealed that four copies were present, and ploidy analysis confirmed that distiller's yeast indeed is a tetraploid strain. The deletion of the HSP26 gene did not influence yeast sensitivity against lactic acid, acetic acid, ethanol or oxidative stress. Interestingly, prolonged fermentations (>72 h) with IlHSP26 mutants showed that ethanol yield was reduced compared to wild type cells.