University of Waterloo
BIOL 443
BIOL 443L: Wine Making B443 Fermentation Biotechnology December 2nd 2013 Performed: October 22nd – November 20th Introduction The purpose of this lab was to produce a white wine using wine juice inoculated with Saccharomyces cerevisiae. Specific gravity, Brix/Balling, and Potential Ethanol levels were a
...[Show More]
BIOL 443L: Wine Making B443 Fermentation Biotechnology December 2nd 2013 Performed: October 22nd – November 20th Introduction The purpose of this lab was to produce a white wine using wine juice inoculated with Saccharomyces cerevisiae. Specific gravity, Brix/Balling, and Potential Ethanol levels were all monitored during the process. Specific gravity is the measure of the weight of a liquid in relation to water. The specific gravity of water is 1.000. The weight of the liquid is changed by its contents. In the context of wine, dissolved sugars are the deciding factor in specific gravity. There are other components in wine, such as certain vitamins, tannins, etc. However, due to the ethanol production by glucose, sugars are the most important factor of wine weight, and therefore specific gravity. With this being the case, the higher the specific gravity, the sweeter the wine. For example, a very dry wine will have a final specific gravity of around 0.990. Related to this, the Brix/Balling scale is calibrated based on the weight of sugar in solution. Unlike specific gravity, this is shown as a percentage. Finally, the potential alcohol scale is calibrated to dissolved ethanol is water. All three values are important in determining the quality of the wine (Ough, 1987). In the presence of oxygen, yeast cells will utilize glucose in the grape must or juice to multiply and produce elements essential for their propagation and survival (Fugelsang & Edwards, 2010). Glycolysis is the most important metabolic pathway during wine fermentation. It is very important to allow the yeast cells to grow in the presence of oxygen in order for them to tolerate the toxic byproducts of their fermentation (e.g. alcohol). In the absence of oxygen, yeast cells will rely on the production of ethanol from acetaldehyde to continue metabolism (as seen in Figure 1)(Fugelsang & Edwards, 2010). If fermentation is allowed to continue until completion, the yeast will use all fermentable sugars and primary fermentation is considered to be over. The breakdown of sucrose in the wine juice is essential for glycolysis and therefore essential for the wine fermentation process. Yeasts have sucrose activity, which will hydrolyze the sucrose splitting it into fructose and glucose (Zoecklein, et al., 1999).
[Show Less]