Can I use yeast that I buy at the supermarket?
Bread, beer, and wine yeast are all the same species of yeast, Saccharomyces cerevisiae. Over the years special strains of yeast have been selected for use in each product and do not do well in other conditions. Bread yeast used in beverage fermentation can produce very unpleasant flavors, and will almost never completely ferment beer or wine. Beer and wine yeast have been selected specifically to withstand high sugar environments that turn into high alcohol environments rapidly, whereas bread yeast has been selected for a much different set of factors and cannot tolerate the harsh conditions in beer and wine.