Fermentation is a natural process that occurs when yeasts combine with plants, be
they potatoes, fruit, or grains. The sugar in the plants, exposed either to
wild yeasts from the air or to commercial yeasts, produces an enzyme,
which in turn converts sugar into alcohol. Fermentive yeast very rarely
survives in solutions stronger than 15% alcohol. When that level is
reached, the yeast ceases to produce and dies.
