Ale is fermented usingSaccharomyces cerevisia, a very common yeast type used for a number of different applications, including wine and bread making. It’s a hardy variety that deals better with varying environments, whether it’s a wider range of temperature, a higher alcohol content or many other changes. It’s the original yeast of civilizations and has been found across the entire world, including Antarctica.
It’s referred to as a top-fermenting yeast because it will first rise to the top and then will sink to the bottom of the brewing vessel when fermentation is ending. This quality also makes it very easy to harvest the yeast without disturbing the process. In historical cultures where bread making was developed alongside the brewing industry, this would make it easy to use the excess yeast at the top of the vessel for leavening bread. The fast action of this yeast species brews the ale in as short a time as a week, with the yeast products floating to the top due to the increased motion within the fermentation vessel.