Which type of yeast is commonly used for brewing ales?

Saccharomyces cerevisiae is the primary yeast strain used in the brewing of ales due to its top-fermenting characteristics. This yeast thrives at warmer temperatures typically between 65°F to 75°F (18°C to 24°C), which aligns well with the fermentation process for various ale styles. Its ability to ferment quickly, along with its production of a range of desirable flavors and aromas, such as esters and phenols, contributes significantly to the complexity and character of ales.

In contrast, Saccharomyces pastorianus is mainly used for lager brewing as it is a bottom-fermenting yeast that operates best at cooler temperatures. Brettanomyces, often referred to as "Brett," is a wild yeast that can introduce funkier flavors and is typically found in certain specialty and farmhouse ales rather than standard ales. Kluyveromyces is primarily associated with the production of certain dairy products and wines rather than beer, making it less relevant in the context of ale brewing.

Thus, Saccharomyces cerevisiae is the correct choice for ale fermentation, highlighting its critical role in creating the diverse flavor profiles associated with this category of beer.