How do ales and lagers differ in terms of yeast fermentation?

Ales and lagers primarily differ in terms of the type of yeast used for fermentation and the fermentation temperature. Ales are characterized by the use of top-fermenting yeast, which typically ferments at warmer temperatures (ranging from approximately 60°F to 75°F). This top-fermenting yeast (Saccharomyces cerevisiae) rises to the top of the fermentation vessel, resulting in a quicker fermentation process and contributing to the development of fruity and complex flavors that are characteristic of many ales.

In contrast, lagers are made using bottom-fermenting yeast (Saccharomyces pastorianus), which works best at cooler fermentation temperatures (usually between 45°F and 55°F). This process tends to produce cleaner, crisper flavors with fewer fruity esters compared to ales.

Therefore, the correct choice highlights the key aspect of ale fermentation, emphasizing the type of yeast employed, which is essential in distinguishing ales from lagers.