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How are ale and lager fermentation methods different?

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Six small glasses of craft beer in varying amber and golden hues are arranged on a metal tray atop a wooden bar counter in Brussels, Belgium. — Beer Glasses of beer in a bar in Brussels.

The primary differences between ale and lager fermentation lie in the temperature ranges used and the behavior of the yeast during the process.1

Fermentation Characteristics

Ale (Top Fermentation): Traditionally, ale is produced using top-fermenting yeast that rises to the surface of the liquid. This process typically occurs at warmer temperatures, with the wort pitched at 15 to 18 °C (59 to 65 °F) and allowed to rise to 20 to 23 °C (68 to 74 °F).234
Lager (Bottom Fermentation): Lager is produced using bottom-fermenting yeast that collects at the bottom of the vessel. This process is slower and occurs at cooler temperatures, with the wort pitched at 7 to 12 °C (45 to 54 °F) and allowed to rise to 12 to 17 °C (54 to 63 °F).542

Modern Brewing

While these distinctions are traditional, modern brewing practices have evolved. Many breweries now use closed stainless steel vessels for both types of beer, and some ale breweries utilize bottom-removal systems for yeast. Additionally, while lager is historically defined by bottom-fermenting yeast, modern yeast systematics classify most brewing strains as Saccharomyces cerevisiae, and some ales are now produced using bottom fermentation.26