Although beer comes in hundreds of styles, from porter to pilsner to pale ale, those styles can be helpfully grouped into two broad families: ales and lagers.
As with so many fermented foods and drinks, the difference is not in the ingredients, but in the method.
Beer is made by allowing yeasts to colonize a sugary grain-based liquid (called wort), where they convert sugar to alcohol and carbon dioxide, the building blocks of beer. The fundamental difference between ale and lager is that different species of yeast do that conversion at different temperatures. It’s a subtle difference in theory but profound in practice.
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What Is Ale?
Ale is the original beer, beloved since the dawn of beer. Saccharomyces cerevisiae, the same species of yeast we use in baking, is the brilliant organism that makes ale. As it works, the yeast cells clump together and float to the top of the fermentation vessel, forming a frothy raft on top. That floating yeast can be easily harvested and added to another batch. Because of that habit, ale yeast is often called top-fermenting yeast.
It thrives around room temperature, 65° to 75°F. In that temperature range, S. cerevisiae produces many flavor compounds characteristic of ales, particularly the esters that contribute fruity notes like banana and apple.
What Is IPA?
Around the turn of the 19th century, English brewers started to take advantage of the preservative and antioxidant effect of hops by increasing the amount of hops in the dry ales they manufactured to ship overseas to India and other colonies. Soon enough, the bitter taste of heavily hopped ales became popular, in the colonies and domestically, and the style called India pale ale (IPA) developed a following.
After losing popularity throughout the 20th century, IPA started getting new attention around 1990, first as a historical curiosity, then as a microbrewery specialty, and by now as a rampant cultural phenomenon that dominates craft brewing, with the pursuit of new varieties and ever-higher doses of hops.
What Is Lager?
In the 19th century, central European brewers began to popularize a wholly different type of beer: lager, which became the dominant style in the 20th century. Lager, by definition, is made with Saccharomyces pastorianus, a different species of yeast. S. pastorianus still does the basic job of any self-respecting yeast, turning sugar to ethanol, but with some differences. When the cells clump together, they sink to the bottom of the vat, rather than floating, which earned lager yeast the name bottom-fermenting yeast.
More important than its predilection for sinking is lager yeast’s love of cool working conditions. Saccharomyces pastorianus does its best fermenting down between 40° and 55°F—considerably chillier than Saccharomyces cerevisiae, and it works more slowly. What that means for the beer, in general, is that lagers have less of the fruity, spicy, complex flavors of yeast metabolism, and more of a simple, clean flavor that comes from the grain.
After the fermentation, lagers traditionally, but not mandatorily, undergo a resting period of up to several months in contact with their yeast. This is known as “lagering” (from a German word meaning to lay down or store). This process (which also happens in a chilly temperature range) additionally clarifies the flavor as aroma compounds, such as those responsible for butterscotchy and fruity flavors, are absorbed and removed by the bed of yeast.
Is Lager Bad and Watery?
Meanwhile, lager has come to be associated with mass-market beers that are lighter in color, flavor, and body, whose dominant characteristics are cold, refreshing crispness: the Millers, Buds, Coorses, and so forth, brewed and drunk in vast quantities. According to the Oxford Companion to Beer, 90 percent of beer consumed worldwide is such lager. This style is often called adjunct lager, referring to the use of adjunct grains—grains such as unmalted rice or corn, which impart less flavor than malted barley. And they’re sold fresh and served as cold as possible, all to maintain that uncomplicated, unblemished flavor.
The world of lager is more than that, though. Lager beer styles include grassy, bitter pilsners; dark and malty Vienna lager; high-proof, bready-tasting bock and double bock; and even smoked lagers that taste compellingly of bacon.
But the rise in craft brewing since the 1980s has embraced ales with a vengeance: IPAs, DIPAs, NEIPAs, Belgian-style ales, stouts and porters, and all else top-fermented.
The yeast are happy either way.