Ask Kate About Beer: What's The Difference Between Ales And Lagers?

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Though it's a core distinction within beer, the difference between ales and lagers is easily misunderstood. It's not based on color, alcohol strength, appearance, or the brewery producing it. All that distinguishes an ale from a lager is yeast. Lager and ale yeast are two different species: ale yeast is Saccharomyces cerevisiae, while lager yeast is Saccharomyces pastorianus. If a beer is fermented with ale yeast, it's an ale. If a beer is fermented with lager yeast, it's a lager. Both convert what is essentially sugar water (wort, in brewing terms) into beer through the process of fermentation.

So, we're done here? Okay, not quite. The sentences above form the 10-second answer, and while true—the yeast is what determines an ale versus a lager—they don't present the the entire picture. If you want the extended, director's-cut version of this answer, keep reading.

Within the two species of yeast, there are numerous yeast strains that behave in particular ways and create particular flavors. Some yeast strains are finicky and only want to ferment beer at a certain temperature. Others are hardier and work well under many conditions. Some create smoky or clove-like flavors; others create fruity notes; others are clean and neutral.

Generally, ale yeasts like to ferment at higher temperatures while lager yeast like to ferment at lower temperatures. Sometimes, ale yeast is referred to as "top-fermenting" yeast, because the yeast clump together and hang out on top of the beer in the fermentation tank. Lager yeast, on the other hand, are sometimes called "bottom-fermenting," because—you guessed it—they clump together and hang out near the bottom of the tank.

Em Sauter, an Advanced Cicerone and the founder of Pints & Panels, offers an easy analogy: She tells me to imagine yeast as pets. Say ale yeast is a dog and lager yeast is a cat. Sure, they both have two eyes, four legs, and fur, but they behave remarkably differently. And even within the cat category, you have plenty of variation—tabbies, black, Siamese, Persian, Maine Coon—that also have their own personalities.

As I said before, some yeast strains are very versatile. A brewer could create both a porter and an IPA with White Labs' California Ale Yeast, one of the most widely used commercial yeasts. But if a brewer wants to make a true saison, they'd better reach for a saison yeast. That's because certain styles of beer, like saison, are defined by the flavors the yeast itself produces.

"When you want to brew a hefeweizen, you need a certain yeast," Sauter says. "If I want a cocker spaniel, this pug isn't going to do."

Let's break for a pop quiz: Name some aromas and flavors that come from hops. Maybe you said pine, grapefruit, white flowers, mango, orange peel, grass. All of those and more are correct. What about aromas and flavors that come from malts? Bread, rolls, toast, cereal, pastry dough, bagels—all of those are also correct. Now, what about aromas and flavors that come from yeast? People tend to have a tougher time identifying those. And yet, like we established before, those flavors and aromas—or the absence of them—are crucial to certain styles of beer.

For the most part, ales have more yeast-derived aromas and flavors than lagers do. Ales might be spicy and fruity just from the yeast alone—without any spice or fruit added—while lagers are in general clean and neutral when it comes to the yeast's influence. (That's what makes lagers so ahhhhh, refreshing, just like Coors Light commercials say.) Where do ales' yeast aromas and flavors come from? Esters and phenols, two by-products of fermentation. Esters typically give off fruity-floral notes: banana, pear, apple, rose. Imagine a hefeweizen and its beautiful banana aroma. Those are from the yeast esters. Phenols are a different type of compound, and they creates clove-like or peppery notes. Imagine a complex Belgian saison or tripel and its spicy aroma: Those are phenols. Ale yeasts produce both esters and phenols to some degree, which is why ales have a more noticeable yeast profile than lagers.

That's not to say lager yeast doesn't produce flavor compounds at all: It does. But brewers have learned that the yeast itself will clean up or reabsorb those flavors and aromas if left to rest for a period of time. (Lager means "storage" in German.) Again, Em Sauter has a fun analogy for me: Lager yeast fermentation is like a raging house party. "Yeast get introduced to sugar water, which is their huge feast. They're like 'We're going to stuff our faces!'" So they have a massive eating and reproduction party (quite the bash), during which time, the yeast of course make a huge mess. They can produce esters and chemical precursors to diacetyl—the stuff that makes your beer taste like butter—which brewers don't want in their lagers.

So, how to get rid of those esters and diacetyl? Let the beer rest. After a while, lager yeast realize they have made this big mess during the initial fermentation party. They slow down and realize: "Crap, we should clean this place up." So before they die and fall entirely out of suspension, they do their best to eat up the mess they produced during the party. If a beer is lagered properly, those messy compounds will have been reabsorbed and won't affect the final beer.

You've read this far—woo!—and now you want to know what all this means for you, the drinker. The rough answer is that ales, because of the yeast used to brew them, will generally have more fruity and spicy yeast flavors. Lagers, because of their yeast, will have cleaner, more neutral profiles. That's not to say lagers aren't flavorful—oh, they are so delicious!—but most of that flavor comes from the malts and hops, and hardly any from the yeast. Whether you'd prefer a beer that's an ale or a lager depends on your own palate and what type of beer you're craving that day. The best way to figure out your favorite styles, of course, is to explore as many different types as you can.