One of the most frequently asked questions on any virtual beer tasting that we lead is, "Hey, what's the strongest beer you've ever drank?", but riiiiiight after that question is, "What does 'Ale' mean? What does 'Lager' mean?". So, let's dive into the difference between Ales and Lagers.
It's actually a fantastic question because it can lead into a ton of different areas of discussion, such as, what are different styles of beer and what makes them different, or it can go deeper into focus on the science of beer production, or you could talk about the industrialization of the American Light Lager in the 1950s, etc.). In fact, when this question is asked I tend to start to ramble and just needlessly go on and on, kind of like what I'm doing right now….
So Ale vs Lager! The major difference? Yeast. When calling something an Ale you're reaching into a very broad class of beers: IPAs, Brown Ales, Stouts, Saisons, etc... All of these beer styles typically utilize an Ale yeast strain known as Saccharomyces Cerevisiae. Similarly, a Lager is also a very broad class of beers including American Light Lagers, Pilsners, Helles Lagers, etc. And they are use a yeast strain called Saccharomyces Pastorianus. Notice that they are both Saccharomyces yeasts, but that they're very different. It's like both of them are dogs, but Cerevisiae is a Husky where Pastorianus is a Chihuaha.
One of the key differences that helps people identify the difference between an ale yeast strain is where they ferment. Ales are a top-fermenting yeast strain and Lagers are a bottom-fermenting yeast.
Now when I say top-fermenting yeast (Ales) and bottom-fermenting yeast (Lagers) I mean that the yeast strains are literally doing their work at the top or bottom of the fermentation tanks. It's difficult to explain why, so let's just chalk it up to the fact that Huskys and Chihuahuas are different kinds of dogs that do things differently.
For the most part these two yeast strains do the same thing. They eat (metabolize) simple sugars that are produced earlier in the beer making process, and turn those sugars into alcohol, flavors (phenols and esters), and CO2. Where they really differ is in the details. Top-fermenting yeast (ales) ferment in 2-7 days, at around 60°-80° Fahrenheit, and typically make more fruity, complex flavors (more phenols and esters). Whereas a bottom-fermenting yeast (lagers) will take a bit longer to ferment at 5-10 days, ferment at a lower temperature around 45°-55° Fahrenheit, and make beers that are typically 'cleaner' in overall taste (fewer phenols and esters).
Now that's definitely a simplification and a generalization (believe it or not, microbiology is kind of complex!). Just remember that Lagers are lower temperature, longer fermentation time, lower (bottom) fermenting, and have a lighter flavor - notice all those Ls! And Ales are the opposite: higher temperature, quicker fermentation, top fermenting, and typically have more complex flavors.
I had mentioned earlier that Lagers are generally lighter and Ales are more complex, well, here I am to prove myself wrong. Lagers, while typically more subtle, and easy drinking are not always that. A good example of a more complex lager is the IPL - India Pale Lager. It's a beer style that is basically the Lager equivalent of an IPA - India Pale Ale but generally lighter in body and crisper in the finish. The IPL will typically clock in at around 6% ABV and are a great little alternative when you want something that's a little lighter, but has that distinct hoppy bitter finish. Quick shout out to the Baltic Porter as well, a Porter that uses a lager yeast strain. Fantastic beer style that's often overlooked.
As the alternative to the generally more complex Ales I would mention the humble Kölsch. Originally a beer brewed in Cologne, Germany, it is a bright, clear, crisp, crusher of a beer. That brief description might make it sound more like a Lager, but nope, this is a top-fermenting beer, meaning it's using an Ale yeast strain!
Side note: Sometimes a brewer will throw Lager yeast into the beer once the Ale yeast has done its job, making the distinction between Ale vs Lager a bit murky, but the main fermentation is done with an Ale yeast, so I'm gonna call it an Ale!