The simple answer: Yeast. While ales use a “top-fermenting” yeast (Saccharomyces cerevisiae), lagers use a “bottom-fermenting” yeast (Saccharomyces uvarum). So what does this mean in simpler terms? Basically, during fermentation, the yeast will either predominantly float to the top of the fermentation tank or sink to the bottom, depending on the style. A more in-depth answer would also point out that ales ferment at higher temperatures, while the opposite is true for lagers.
There are also certain characteristics more common in each style. As a general rule, ale yeast often contributes more flavor to a beer (fruity, spicy), while lager yeast tends to impart less character, leading to a crisper, cleaner drinking experience. Often, ales tend to be darker, cloudier and more bitter, whereas lagers tend to be clearer, crisper and lower in alcohol. However, it is important to note that these are general guidelines and that there are always exceptions. You can certainly have dark lagers (ex: Schwarzbier), high-alcohol lagers (ex: Doppelbock), and light-colored ales (ex: West Coast IPA). Alcohol and color are a result of the malts used in a given recipe (but we’ll get into that in another post). At the end of the day, both ales and lagers are made up of the same 4 base ingredients: water, malted barley, hops, and yeast.
Ales: Water, Malts, Hops, Yeast (Saccharomyces cerevisiae)
Lagers: Water, Malts, Hops, Yeast (Saccharomyces uvarum)
Ales: Top-fermenting yeast floats to top of tank and beer ferments at higher temperatures
Lagers: Bottom-fermenting yeast sinks to bottom of tank and beer ferments at lower temperatures
Typical Flavor & Appearance
Ales: Darker color, higher alcohol, more bitter
Lagers: Clearer appearance, lower alcohol, maltier, crisper flavors
Ales: Pale Ale (Easy Up), Stout (Blue Bridge), IPA (Islander IPA), Wheat Beer (Orange Ave. Wit), Belgian Styles (Silver Strand Saison), Amber/Red Ale (Mermaid’s Red)
Lagers: Pilsner (Seacoast), American Lager, German Schwarzbier (Sea Lady Black Lager), Oktoberfest, Doppelbock
And for those of you saying, “what about sour or spontaneously fermented beers?”, don’t worry—we’ll cover those in a future blog post. In the meantime, no matter what yeast is used, we hope you’re enjoying this post with a cold one in your hand.