You’ve got your thick-rimmed spectacles on, a wardrobe full of flannel and you can answer the question “What’s your favourite hop?” without hesitation, but you can’t really call yourself a beer geek without knowing the difference between lager and ale. It’s a fundamental. So, if you don’t know, you will by the end of this page.
First of all, lager and ale are both beers; this is important. And the simple, base-level answer as to what makes them different is that it’s all in the yeast. Ale uses what’s referred to as top-fermenting yeast due to its penchant for rising to the top of the liquid at the start of the fermentation process and leaving a lovely, thick krausen (or ‘foamy gunk’ as I like to call it). Lager, on the other hand, uses what’s known as bottom-fermenting yeast (or, simply, lager yeast) due to the fact it doesn’t really show any activity at the top of fermentation vessels. There’s a little bit more to it than that, though.
Just as important as the yeast itself is the temperature at which these beers are fermented. Due to the yeasts used, ales tend to be fermented at warmer temperatures in a shorter timeframe than their lager counterparts. This quicker fermentation leaves more esters (and therefore flavours from the yeast) in the beer while ale yeast has a greater tolerance to alcohol, meaning it can produce stronger beers.
Lager yeast, on the other hand, is more fragile and the beer is fermented at colder temperatures, then cold-conditioned (left in the cold, allowing sediment to drop out). It has a lower tolerance to alcohol and attenuates (converts sugar to alcohol) at a slower pace leaving much less estery flavours behind, a clearer beer and a ‘cleaner’ palate. Indeed, the name lager itself is derived from the German for storeroom or warehouse due to the process of maturation in cold storage.
There are a few beer styles which straddle the line between lager and ale, leaving us both baffled and refreshed. A Kölsch is a traditional German beer that originates in Cologne. It is warm-fermented with top-fermenting yeast then cold-conditioned like a lager. Then there’s the Baltic Porter. These strong, dark and usually quite sweet beers are often cold-fermented with bottom-fermenting lager yeast despite the name ‘porter’. The beer industry certainly likes to keep us all on our toes.