What is the difference between a lager and an ale?
The difference is the yeast and the fermentation temperature, not the colour — which is the most common misconception, since both come in pale and dark versions.
Ale is made with top-fermenting yeast (Saccharomyces cerevisiae), fermented warm, typically 15–24°C, over a relatively short period — often days. The yeast congregates near the surface during fermentation.
Warm fermentation produces more esters and phenols — aromatic compounds giving fruity, spicy and complex flavours. This is why ales taste of things: banana, clove, stone fruit, pepper. The yeast itself is a major flavour contributor.
Ale styles: bitter, pale ale, IPA, porter, stout, wheat beer, Belgian styles, barley wine.
Lager is made with bottom-fermenting yeast (Saccharomyces pastorianus), fermented cold, typically 7–13°C, then conditioned at near-freezing temperatures for weeks or months. The word lager is German for storage, describing exactly this.
Cold fermentation suppresses ester production, so lager yeast contributes far less flavour. The result is cleaner and crisper, with malt and hops more exposed — which means flaws have nowhere to hide, and a well-made lager is technically demanding despite its reputation as the simple option.
Lager styles: pilsner, helles, Märzen, bock, dunkel, schwarzbier. Note that dunkel, bock and schwarzbier are dark lagers, and Guinness is a dark ale — colour comes from roasted malt, not from the yeast.
Historical note. Lager yeast is a hybrid, combining S. cerevisiae with a cold-tolerant wild species identified relatively recently in Patagonia and elsewhere. It emerged in central European brewing where cold cellars and caves allowed cold storage, which is why lager is associated with Bavaria and Bohemia.
Other categories exist: Kölsch and altbier are warm-fermented then cold-conditioned; lambics use spontaneous fermentation by wild organisms.