Lager vs Ale: The Yeast and the Temperature

Beer drinkers tend to sort the world into lagers and ales as if the distinction were obvious, like cats and dogs, when in fact the line is drawn by something most drinkers will never see: a single-celled fungus and the temperature of the room it lives in. The yeast does not particularly care what the drinker calls the result. The brewer, the regulator, and the style judge care a great deal.

What follows is a tour of that quiet little division — where it came from, what the yeasts actually do, why the temperature matters, and how the people who taste beer for a living try to put words on the difference.

A division drawn by biology, not by color

The popular shorthand says ales are dark and warm and bitter while lagers are pale and cold and crisp. This is wrong in roughly every direction. There are pale ales the color of straw and there are black lagers the color of espresso. Stout can be brewed as a lager. Pilsner is, definitionally, a lager, but a perfectly respectable cream ale will sit beside it on the shelf looking nearly identical.

The actual split is microbiological. Ales are fermented by Saccharomyces cerevisiae, the same broad species that raises bread and ferments wine. Lagers are fermented by Saccharomyces pastorianus, a hybrid yeast that arose, as best the genome evidence suggests, when S. cerevisiae met a cold-tolerant cousin called Saccharomyces eubayanus somewhere in central Europe several centuries ago. Reviews collected by NCBI PubMed Central on Saccharomyces and beer flavor describe the lager hybrid as carrying genes from both parents, which is why it can ferment in conditions that would make an ale yeast sulk.

That hybrid, in other words, is the whole reason lager exists as a category. Without it, beer would simply be ale brewed in various ways.

What the yeast is actually doing

Fermentation, stripped of romance, is yeast eating sugar and producing roughly equal masses of ethanol and carbon dioxide, plus a long tail of minor compounds that account for almost everything interesting about flavor. Esters, which smell of banana, pear, apple, or rose. Higher alcohols, sometimes called fusels, which can smell of solvent if the yeast is stressed. Phenols, which at low concentrations smell of clove and at higher concentrations smell of band-aids. Diacetyl, which smells of butter or butterscotch and is generally regarded, in a finished pale lager, as a fault.

Ale yeast, working at warmer temperatures, makes a great deal of this material on purpose. The fruity, slightly spicy character of a Belgian witbier or an English bitter is the yeast leaving its signature in the glass. Lager yeast, working cold, makes much less of it. The flavors that survive are the malt and the hops, presented without much editorial comment from the fermentation. This is why a flaw in a pilsner is so pitilessly obvious. There is nowhere for it to hide.

The PMC review on Saccharomyces cerevisiae and beer flavor walks through the enzymatic pathways in some detail; the practical summary is that warmth gives ale yeast permission to express itself and cold tells lager yeast to keep quiet.

Temperature, and the meaning of "lagering"

The German verb lagern means to store. Before refrigeration, brewers in Bavaria noticed that beer left in cold caves over the winter came out cleaner and brighter than beer fermented in a warm cellar. They were, without knowing it, selecting for cold-tolerant yeast. Generations of this selection produced what eventually became S. pastorianus, and the practice of cold storage gave the resulting beer its name.

In modern brewing, the temperatures roughly sort like this:

The cold conditioning matters as much as the cold fermentation. Sulfur compounds produced during primary lager fermentation slowly dissipate. Yeast and protein haze drop out. Diacetyl, if the brewer has handled the yeast correctly, is reabsorbed and metabolized. The beer becomes, as the trade has it, "round."

A brewery making a pale lager is therefore tying up a tank for considerably longer than a brewery making a pale ale. This is one of the unglamorous reasons the German and Czech brewing traditions, which built their reputations on lager, also built rather a lot of capital-intensive cellar space. The Pilsner Urquell brewery, which has produced pilsner on the same site since 1842, retains historical lagering cellars carved into sandstone beneath the town of Plzeň.

Where the styles live, in the BJCP and EBC sense

The Beer Judge Certification Program publishes a style guideline document that organizes beer into roughly a hundred recognized styles, grouped first by family. The lager families — pale lager, pilsner, amber lager, dark lager, bock — sit alongside the ale families — pale ale, IPA, brown ale, stout, Belgian ale, wheat beer, sour. According to the BJCP, style judging at sanctioned competitions is done blind and to the published descriptors, which means a beer entered as a Munich Helles is judged on whether it tastes like a Munich Helles, not on whether it is delicious in some general sense.

The European Brewery Convention, which publishes the EBC analytical methods used across European brewing science, provides the laboratory framework: color expressed in EBC units, bitterness in IBU, original gravity in degrees Plato. The BJCP guidelines lean on this kind of framing. A Czech Premium Pale Lager has a defined color range, a defined bitterness range, a defined gravity range, and a defined flavor profile. So does an English Best Bitter. The difference between them, on paper, is a list of numbers and adjectives. The difference in practice is mostly the yeast and the temperature.

Master Brewers Association of the Americas and the Institute of Brewing & Distilling, both of which run technical qualifications for working brewers, treat the lager-versus-ale split as a foundational topic in their curricula because it determines so much downstream: tank scheduling, yeast handling, attenuation expectations, packaging timing.

The drinker, and the small problem of expectations

Drinkers arrive at the bar with assumptions, most of them inherited from advertising. American mass-market lager has, for several decades, been positioned as cold, light, and unobtrusive, with the result that a great many drinkers believe "lager" means "the yellow one that is not very interesting." This is a reasonable inference from the available evidence and a slightly unfair one to the category. A Munich Dunkel, a Czech amber, a Baltic porter, and a doppelbock are all lagers, and none of them are unobtrusive.

Ales, conversely, have benefited from the craft movement positioning them as the interesting beers. The Brewers Association, in its national beer statistics and craft brewer definition, tracks the growth of small and independent brewers in the United States, and the styles that drove that growth — pale ale, IPA, stout, sour — are predominantly ales. Ale ferments faster, ties up less cellar time, tolerates a wider temperature window, and forgives a great deal of brewer enthusiasm in the form of late hop additions and odd ingredients. For a small brewery deciding what to make first, ale is the path of less resistance.

This is not a value judgment. It is a scheduling reality. Several of the most respected small breweries in the United States are lager-focused, and their beers tend to command attention precisely because the format is unforgiving.

The slightly absurd edge cases

Any system of definitions, examined closely, develops barnacles. A few worth noting:

Kölsch and Altbier. Both are German. Both are made with ale yeast. Both are then cold-conditioned, lager-style, for weeks. The result is sometimes called a "hybrid" beer in BJCP framing. Drinkers tend to read them as lagers. Microbiologists insist on calling them ales.

California Common, sometimes called steam beer. Made with lager yeast at ale temperatures. The lager yeast, asked to work warm, produces some ester and some fruit. The result tastes, to most palates, like a slightly fruity amber lager. Microbiologists insist on calling it a lager.

Cream Ale. An American style, often brewed by breweries that historically also made lager, sometimes by blending the two or by using lager yeast at ale temperatures or vice versa. The category survives mostly because drinkers like the beer.

Lambic and other spontaneous fermentations. Belgian lambic, governed in part by HORAL, the High Council for Artisanal Lambic Beers, is fermented by whatever airborne yeast and bacteria happen to land in the cooling wort. Saccharomyces is in there, and so are Brettanomyces, Pediococcus, Lactobacillus, and a supporting cast. Lambic is technically an ale by default classification, but the question is rather like asking what species of dog a wolf is.

The TTB, in 27 CFR Part 7, regulates how malt beverages are labeled and advertised in the United States, and it does not require a brewer to disclose on the label whether a beer is an ale or a lager. The distinction is a matter of style and tradition, not federal law.

What to taste for

A drinker who wants to develop a feel for the split can do worse than pour a pale ale and a pilsner side by side, at the same temperature, and pay attention to the aroma before the first sip. The ale will tend to offer something fruity or floral from the yeast itself, sitting on top of the malt and hops. The pilsner will tend to offer the malt and hops more or less alone, with the yeast standing politely behind them. Neither is better. They are doing different jobs.

Candidates studying for the Certified Cicerone® exam, which is administered by the Cicerone Certification Program®, are expected to identify these yeast-derived characteristics and to associate them with the appropriate style families. The BJCP exam program asks much the same of its judges. Both organizations rely on the same underlying biology: warm yeast talks, cold yeast listens.

Further reading

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