At first, we all think beer is one single thing: golden, cold and foamy. Then someone serves you a hazy IPA, with aromas of mango and resin, and you realise that what you knew was only one part of the map.
That is the first crack in the idea of "beer". And that is where curiosity begins: why does an IPA taste so different from a lager? The answer is not in the colour or the hops, but in the yeast and the way it works.
Lager yeasts ferment cold and slowly, producing beers that are clean, dry and easy to drink.
Ale yeasts, by contrast, ferment warmer and faster, releasing aromatic compounds that can make an IPA smell like tropical fruit or a saison like pepper.
Fermentation: the point where beer is defined
Yeast is a living microorganism that transforms wort sugars into alcohol and carbon dioxide.
What often goes unnoticed is that, during this process, it also produces aromatic compounds - esters, phenols, higher alcohols - that give each beer its sensory character.
Yeast behaviour depends above all on temperature and fermentation time.
And that is where the boundaries between the great beer families are drawn.
The three yeast families
1. Ale - top fermentation
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Species: Saccharomyces cerevisiae
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Working temperature: 15-25 °C
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Fermentation speed: fast
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Sensory profile: fruity or spicy aromas
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Typical styles: IPA, Pale Ale, Stout, Porter, Saison
These yeasts ferment at the top of the tank and at moderate temperatures.
The result is beer with aromatic expression: fruit, flowers, spices, bread or caramel notes.
Most modern craft styles - IPAs, NEIPAs, Belgian Ales - belong to this family.
2. Lager - bottom fermentation
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Species: Saccharomyces pastorianus
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Working temperature: 7-13 °C
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Fermentation: slow, with cold maturation (lagering)
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Sensory profile: clean, dry, balanced
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Typical styles: Pilsner, Helles, Marzen, Bock
Here the yeast works slowly and at low temperature.
Cold reduces the production of secondary aromas, leaving cleaner and more precise beers.
That is why a lager feels dry, crisp and refreshing: every sip is direct, without decoration.
3. Mixed or wild - spontaneous fermentation
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Microorganisms involved: Brettanomyces, Lactobacillus, Pediococcus
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Temperature: variable
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Fermentation: slow, often in barrel
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Sensory profile: acidic, earthy, complex
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Typical styles: Lambic, Gueuze, Sour Ale, Wild Ale
These fermentations happen when the brewer does not inoculate a pure strain, but lets the environment act.
Wild yeasts and bacteria intervene, generating acidity and funky aromas.
They are more unpredictable beers, but also more alive and unique.
The practical difference: what the drinker notices
A lager tends to be pale, dry and free of fruit notes; an ale is more expressive and aromatic.
That is why a Pilsner and an IPA can seem opposite, even though both contain the same basic ingredients: water, malt, hops and yeast.
The change lies in how that yeast acts on the wort, how long it works and at what temperature.
When a drinker learns this, the way they drink changes.
They no longer look only for "a beer", but start to understand which style they want and why.
They discover that an IPA is not "stronger", but different; that a lager is not "simple", but precise.
And that behind every sip there is a technical decision and a type of fermentation that defines the result.
