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Beauty and the yeast

After exploring the basics of brewing in my last article, today I’m venturing to tackle a more specific subject. Still knowledge of brewing basics, but with potential for some “impressive geekery”: the difference between top- and bottom-fermented beers! Probably every beer-drinker has heard of this classification, but what exactly is behind it?

The yeast is to blame! There are top-fermenting and bottom-fermenting yeasts, and it’s precisely these that make the difference and divide all the world’s beer types into two groups: the “top-fermenting team” (ales) and the bottom-fermenting team (lagers).

As we’ve already learned in “Hops spring eternal”, the yeast does its work in the fermentation tank. Its task is to convert the malt sugar that was previously dissolved in the wort into carbon dioxide and alcohol.

In simple terms: the yeast turns the cheerless, murky decoction into an exhilaratingly sparkling, exuberantly refreshing beer. Quasi the good fairy who transforms the ugly duckling into a beauteous princess. But enough of mixed fairy-(t)ale metaphors and back to our original topic!

The conversion of a cheerless decoction into amber nectar is not accomplished overnight, of course; you need a little bit of patience – namely around six to eight days. During this time, the yeast labours away, and is finally removed.

BOTTOM-fermenting yeast – what a surprise! – settles to the BOTTOM of the fermentation tank.

TOP-fermenting yeast, by contrast, floats to the TOP when its work is done, where it is finally skimmed off.

Some like it hot

Another difference between top- and bottom-fermenting yeasts is their preferences in terms of working temperature. The busy little single-cell organisms from the “top-fermenting team”, you see, like it warm! Their ideal temperature is around 15 to 20 degrees, then they hit their best form, working significantly faster than their bottom-fermenting counterparts. On average, the top-fermenting yeast needs just four to six days to do its job.

The couch potatoes from the “bottom-fermenting team” are not so impetuous! What’s more, they prefer a cool environment. Bottom-fermenting yeasts need between six and ten degrees for optimum efficacy.

The picture shows an open fermentation tank at Erl-Bräu in Geiselhöring. Here you can watch the yeast during the different fermentation stages. Especially bottom-fermented beers, like here the Erlköng Festbier, are nowadays rarely open fermented.

But how does the yeast know when enough is enough? After all, the beer’s alcohol content is not supposed to overstep the mark! In order to prevent this, the yeast possesses an “internal clock”, and so it stops the fermentation process all by itself if the beer’s abv threatens to become too high.

Which came first – top- or bottom-fermenting yeast?

Nowadays, both types of yeast are integral parts of the brewing scene, but this hasn’t always been the case. Top-fermenting yeast came first – this is why the ancient types like wheat beer, IPA, Pale Ale, Stout or Porter are all top-fermented beers. Back then, the yeasts were still wild, and tended to turn up in the fermentation tub by accident – no one had a watertight explanation for what precisely was going on there.

Only later on, when it was easier to maintain lower temperatures, was bottom-fermenting yeast discovered, and the “new” bottom-fermented beers like Pilsener, Helles or Märzen found a place in our hearts.

To cut a long story short

Top-fermented beers (ales) are brewed using top-fermenting yeast. This yeast likes it warm, and at suitable temperatures hits top form. Its task completed, it floats obligingly to the top, where it is then skimmed off. The top-fermented beers include wheat beer, IPA, Pale Ale, Stout and Porter, for example.

Bottom-fermented beers (lagers) are brewed using bottom-fermenting yeast. This yeast is a really cool guy, prefers low temperatures, and has a high leisure preference. After its work is done, it chills out at the bottom of the fermenting tank, and is finally removed as well. This method is used for making Pils, Helles or Märzen, for example.

As you can see, these yeasts are actually rather wacky creatures, with an impressive array of capabilities! I hope I’ve succeeded in familiarising you with the brewing craft’s good fairy, and you’re now just as enamoured of these beauties as I am 😉

If you want to know even more about our new friends, this article has information from a genuine yeast expert!

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