WHAT IS THE DIFFERENCE BETWEEN TOP AND BOTTOM FERMENTATION?

What is the difference between top and bottom fermentation?

The terms top-fermentation and bottom-fermentation, which appear frequently in brewing, can seem complicated, so it's worth learning more about them, as they result in one of the biggest divisions in the beer world.
The distinction between top and bottom fermentation stems from the use of different varieties of yeast - each group requires slightly different conditions and produces a different type of beer. This is so important because this distinction affects the entire beer world by causing a division between the two main branches of brewing, from which almost all beer styles originate. In the case of bottom-fermented yeast, we collectively refer to it as Lagers; in the case of top-fermented yeast, the effect of its work is classified as Ale.

SOWIE Top-fermenting yeasts (Saccharomyces cerevisiae) appeared earlier in the history of beer - they work at higher temperatures, usually in the 15-25°C range, produce beer (ferment the wort) quite quickly, and in the process of their work cause the formation of many characteristic flavour and aroma compounds in addition to ethanol, mainly higher alcohols and esters. They are used in all styles bearing the collective name Ale, as well as in stouts, in old and traditional beers, including wheat beers. The name of this type of fermentation comes from the characteristic behaviour of the yeast, which floats on the surface of the wort during fermentation, often forming a spectacular foam or dross. The effect of this type of yeast is its significant influence on the bouquet of the finished beer - enriching it with spice, spice, floral, herbal, nectar, fruit notes. The presence of such flavours and aromas in beer may seem surprising, but they are natural remnants of the action of top-fermenting yeast - these beers are richer in flavour and aroma, so it is worth savouring them by serving them at the right temperature and selecting the right glass.

SOWIEBottom-fermenting yeasts (Saccharomyces pastorianus), as the name suggests, sink to the bottom of the fermenter when they have finished working, and also have a lower temperature optimum, usually between 5-15°C (optimally 8-12°C), so their use requires special conditions - deep cellars or refrigeration equipment. The result of their work is a beer with a very clean aromatic profile, as they produce minimal amounts of aromatic compounds and higher alcohols. Thus, the flavours and aromas from the other raw materials used - malt and hops - come to the fore during drinking. Bottom fermentation made its appearance in the beer world relatively recently - only in 1883, when Emil Christian Hansen obtained a pure culture of this yeast for the first time in a laboratory in Copenhagen (earlier, in 1842, Josef Groll - head brewer of the Pilsen brewery - was the first to use it). However, lagers quickly gained a reputation among beer drinkers by successively displacing Ale from the market - it is estimated that bottom-fermented beers now account for around 90% of breweries' production worldwide. With bottom-fermented yeast, the fermentation process is much quieter and takes longer, plus the beers require so-called lagering, i.e. maturation and clarification at a low temperature for a longer period of time before they go into mugs, glasses and decanters. Although lagers are often associated with limited sensory experience and a golden colour, there are also very rich styles, full of flavours and aromas such as Baltic Porters or dark beers such as Bock. It should also be remembered that while lagers have a less diverse bouquet of flavours, they are not forgiving of mistakes, so brewing an exemplary lager is quite an art.

 

The distinction between top-fermented and bottom-fermented beers thus has a fairly short history, yet it is extremely important because it describes not only how the yeast works during fermentation, but above all the flavour and aromatic effects of these micro-organisms. If you are one of the many lager lovers it is highly likely that you are missing out on a significant part of the beer feast. It is worth considering your choice of Ale on your next visit to the pub or beer shop :)

 

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