With society returning to a bit of normality, beer gardens and pubs have opened their doors for us again, just in time for National Beer Day. To mark the occasion, our BioLabTests scientists have looked at the microorganisms behind one of the nation’s favourite alcoholic drinks.

History of National Beer Day

Beers such as ale and lager have long since been an integral part of British society and were often safer to drink than water in the Middle Ages, so of course it needed to be marked with a national day of celebration. The 15th of June was designated for National Beer Day for a specific reason, it is the day King John signed and sealed the Magna Carta peace treaty. Article 35 of the Great Charter said: “Let there be throughout our kingdom a single measure for wine and a single measure for ale and a single measure for corn, namely ‘the London quarter’.”

The Brewing Process

The actual process of brewing can take quite a long time and requires many steps. The first step is to mash the malt into fine grains, and those grains are then left to steep in hot water for approximately 1 hour. This process produces the wort, which is the main nutrient needed for yeast to grow. The wort is then boiled, and hops are added at this stage to add a variety of flavours to the beer. This liquid is then cooled and the process of fermenting the beer can begin.

Fermentation is the process whereby yeast metabolises the glucose in wort to produce ethyl alcohol and carbon dioxide gas (CO2). During this process the bubbles of C02 gas rise to the surface and produce the distinctive frothy layer of foam.

There are several methods of fermenting beer such as warm fermenting, cool fermenting and wild fermenting using wild strains of yeast. Beers such as ale are produced using warm fermentation at about 17-20°C using Saccharomyces cerevisiae. However, lager is fermented at much lower temperatures of 8–14°C and uses Saccharomyces pastorianus.

During fermentation, Saccharomyces cerevisiae produces many secondary metabolites which contribute significantly to the flavour profile and aroma of the beer. For example, under the right metabolic conditions, esters are produced (the most common being ethyl acetate) which brings floral and fruity flavours to beers. Additionally, carbonyl compounds such as acetaldehyde can bring an apple like flavour.

The synthesis of secondary metabolites is largely affected by the sugar content within the wort and if the yeasts cells are evenly dispersed by a process called flocculation in the fermenting column.

This is when sugars such as maltose and glucose block the receptor sites on the zymolectin protein (flocculin), which causes yeast cells to deflocculate. This causes an even dispersion of yeast cells and can greatly increase the quality of the beer.

So when you’re enjoying your pint of beer in celebration of this day, raise your glass and remember all the hardworking microorganisms that made it possible!



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