High or low, different fermentation styles for different tastes!
Fermentation is an essential stage in the brewing process. It involves adding yeasts to the cooled malt. These yeasts are fed by the amino acids in the brew and produce alcohol from the sugar that is present. These natural reactions also produce carbon dioxide.
There are three different types of fermentation and each results in a different type of beer.
Spontaneous fermentation: this is the oldest method and it goes back to the time when the art of cultivating yeast was as yet unknown and unmastered. In this type of fermentation, the malt is left in the open air for a certain amount of time, the wild yeasts that naturally occur in the air settle on it and thus promote fermentation. Today, this ancestral method is hardly used except for the production of lambic, gueuze, kriek and faro beers, specialties of the Senne Valley and the Pajottenland region west of Brussels, where the air contains the precious yeasts Brettanomyces bruxellensis and Brettanomyces lambicus. What’s more, spontaneous fermentation beer is only brewed when the weather is cold (mid-September to mid-May). The oldest brewery producing these traditional beers is Timmermans, today a member of the Anthony Martin Finest Beer Selection.
High fermentation: this type of fermentation, which is also a traditional process, lasts three to eight days and involves adding Saccharomyces cerevisiae yeasts to the malt. These yeasts are active between 15°C and 25°C and rise to the surface of the malt once all the glucose has been used up, hence the name “high”. This process generally produces beers with a high alcohol content, more complex aromas and less carbon dioxide than low fermentation beers. These beers are also drunk at a higher temperature than the latter, generally between 6°C and 12°C. This category includes amber-coloured beers and a number of specialty Belgian beers. These beers for connoisseurs are usually classified as ales. Indeed, many Belgian specialty beers have English roots.
Low fermentation: this fermentation method popularised by the famous Pilsner, first brewed in the middle of the 19th century in the Czech town of Pilzen, is carried out at between 4°C and 12°C and is characterised by the addition of Saccharomyces carlsbergensis yeasts to the malt. During this process, that lasts seven to ten days, the yeasts migrate to the bottom of the vat, hence the name “low fermentation”. The bees produced via this process are generally less fruity than high fermentation beers and are classified as lagers. They also have a lower alcohol content and a higher CO2 content. Very refreshing, with a pronounced flavour of hops, they are served chilled, generally between 4°C and 7°C.
Mixed fermentation: mixed fermentation is when two types of micro-organisms are used to ferment the beer. Master brewers use on the one hand yeasts that are identical to those used in high fermentation, and on the other, they also use bacteria. In other words, they combine the high fermentation and spontaneous fermentation processes. Some beers are also aged for a number of months in oak barrels, which gives them a fruitier flavour thanks to the presence of micro-organisms.