Fermentation occurs in special vessels called cylinder-conical tanks.
We place cooled wort in the tanks and add brewing yeast to it. Fermentation takes from 7 to 10 days depending on a type of beer we want to brew. At this time the yeast consumes sugars and some other substances from the wort and converts them mainly into alcohol and carbon dioxide. Also there are other substances forming during fermentation: fusels, glycerin, acetic aldehyde, acetic, siccine, citric and lactic acids. All products of fermentation contribute to beer's flavour and taste.
At an early stage of fermentation the yeast rapidly multiply themselves. Gradually this process slows down, as the amount of nutrients reduces and the alcohol content increases. If we brew lager or pilsner, we use the type of yeast that by the end of fermentation precipitates and settles in the bottom of the tank. This is called bottom fermentation. If we brew ale or stout, we add yeast of a different type: it floats on the surface like foam (top fermentation).
At SUN InBev we brew bottom-fermented beers.
We chill the tanks down to 0°C in order to expedite the settlement of the yeast at the bottom. Then we remove the settled yeast and keep it for next batches. Quality of brewing and purity of yeast determines how many more times the yeast can be used. Different beers are brewed with different yeast. Usually each brewery uses its own pure culture.
Once our wort has undergone fermentation, it is called «green beer» - rough and unrefined. We send it for further conditioning and maturation.