The fermentation process is carried out in fermentation vats: coated, reinforced tanks. Until 1960 all the tanks were made of wood. Fermentation is a process of glycolysis during which alcohol (ethanol) and carbon dioxide develop. A very important factor which influences the fermentation process is the low temperature, which must not rise above 4 °C; otherwise the process would be endangered by contamination. To maintain the above-mentioned temperature, the tanks are equipped with ammonium refrigeration equipment. The fermentation agent is special brewers’ yeast; 0.5 l of brewers’ yeast is added to 1 hectolitre of wart. The so-called bottom fermentation process proceeds here. The yeast precipitate to the tank bottom and the fermentation process continues from the bottom upward to the surface. Wine yeast and the older types of beer yeast are top fermenting: the yeast sit on a layer on top of the wort and ferment from the surface to the bottom. The fermentation process has three phases: the powdering phase (the beginning of the fermentation process), thin white rings, thick white rings (intensive, turbulent fermentation, thick yellow-white foam). At the end of the fermentation process the foam settles down and a so-called blanket (a dark brown layer) remains on the surface. This layer contains ballast substances including yeast, tannins and others. The blanket is taken away manually, using a perforated shovel. The process in the fermentation vat lasts 10 days for draught beer and 12 for lager beer. In the big vessels, down over there, some stuff can be seen – it is brewers’ yeast which is being washed there to be used again. It is possible to use it 5 or 6 times.