Main fermentation

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There are two fermentation phases in beer production, the main fermentation and the secondary fermentation , better maturation or storage (see also young beer ). The main fermentation takes place immediately after the actual brewing in the brewhouse.

Explanation

After the wort has cooled to fermentation temperature, it is ventilated and inoculated with yeast cells .

Some breweries have their own cellar in which the pure yeast (the most common fermentation yeast is Saccharomyces cerevisiae var. Carlsbergensis) is produced in sufficient quantities for the main fermentation. A concentration of approx. 10 to 20 million yeast cells per milliliter of wort is aimed for. Before the yeast is added, the wort is aerated; Venturi nozzles are commonly used for this purpose, which blow fresh air in through a sterile filter system. The aim is to achieve an oxygen input of approx. 8 mg per liter of wort. The ideal starting conditions for this fermentation phase are only achieved by enriching the wort with oxygen.

Yeast cells are facultatively anaerobic and have two metabolic pathways:

• Breathing (energy is gained through the citric acid cycle , aerobic )
• alcoholic fermentation (energy is obtained by converting sugars into alcohol, anaerobic )

The energy gain through breathing is much higher than through fermentation. In this way, the yeast gains strength through breathing in order to carry out the main fermentation in sufficient time, approx. 5 to 8 days with classic main fermentation. It goes through the frizz stages :

• Young or curled curls
• Ruffles
• Breakthrough (end of main fermentation)

In the past, these stages could be easily observed in the open fermentation vats, but this is no longer possible in the cylindro-conical fermentation vessels that are mostly used today. The fermentation is monitored by taking samples for the purpose of determining the residual extract, accompanied by the biological control. The company laboratories determine the EVG (final degree of fermentation) within two days and thus specify the hose time. After the main fermentation, the intermediate product obtained is called green beer .