The amount of fermented extract determines the attenuation of wort, which is
the main parameter indicating the course of fermentation. Regular worts contain
about 80 % of fermentable extract. At the stage of beer transfer, movement of the
green beer from fermentation cellar to lager cellar, the green beer should contain
approximately 10 % of unfermented fermentable extract in order to obtain sufficient
formation of dissolved CO2 during maturation. However, some breweries
allow all extract to be utilized during primary fermentation and then add more of
the original wort (or sugar adjuncts) for carbonation. A proper primary fermentation
can be achieved usually in about 5–7 days, but the exact duration will strongly
depend on the original wort extract, fermentation temperature (7–15 °C for lager
beers), and yeast physiology.