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Craft beer: Yeasts and fermentation
Yeasts are unicellular microorganisms. The dimensions of yeasts are 5-10 micron, much
larger than bacteria (which are around 0.5 -2 micron). The dry weight of yeasts is composed of 45-60% proteins, 25-35% carbohydrates, 4-7% fats and 6-9% minerals, they also contain many vitamins of the B group.
Traditionally, within brewers, we still speak of s. cervisiae and s. carslbergensis to indicate respectively the yeasts of top and bottom fermentation. However, according to the latest classification of 1997, four species of saccharomyces are recognized: s. cerevisiae, s.bayanus, s. pastorianus e s. paradoxus.
In the past, the terms top and bottom fermentation were referred to the peculiar characteristics of yeasts which accumulated at the top of the kettle (bottom fermented) or surfaced (top fermented). Today these terms are used more specifically to classify beers based on the temperature of the fermentation: 6° to 14° for bottom fermented, 15° to 25° for top fermented.
The English term "ale" is generally used for top fermented beers, while the German term
"lager" is used for bottom fermented brews. Over 90% of beers produced in the world are bottom fermented, while the rest are ales, exception made for spontaneously fermenting beers like the Belgian lambic beers.
Most Italian craft beers are top fermented brews with a second fermentation in the bottle. Our brews instead are traditional bottom fermented beers, produced with craft methods and with great attention to the raw material and the details of the process.