The fermentation process begins when you mix the yeast with the wort. The yeasts convert the sugars into ethanol and CO₂. In this process must be tightly controlled temperature, since according to the yeast you mix with (high or low fermentation) should be maintained between certain limits. For example, a high fermentation temperature should be between 18ºC and 22ºC (ales), while in low fermentation the threshold is between 7ºC and 12ºC (lager).