Yeast is responsible for carrying out the fermentation process in beer making and overall brewing. This is one of the most important part of brewing. Yeast takes up sugars like maltose, glucose and produces carbon dioxide and alcohol. It has the credit for providing various beer styles. The brewer picks up the yeast according to the recipe or the style of the beer they want to make.
Yeast is either an ale yeast or a lager yeast. The former involves warm temperatures while the later needs cool temperatures. This difference in temperature produces different flavor and aroma characteristics and thereby providing various beer styles.