Yeast plays a major aromatic role in brewing and is often a brewers' secret ingredient.

Some strains of yeast produce prolific quantities of esters during fermentation. Esters are aromatic organic chemicals that we perceive as flavours. Some esters taste like banana, others may taste like cloves while still others can taste like vanilla and many other flavours, some are agreeable, some are not so agreeable depending on your taste

The same strain of yeast can produce different flavours just by fermenting at different temperatures!

It is important to choose the most appropriate strain of yeast for the style of brew that you wish to produce.