From BeerAdvocate website: It's about beer but has clear implications regarding the taste of wines...
Yeast impact the flavour and aroma of beer more than you might think. The flavour and aroma of beer is very complex, being derived from a vast array of components that arise from a number of sources. Not only do malt, hops, and water have an impact on flavour, so does the synthesis of yeast, which forms byproducts during fermentation and maturation. The most notable of these byproducts are, of course, ethanol (alcohol) and carbon dioxide (CO2); but in addition, a large number of other flavour compounds are produced such as:
acetaldehyde (green apple aroma)
diacetyl (taste or aroma of buttery, butterscotch)
dimethyl sulfide (DMS) (taste or aroma of sweet corn, cooked veggies)
clove (spicy character reminiscent of cloves)
fruity / estery (flavour and aroma of bananas, strawberries, apples, or other fruit)
medicinal (chemical or phenolic character)
phenolic (flavour and aroma of medicine, plastic, Band-Aids, smoke, or cloves)
solvent (reminiscent of acetone or lacquer thinner)
sulfur (reminiscent of rotten eggs or burnt matches)
There are other yeast byproducts, and some of the listed can be both desired byproducts and/or undesired depending on the beer style or what the brewer was trying to achieve.
