What Do We Mean By "Barnyard" Smells in Wine?

When we talk about smells and flavors in wine, most make sense. We all know what strawberries or lemons taste like. On the other hand, when we talk about the less pleasant flavors of wine, we tend to use euphemisms or shocking phrases. "Cat's Pee" really gets the point across. When we talk about a "barnyard" flavor, we are looking at strange organic smells; mold, old hay, wet straw, maybe even some mud or manure. These are smells close to some of our favorites; mushrooms, fresh hay, earth, but with an off flavor that makes them upsetting to the palatte. It comes from spoiled yeast creating that strange fermented smell. While some wine drinkers enjoy it at low levels, it is technically a spoiled wine.