The beauty of wine is supposed to be that, unlike so much of the food and drink we consume today, it is so “natural”. To produce wine, as all of us wine students have been taught, all you need are grapes. Once the grape skin is broken, the yeasts that are naturally present in the atmosphere get to work on the fermentable sugars in the grape pulp and transform them into alcohol.
That is the nice theory, but in fact this is very far from modern practice. The overwhelming quantity of wine on sale today was fermented using commercially available strains of yeast, yeasts specially chosen for their particular and powerful attributes.
Just about the worst thing that can happen to a winemaker is a “stuck” fermentation, one that will not complete the process of turning sugar into alcohol. What's left is semi-sweet, low-alcohol grape juice that is dangerously vulnerable to harmful bacteria and completely unsaleable. The yeast attribute therefore prized above all others by the majority of winemakers is efficiency. So, especially in our current era of very ripe grapes, winemakers increasingly choose yeasts that have been specially designed to act in high-alcohol environments.