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Traditional methods of making wine did/do not involve the addition of "domesticated" yeasts. Instead they rely on the wild yeasts which occur naturally on grape skins - and which impart the bloom which is easily visible. If you use wild yeasts then you just crush the grapes and leave the wine to make itself.

It is generally thought that the first wine resulted from grapes being stored in large jars. The grapes at the bottom were crushed by the weight of those above. Natural yeasts fermented the juice and wine resulted.

These days artisan and traditional winemakers generally prefer to use wild yeasts wherever possible. They can produce more interesting results with more local character. (Think sourdough bread). The differences between wines from different regions result in part from differences in the local yeast population. The wild yeasts found in Barolo are different from those in Burgundy. So chardonnay grown/vinified in one will taste different from that produced in the other (there are of course many other differentiating factors, but yeast is definitely one). Regions which are pre-eminent in particular kinds of wine owe at least part of their success to the fact that they have the right kind of yeast.

Industrial producers do not want variation between batches which come in to their factory with different yeasts. So they first kill off the wild yeast using some sterilising additive and then add in their preferred strain of cultured/domesticated yeast. Different strains produce different results - some emphasise fruity characteristics, others floral, mineral or whatever. Tolerance to alcohol is also different so the strength if the wine can be affected too - and all the other characteristics that vary in proportion to length of fermentation.

There are some parts of the world where wine production is relatively new and the local yeast population has not yet achieved critical mass. In those areas the winemaker has to use cultured yeasts.

It is instructive to look at cases where winemakers use both approaches. For example, at Greywacke in NZ, Kevin Judd makes a world beating sauvignon blanc using cultured yeast. He has access to a library of yeasts used by all the other NZ producers and can choose a cocktail of yeasts that helps the production of big intense SB in the classic NZ style. But he also makes a wild yeast version. That is made in small quantities, is partly oak aged and is a completely different animal. It is magnificent, but also expensive. I would hope that in the fullness of time the wild yeast population of the Greywacke vineyards would allow him to use wild yeast throughout his entire production.

The parallel I would make is with sourdough bread. Industrial bakers use industrially produced yeasts. Artisan bakers often elect to make sourdough. Anyone who has ever tried to make a sourdough starter by getting a wild yeast to develop from thin air knows the results are much less controllable than using Allinson dried yeast. But when it works the outcome can be sublime.
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