That’s what I understood. But week before last I attended via Zoom a presentation by Matt Wengel who is winemaker for Lemelson Vineyards in Oregon (TWS stock one of their Pinot Noirs.)
Matt’s talk was titled ‘Let’s talk about Wine Microbiology – The Hidden Warfront’. It was supported by lab reports on the amount of microbes present in his wine. At the beginning the natural yeast on the grapes and brought in from in the vineyard were in the majority - but left to their own Matt said they wouldn’t make more than 4% abv.
The winemaking yeast numbers grew and killed off the wild yeasts. Where do the winemaking yeasts come from? Matt couldn’t answer the question whether a brand new winery could make wine with introducing a wine yeast. Subsequent years spontaneous fermentation could happen as that initial yeast was in the winery fabric.
Matt said that if he went to other wineries, he introduced yeast from Lemelson’s as it was on his person and vice versa. “I’m covered in it” he said.
He was flatly denied that yeasts on grape skins and in the vineyard could make wine.
I’m not a scientist, but this guy has studied the matter, has the laboratory reports which he showed us, and makes his living from that knowledge.
Re commercially bought yeasts: wineries claiming they use natural yeasts can be buying commercially and still be telling the truth. The yeasts are natural, and naturally propagated and dried as opposed to genetically modified.
In the case above, where did those yeasts come from? Could be spontaneous fermentation, i.e. they didn’t inoculate but the yeast could come from the fabric of the winery a descendent of past years fermentations, I don’t know how old it is, or where the old demi-muids came from - or how old the concrete tanks are.