I worked in the wine industry when I was younger, we would crush and destem the grapes (crushing isnt an accurate description though, you really just damaged the skin of the grapes enough to allow the juice to leak) and place them in a fermenter with a bunch of dry ice for a few days to a week. Little to no fermentation took place. After this we'd then ferment with a yeast of our choosing.
The whole "native fermentation" thing for wines is big right now, and in most cases, its total BS. Wineries are teeming with whatever yeast that has been pitched alot, and the winery definition of clean is not at all what the brewery definition is.