Winemaking: Choosing native or introduced yeasts for fermentation

How do you start the fermentation of grapes to make wine? Winemaker Fred Scherrer talks in detail about how native and commercial yeasts interact in the fermenter. This is part of a series of questions we asked Fred intended for home winemakers and
professionals alike.

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Filmed with Fred Scherrer at City Winery Chicago.

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Video Text:

I employ a lot of different ways to conduct a fermentation, or allowing it to be conducted.

I do some without inoculation, I do others with inoculation with commercial yeasts and I make that choice based on whether I feel that my intervention is going to give me more of the desired outcome.

And we are fooling ourselves if we think that actually all of the yeasts we innoculate something with are actually doing all of the work, because there is other things in there that are actually working as well.

Personally I kind of do a hybrid of the two. I allow the population of indigenous yeasts on healthy grapes to actually begin to proliferate and do a good bit of the fermentation before I consider adding commercial yeasts as well to augment that. I don’t always do that, but when Ido augment I tend to allow a lot of indigenous things to build up a population.

If the grapes are very unhealthy and it is a rot challenged vintage I tend to inoculate sooner rather than later because I’d like to get that more oxygen deprived situation having the yeasts active early because it tends to pre-empt the decay, the potential decay of that grape mass by the mold enzymes that are there in a more rainy or rot prone vintage.

As far as if I am going to inoculate something, Itend to inoculate the surface which is where the oxygen is, where the air is. Yeast like air and they build up stronger membrane, they have higher alcohol tolerance, which in California tends to be something we think of more than they might in very cold places.

And then I allow that population of yeast to really proliferate in the surface. Once they begin fermenting, or growing and fermenting more, as we stir or punch-down the surface we’re gradually spreading them deeper and deeper into the mass. At the same time on the bottom there may be some things growing naturally from below and Ithink that gives a nice complexity to the whole situation, but we are still getting more of our desired outcome.

Even with natural ferments I tend to only work with the tops of the tanks a little bit and I leave the bottoms alone. I don’t want to break all those grapes that are happily moldering down below, possibly getting some really interesting carbonic maceration type characteristics which I think helps layer in more interesting characteristics and mouthfeel into the wines.

But I don’t really feel that we need to try to homogenize things right away. You know there are a lot of people who view it very differently. They want homogeneity, or at least they want the illusion of it. I don’t have any illusion that we have homogeneity in a fermenter. And things really do stratify fairly early on and I am totally ok with that.