Q: I tried to let a natural fermentation work on a 3-gallon (11-L) sample wine. At five days no discernible action was taking place and I added a cultured yeast. Should I have waited longer? When should a natural fermentation be expected to commence? What are the indicators?
— Jack Kerr • Santa Fe, New Mexico

A: Well, I would’ve inoculated right off the bat if I didn’t see anything happening within 24 to 48 hours. Contrary to popular belief, yeast cells that can carry out a complete alcoholic fermentation rarely come in on the fruit from the vineyard. The species that do are typically those kinds that can only ferment to about 5% alcohol. Especially if you are using frozen juice, must, or concentrate, don’t expect to be able to rely on any indigenous microbes from the raw material to get your fermentation going. The freezing or concentration process will have significantly knocked down the percentage of viable native yeast cells.

The microbes that conduct so called “natural” or “feral” complete alcoholic fermentations usually come from the wineries themselves. This is why “well-seasoned” wineries, meaning those that have had a history of many successful fermentations over many harvests, are more able to have complete fermentations without having to inoculate. These yeast strains, ambient in the air and on equipment, are robust and have been selected over time as strains able to conduct a fermentation to dryness and often are related to or are a “domesticated” version of a commercial strain that was added to a fermentation at some time. This is why “new” facilities or even new home hobbyists often have a hard time starting up “feral” fermentations unless they’ve got a good naturally-present inocula.

My recommendation? If you don’t see any action after 24 hours, inoculate with a commercial yeast strain so you don’t have volatile acidity or ethyl acetate problems as bacteria and spoilage yeast take hold. After a few successful fermentations, you might have enough residual ambient yeast to conduct a “feral” fermentation without inoculating.

For much more information and another author’s take on fermenting wine with wild yeast, check out the story beginning on page 52 of this issue. The roundtable yeast story beginning on page 30 of this issue also addresses this topic.