Question about "natural" yeasts

Roughly speaking, is my understanding correct that when winemakers use “natural” yeasts, they can either:
a) let the wild yeasts present in the cellar do their work and hope for the best, or
b) obtain a measure of control by using yeasts that they have “domesticated” by selecting and cultivating certain strains from among those naturally occurring in their cellar?

Roughly speaking, is my understanding correct that when winemakers use “natural” yeasts, they can either:
a) let the wild yeasts present in the cellar do their work and hope for the best, or
b) obtain a measure of control by using yeasts that they have “domesticated” by selecting and cultivating certain strains from among those naturally occurring in their cellar?

Hi Oswaldo - I've been a home winemaker for over 30 years and have done a lot of studying about making wine. The wild yeasts are not present in the cellar, but on the grapes themselves, as a part of that "bloom" that looks like a thin layer of dust on the outside of the grape skins. Most commercial strains of yeast have been isolated from these wild yeast strains. If winemakers wish to use the wild yeasts present in the vineyard, they will often crush up a small quantity of grapes to propagate a "starter" about a week or so before inoculating the batch. This is similar to your "b)". Wild yeasts are often used to make Beaujolais Nouveau in a process called "carbonic maceration", where the whole grape clusters are placed in a closed, unpressurized container and left alone. Some of the grapes on the bottom of the container will break and the released juice will start to ferment, filling the container with CO2, thus smothering any organisms that need oxygen, etc.

Hi Oswaldo,
If by native or wild you mean yeast belonging to the genera;
(99% of the wild yeast population found on grape berries very likely comprise of these two genera) Kloeckera and Hansieniaspora.
Other genera of yeast that can be found on grapes include the following Picha, Candida, Hansenula, and Brettanomyces.
Prepared juice or must at a winery besides having populations of the wild or native yeast very likely will have a very small population of yeast belonging to the genus Saccharomyces.
So if the must or juice is not cooled down or sulfited and the yeast is just allowed to start fermentation, early stages of fermentation will be dominated by the “native” yeast strains (those dominating in population) and then Saccharomyces will more or less finish fermentation. (This will depend upon how healthy and ripe the fruit was).

Salute

If you want to see descriptions of various wine yeasts from one producer click on the following link: http://www.lallemandwine.us/products/yeast_strains.php.

I've been a home winemaker for over 30 years and have done a lot of studying about making wine. The wild yeasts are not present in the cellar, but on the grapes themselves, as a part of that "bloom" that looks like a thin layer of dust on the outside of the grape skins.

My understanding is that there has been disagreement among experts, but now it is accepted that in the absence of innoculation, fermentation takes place mainly using the yeasts (wild or otherwise) present in the cellar. I suppose originally the cellar yeasts would have come from grape bloom, and quite possibly other sources, but the proportions would be according to the predominant yeasts in previous fermentations.

I don't make wine. My information (for sentence 1 above) was gained from "Principles and Practices of Winemaking" by Boulton et al. They cited Bisson and Kunkee, Microbial Interactions during wine production, in "Mixed cultures in biotechnology", Ziekus and Johnson, 1991. I presume these are authoritative works - but frankly I am in no real position to judge.

I have read that also. From the following link: http://www.enologyinternational.com/yeast/wildyeast.html :

The Nature of the Yeast

An indigenous yeast fermentations starts by itself when wild yeast strains – originating in the vineyard - start fermenting. Wild yeast can take up to a week to begin the fermentation because their initial populations are small compared to an inoculated fermentation. But there is strenuous debate as to whether the wild yeast come in from the vineyard or are already present in the cellar on winemaking equipment.

A proponent of the vineyard theory is Robert K. Mortimer, Professor emeritus of Molecular and Cell Biology at UC Berkeley who has worked closely with several California winemakers studying the role of yeast in natural fermentations. He and others have shown that Saccharomyces cerevisiae is on the grapes but only on about 1 in 1,000 berries. Saccharomyces cerevisiae is referred to as the “true” wine yeast because its alcohol tolerance enables it to ferment up to and beyond 13% alcohol. Also on these grapes are other species of wild yeast, bacteria and mold. Generally, Saccharomyces cerevisiae is the least prevalent of these microbial species. When the grapes are crushed, all of these organisms enter the fermentation, whether inoculated or non-inoculated. For the first one to three days of a natural fermentation, the wild yeast predominate. As alcohol levels reaches 3-4%, the wild yeast give way to the increasing numbers of alcohol tolerant Saccharomyces so that by two to five days this yeast predominates. At the end of a natural fermentation usually only Saccharomyces cerevisiae is present. Professor Mortimer has shown that there is a multiplicity of strains (as many as 16) of this yeast in such fermentations. Whereas in inoculated fermentations, Saccharomyces cerevisiae predominates from beginning to end because of the high level of inoculum. The end result of what also may be referred to as a sequential fermentation is a wine believed to have added texture and finesse. Proponents claim that red wines are lower in tannin. This extra degree of complexity is subtle and owes itself in part to the array of by-products from the different native yeast strains as well as the longer lag period prior to the start of fermentation.

But there are situations when even devoted followers of wild yeast would opt for an inoculated fermentation. Rain at harvest washes off the native yeast, reducing their populations. The ensuing rot contains bacteria and mold which can, during the longer lag phase of a native yeast fermentation, proliferate and ruin the wine. Large winery size is another deterrent to the use of wild yeast. The irregularities of natural fermentations require closer monitoring of individual barrels, which may be impractical on a large scale.

The wild yeasts are not present in the cellar, but on the grapes themselves, as a part of that "bloom" that looks like a thin layer of dust on the outside of the grape skins.

now it is accepted that in the absence of innoculation, fermentation takes place mainly using the yeasts (wild or otherwise) present in the cellar

Research (including the references Steve provided and more recent work) has shown that Steve's statement above is infact the case, though replacing "cellar" with "winemaking equipment" would be a more accurate description (i.e., it's the yeast present on equipment surfaces rather than "air-borne" yeast that provides the inoculum of the dominant specie(s) in the fermentation).

The second paragraph of the enologyinternational.com quote Howie provided sums up what is meant when referring to "wild/spontaneous" yeast fermentations. The primary difference between "wild" and inoculated fermentations is that the inoculated fermentations start with a selected Saccharomyces strain (usually S. cerevisiae or S. bayanus) and this selected yeast is dominant throughout alcoholic fermentation, whereas in "wild" fermentations other yeasts (such as Kloeckera, Picia, etc) play a significant role (typically during the initial stages of fermentation). Typically, yeasts like Kloeckera, Picia, etc can't handle living in alcohol environments of approx. 6-10% (those numbers are a generalisation), and the fermentation then gives way to Saccharomyces (which can survive higher alcohol environments).

obtain a measure of control by using yeasts that they have “domesticated” by selecting and cultivating certain strains from among those naturally occurring in their cellar?

Yes, though it's more a process of selection of a particular strain (based on that strain's attributes) to increase control than it is "domestication".

Thanks for the highly informative replies!

I guess the "agenda" behind my question was triggered by reading the following in Roagna's website:

We think it is a priority to select our autochthonous (sic) yeasts, with the aim to find out the most interesting ones, so that we can get the top quality. This super-selection has been obtained by blending the tradition of our family and the support of friends and academics with a wide microbiological knowledge.

This raised all sorts of questions for me. From the point of view of so-called "natural" winemaking, seeking minimal intervention and "direct to glass transfer," obviously it would be anathema to innoculate with purchased yeasts (not to mention genetically modified ones), but it sounds like using native yeasts has its own spectrum of naturalness, ranging from what we are calling wild, i.e., complete non-intervention, wing and a prayer, hail mary pass (apparently habitual in carbonic maceration but, I imagine, far less so in ordinary fermentation, even for natural winemakers) to the use of cultured native yeasts, that can no longer be called wild, but still respect the notion of terroir, albeit in a somewhat eugenic and non-natural way (if done as selectively as suggested by the Roagna sentence).

If you want to see descriptions of various wine yeasts from one producer click on the following link: http://www.lallemandwine.us/products/yeast_strains.php.

Amazing, Howie! From the terroir point-of-view, there goes the neighborhood...