originally posted by Florida Jim:
In a custom crush facility with over 18 different clients, I have seen a "house" yeast develop that is so strong that, even if cold soaks are treated with 20 ppm SO2 and kept in a cold room, the must will start fermenting after several days.
This year, I saw a tank in cold soak that was laced with dry-ice twice daily and the glycol jacket set at 50 degrees go off on the third day. (One assumes that the jacket had effect only so far into the tank.)
David's point about winery yeasts is not to be taken lightly.
Sometimes, fermenting native is not anything even remotely native.
Best, Jim
If I understand your last sentence can I assume you are referring to a winemaking situation where commercial yeasts used in the past have become a powerful or even dominant presence in the winery [a house yeast] and musts no longer require inoculation - and therefore 'fermenting native' might be more accurately described as 'relying on spontaneous fermentation from a "house" yeast of commercial origin' rather than 'anything necessarily or remotely native'.
There are also those who appear to believe that the main fermentation yeast S.cerevisiae does not [ever]'come in on the grapes' [incidentally they apply the same argument to Brettanomyces.bruxellensis] because these yeasts have not previously been observed on grapes - despite the fact they have been observed in the vineyard and more recently with new sample enhancing techniques have also been shown to be present on grapes [in tiny population sizes relative to the other much more easily observed yeasts and bacteria].
The traditional winery-based yeast position and rejection of the vineyard as a source of S.cerevisiae [and B.bruxellensis] has been, at least partially, based on the lack of evidence that Saccharomyces.cerevisiae exists on grapes as well as the clear demonstration of their presence in wineries. However now that they have been shown to be in vineyards and even on grapes the continuing argument against vineyard based versions as viable fermentation agents has shifted to its small population relative to all the other microbials that are present in much larger quantities.
The argument goes that musts are either inoculated by the winemaker with prepared yeasts or are spontaneously started by winery-resident yeasts and the idea that S.cerevisiae and B.bruxellensis have any origin other than the winery as far as spontaneous fermentations are concerned is still rejected by many. However there are at least some famous winemakers who appear to believe that their natural ferments have an original genesis in their vineyards.
In addition I have never had an answer to the question [except for commercial preparations] of where the winery-resident Saccharomyces or Brett originally comes from if not from the vineyards that feed the winery.
The rejection of the vineyard underpins a traditional objection to the idea of the yeast in a spontaneous fermentation being in any sense component of terroir.
However if winery-resident yeasts [or, even more radically, yeasts brought in on the grapes in the ferment itself] could be shown to have derived originally from the vineyards feeding the winery the idea of terroir becomes more plausible.
Other non-Saccharomyces yeasts that are present in the vineyard can certainly start a fermentation that hasn't been sterilised by SO2 and will gradually die off [at different levels] as alcohol levels rise and S.cerevisiae begins to dominate and alcohol levels continue to rise until [depending on sugar levels] it too can begin to wobble - at which time, without appropriate dosing with SO2, any Brett present [from wherever] might have its wicked way. Brett apart those 'early' yeasts presumably play some part, possibly major, in how the wine ultimately presents.
A recent study by Mat Goddard and his team at the Kumeu River winery in New Zealand appears to show that S.cerevisiae can have a local identity removed from commercial/international versions and that study also concluded/hypothesised that the yeasts in the ferment had indeed come in on the grapes in the ferment not least because they had extensively sampled the winery before the study and found no such yeasts present.
This study has been used by Dr. Jamie Goode in a recent article in the World of Fine Wine to again raise the issue of terroir in connection with spontaneous wild yeast fermentations although a lot of research remains to be done before these ideas can be supported more convincingly.
It would be interesting to know how many of the worlds great winemakers utilise wild local yeast ferments and how and from where these yeasts come to the fermentation and what differences these provide in their wines.
originally posted by SFJoe:
I'm trying to find a recent article from Science or Nature on what yeasts were present in a NZ fermentation. Did we not discuss here?
If you are referring to Mat Goddard's Kumeu River research and Jamie Goode's further related article Goddard's piece is
http://onlinelibrary.wiley.com/doi/10.1111/j.1462-2920.2009.02035.x/full
