# White mold on fermenting must



## SGX (Oct 20, 2018)

Hello,
In something of an experiment, I have a stainless steel vat filled with about 30 kg of wine and juice. 
- crushed the grapes by hand
- no so2
- wild yeast
- no stirring or pumping over
22 brix on the 16/October, after throwing it all in the stainless steel vat. Covered with a towel to provide wild yeast more oxygen. 
Now 4 days later, the juice is at 12.5 brix, yet there is a white mold or scum that has appeared on the must. When draining some juice for the brix count, the juice itself smells decent and just like the other two wines of larger volume that I made (currently racked and idling on airlock) with grape from the same vineyard. However, in these two, I used so2 and was of course stirring and pumping over. 
Could you advise what could that be, and what would you advise doing? I am thinking of taking away the must with something like a big fork so I can stop the contact of this white mold with the juice. Yet dont know if that will lower the yeast drastically?
Also, could unfavourable bacteria from this fermentation somehow spoil the other two tanks, as they are in the same room (the ones that are airlocked and idling after the completed fermentation)?


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## Johnd (Oct 20, 2018)

I’ve seen a small amount of mold show up on the surface of my must after sprinkling yeast on top, before I started punchdowns. Once the yeast took over, never saw it again. Using native yeast, it may not overpower other must lovers like cultured yeast. We’re it me, I’d spray some sulfite on the whole surface, then skim it off, and punch down much more frequently.


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## stickman (Oct 20, 2018)

Most likely the grapes had significant mold contamination from the vineyard. Usually un-inocculated fermentation is conducted with grapes that have been highly selected and sorted to remove damaged fruit, which are sources of mold and microbes.


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## salcoco (Oct 20, 2018)

the mold build up because you wee not punching the must down. you should be able to remove the must . the yeast if it is still working is resident in the juice and should keep going. this vat should not contaminate the others. In future punching down should be done to add oxygen to the must as well as keeping the must wet. color extraction also occurs. using wild yeast is not a reason not to do these things.


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## stickman (Oct 20, 2018)

If you are not stirring or pumping over, how do you know it's at 12.5 brix? Without mixing the batch, the sample may not be representative.


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## hennietaljaard (Mar 4, 2021)

SGX said:


> Hello,
> In something of an experiment, I have a stainless steel vat filled with about 30 kg of wine and juice.
> - crushed the grapes by hand
> - no so2
> ...


Hi, I am curious to know how did your wine turn out at the end? I have the same problem. 3 days ago harvested and crushed syrah grapes without destemming. added 30 ppm SO2. no yeast added (I do wild ferments). Covered the container and left it alone for 2 days. At the end of day 2 when I opened the container it showed some white mould. Its fermenting now on day 3 and im doing punchdowns. Everything seems OK now so will have to wait and see how it turns out.


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