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So I have been doing a few grape based ferments lately and one of the things I am struggling with is the clarification of the wine once fermentation has completed.
When I make small batches (say for Pisco) I can use my stainless fermenter which seals beautifully and has an internal cooling coil so I can crash cool at the end of the fermentation. I am finding that it takes about a week for the wine to clarify, so far infection hasn't occurred because I thoroughly sterilise and once fermentation is complete I crash cool to about 2 Degrees C and don't open the fermenter.
My issue is when I do a larger batch say to make neutral, where my 200L fermenter is open top. I don't want to leave the wine in that state for a week as I am concerned about it getting an infection. I had thought about using cling film over the top of the fermenter but I just dont think it will create enough of a seal. Also my cooling jacket on that fermenter struggles to keep thing below 15 degrees during summer.
For the larger batches I was thinking about using Bentonite to help clarify the wine however this still takes about a week, I also have read its very effective between 15-20 Degrees C which would work well with that set up.
If I am to use Bentonite or any other clarification technique (except filtering) I need to stabilise the wine to prevent a bacterial infection. I have read up on this subject in the Fermented Beverage Production book which in the section on Pisco discusses that the use of sulfur dioxide up to a maximum dose of 5 g/hL has minimal effect on the finished spirit. However, this dose is insufficient to guarantee microbiological stability, especially in low acidity wines, which given I'm using white grapes mine is.
The FBP book in the Pisco section then goes on to talk about mixing the non potable phase from previous distillations as a way of achieving microbiological stability, specifically the book states:
"The mixture of wines with a 10% of these distillates allows for the increase of wine degree up to 14 to 15 GL. Obtaining thus, their microbiological stability without damaging the quality of the spirit."
Am I interpreting this correctly that if I have say 200L of wine then add 20L of feints from previous neutral runs (or neutral low wines)? I would have thought the ABV of what gets added would also be important.
I was just wondering if anyone out there uses a similar method and might be able to shed some light on what they do? I don't want to use campden tablets as from what I can see that will have a negative effect on the finished spirit.
Also silly question, I can't find anywhere what GL is a measurement of...