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Greg Corey

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I racked my Aromella today, which is it's first racking after primary. As I was rinsing the carboy, I noticed these hard flakes in the bottom. You can see in one photo that it actually molded to the shape of the carboy. I have no idea what this is. I thought maybe it is potassium bitartrate but seems far too structural for that. It's been stored at 63ºF +/- 2º the entire time. The wine tastes excellent so I'm not terribly worried, I've just never seen a deposit quite like this before.
 

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Tartrates can form discrete crystals and they can form sheets. The Vidal and Chambourcin I started in October dropped a lot of crystals at low 60's F temperatures. Any time the amount of acid exceeds a saturation threshold, crystals can drop. Which is a good thing normally, as the wine is probably acidic. Just rack off the crystals.
 
Yup. The wine tastes great. The beginning TA was 8.1 so it would be reasonable to think that tartrate would precipitate out. I always thought that cold stabilization was needed to precipitate out the crystals. I guess not

You did a form of "cold Stabilization". At least you held it at a temperature that allowed the tartrate to become unstable and fall out of suspension. I would imagine if you got it really cold, like down around 32F for an extended period of time much more would fall out. I do this every year with my Chambourcin and when I make Vidal Blanc. They both will drop about two inches of tartrates, if I hold them for about a month or so.
 
I concur -- I have Chambourcin and Vidal in progress, and both dropped crystals at ~63 F. The Vidal I made from juice dropped crystals during 3 weeks of cold stabilization in the fridge at ~38 F.

As the temperature drops, the threshold of saturation drops, so if the amount of tartrates is above the threshold, crystals drop.

Mine are currently being cycled in 4 liter jugs through a small fridge, as both are too acidic. I may have to backsweeten the Vidal a bit, and hope to avoid that for the Chambourcin.
 
I purchased some commercial MLF bacteria to inoculate my Frontenac because it was so acidic. I did 5 gallons with MLF, and 3 gallons I'm leaving alone to see how it behaves (no SO2 up to this point but so far MLF hasn't really occurred naturally, which is surprising because all of my cider spontaneously went through MLF).

So, I wonder if I can also cold stabilize to improve balance. It's been unseasonably warm but I can probably keep things around 40ºF during the day and then they will get quite cold at night 25-30ºF. Any insights if the temperature fluctuations would be detrimental to the overall outcome? I usually just keep my winemaking in the cellar since 63º seems like a nice sweet spot for most of what I do.
 
Wine can be cold stabilized down to the freezing point of the wine, but that is not a set value. The freezing point depends on the ABV and other constituents in the wine.

Additionally, I found several studies the concluded that lowering the temperature below freezing does not improve the cold stabilization. My take is that there is no value going below 32 F as it introduces risk with no benefit.

Regarding a jump of 10-15 F between day and night? I don't have evidence that it's bad, but my wine is best kept at a steady temperature, so I have concerns that repeated jumps in temperature are not good.
 
I racked my Aromella today, which is it's first racking after primary. As I was rinsing the carboy, I noticed these hard flakes in the bottom. You can see in one photo that it actually molded to the shape of the carboy. I have no idea what this is. I thought maybe it is potassium bitartrate but seems far too structural for that. It's been stored at 63ºF +/- 2º the entire time. The wine tastes excellent so I'm not terribly worried, I've just never seen a deposit quite like this before.
tartrates mixed with dark tannins
 
tartrates mixed with dark tannins
Tannins! That's interesting. That would explain the deepness of the color.

@winemaker81 Regarding a jump of 10-15 F between day and night? I don't have evidence that it's bad, but my wine is best kept at a steady temperature, so I have concerns that repeated jumps in temperature are not good.

I do believe the general consensus is that temperature swings and wine do not mix. I won't worry about further stabilization as this is for home consumption and if I want to try to really force out more tartrates, I can do that on a smaller scale and see if it affects flavor.
 
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