What is this in my red wine?

bathman · Nov 4, 2018

So about 10 days ago I racked my Cab Sauv after completion of MLF and dosed with SO2 and also added a bit of tartaric as the pH was a bit high. This went back into my 25litre S/S tank filled to the top and then into my new chiller and has been held at 50 - 55F since then.

Needed to adjust the SO2 after testing today (tester only just arrived in the post) so took the lid off to mix it in and found some sort of skin over the surface of the wine. A little hard to describe, but almost looks like lots of tiny white crystals floating on the surface. There is no off-smell/taste. See photos below.

Does anyone know what this could be and whether it needs treating? Had a look at some photos on google and it didn't seem to match with photos of surface yeast, so not sure it is that.

The other thing I noticed when stirring with a spoon was that it felt like there was grit/crystals stuck all around the sides of the tank. When I took my spoon there was evidence of this 'grit' on the spoon, see below.

All I can think is that the tartaric acid crystals have started to form due to the change in temperature - but can this even happen at 50F? I thought it had to be a lot colder than that. And do the crystals even show on the surface? I thought they only formed on the sides/bottom of the vessel.

Last point to note is I have a small glass demi-john with a few spare litres of the same wine in and there is absolutely no evidence of any skin/crystals forming. This has been in the same chiller for the past 2 weeks, the only difference being is that I never treated it with tartaric.

Appreciate any thoughts/advice!

Johnd · Nov 4, 2018

Yes, it’s quite common to have diamonds develop at those temps, the lower the temps, the more crystallization will occur. I store my reds at 55F for a month or so before loading up my barrel to allow it to happen before barreling, and do see it frequently, particularly when I’ve added tartaric before fermentation or just after.

I cannot tell you whether or not the surface film you photographed is related.

stickman · Nov 4, 2018

Agree with John, and based on the fact that you added tartaric acid, the likelihood is high that the the film is actually potassium bitartrate crystals. If you look at the film with a jeweler's loop you'll see what looks like decorative snowflakes.

Ajmassa · Nov 4, 2018

Dude— note for note same thing happened to me last year. High ph -added tartaric. Put through some colder temps. And crystals at the surface. Was a curveball. Didn’t know that could even happen.
There’s so many variables effecting all things. I quit trying to figure out why. Lol. Just kinda went with it.
And in the end accomplished what I wanted to—- dropping out some acid since I had a heavy hand when adding.
Lesson learned was safely adjust pre ferm as much as Im comfortable doing to try and make any post MLf adjustments be as minimal as possible.
Here’s what it looked like for me.

bathman · Nov 5, 2018

Yeah that looks identical to yours, Aj. So looks like it is nothing to worry about too much, I will just leave it there till I rack off the oak in a few months. I wonder if any of the tartaric I added before going in to the cooler actually remains or if it has all just dropped out. Thanks all for the replies and setting my mind at ease!