Very fine film on wine

Probably a "Film Yeast"

(2) the bottom of the top (the

Possibly dried foam and possibly some tartrates

I'm assuming the two are one in the same.

Probably not.

If your wine were in a carboy and close to the neck, or in a barrel that was just a tad from being full, you could "float it out" by topping up and then correct the acidity and sulphites.

Since you are in a stainless tank with a constant radius, this might not be very easy. I suggest racking, checking the pH, raise the acidity if necessary and sulphite to the proper level.

I would be willing to bet that your pH is greater than 3.5 You can greatly diminish film yeast by keeping your wine at 3.5 or a tad below, keeping your tank topped up to avoid air space and keep right amount of sulphites.

Sounds like film yeast (a spoilage organism), which would be caused by leaving an airspace over the wine. Isn't the floating lid slightly conical, with a little faucet in the middle? If so, you should lower the lid with that faucet open until wine just starts to come out, lock the lid in place and close the faucet. Then you'll have zero headspace and no room for the bugs to grow. Even so, if the wine is finished fermenting, you should maintain adequate free SO2 to prevent problems.

(2) the bottom of the top (the

That would be potassium bitartrate. It's harmless.

Tom S

Thanks Paul and Tom. The floating lid is slightly curved and indeed has a overflow valve (there is a marble in there to keep air from getting in). I let the lid just float on the surface and then pump up the bladder on the outside of the lid that keep it in place and creates an air-tight barrier. I doubt there is any air between the wine and lid as a fair amount of wine actually comes out of the overflow valve. Over the course of a week, up to a half-liter may accumulate (I've taken to keeping a tarp on top of the tank to keep out any insects). Why is so much wine escaping? Could this be the source of oxygen? Otherwise I don't know where oxygen could come from.

I have not added any SO2 after fermentation as I wanted to get through malos, but it's not a lot of wine relative to what I've got in barrel so I'll dose it. pH is in the 3.6 range.

I'm currently using this to top off the barrels, but I'm drawing wine from the bottom, not the top of the tank. Is this putting the barrels in danger? Note that I'm planning to let most of the barrels go through malos very slowly and not planning to make SO2 additions until Spring.

Here's what's happening (I think): the tank is only about 10% full now and something's happening to force wine through the release valve on the lid. Maybe the tank shrinks as it gets cold at night? Then as it warms up, the lid is suspended above the wine. But why would more wine come out over time? One would assume the constriction would be the same every night and it would force out wine on night 1, but no more after that? In any case, I think I'm going to move this wine to a carboy as it's only about 20 liters.