I just fermented my Concords and the pH was a bit lower than I would have liked (3.2) and the SG also. I brought the brix up by chaptalization.
I’m usually a bit hesitant to add things that bring up the pH because (I feel) it tends to add a little bit of a mineral-ish taste to the wine. This is merely my personal experience. Other ways to reduce acidity are cold crashing (which you were referencing above), blending afterwards with other similar types (DeChaunac works well for this), MLF for malic acid co-inoculation, yeast selection (Lallemand 71B), adding water (this however will thin it out), sur lie aging, sweetening afterwards…
This also sounds like an opportunity for experimenting to me. Do you have a way to ferment half with one of the methods above, and half with the potassium bicarbonate? You could see at the end how each one does. That would give you an idea of taste by each method without affecting the whole batch. If you had the means, you could try each method even if you ended up combining them at the end.
If you do decide on the potassium bicarbonate, go slow and test often. It will create a small and immediate reaction in the must so be prepared for a minor eruption depending on how much you add at a time. Yep. That's experience on my part LOL... also, you don't want to overshoot and then yo-yo back and forth by adding acid, then bicarb, then acid...
How much are you going to make?
