Ask Wine Wizard

Tartrate Crystals


Roy McGuill — Monson, Massachusetts asks,

If potassium bicarbonate was added to my must (or juice for my whites) and my acid now is where I want it, do I still have to move it outside to cold stabilize? I am only in my third year of winemaking and The first two years I added potassium bicarbonate (KHCO3) in February and moved my high-acid wine outside for a week or so in hopes to lower acidity. This year I was advised to try adding it at the start (September/October). I did and now my acid is where I want it.


I always think that trying to precipitate out some of the worst crystals that could form is a good idea, especially for any wine that may be sold commercially or entered into competitions. You probably won’t change your pH/titratable acididty (TA) balance that much. In my experience, doing a traditional cold stability where you chill the wine down and then filter off any precipitation won’t shift the acidity enough to notice it in the taste. It’s far better that you got it down to where you liked it style-wise in the first place.

If you’d rather not go through the bother of chilling and fermenting (however, this would be my top advice to prevent these crystals from forming to the sides of your bottle or bottom of the cork, as pictured to the left) and want to prevent some if not all crystals from forming, you could try adding one of the newer carboxymethyl cellulose (CMC) products that many winemaking suppliers are selling. CMC is an FDA- approved cellulose gum commonly used in food as a thickener and emulsifier. If you add 1 mL of CMC per liter of wine, it actually prevents the crystals from forming even though the acid chemistry of your wine will not change. It is clear, colorless, odorless, and tasteless, and should be added after the final filtration. Be sure to wait 48 hours before bottling if you will be passing the wine through a further 0.45 micron membrane on your bottling set up; if not, you might plug your membrane.

I’ve been using CMC with great success for the past few years in many of my white and rosé wines. The only thing you need to take into account is that each product is a little different and each manufacturer may have different criteria for how you work with their CMC. Some, for example, suggest you test for how “unstable” your wine is. CMC can prevent most crystals from forming, but if you have a wine that is very unstable, the product may not be effective at stopping all crystal formation. In which case I would recommend doing a light chilling to precipitate some crystals and to make the remaining “lightly unstable” wine a candidate for the CMC approach. As I say, every manufacturer tends to have their own protocol and CMC-type product so I don’t want to single out one over the other. If you’re curious to try a new way to approach cold stability, you should look into CMC!

Response by Alison Crowe.