Cold Stabilization of Wine

Cold stabilization of wine is a method used to keep tartaric acid crystals from forming after the wine has been bottled. This process is referred to as cold stabilization because it is the act of cooling the wine that causes tartaric acid to form tartrate crystals, also known as wine crystals or wine diamonds.

If wines are not cold stabilized there is a chance that these crystals will form when consumers place bottles of wine in the refrigerator or store it for long periods of time. While the crystals are harmless it can be rather unsettling to find what looks like broken glass in your wine if you don’t know what it really is.

Why do Tartrate Crystals Form?

Tartaric acid is naturally present in wine making grapes so we can expect all grape wines to have it. However, after fermentation some wines will be supersaturated with tartaric acid, meaning that there is more tartaric acid in solution than what wine can naturally sustain.

The excess tartaric acid will solidify and form crystals. This will continue until the acid reaches a concentration that can be sustained. When wines have this excess acid they are considered to be tartrate unstable.

Things such as temperature changes, blending of wines, moving your wine around, and additives such as bentonite can cause the suspended acid to crystallize. Also, the higher your pH the higher your chances are of crystals forming

Are Tartrate Crystals Harmful?

No, tartrate crystals will not harm you if you happen to swallow a few. The only real hazard they pose is causing you to choke if you weren’t expecting chunks of stuff in your wine.

In fact crushed tartrate crystals is the same thing as cream of tartar, yes the same stuff you have in your pantry right now. Wine barrels used to be a major industrial source of tartrate crystals for the production of cream of tartar.

How to Cold Stabilize Wines

Now that we understand how tartaric acid can lead to tartrate instabilities let’s talk about what we can do about it.

The process is quite simple. Just reduce the temperature of your wine temperature to 30 degrees (F) or less for at least 36 hours. A spare refrigerator or a cold garage in the winter may be sufficiently cold to carry this process out. The warmer your wine is the longer this process will take though.

To help things along you can optionally add potassium bitartrate powder which is merely small tartrate crystals. These additional crystals serve as seed crystals for the tartaric acid the bond to. This speeds up the crystallization process.

While getting your wine down to 30 degrees (F) can help facilitate this process it’s not really cold enough to do a complete cold stabilization. Most amateur wine makers don’t have access to the sorts of equipment required to drop the temperature far enough to make their wines completely tartrate stable.

Wineries use large cooling tanks where they can store huge amounts of wine and control the temperature very carefully. However, the process outlined above will still help you get rid of a lot of the tartaric acid, just know that it may not be completely stable. A prolonged stay in the refrigerator after bottling may cause more crystals to form.

If you do have the means to reduce the temperature of your wine here is a simple formula for determining what the ideal cold stabilization temperature is.

For example, if you have a wine at 15% alcohol by volume your ideal cold stabilization temperature would be -6.5 degrees (C) or 20.3 degrees (F).

Adverse Affects of Cold Stabilization

There is one rather unfortunate side effect of cold stabilization. Colder temperatures increases a wines’ ability to absorb oxygen which leads to premature aging.

Be very careful about oxygen exposure while your wine is cold. Keep those bung plugs on there nice and tight. This is especially important when dealing with PET carboys as they can flex when being moved causing the seal to break.

Photograph of tartrate crystals by: Paul A. Hernandez