tartrate crystals
A Common Question: What is the “Gunk” Left In My Wine Glass?
Photo ©Michael Kelly
While “gunk” may not be the official technical term, it best describes the sediment deposit in the bottom of a glass or in the above stainless-steel filter. Deposit matter can best be described as either tartrate crystals or sediment particles.
Tartrate crystals, usually dark in color in red wine are harmless deposits often referred to as “wine crystals” in white wine. This is a simple chemical reaction when potassium and tartaric acid, both naturally present in wine grapes, bind together. Often “unsightly” but are harmless and many wineries remove them through a process called cold stabilization and can appear in aged bottles or if the wine being stored in a cool temperature.
Red wine tartrate crystals develop when a bottle is stored on its side, typically on the bottom of the cork. These dark purple particles are often referred to as “tiny purple icicles”. In white wine they can look like tiny salt or sugar crystals.
Photo ©Michael Kelly
Next is the sediment that forms on the side of stored bottles of wine and can even clog up a bottle of aged wine. Unfiltered wine has not been processed at the winery to remove yeast, microbes and other particles before bottling. Should one consider this an issue? Actually, just the opposite may be deduced. Having the wine unfiltered and/or unrefined, can provide a more complex flavor profile despite a cloudy appearance in the glass or bottle.
Unfiltered wine leaves suspended particles in the wine. Typically, these will form if the bottle is stored on its side along the bottom length of the bottle or if stored upright, the bottom of the bottle.
Why don’t winemakers remove this suspended material before being bottled? First it preserves desirable flavor compounds giving wines a richer, more complex and expressive taste. With wines being “more natural” this can provide an authentic expression of the grape varietal and winemaking process. There are a few negative justifications for removing them besides aesthetics.
So how do winemakers remove tartrate crystals, grape pulp, yeast cells (lees) and tannins from wine? There are two primary methods. The first is racking or simply letting gravity allow the suspended particles to fall to the bottom of the tank and the “cleaner” wine to be siphoned off to another tank/barrel, leaving the deposits behind.
The second method is called fining which is the use of a clarifying agent, such as bentonite clay or egg whites are added to bind the “floating or suspended particles” and assist gravity helping them settle to the bottom of the vessel.
When opening a bottle of “unfiltered or unrefined” wine that is why decanting through a filter provides a “clear and clean” wine to be poured and served in a glass. When knowing in advance you can take a bottle of wine stored on its side and stand upright for up to 48 hours allowing the material to settle to the bottom of the bottle. It is then incumbent to pour slowly so as not to allow the sediment to come out with the wine. Still filtering is recommended.
Photo ©Michael Kelly
Fully one-third to one half of the wines stored in my cellar are unfiltered and unrefined wines and must be carefully decanted/filtered before serving. This was the case recently with a 2010 Trespass Vineyard Escapade (50% Cabernet Sauvignon and 50% Cabernet Franc) stored for 12 years in the cellar. The previous pictures in the story were from this bottle. Once double filtered and double decanted, this wine was a delicious blend, providing fruit flavors and with smooth and silky tannins. You can see the clarity in the finished presentation. (see review of this wine & winery at: https://californiawinesandwineries.com/2025/10/08/2010-trespass-vineyard-escapade-continues-to-impress/ ).
There is more to be said about unfiltered and unrefined wines, but this should provide a quick and general overview.
Sláinte,
Michael Kelly
https://californiawinesandwineries.com
https://trespassvineyard.com