Sediment In Wine

Some red wines throw sediment when the age. Should you be straining sediment in wine?
Browse our current wine selections

The particles in wine actually differ depending on the type of wine you're working with. Though red and white wines are the result of the fermentation of sugar in a wine grape, the processes only parallel each other to a certain point. As well, a traditional Rose from let's say the south of France is a blend of red and white wine, a Rose like "white" Zinfandel is actually a red grape vinted like a white wine.  Below are the basic processes of making both red and white wine.

Red Wines
The juice of most red grapes is white. Only by coming in contact with the skins can it change color. Otherwise it will come out like a white wine. In making red wine, grapes are passed through a "crusher," a machine that de-stems the grapes and cracks their skins to allow the pulp to come in contact with the yeast. At this stage, the combination of skins, seeds, pulp and juice is called "must."  The must is then placed in a temperature-controlled fermenting tank where either a commercial yeast is added or the natural yeast is allowed to start fermentation. The pulp of the grape must stay in contact with the skins in order for it to pick up color.

When fermentation is completed the liquid is now technically wine. The mass of skins and seeds, called "lees," settles to the bottom of the fermenter. The clear wine above the lees is then drawn from the fermenting tank until all of the clear wine has been removed and only the lees and pulp remain at the bottom. This is called racking and is how most red wines are clarified before bottling. The wine may be further clarified by passing it through a filter or by use of a fining agent such as beaten egg whites. Egg whites, being positively charged, attract the free-floating sediment, which is negatively charged, and together fall to the bottom of the tank or barrel. The wine must still be racked to a clean barrel or tank in order to keep it clear. This is the gentlest technique with regard to not removing any of the flavors of the wine, just the solid particles in wine, which can taste bitter and astringent.

If the intent is to process the wine as little as possible, regardless of any sediment that may occur in the bottle, it won't be filtered or fined. It is then aged, either in stainless steel tanks or small or large oak barrels. Wines such as these are made to age over many years, even decades. Within even 4 or 5 years of the vintage the tiny pieces of pulp that were pulverized during fermentation begin to attract each other to form sediment in the bottle. Unlike tartrate crystals (explained below), however, sediment tastes awful. You should strain wine sediment by decanting or very careful pouring.

At this stage there are hundreds, maybe even thousands of choices for the winemaker. What kind of barrels do we age in?  How old should they be?  For how long?  Most red wines go through another, different type of fermentation called malolactic. Instead of yeast interacting with sugar and creating alcohol and carbon dioxide (CO2) by-products,  a bacterial culture attacks the harsh malic acid in the wine (the same acid as on the inside of green apple skin) and converts it to lactic acid (the same as lactose in milk). This lowers the wine's overall acidity and makes it a little smoother and easier to taste. Malolactic (ML) can occur normally or can be induced with natural cultures.

When ready (a matter of months or years depending on the winemaker's desire), the wine is bottled and aged further before release. Aging in the bottle develops what is called "bottle bouquet," the final melding of the grape flavors mixed with the processing techniques.

White Wines
White wines are made in a similar fashion except, in most cases, without the skin contact. After crushing, the grapes are pressed quickly to avoid contact with the skins. The tannic acid in all grape skins (red or white) adds astringency to the wine. This astringency in reds helps the aging potential. In whites this astringency may overpower the delicate flavors so very little, if any, astringency is wanted. Therefore, the pre-fermented juice is separated from the skins and seeds in a gentle centrifuge. The remaining liquid is placed in a fermenting tank or barrel, yeast is added, and fermentation begins.

Unlike red wines, white wines are fermented at very cool temperatures, sometimes between 50-60 degrees F. This is done to preserve the fresh fruit qualities and delicacy of white wines. Following fermentation, the new wine is clarified, then aged in stainless steel or oak barrels before bottling. Chardonnay and Sauvignon Blanc are occasionally aged for an additional time in small oak barrels to add extra nuance and complexity.

Fermentation of white wines is much longer than reds, usually requiring several weeks versus 7-10 days for reds. During each stage of winemaking, great care is taken to prevent the wine from coming in contact with air that can "oxidize" it and cause browning. Oxidation in wine is best understood by comparing it to the oxidation that takes place when one cuts an apple. It turns brown within minutes, as do potatoes when peeled.

Two additional precautions usually are taken with white wines, but seldom with reds. These precautions are called "heat stable," and "cold stable." Heat stability is nothing more than making certain, before bottling, that no yeast cells remain in the wine. If the smallest amount of yeast were present and the wine subjected to even moderate heat, it could begin to ferment even the smallest amount of sugar. It has been known to happen with sugar levels as low as .5%. Yeast cells are destroyed by heating the wine to 120 degrees F for 30 minutes, or passing it through a special membrane filter capable of straining out even microscopic yeast cells, or waiting until fermentation has completely stopped and all the yeast cells have expired. Most wineries choose the latter method since the heat and filtration process can remove certain nuances, which would take away from the finished wine.

Cold stabilization is often done in white wines to remove excess potassium bitartrate, a natural substance found in grapes also known  as "cream of tartar."  White grapes contain fairly large amounts of potassium bitartrate. If most of it is not removed, the wine will form crystals when placed in the refrigerator. These tartrate crystals will either cling to the underside of the cork or fall to the bottom of the bottle where they appear to be ground glass to the uneducated eye. To remove excess potassium bitartrate before bottling, the wine is placed in a stainless steel tank and its temperature dropped to about 30 degrees F. The wine is held at that temperature for a period of approximately 2-3 weeks. Excess potassium bitartrate will then crystallize and drop to the bottom of the tank where it is removed either by filtration or by pumping the wine out of the tank until the hose is just above the bottom where the crystals have formed. The "cold stabilized" wine is then bottled. Some wineries prefer to skip this step, feeling that the process detracts from the wine's flavor and nuance. Having the tartaric crystal particles in the wine means nothing more than it was not cold treated and, thus, may be of higher quality.