Why does my wine have a brown tint to it?
The reason your wine browns is because it is oxidizing. All wines oxidize, but well-made, well-protected, and well-balanced wines resist oxidation for many, many years, and exceptional wines can last for 50-100 years without doing so. To last that long, the wine has to have three characteristics:
1. It must be well-balanced for aging. This means the wine has more than normal tannin and acid. The wine will taste “rough” and harsh before being aged sufficiently. The average red wine, made well and balanced for taste, will require 1-4 years of aging to mature without oxidizing, all other things being equal. Good wines might go out to 10 years. Exceptional wines reach out for decades.
2. Exceptionally well-made. This means the wine is made from the very best grapes of a very good year, picked at the hour of perfect ripeness, and are crushed, pressed, fermented, bottled, and aged with perfection. The average wine may be well-made, but if it lacks the perfect fruit required for long age it will simply mature faster and then head downhill.
3. The wine must be well protected against oxidation. To resist oxidation, a wine must be sulfited when the grapes are being crushed, its sulfite level maintained according to the demands of its pH during fermentation and bulk aging, its exposure to air minimized or eliminated during fermentation, racking and aging, and it must be bottled using only the finest (not the cheapest) corks.
The biggest cause of early oxidation in homemade wines is the failure to use sulfites, or not using them properly.
The second biggest cause of early oxidation is improper handling of the wine during fermentation, rackings, aging, bottling, and storage.
Sulfites are derived from adding potassium metabisulfite (or one finely crushed and then dissolved Campden tablet per gallon of wine) to the must and wine. Some of the potassium metabisulfite binds with various components of the wine but about half is “free” or unbound sulfur in the form of sulfur dioxide gas. This gas is initially trapped in the liquid but slowly escapes into the atmosphere. It therefore must be renewed from time to time.
This sulfur dioxide gas serves many purposes in winemaking, from killing spoilage bacteria that come into the wine on the skins of the grapes to destroying the enzymes that cause fruit pulp to turn brown. Sulfur dioxide gas also drives oxygen out of the wine, and keeps it out by filling all the spaces between the wine’s molecules, the places oxygen usually saturate. By keeping the sulfur dioxide level “just right,” one protects the wine and keeps it from browning.
When racking and otherwise handling wine, the less air contact allowed the longer the wine will last without oxidizing. Since sulfur dioxide is a gas, splashing the wine drives it out of the wine and oxygen in the air immediately rushes in and takes its place, dooming the wine to early oxidation. In commercial wineries, the best wines are not racked until the receiving container (tank or carboy) is “sparged” with carbon dioxide -- filled with carbon dioxide from a tank, which “pushes” oxygen-containing air out of the container so no contact is made between oxygen and the incoming wine. At the same time, potassium metabisulfite is added to the receiving container to make up for any deficiency in sulfur dioxide measured in the wine. This procedure eliminates contact with oxygen and raises the sulfur dioxide level to where it should be even while some of the sulfur dioxide it lost due to agitation of the wine.