Troubleshooting for Red Wine

Brown color - is a sign of oxidation and is usually accompanied by a loss of fruitiness and varietal character. This usually results from excessive oxygen exposure and/or inadequate free SO₂ levels. Wine made from moldy fruit will often contain oxidative enzymes that are difficult to control with SO₂. To avoid oxidative browning, use clean, sound fruit, maintain adequate free SO₂ levels, keep containers of wine full to reduce headspace as much as possible, and use air locks (fermentation locks) and keep them full of water.

Vinegar odor - The smell of vinegar or finger nail polish in association with a wine is a sign of spoilage by acetic acid bacteria. These bacteria can be controlled by the avoidance of excessive oxygen exposure and the adequate use of SO₂. This type of spoilage can also be caused by lactic acid bacteria and yeast. The use of clean fruit and the addition of SO₂ to the must prior to the fermentation helps to reduce this problem. Keep containers of wine full to reduce headspace as much as possible and use air locks (fermentation locks) and keep them full of water.

Rotten egg odor - is caused by hydrogen sulfide, produced by yeast. This is usually a sign of fermentation stress for the yeast during the primary fermentation, caused by a lack of must nutrients or a temperature shock to the fermenting must. This may also occur if elemental sulfur is present in the must. Some strains of yeast are more prone to excessive hydrogen sulfide production than others. Hydrogen sulfide and its related compounds tend to mask the fruitiness in wine. The problem can often be avoided by using yeast nutrients, using properly prepared commercial wine yeast, and keeping proper temperature control of the fermentation.

Crystalline deposit - usually is a deposit of potassium bitartrate crystals. These can be removed by chilling the wine to around 32°F for several weeks.