About The Use Of Sulfurs in Wine Making
Sulfur Dioxide
This most versatile of chemicals comes as close as anything to being recommended for all wines. It inhibits molds, bacteria (including the malo-lactic strains) and yeast cells, but with the latter it is selective; most of the more desirable strains for wine fermentation are more tolerant of sulfites than other strains. It is an effective anti-oxidant, for which there is currently no suitable substitute. Sulfur dioxide is a gas that is released into the wine or juice when potassium meta bisulfite, campden tablets, or other sulfite compound is added. It is also the irritating gas produced when you burn a sulfur wick or pastille. It will not act as a magical additive to prevent a wine from spoiling, nor will it restore one which has been abused, but it will, when properly used, aid in preserving an otherwise sound wine.
Some people show allergic reactions to sulfur dioxide (SO2), but almost always as asthmatic reactions to high levels of atmospheric SO2 rather than in aqueous solution as it occurs in wine. It has been used since the middle ages in most wines produced either by burning elemental sulfur or sulfur impregnated paper or the like. It is also produced in normal fermentations and may occur even when no external sulfur has been used. All of us produce SO2 in our normal metabolism. There have been attempts to demonize SO2 for reasons a cynic would describe as other than science. A few people are truly allergic to this material. About one in every four hundred people will have an overt reaction to SO2 in wine or other foods. For most it is a mild skin flush or headache. There are many other unavoidable contacts with SO2 than one is likely to get from wine.
The Use Of Sulfur Dioxide
It is often used before fermentation by adding 50 to 80 parts per million (ppm) [= mg per liter] of sulfites a few hours before adding yeast. The wild strains are temporarily inhibited and the better wine yeasts, which are more SO2 tolerant, will dominate the fermentation. This is common practice with whites but not as much with reds where a quick startup is highly desirable. Some wineries use no SO2 prior to fermentation. Unless there was a high concentration of spoilage organisms it is highly likely that the final quality of the wine will not suffer.
If you do not use a commercial wine yeast culture and trust to fermentation by the wild yeasts, the better strains will recover more quickly and dominate. Typical dosage of 30 to 60 ppm of sulfur dioxide is used with this practice.
The addition of SO2 at each racking after fermentation has ended and at bottling will do much to retain the fresh flavor of white wine. The addition of 25 to 50 ppm at each transfer would be typical. Use less at lower pH levels and more with high pH wines or when there is residual sugar. Red wines generally need less SO2 than whites because of the anti-oxidative properties of tannins.
It is very poor practice to add SO2 to wines while they are still fermenting. The SO2 quickly becomes tied up in a bound form which will not help in inhibiting microbial growth or oxidation; in the meantime a great deal of acetaldehyde will be produced which may adversely affect wine
