SO2 testing is an integral part of winemaking and SO2 management begins as soon as you add sulfite to the wine. Having the right amount of SO2 in your wine prevents enzymatic browning and guards against premature oxidation. SO2 preserves freshness and color and it helps stabilize a wine against microbial spoilage. If a wine does not contain the required amount of SO2, chances are it won't gracefully make it past one year in the bottle (depending on the wine pH).
Bound & Free SO2:
There are two forms of SO2 that we need to be aware of: Bound SO2 and Free SO2. When you make an SO2 addition, a portion of it binds with elements in the must or wine (acetaldehyde, yeast, bacteria, sugars, tannin, oxygen, etc.) and is referred to as bound. The rest of the addition remains unbound and is referred to as free. It is this latter portion we are interested in because only this free SO2 brings you the previously mentioned benefits/protection.
How Much SO2 Should I Use?:
The actual amount of SO2 needed is quite small, and is referred to as "ppm" (parts per million). The goal with SO2 testing and management is to use the least amount needed in order to maintain a beneficial saturation level (0.8 ppm molecular of SO2), while trying to avoid adding too much, which would flaw the wine by giving it a sulfite smell and/or taste. Interestingly, the amount of SO2 needed to protect a wine is dependent on its pH; at a higher wine pH the required ppm of SO2 is higher than it is at a lower wine pH. For example, a wine with a pH of 3.3 requires 27 ppm free SO2, while a wine with a pH of 3.7 needs 64 ppm free SO2 to remain protected.
Complete information on SO2 management, including the pH/SO2 amount needed chart can be found in our Red Winemaking Manual and our White Winemaking Manual.