I'm confused about bound SO2 and free SO2. Am reading: it was "determined that for white table wines it was necessary to have 0.8 mg/l of this[molecular form of free SO2] to control wine spoilage organisms." Obtaining 0.8 mg/L of free SO2 is dependent on pH. At pH 3.2 you need 23 ppm of free SO2. At pH 4.00 you need 141 ppm of free SO2. My question is this: If you are using a solution of KMBS do you calculate the amount you need based upon the free SO2 and pH? For example, my wine has a pH of 3.60. To obtain 0.8 mg/L I need 57 ppm of free SO2. I use the formula v=(V*P)/(X*10*.576), where V= volume of wine in liters, P = desired ppm of SO2, X= strength of KMBS solution in % and v = volume of KMBS to add in mls. If I have a 5% solution of KMBS and 18.925 L (five gallons) of wine and want 57 ppm of free SO2 I will add 37.5 mls of this solution. Is this right or am I confusing the 0.8 mg/L of the molecular form of free SO2 with something completely different? Should I just forget the pH and just add KMBS to get 50 ppm and call it good? This might work fine for wine with a pH of 3.50. But if the pH is 3.90, is this amount way off target?