The 10% Solution
A much better way to get your SO2 is from a 10% solution of potassium metabisulphite in water. For instance, you could add water to 1 pound of potassium metabisulphite to make a total volume of 1 imperial gallon. Or, if you prefer metric, add enough water to 100 grams of potassium metabisulphite to make up a total volume of 1.00 litres. Fresh 10% solution is 5.7% SO2.
A commonly used unit of measurement for SO2 in must or wine is “parts per million” or “ppm”. 1 ppm is the same as 1 milligram per litre. I will use ppm.
For example, if you add 2.4 millilitres of 10% potassium metabisulphite solution to 1.0 imperial gallons of wine you will be adding 30 ppm SO2. If you have a 19.2 litre carboy to which you wish to add 20 ppm SO2, multiply 0.35 by 19.2 to get an SO2 addition of 6.7 mL of 10% solution. Consider making up your own spreadsheet giving SO2 additions for your own sizes of barrels and carboys.
For SO2 Additions Using a 6% SO2 Solution
1/3 of the so2 will combine instantly in any wine that is not sterile filtered.
Number of Parts Required Multiplied by 3 then divided by 2 (This will adjust for the 1/3 which will combine.)
Divide this number by 1000 then multiply by 3.785.
This will give you the addition in Liters for a single barrel.
If you were adding 20 parts to a barrel
20 * 3 / 2 / 1000 * 3.785 = 0.11355 or 113 ML per barrel to increase the SO2 by 20 Parts
To make this addition to a tank you would multiply the 0.11355 by the number of gallons then divide by 60
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