The Right Way
Potassium metabisulfite and sodium metabisulfite, both are often just referred to as “sulfite”, can protect wine against oxidation and unwanted microorganisms. Like many topics in winemaking, determining the correct dosage of sulfite for a given wine or must can get complicated. The fastidious winemaker will first determine how much free sulfer dioxide (SO2) is already present. Next, because sulfite is more effective at low pH and less effective at high pH, he will measure the pH to determine how much free SO2 is needed. Finally, he will carefully measure this amount and add it to his wine or must.
The Easy Way
This can be overwhelming to home winemakers, and they have long used rules of thumb and premeasured doses to get a handle on sulfite. The practice of adding sulfite to 50 ppm initially and then at every other racking can be good enough. This eliminates the task of measuring free SO2 and determining the correct dosage of SO2. A quarter teaspoon of potassium metabisulfite powder added to 5 gallons is about right for this procedure, but measuring out the small quantities required for a 1-gallon batch is tedious and requires an accurate gram scale.
Campden tablets are premeasured doses that solve this problem. For one gallon batches, the rule becomes one campden tablet initially and then one at every other racking. Campden tablets have always frustrated me, though, because they never completely dissolve. So I dissolve a quarter teaspoon of sulfite powder into five teaspoons of warm water. I have no trouble getting the powdered form to dissolve and whenever I need sulfite for one gallon, I measure out one teaspoon of this sulfite solution. Obviously this isn’t precise, it’s sufficient and it takes some of the tedium out.
Sanitizing with Sulfite
You can sanitize your winemaking equipment with sulfite, but it takes a different approach. To be effecitve, the sulfite must have a higher concentration and be combined with acid. Have a look at this article for details on making a DIY Sanitizer from sulfite and citric acid.
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