Here's the info from the product brochure:
Oenosteryl Effervescent Tablets™ are a blend of potassium metabisulfite and
potassium bicarbonate. They are packaged in 2 g (48/box) and 5 g (48/box) dosage
levels. The effervescent action of the bicarbonate provides mixing in barrels or
small tanks while reducing time and labor needed for stirring. The easy-to-use
tablet form helps prevent overdose problems associated with other forms of SO2
additions. Sealed strip packages keep unused tablets fresh for optimal potency.
Cellar workers and others in the immediate area require no safety equipment
because the tablets are solid and odorless. The potassium bicarbonate fraction
in these tablets has little or no effect on pH.