The working
Two additions, and both are needed: sorbate stops surviving yeast from multiplying, sulfite keeps bacteria from turning the sorbate into a geranium off-smell. For a typical cider at pH 3.3:
Sorbate: target 200 mg/L sorbic acid; potassium sorbate is 74% sorbic, so 200 ÷ 0.74 × 23 ÷ 1000 = 6.2 g.
Sulfite: free SO2 target = 0.8 × (1 + 103.3 − 1.81) ≈ 25 mg/L; potassium metabisulfite is 57.6% SO2, so 25 × 23 ÷ 0.576 ÷ 1000 = 1.0 g, roughly two Campden tablets.
Confirm fermentation is finished with two identical gravity readings first, rack off the lees, dose both, then wait a day before any sugar goes in. Above pH 3.5 the sorbate target rises to 250 mg/L.
Back-Sweetening Calculator →Every figure above is reproducible in the linked calculator, which uses the same formula library as the rest of DistilCalc. Have a question of your own? Use the feedback link in the navigation and it may appear here.
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