Why should I wait 24 hours after adding sulfites before pitching yeast?

Sulfites stun and kill wild microflora in raw pressed juice. Waiting 24 hours in a covered bucket allows volatile sulfur gas to dissipate so your commercial cultured wine yeast isn't inhibited when pitched.

Does sulfite kill active fermentation to back-sweeten cider?

No! Sulfite alone will NOT kill an active yeast colony. To safely stabilize sweet cider without restarting fermentation, you must add Potassium Sorbate (to prevent yeast reproduction) in conjunction with Potassium Metabisulfite.

How do I make a 10% KMS stock solution?

Dissolve 10 grams of potassium metabisulfite powder in distilled water to make exactly 100 mL of total solution. Store in an airtight dropper bottle. 1 mL of 10% stock solution delivers 15 ppm SO2 into 1 gallon of wine.

Free Cider & Wine Sulfite (SO2) Addition Calculator

🍷 Batch Volume & Chemistry

Batch Volume

Volume Unit

Wine / Cider pH Level Critical: Dictates molecular SO2

Beverage Style Target

Current Free SO2 (PPM) Residual from prior additions

Addition Source

📊 Recommended Sulfite Addition

KMS Powder Addition 1.31 g Potassium Metabisulfite

Campden Tablet Count 3.0 Tablets Crushed into small warm liquid

Target Free SO2 Required: 40.0 PPM (mg/L)

Net Free SO2 to Add: +40.0 PPM

10% Stock Solution Dose: 13.1 mL

Microbial Protection Level: Full Antibacterial & Anti-Oxidant

✅ pH 3.4 Sweet Spot: Moderate sulfite required (40 ppm) for robust 0.8 ppm molecular protection.

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The Chemistry of Molecular SO2 vs pH

In cider and winemaking, sulfur dioxide (SO2) exists in three equilibrium forms: bound SO2, bisulfite ions (( ext{HSO}_3^-)), and uncharged Molecular SO2 (( ext{SO}_2)). Only the molecular form can penetrate bacterial and wild yeast cell membranes to inhibit spoilage microbes.

Why High pH Demands Massive Sulfite Additions

The percentage of free SO2 in the active molecular form is governed by the Henderson-Hasselbalch equation and is intensely pH dependent:

At pH 3.0: It takes only 14 ppm Free SO2 to yield 0.8 ppm molecular protection.
At pH 3.4: It takes 40 ppm Free SO2.
At pH 3.8: It takes an enormous 98 ppm Free SO2!

If your cider or wine has a high pH (e.g. 3.8 to 4.0), adding standard "1 tablet per gallon" fails to protect the beverage, inviting spoilage from Acetobacter (vinegar bacteria) and Brettanomyces!

KMS Powder vs Campden Tablets

Potassium Metabisulfite (KMS) powder yields approximately 57.6% free sulfur dioxide by weight. One standard Campden tablet contains 0.44 grams of active KMS, delivering roughly 67 ppm of SO2 into 1 gallon of liquid.