Tartaric Acid, Malic Acid and Potassium Sorbate for Homemade Wine and Cider: Doses
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Short answer: potassium sorbate is added to a finished, clear, sulfited wine at up to 268 mg per litre (equal to 200 mg/L of sorbic acid), which is about 6.2 g for a 23 L carboy. To raise acidity, 1 g per litre of tartaric acid (wine) or malic acid (cider) raises titratable acidity (TA) by about 1 g/L, expressed as that acid. Measure TA before and after, and add acid in small steps.
TL;DR: Sorbate stops yeast from restarting in the bottle after you sweeten; it does not kill an active fermentation, and it needs sulfite alongside it. Tartaric acid is the grape acid, malic acid is the apple acid: use each in its own drink. Targets: cider about 5-6 g/L TA as malic acid; white grape must 8-11 g/L; red grape must near 6 g/L.
How much potassium sorbate per litre of wine?
Purdue Extension gives 268 mg/L of potassium sorbate (equal to 200 mg/L of sorbic acid) as the proper maximum addition to suppress yeast refermentation in the bottle. Virginia Tech enology notes put typical use at 150-300 mg/L expressed as sorbic acid, with more needed for sweet, low-alcohol, low-sulfite or high-pH wines. To convert a sorbic acid target to potassium sorbate, multiply by 1.34.
Ingredient
Typical dose
23 L batch
When
Potassium sorbate
Up to 268 mg/L (= 200 mg/L sorbic acid)
≈ 6.2 g maximum
Finished, clear, sulfited wine, before back-sweetening
Tartaric acid (grape wine)
1 g/L raises TA by ≈ 1 g/L (as tartaric)
23 g per +1 g/L
Must or young wine, after a bench trial
Malic acid (cider, fruit wine)
1 g/L raises TA by ≈ 1 g/L (as malic)
23 g per +1 g/L
Juice or finished cider, after a bench trial
The batch figures are simple arithmetic (dose × litres). Sorbate has a taste threshold: Virginia Tech reports an average detection level around 135 mg/L of sorbic acid, so many winemakers stay at the dose their wine actually needs rather than defaulting to the maximum.
What acidity should you aim for?
Cider: about 5-6 g/L TA expressed as malic acid, pH 3.3-3.7; above pH 3.8 cider becomes less stable (University of Vermont cider workshop).
White grape must: about 8-11 g/L TA (Washington State University).
Red grape must: near 6 g/L, up to about 7 g/L for styles like Pinot Noir (Washington State University).
Finished crisp white: Purdue's Traminette protocol targets about 7.5 g/L after cold stabilization.
Watch the units. Wine test kits usually report TA "as tartaric acid"; cider makers often report it "as malic acid". The same sample reads lower as malic: multiply a tartaric-based result by 0.89 to express it as malic.
How do you add tartaric or malic acid, step by step?
Measure the current TA (titration kit) and, ideally, the pH.
Calculate: grams = (target TA − current TA) × litres. Example: 23 L of cider at 4 g/L aiming for 5.5 g/L needs about 1.5 × 23 = 34.5 g of malic acid.
Bench-trial first. Add the proportional amount to a 1 L sample (1.5 g in the example), taste it, and measure again.
Dissolve the acid in a little of the wine or cider, then stir it into the full batch.
Re-measure after a day. Add the rest in smaller steps if needed; it is easy to add acid and hard to remove it.
Which acid for which drink? Tartaric acid is the grape's own acid and the main contributor to a wine's tartness. Malic acid is the dominant acid in apples, so it is the natural choice for cider. One caution: malic acid is easily consumed by malolactic bacteria, so adding it to a wine that will go through malolactic fermentation can leave you with less acidity than planned. For more on tartaric acid itself, see our tartaric acid guide (sour candy, winemaking, effervescents).
Why does tartaric acid drop out of wine?
Tartaric acid combines with the grape's potassium to form potassium bitartrate (cream of tartar), the "wine diamonds" that crystallize when wine gets cold. Chilling a wine before bottling (cold stabilization) removes some of it on purpose, which also lowers TA slightly. Check TA again after cold stabilization before deciding on a final acid addition.
How do you add potassium sorbate correctly?
Finish fermentation. Sorbate prevents yeast from restarting in the bottle; it is not meant to stop a fermentation that is still active.
Clear and rack the wine off the sediment.
Adjust sulfite. Virginia Tech notes that a high free SO2 level (about 30 mg/L, depending on pH) is needed at bottling to stop lactic acid bacteria from growing in the presence of sorbate. Follow your kit or recipe for the metabisulfite amount.
Dissolve the sorbate in water first. Purdue explains that stirring the powder straight into a small volume of wine makes white flakes of insoluble sorbic acid form. A small amount of cool water avoids this.
Stir it into the full batch, then back-sweeten if you are making a sweet wine or cider.
When should you not use potassium sorbate?
After malolactic fermentation, or when it is likely. Lactic acid bacteria convert sorbic acid into a strong-smelling compound responsible for the defect Virginia Tech calls the "geranium tone".
Wines meant for long ageing. Virginia Tech lists sorbate as contraindicated for wines designed for long-term ageing.
Dry wines you will not sweeten. A fully fermented dry wine with no added sugar leaves nothing for yeast to ferment, so sorbate adds little.
Right after cold stabilization, mind the potassium. Purdue notes that sorbate also adds potassium (about 70 mg/L at the maximum dose), which can make a cold-stabilized wine slightly less stable.
