It depends on your wine’s pH. In a red, aim for 0.5 mg/L of molecular SO₂; in a white or rosé, 0.8. For
example, a red at pH 3.6 needs about 31 ppm of free SO₂.
By the Cellari team
Written with AI assistance
Published
What sulfite does for wine
Sulfite, or SO₂ (sulfur dioxide), does two jobs: it protects wine from oxidation, and it holds back unwanted bacteria and yeasts, such as acetic acid bacteria. Homemade wine without SO₂ tends to brown, lose its aroma and turn to vinegar within months.
Much of the SO₂ you add binds to compounds in the wine and stops protecting it. The part that stays free is what you measure and aim for, and only a small share of it is in the most active, molecular form.
Bound
Free
Bound SO₂
Tied up by acetaldehyde, sugars and other compounds. Barely protects.
Free SO₂
The part that protects. It is what you measure and aim for.
Molecular SO₂
A few percent of the free SO₂, or less at high pH. It is the part that stops microbes.
The proportions here are for illustration only. Total SO₂ = bound + free.
Opens full screen. Turn your phone sideways for the best view.
Animation: what happens to wine when you add sulfite, in six steps (about two minutes).
How much you need: it all depends on pH
The higher the pH, the smaller the share of free SO₂ that is in the molecular form. So a high-pH wine needs much more free SO₂ for the same protection. The usual target is 0.5 mg/L molecular in reds and 0.8 in whites and rosés.
Free SO₂ = Molecular SO₂ × (1 + 10pH − 1.81)
In words: multiply the molecular target by a factor that depends on pH, and grows fast as pH rises. All values in
mg/L (ppm).
Red wine (0.5 molecular)White and rosé (0.8 molecular)
Free SO₂ needed (ppm) by pH. The shaded band is the pH range common in reds from warm regions. Formula: Margalit, pKa 1.81 at 20 °C (Zoecklein et al.; AWRI rounds it to 1.8).
pH
Red wine: free SO₂ (ppm)
White and rosé: free SO₂ (ppm)
3.0
8
13
3.1
10
16
3.2
13
20
3.3
16
26
3.4
20
32
3.5
25
40
3.6
31
50
3.7
39
63
3.8
49
79
3.9
62
99
4.0
78
125
These are the free SO₂ levels the wine should hold, not amounts to add. To know how much to add, subtract what is already in the wine.
In warm regions, wine pH tends to run high
A hot vintage gives grapes with low acidity and high pH, and reds from warm regions often reach pH 3.6 to 3.9. At pH 3.9 a white needs about 100 ppm free to reach 0.8 molecular, an amount you can smell and taste.
In that case the answer is not more sulfite. First lower the pH with tartaric acid, after a bench trial on a small sample, then measure and work it out again. The range here is a rough guide, so measure your own wine.
Worked example: a 20-liter demijohn
Cabernet Sauvignon
After malolactic fermentation
Volume 20 L
pH 3.7
Free SO₂ measured: 10 ppm
The target for a red: 0.5 × (1 + 103.7 − 1.81) ≈ 39 ppm free.
How much to add: 39 − 10 = 29 ppm.
How much powder: (29 × 20) ÷ (1000 × 0.576) ≈ 1.01 g of potassium metabisulfite. The 0.576 is the share of SO₂ in the powder (57.6%).
Add about one gram
The calculator shows 1.0 g, because it rounds to a tenth of a gram. In Campden tablets that is just under two and a half, since a standard tablet adds about 65 ppm to 3.8 L (one US gallon). Tablet weights vary between brands, so weighed powder is more accurate.
Some of the SO₂ you add binds right away, so free SO₂ will come out a little under the target. Measure again after a few days.
Work out the amount for your wine. Enter your current free SO₂, the target from the table and the volume.
These are the addition points from harvest to bottle, with the amounts home winemaking books recommend. After fermentation ends, it is better to measure and top up to the target from the table at every point.
Crush
Protects the must until fermentation starts. More if there are damaged or rotten grapes
30–50 ppm
Fermentation
None added. The CO₂ from fermentation protects the wine
0
End of fermentation / end of MLF
Bring it to the target for its pH
Per the table
Aging
Measure monthly. Free SO₂ usually drops 10–15 ppm a month; top up to what you measure
Per measurement
Bottling
A last check, a top-up to target, and about 10 ppm more for the oxygen picked up at bottling
Target + ~10 ppm
Keep an eye on total SO₂ too: repeated additions add up. In the EU the limits for commercial dry wine are 150 ppm for red and 200 ppm for white, and homemade wine has no need to come close to them.
If you want a malolactic fermentation, don’t add SO₂ at the end of the alcoholic fermentation. Wait until the malolactic is done, because SO₂ holds back the bacteria that carry it out. If you are not doing a malolactic, add right at the end of fermentation.
How to add it, step by step
Measure. pH with a calibrated pH meter, and free SO₂ with a home titration kit or at a lab. Simple titration kits are less accurate in red wine, because the color change is hard to see.
Calculate. Find the target in the table, and enter it in the calculator together with your reading and the volume.
Weigh. On a digital scale that reads to 0.01 g. A measuring spoon is not accurate enough for amounts around one gram.
Dissolve the powder in a little water or wine, until there are no grains left.
Add and stir. Gently, or while racking, so the SO₂ spreads through the whole volume.
Measure again after a few days, and correct if needed.
Metabisulfite powder releases sharp SO₂ gas. Don’t breathe it in, and work somewhere ventilated, especially if you have asthma. People sensitive to sulfites, asthmatics above all, may also react to the wine itself.
Common mistakes
“A teaspoon per demijohn”
With no measuring and no math, the wine gets either too little or too much.
Starting from zero
Forgetting the SO₂ already in the wine, and adding more than needed.
Ignoring pH
30 ppm protects well at pH 3.3, and too little at pH 3.8.
Swapping products
Potassium metabisulfite releases 57.6% of its weight as SO₂, sodium metabisulfite about 67%. You can change the share in the calculator.
Sulfite before the malolactic
The malolactic does not start, or sticks halfway.
Trusting your nose
A burnt-match smell means you overdid it, but no smell does not mean there is enough.
Frequently asked questions
What is ppm?
Parts per million. In wine it is almost exactly milligrams per liter, so 30 ppm is 30 mg of SO₂ in every liter.
Can I make wine with no sulfite at all?
You can, but the wine is far more exposed to oxidation and spoilage. It takes thorough cleaning at every step, vessels filled to the neck with no air space, and drinking it young.
What is the difference between Campden tablets and powder?
Both are metabisulfite. Tablets are handy for small batches, but their weight varies and is not always printed. With weighed powder you hit the target exactly.
How long after an addition should I measure again?
After a few days, once the SO₂ has spread and bound. If free SO₂ has dropped below the target, top up using the calculator.
Why is the target higher for white wine?
Whites and rosés lack the tannins and pigments that help a red stand up to oxidation, so they rely more on SO₂.
Short glossary
SO₂, SO2
Sulfur dioxide. Called “sulfite” or “sulfites” in everyday speech.
Potassium metabisulfite
The usual powder for adding SO₂ (KMBS, or K-meta).
ppm
Parts per million. In wine, about mg per liter.
Free SO₂
The SO₂ not bound to compounds in the wine. The part you measure.
Molecular SO₂
The active part of the free SO₂, worked out from free SO₂ and pH.
