When acidifying makes sense
A high-pH must, typical of very ripe harvests or warm regions, brings three problems. First, SO₂ works less: the higher the pH, the smaller the molecular fraction (we covered it in the molecular SO₂ guide). Second, red wine color is less stable. Third, the wine is more exposed to microbial faults.
There is no universal correct pH. As a rough guide, many wineries tend to aim for 3.3–3.6 in reds and 3.1–3.4 in whites, and adjust to their style. One detail to keep in mind: every g/L of tartaric acid you add also raises total acidity by roughly 1 g/L, expressed as tartaric acid.
How much each gram lowers pH
ΔpH = − (g/L of tartaric × 0.15) ÷ buffer
The buffer measures how strongly the must resists a pH change: musts rich in polyphenols and potassium resist more, and it takes more acid to move the same tenth. The laboratory estimates it from the terroir's tannin potential: buffer = 1 + (tannin ÷ 10) × 0.5, which runs from about 1.0 in a light white to about 1.4 in a very structured red (Agrelo gives 1.375).
Important: 0.15 per g/L is the laboratory's model. In a real wine the change varies with potassium, color compounds and the pH itself, so use the formula to estimate and a bench trial to confirm.
How to calculate the dose
Rearrange the formula: dose (g/L) = ΔpH × buffer ÷ 0.15, and multiply by the tank's liters for the total grams.
An example with data from the laboratory's catalog: an Agrelo must at pH 3.75 and TA of 5.2 g/L. To bring it down to 3.60 (a ΔpH of 0.15) you need 0.15 × 1.375 ÷ 0.15 = 1.375 g/L, which is 1,375 g in a 1,000 L tank.
That drop has a direct effect on SO₂: to reach 0.5 mg/L of molecular SO₂, the free SO₂ you need falls from 44.0 to 31.3 mg/L (and for 0.8 mg/L, from 70.5 to 50.1 mg/L).
Table: grams per liter by how much you want to lower it
| Lower pH by | Buffer 1.0 | Buffer 1.375 (Agrelo) |
|---|---|---|
| −0.05 | 0.33 | 0.46 |
| −0.10 | 0.67 | 0.92 |
| −0.15 | 1.00 | 1.38 |
| −0.20 | 1.33 | 1.83 |
| −0.30 | 2.00 | 2.75 |
Values in g/L of tartaric acid, calculated with the laboratory's own formula.
How to do it in practice
- Measure pH and total acidity (TA) before touching anything.
- Run a bench trial. Dissolve a known amount of acid in a small volume of must or wine, mix it, wait and measure the pH again. That shows how much your wine really drops.
- Scale the dose using that real response and multiply by the tank's liters.
- Dissolve the acid in a little must or wine before adding it, and homogenize the tank.
- Adjust in small steps, measuring in between, instead of one big dose.
Before or after fermentation: many wineries prefer to adjust the must or during fermentation, because the acid integrates better. In a finished wine, adding tartaric acid can raise the risk of cold tartrate precipitation. Also check the regulations in your country and region: the limits and conditions for acidification vary.
If you overshoot
Calcium carbonate does the opposite: it raises pH. The laboratory models it at 0.125 per g/L, divided by the same buffer. In a real winery it deserves even more careful dosing, because the correction is hard to reverse. That is why the golden rule is to acidify a little at a time.
Why this is practiced in LagarLab: the dose is calculated on the tank's liters, not on raw grams: 150 g in 1,000 L does not give the same result as 150 g in 100 L. Each terroir has its own buffer, so the same amount moves pH differently in Chablis than in Agrelo.
What if you tried it on your own tank?
In LagarLab you add tartaric acid to a tank, see the new pH and how molecular SO₂ changes, without risking a real batch.
Vinify for free: Agrelo (red)No sign-up. Prefer a white? Try Chablis.
Frequently Asked Questions
How much tartaric acid should I add to lower pH by 0.1?
According to the laboratory's model, about 0.67 g/L in a must with buffer 1.0 and about 0.92 g/L with buffer 1.375. In a real wine, confirm it with a bench trial.
Does adding tartaric acid raise total acidity?
Yes. Every g/L adds roughly 1 g/L of total acidity, expressed as tartaric acid, in addition to lowering the pH.
Why does the same amount lower pH less in a highly structured red?
Because of the buffer. Musts rich in polyphenols and potassium resist pH change more, so it takes more acid to move the same tenth.
Is it better to acidify before or after fermentation?
Many wineries prefer to adjust the must or during fermentation, because it integrates better. In a finished wine it can raise the risk of tartrate precipitation. It depends on the style and on each winery's control.
What if I lowered the pH too much?
Calcium carbonate raises pH. The laboratory models it at 0.125 per g/L divided by the buffer, but in a real winery the correction is hard to reverse, so it pays to always acidify a little at a time.
What does tartaric acid do in wine?
It's the grape's main acid and the one that most defines a wine's pH. Winemakers add it to correct musts that lack acidity, which is common in warm climates: it lowers pH, adds freshness and makes the wine more stable against bacteria. It also makes SO₂ work better: at pH 3.75 you need about 44 mg/L of free SO₂ to reach 0.5 mg/L molecular SO₂, while at pH 3.60 about 31 mg/L is enough.