By Magnus von Kageneck, cellar master · Updated: August 2026
Of all the adjustments in winemaking, acidity is the one where the most damage is done — usually for one single reason: people taste instead of measuring. The tongue is a lousy acid meter. Sugar masks acidity almost completely; the same must tastes “pleasant” before fermentation and, once the sugar has fermented out, suddenly sits sharp and green in the glass.
Measure first — five minutes that save the vintage
An acidometer is nothing more than a small titration cylinder: pour in the must sample, add the blue titration solution drop by drop until the colour changes, read the scale — done. The result is the total acidity in grams per litre. As rules of thumb:
- White wine: pleasant at 6–8 g/l
- Red wine: pleasant at 5–7 g/l (the tannins amplify the impression of acidity)
- Fruit wines: depending on the fruit, 6–9 g/l — currants like to start at 25 g/l and MUST be diluted or deacidified
Too sour? Deacidify with calcium carbonate
Precipitated chalk (calcium carbonate) binds the acid as a salt that settles out. The calculation is simple: 0.67 g of chalk per litre lowers the acidity by 1 g/l. Two rules go with it: first, never take away more than 2–3 g/l in one go — otherwise the wine tastes soapy and hollow, and the calcium later precipitates in the bottle. Better to do part of it before fermentation and measure again after the first racking. Second: the chalk foams vigorously as you stir it in (that is the carbon dioxide) — use a large vessel. With high-acid fruits such as currants, diluting with water and sugar is the better first step; only the remainder gets deacidified.
Too flat? Acidify with lactic acid
The opposite case comes up more often than you would think with overripe fruit, pears and shop-bought juice: below 5 g/l a wine seems broad and tired and spoils more easily, because bacteria love flat musts too. Lactic acid 80% is the remedy of choice here — it tastes softer than citric acid and is microbiologically stable (bacteria can break citric acid down again). Dosage: 1 ml of lactic acid 80% per litre raises the acidity by about 1 g/l. Work in steps and measure in between.
The order of work in the cellar
- Measure before fermentation and bring it roughly into the target range (±1 g/l is enough)
- Measure again after fermentation and the first racking — fermentation itself changes the acidity
- Fine-tune only on the almost finished, clarified wine — small steps, days of patience in between
My grandfather claimed all his life that he could taste a tenth of a gram. Even so, the scale on his acidometer was as worn as the handle of a tavern door. You can know and measure — the one does not rule out the other.
Related in the shop: Measuring & Testing and Making Wine