Acidity in wine
Two acids determine almost everything that reaches the glass as freshness: tartaric acid and malic acid. Both are already present in the green berry, but from colour change onwards they behave differently — tartaric acid is largely preserved, while the berry respires the malic acid, and all the faster the warmer the nights in particular are.
Acidity is therefore less a measured value than a clock: it starts running in midsummer, it runs at a different speed on every plot, and every year it poses the same question about the right day to pick.
Why warmth costs acidity
Until colour change the berry works like a store and builds up acid, above all malic acid, which reaches its maximum around véraison. After that, metabolism reverses: the berry breaks down its chlorophyll, has less sugar available to respire and increasingly covers its energy needs from the stored malic acid. Tartaric acid is largely unaffected by this and is merely diluted as the berry grows. The decline measured in September is therefore almost entirely malic acid — and because respiration runs faster in warmth, warm nights above all take their toll. This is the sober reason why hot vintages bring not only more alcohol but also less tension; that in the process sugar ripeness and phenolic ripeness drift apart is the same movement seen from the other side.
Why acidity and pH do not say the same thing
Between the two stands an element that cannot be tasted: potassium. The vine takes it up into the berry and releases hydrogen ions in exchange, and the more potassium arrives, the higher the pH. Part of it additionally binds tartaric acid to form tartrate, which precipitates during fermentation and thus removes acid from the wine without lowering the pH. That is why there are wines that are analytically high in acid and still have a high pH. In practice this means: acidity tells you above all how fresh a wine seems, the pH above all how well protected it is — the usual ranges for both values appear on every data sheet.
The day on which it is decided
The two clocks run against each other. While acidity falls, the tannins are often not yet ready; whoever picks early keeps tension and accepts unfinished tannins, whoever waits gets ripe tannins and has to find freshness elsewhere. A day on which both are at their best at the same time is rare, and on our sixteen plots it does not fall on the same date. We therefore pick them separately and decide for each which side of this compromise it should carry.
After that, what remains in the cellar is above all a deliberate decision about acidity: whether and when malolactic fermentation converts the sharp malic acid into the milder lactic acid. Everything else was settled on the day of picking.
What of it reaches the bottle
A low pH slows reactions with oxygen, keeps the sulphur more effective and the colour more stable. That is the factual core behind the saying that high-acid wines keep longer; it is only half true, however, because acidity alone does not carry a wine. It has to stand up to alcohol, extract and tannin, otherwise after a few years an edge remains with nothing left attached to it. And what one takes for acidity when drinking is seldom the measured value: residual sweetness, alcohol and a soft texture mask it, a lean wine lets it stand out.
Whether an acidity has carried the wine only becomes apparent late. Because at LaSuite aux Conseillans we only release a wine once it is ready to drink, we watch every vintage for years to see what has become of the decision made on the day of picking. You learn more about the summer behind it that way than from any measurement in September.