Acidity

What acidity is in wine

Wine acidity is measured two ways. The first is a chemical measurement of total titratable acidity, usually expressed in grams per litre of tartaric acid equivalent. The second is pH, a logarithmic scale from 0 to 14 that measures how strong those acids actually feel. A wine can have high total acidity but a high pH if potassium is also high, which is why UK winemakers track both numbers throughout the season.

The main acids in grapes are tartaric (the most stable and the one that precipitates as tartrate crystals in cold tanks), malic (the sharp green-apple acid that is converted during malolactic fermentation) and citric (small amounts, but it is a key component in Bacchus and other varieties). Lactic and acetic acids can appear later, produced by bacteria or yeasts.

Why acidity matters

Acidity does three jobs at once. It gives the wine freshness on the palate, making it feel clean and vibrant rather than flabby. It carries flavour, because aroma compounds are perceived more sharply in an acidic environment. And it acts as a natural preservative, slowing oxidation and inhibiting spoilage microbes. A wine with too little acidity feels dull, heavy and short. A wine with too much feels aggressive, green and hard.

Acidity in the UK climate

England, Wales and parts of Scotland sit at the northern edge of viable viticulture. Long daylight hours in summer drive sugar accumulation, but cool nights preserve the natural acids in the grape. Most UK harvests come in with total acidity of 9 to 12 grams per litre, considerably higher than the 6 to 7 grams common in southern Spain or southern Australia. The skill of the UK winemaker is to retain enough of that acidity to make balanced wines while still allowing the fruit to ripen fully.

Sparkling wine producers deliberately pick early, when total acidity is high and pH is low, because that crispness becomes the backbone of the finished bottle after the second fermentation. Still wine producers aiming for leaner styles such as Bacchus, Pinot Gris or Riesling will also harvest early, while those making richer Chardonnays and Pinot Noirs may wait a few extra days for softer acids and riper phenolics.

How UK winemakers manage acidity

Three tools are used constantly. The first is picking date. A vineyard in Sussex may take a single block of Chardonnay across a week, sampling every other day, watching the balance of sugar, acid and flavour rather than just sugar alone. The second is malolactic conversion, the bacterial fermentation that turns sharp malic acid into softer lactic acid. Most red wines and many Chardonnays go through full malolactic, while aromatic whites such as Bacchus and Riesling are often kept on the lees without it, to preserve freshness.

The third tool is acid addition, which is permitted within strict UK and EU limits for still wines and is tightly controlled. A small dose of tartaric acid at pressing can correct a flat year. Acidity is also reduced naturally through cold stabilisation, where tartrate crystals form in chilled tanks and are filtered out, taking some acid with them. The end-of-year target for a still English white is usually a total acidity of 7 to 9 grams per litre and a pH of 3.1 to 3.4, depending on style.

UK examples and benchmarks

Chapel Down in Kent, Nyetimber in West Sussex, Ridgeview in East Sussex, Hambledon in Hampshire, Gusbourne in Kent and the rapidly expanding Forty Hall in North London all publish technical sheets on their websites, and acidity is always a featured number. The English sparkling wines from these houses typically end with total acidity of 7.5 to 9.5 grams per litre, which gives the refreshing bite that has won them blind tasting comparisons with Champagne.

Among still wines, Bacchus from producers such as Chapel Down, Bolney, Litmus and the newer Mount Harry in Sussex regularly shows total acidity of 7 to 8.5 grams per litre, with zingy citrus and elderflower character. Pinot Noir from the same sites tends to be picked at higher acid than its Burgundian counterparts, which is part of why English Pinot often shows bright red fruit and structure rather than the jammy black fruit of warmer climates.

Acidity on the label and at the table

UK law does not require acidity on the consumer label, but the technical sheet that follows a wine through the supply chain will list both total acidity and pH. At the table, acidity is what makes a glass of English sparkling cut through fish and chips, what makes a chilled Bacchus work as an aperitif and what gives a young English Pinot Noir the snap to pair with duck or grilled lamb.