Acidity

Also known as Wine acidity

Acidity is both a sensory impression and a set of chemical conditions that shape wine. Organic acids provide sourness, influence how the mouth responds, and help determine microbial, colour, tartrate, and oxidation behaviour. A wine’s acidity cannot be understood from one number: pH, titratable acidity, the kinds of acids present, alcohol, sugar, phenolic compounds, and the wine’s buffering salts interact.

The main acids

Grapes accumulate chiefly tartaric and malic acids, with smaller amounts of citric acid. Tartaric acid is unusually characteristic of grapes and is relatively persistent through ripening and fermentation, although potassium and ethanol can later move some of it into precipitated potassium bitartrate. Malic acid is also formed early in berry development but is more readily metabolized as berries ripen, particularly under warm conditions. This is one reason a grape can lose titratable acidity while its sugar concentration rises; the change is physiological, not a simple dilution by increasing berry size. The review by Burbidge and colleagues describes tartaric-acid accumulation as largely an early developmental process and malic acid as the acid more susceptible to enzymatic loss during ripening.1. Crista Ann Burbidge et al., “Biosynthesis and Cellular Functions of Tartaric Acid in Grapevines,” Frontiers in Plant Science 12 (2021), article 643024, https://doi.org/10.3389/fpls.2021.643024.

Fermentation adds to this starting mixture. Yeast produce succinic acid, which can contribute to titratable acidity, as well as small amounts of other acids. Lactic acid is especially important after malolactic conversion, while acetic acid is a volatile acid associated with fermentation and, in excess, microbial spoilage. The acid profile therefore records both grape composition and what happened after harvest; calling a wine simply “high-acid” leaves out useful information about which acids remain.

pH, titratable acidity, and buffering

pH describes hydrogen-ion activity. Titratable acidity (TA) measures how much base is required to neutralize the wine to a defined endpoint, commonly reported as grams per litre of tartaric-acid equivalent. It is therefore a measure of neutralizable acidity, not a second way of writing pH.

The two measurements often move together, but they are not interchangeable. Weak organic acids exist in dissociated and undissociated forms; their conjugate bases, potassium and other ions, and the wine’s other acid systems buffer changes in pH. A wine can therefore have the same TA as another wine while presenting a different pH, or the same pH with a different amount and composition of acid. AWRI summarizes the practical consequence: there is no direct, predictable relationship between pH and TA.2. Australian Wine Research Institute, “Acidity and pH”, accessed 7 September 2026. This buffering is why a small addition or loss of acid does not translate into a fixed pH change across wines, and why chemical analysis cannot by itself predict a wine’s perceived freshness.

Acid species and the wine matrix matter in the glass as well. Sourness is related to hydrogen-ion activity and the amount of acid that saliva must neutralize, while sugar, alcohol, tannin, extract, and carbonation alter the balance of sensations. TA can help describe the acid load and likely salivary response; pH is especially important to the chemical and microbial environment.

Ripening and malolactic choices

Harvest decisions often consider sugars, pH, TA, malic acid, potassium, and phenolic or aromatic maturity together. Ripening changes these variables at different rates. Tartaric acid is comparatively stable in the berry, whereas malic acid can decline rapidly with heat. Water status, cultivar, crop development, and season still affect the resulting balance.

Malolactic conversion is a bacterial process in which malate, a dicarboxylic acid, becomes lactate, a monocarboxylic acid, with carbon dioxide produced as part of the energy-generating pathway. Because the bacteria fix a proton in the process, hydrogen-ion activity decreases and pH generally rises; TA also usually falls. UC Davis describes the sensory result as dependent on the wine matrix, with lactate often perceived as less tart than malate.3. University of California, Davis, Viticulture and Enology, “Introduction to malolactic fermentation”, accessed 7 September 2026.

The choice to allow, encourage, or prevent this conversion depends on the wine’s acid composition and intended stability. Lactic-acid bacteria need different conditions from yeast: pH, temperature, ethanol, nutrients, and sulfite all affect their growth. Oenococcus is generally more tolerant of low pH than many lactobacilli and pediococci, but the conversion itself can raise pH and make subsequent bacterial growth easier. Bacteria can also form diacetyl or other undesirable compounds. A completed, monitored conversion before bottling can remove malate as a later microbial substrate; an unplanned conversion in bottle can produce cloudiness or fizz.4. University of California, Davis, Viticulture and Enology, “Factors impacting the fermentation”, accessed 7 September 2026.

Microbes, colour, and sulfur dioxide

pH is a central link between acidity and stability. More acidic conditions tend to constrain wine microorganisms, while higher pH can make growth by spoilage yeasts and bacteria easier. TA alone does not explain that effect because pH also governs the wine’s microbial environment.2. Australian Wine Research Institute, “Acidity and pH”, accessed 7 September 2026.

The same distinction matters for sulfur dioxide (SO₂). Its molecular form is especially important for antimicrobial effectiveness. As pH rises, a smaller fraction of free SO₂ is molecular, so the same free-SO₂ concentration gives less antimicrobial protection at a higher pH.2. Australian Wine Research Institute, “Acidity and pH”, accessed 7 September 2026.

In red wine, pH also affects colour and oxidative reactions, among the properties influenced by pH according to the Australian Wine Research Institute.2. Australian Wine Research Institute, “Acidity and pH”, accessed 7 September 2026.

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