pH and TA: The Winemaker's Most Important Numbers

Acidity in wine is measured two ways — pH and titratable acidity (TA). Beginners often assume these measure the same thing. They don't. Understanding the difference between them — and why both matter — is fundamental to making balanced, stable wine.

pH: Acid Strength

pH measures the concentration of hydrogen ions in a solution on a logarithmic scale from 0 to 14. Lower pH = more acidic. Wine sits between 2.8 and 4.2 for most purposes.

pH is logarithmic: a change from pH 3.5 to 3.0 represents a 10× increase in hydrogen ion concentration. This means small changes in pH have outsized effects on wine chemistry.

Why pH matters in winemaking

Microbial stability: Bacteria struggle to survive at low pH. Below pH 3.3, spoilage bacteria find it very difficult to grow. Above pH 3.8, the wine is genuinely vulnerable.

SO₂ effectiveness: The molecular SO₂ fraction — the only genuinely antimicrobial form — depends on pH. At pH 3.2, approximately 3.8% of free SO₂ is in the molecular form. At pH 3.8, only 0.95%. This means high-pH wines need much more total SO₂ to achieve the same protection.

Colour: In red wines, anthocyanin colour exists in different forms depending on pH. Lower pH favours the red ionised form; higher pH shifts colour towards blue-purple and eventually brown.

Taste: pH correlates with perceived acidity but is not the only determinant — TA matters too.

TA: Acid Quantity

Titratable acidity measures the total concentration of all acids in the wine — not their strength, but how much of them there is. It's measured in g/L of tartaric acid equivalent, by titration (adding base until all acids are neutralised).

The main acids in wine and their contributions to TA:

• Tartaric acid: metabolically stable, doesn't change after harvest. The primary structural acid.
• Malic acid: sharp, green apple. Decreases with ripening and during MLF.
• Lactic acid: softer, milky. Produced during MLF.
• Citric acid: in small amounts naturally; also used for sanitisation. Can be metabolised by LAB.
• Acetic acid: volatile — see the volatile acidity article.

Why TA matters

TA is what you taste as sourness on the palate — the mouthfeel of acidity. A wine with TA 9 g/L will feel sharp and tart; one at 4 g/L will feel flat and soft.

Target TA:

• White wines: 6.5–8.5 g/L
• Red wines: 5.5–7.5 g/L
• Sparkling base: 8–10 g/L
• Dessert wines: 5–8 g/L (sweetness compensates)

Why pH and TA Can Disagree

This is where it gets interesting. A wine can have:

• High pH and high TA: sounds contradictory but happens when potassium content is very high. Potassium from the grapes acts as a buffer — it neutralises some acid hydrogen ions (raising pH) without removing the acid molecules (TA stays the same).
• Low pH and moderate TA: common in very acidic musts with low potassium. The acid is strong (aggressive pH) but not necessarily abundant.

Example: A Chardonnay from a very warm vintage might show pH 3.75 and TA 6.2 g/L. The high pH indicates poor microbial protection; the moderate TA says there's some acid there, but it's strongly buffered by potassium.

This scenario requires acidification with tartaric acid — which lowers pH because tartaric acid doesn't buffer as strongly as the organic salts that were providing the high potassium buffering.

Measuring pH and TA

pH

Use a calibrated digital pH meter. Calibrate with fresh buffer solutions (pH 4.0 and pH 7.0 are standard) before each measurement session. Temperature affects pH readings — measure samples at 20°C or apply temperature correction. Rinse the probe with distilled water between samples.

Paper pH strips are inadequate for winemaking — the colour resolution is insufficient for the precision required.

TA (Titration method)

1. Measure exactly 10mL of wine into a flask using a pipette
2. Add 2–3 drops of phenolphthalein indicator (colourless in acid, pink in base)
3. Fill a burette with 0.1N NaOH (sodium hydroxide)
4. Add NaOH drop by drop, swirling, until the wine turns a persistent pale pink
5. Note the volume of NaOH used (in mL): TA (g/L tartaric acid equivalent) = mL NaOH × 0.75

Phenolphthalein changes colour at pH 8.2 — you're neutralising all the acids, not just the strong ones.

Red wines are harder to read with phenolphthalein (red colour masks the colour change). Use a pH meter to detect the titration endpoint at pH 8.2 instead.

Adjusting pH and TA

Acidification (raising TA, lowering pH)

Add tartaric acid — it lowers pH more effectively than malic or citric acid at equivalent amounts because it's a stronger acid and doesn't buffer as much. 1g/L of tartaric acid added to wine with moderate potassium typically lowers pH by 0.07–0.15 units and raises TA by approximately 1 g/L.

Never add citric acid if the wine is at risk of MLF — LAB metabolise citric acid to acetic acid, raising volatile acidity.

Deacidification (raising pH, lowering TA)

• Potassium bicarbonate (KHCO₃): 1g/L lowers TA by approximately 1 g/L and raises pH. Selectively precipitates tartaric acid.
• MLF: Converts malic acid to lactic acid. Reduces TA (lactic is weaker than malic) and raises pH.
• Cold stabilisation: Precipitates potassium hydrogen tartrate, reducing TA slightly.

Making Decisions

The most important practical rule: always measure both pH and TA, and use both to make decisions. Neither alone tells the full story.

A wine at pH 3.4 with TA 5.5 g/L needs acid addition (it will taste flat despite adequate pH). A wine at pH 3.7 with TA 8 g/L has high acid but a buffering problem (potassium is high) — add tartaric acid specifically.