Titratable Acidity

Titratable acidity (TA) and pH measure two different things, and a finished ferment is described by both. pH is the strength of the currently dissociated acid — the free H⁺ your tongue and the safety threshold respond to. TA is the total acid present, dissociated and undissociated, expressed as a mass percent of a reference acid. TA is the acid reserve; pH is the acid intensity.

Info

Lactic and acetic acids are weak — most of their molecules stay undissociated in solution. So two brines can share a pH yet hold very different total acid. As bacteria keep producing acid late in a ferment, TA climbs while pH barely moves (the new acid is buffered and weakly dissociated). That is why TA, not pH, is the better gauge of how finished and how sour a product is.

Which acid you report

TA is always quoted “as” a specific acid, because each has a different equivalent weight:

Product family	Dominant acid	Report TA as
Sauerkraut, kimchi, lacto-veg	Lactic acid	% lactic
Kombucha, vinegar, water kefir	Acetic acid	% acetic
Citrus, wine, most fruit	varies	% tartaric or % citric

A “1.0% acidity” sauerkraut (lactic) and a “1.0% acidity” vinegar (acetic) are not the same molar acid load — always state the reference acid.

Target windows by product

Product	Finished pH	TA (as named acid)
Sauerkraut	3.4–3.6	1.0–1.5% lactic
Kimchi	4.2 → 4.0	0.6–0.8% lactic
Lacto-veg (general)	3.4–4.0	~0.6–1.5% lactic
Kombucha	2.5–3.5	0.5–1.0% acetic
Vinegar (table)	—	≥ 4% acetic
Vinegar (for canning)	—	5% acetic

Caution

Acidity is what makes an acidified canning recipe safe. Use vinegar of at least 5% acetic acid for any water-bath/acidified process, and never dilute the acid in a tested recipe. Verify the bottle’s labeled acidity; “reduced-acid” vinegars exist. See Safety and Botulism.

A simple titration

You neutralize the sample with a base of known strength and read how much it took. The endpoint is where all the acid is consumed.

Prepare the sample

Pipette a measured volume of strained brine — typically 5.0 mL — into a flask and add ~50 mL distilled water plus 3 drops phenolphthalein indicator.

Titrate to the endpoint

Add 0.1 N sodium hydroxide (NaOH) drop by drop, swirling, until a faint pink holds for 30 seconds. Record the volume of NaOH used. (A pH meter to 8.2 replaces the indicator for opaque samples.)

Calculate % acid

% acid = (mL NaOH × N × milliequivalent weight × 100) ÷ mL sample. Milliequivalent weight is 0.090 for lactic acid and 0.060 for acetic acid.

Info

Worked example. 5.0 mL of sauerkraut brine takes 6.5 mL of 0.1 N NaOH: (6.5 × 0.1 × 0.090 × 100) ÷ 5.0 = 1.17% lactic — squarely in the 1.0–1.5% target band.

Tip

Track TA alongside pH over a ferment: pH falls fast and then plateaus, while TA keeps rising. When TA enters the target window and pH has stabilized, the ferment is done. Cold storage at 2–4 °C arrests both.

See also

• Acidity and pH — what pH measures and the 4.6 / 4.2 lines
• Safety and Botulism — vinegar strength and the canning classification
• pH safety calculator