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The pH of food: what it changes, and what it does not

pH is the one number in this whole family that is genuinely measured on the food, in the food, with an instrument. It also has almost nothing to do with the acid load a food places on the body — but a great deal to do with whether that jar of tomatoes is safe to keep in the cupboard.

The pH figures here are the ranges published in food-safety reference tables and are for orientation only. They are not a diagnosis and they are not a substitute for a tested recipe: home canning safety depends on the finished, equilibrated pH of your jar, which varies with the variety, ripeness and recipe. Use a tested canning recipe from a food-safety authority, and if you have dental erosion see a dentist.

Why 4.6 is the most important number in a kitchen

Clostridium botulinum, the organism behind botulism, cannot grow and cannot produce toxin below about pH 4.6. That single fact splits every preserved food into two worlds. Foods whose finished pH sits at or below 4.6 are “acid foods” and can be processed in a boiling-water bath, because anything that could survive that temperature cannot grow at that acidity. Foods above 4.6 are “low-acid”, and the only home method that makes them shelf-stable is a pressure canner, which reaches temperatures a boiling-water bath cannot.

This is also why so many preserving recipes tell you to add something acidic. Tomatoes are the classic case: their pH straddles the line, with many varieties landing between about 4.3 and 4.9, and modern low-acid cultivars sitting on the wrong side of it. Adding a measured amount of bottled lemon juice or citric acid to each jar is not a flavour decision — it is what pulls the finished product reliably under 4.6.

The same threshold appears in food law. Acidified foods — low-acid foods deliberately brought under the line with vinegar or another acid — are regulated on the basis of the finished equilibrium pH, the pH after everything in the jar has had time to even out. A cucumber that measures 5.2 on its own is irrelevant; what matters is the pickle a week later.

pH versus acid load: the distinction that clears up the “alkaline” confusion

A food’s pH is a property of the food in your hand. Its acid load is a property of what is left after digestion. These two frequently disagree, and lemon juice is the standard example: pH around 2, acid load negative, because what actually gets absorbed and metabolised is potassium citrate, which the body turns into bicarbonate.

The reverse case exists too. Egg white sits on the alkaline side of neutral in the shell — and rises further as the egg ages and loses carbon dioxide — yet egg is one of the more acid-forming foods once digested, because of its sulphur-containing protein. Cheese, milk and meat are all mildly acidic to neutral in the mouth and firmly acid-forming afterwards.

So a list of “alkaline foods” built from pH readings and a list built from acid load are different lists, and neither of them changes your blood.

Where food pH really does touch health: teeth

Tooth enamel begins to demineralise below a pH of roughly 5.5, and dentine — exposed at the gum line as gums recede — starts higher, closer to 6.2. Most soft drinks, fruit juices, sports drinks, wine and vinegar dressings sit well below both. This is erosion, and it is not the same process as decay: no bacteria are needed, and it happens to the surface of the tooth wherever the acid touches.

What determines the damage is exposure time far more than the pH number. A glass of juice drunk in three minutes is a short acid episode that saliva neutralises; the same glass sipped across an hour of work is a long one. Frequency does the same thing — several acidic drinks spread over a day keeps the mouth below the threshold for much of it.

Practical mitigations are unglamorous: drink acidic things with a meal rather than between meals, follow with water or milk, and give the mouth time before brushing so the softened surface is not scrubbed. Erosion that has already happened is a dentist’s problem, not a diet problem.

Food pH by food group

Bands, not decimals. Where a published quantity for a specific food could not be verified against a document, this surface prints the band rather than a number — and every food below links to its own nutrition page so you can see what else is in it.

What changes the number

• Ripeness moves it. Fruit becomes less acidic as it ripens, and tomato varieties differ enough to cross the 4.6 line.
• Fermentation drives it down. Lactic-acid bacteria turn sugars into acid, which is exactly how sauerkraut and yoghurt preserve themselves.
• Cooking with acid changes the finished value, not the raw one — and it is the finished, equilibrated value that determines safety.
• Age raises egg-white pH as carbon dioxide escapes through the shell, which is why older eggs peel more easily after boiling.
• Water hardness and added minerals shift the pH of anything you brew or pickle in it.

Where else these foods are flagged

Foods raised on this page that also sit in a raised band on at least two of the other fifteen. Reassuring bands are not counted, so a row here means the food genuinely collects labels rather than merely getting mentioned a lot.

It is worth reading before removing anything. The lists on this surface were each written for a different person with a different problem, and they converge on the same small group of nutrient-dense foods. Satisfying all of them at once produces a diet nobody designed and nobody has tested.

Talking to someone who can actually test

Nothing on this surface is personal medical advice. If a food genuinely makes you ill, if you have had a kidney stone or a gout attack, or if you are considering removing a food group from your diet, the person to talk to is your doctor, pharmacist or a registered dietitian — they can test for the things that can be tested for, which a table cannot.

Sources: US Food and Drug Administration — Approximate pH of Foods and Food Products, the reference table behind most published food-pH ranges. · USDA Complete Guide to Home Canning — the origin of the pH 4.6 split between boiling-water and pressure processing. · Reference values for the critical pH of enamel (about 5.5) and dentine (about 6.2) are long-established in the dental erosion literature. · Food names and links: the site food database. Checked 2026-09-06.

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