Acidified Water-Bath Tomatoes

Home-canned crushed tomatoes are a pantry staple — bright, clean, and ready for sauce all winter. But tomatoes are the classic borderline food: many modern cultivars and overripe fruit drift above the botulism line, so this is a safety-critical recipe. The acid dose is not seasoning; it is what makes the jar safe.

Caution

Tomatoes are NOT reliably high-acid. You MUST add the tested acid dose to every jar, verify the finished pH is at or below 4.6 with a calibrated meter, and water-bath process for the full time. Never reduce the acid to soften the flavor — add sugar instead. Taste is never a safety test; pH is. This page reproduces the tested NCHFP process — follow it exactly and do not improvise. See acidification, water-bath canning, the pH safety calculator, and safety and botulism.

Why acid, not just heat

A boiling-water bath holds jars at 100 °C / 212 °F, which destroys yeasts, molds, and spoilage bacteria — but it does not kill Clostridium botulinum spores. Those spores survive boiling and, in a sealed anaerobic jar, can grow and produce toxin unless the food is acidic enough to stop them. That line is pH 4.6. Acidification adds a measured amount of bottled lemon juice or citric acid so the finished tomatoes land at or below 4.6 (we target 4.2), turning a borderline low-acid food into a verified high-acid one that a water-bath canner can make safe.

Ingredients

The acid dose is per jar, added before filling. Tomato quantities follow the NCHFP crushed-tomato yields.

Ingredient	1 Jar (1 quart)	1 Crock (per pint)
Cored, peeled tomatoes (crushed)	~1.4 kg fresh per quart	~0.9 kg fresh per pint
Bottled lemon juice (per jar)	2 Tbsp	1 Tbsp
OR citric acid (per jar)	1/2 tsp	1/4 tsp
Salt (optional, flavor only)	1 tsp	1/2 tsp

Use bottled lemon juice of standardized strength — fresh lemon juice varies and is not safe as the acidifier. Salt is for flavor only and does nothing for safety here.

Yield: about 7 quarts per ~22 lb (≈10 kg) of fresh tomatoes, or 9 pints per ~14 lb (≈6.4 kg), per the NCHFP crushed-tomato process.

Calculated values

Parameter	Value
Acid dose (quart)	2 Tbsp bottled lemon juice or 1/2 tsp citric acid
Acid dose (pint)	1 Tbsp bottled lemon juice or 1/4 tsp citric acid
Finished pH target	at or below 4.6 (working margin 4.2 or lower), meter-verified
Headspace	13 mm (1/2 in)
Process (0–1,000 ft)	quarts 45 min; pints 35 min at a full boil
Altitude	add time per the NCHFP table above 1,000 ft

Readiness window

This is a canning process, not a ferment — “readiness” means a verified-safe, properly sealed jar, not a flavor window.

• Done-when: the finished, mixed tomatoes read at or below 4.6 on a calibrated meter before processing, the jars have been boiled for the full time plus altitude adjustment, and after cooling each lid is pulled down concave and does not flex.
• If pH reads above 4.6 at the tested dose (common with very ripe or low-acid varieties): do not guess in more acid. Refrigerate or freeze the batch instead — acidification is verification, not negotiation.
• Arrest / hold: any jar that fails to seal goes straight to the refrigerator at 2–4 °C and is used within a few days, or is reprocessed within 24 hours with a fresh lid.

Method

Start from the tested recipe

Use the NCHFP crushed-tomato process. It fixes the acid dose, headspace, and processing time as one validated package — do not alter any of them.

Peel and crush

Dip washed tomatoes in boiling water 30–60 seconds until the skins split, then into cold water; slip off skins and cores. Quarter, heat to a boil while crushing with a spoon to release juice, then boil gently 5 minutes.

Acidify the jar first

Put the measured bottled lemon juice (or citric acid) into each empty hot jar before filling. Adding it first guarantees the dose is present and evenly available. Add optional salt now.

Fill, stir, and verify pH

Ladle in hot crushed tomatoes to a 13 mm (1/2 in) headspace, run a bubble tool around the inside, and re-check headspace. Stir to distribute the acid, then read the finished, mixed product on a calibrated meter — confirm it is at or below 4.6. Cross-check with the pH safety calculator.

Wipe, lid, and load

Wipe rims clean, center new flat lids, and screw bands to fingertip-tight. Lower jars onto the rack into near-boiling water with at least 25 mm (1 in) of water over the lids.

Process the full time, then cool

Return to a full rolling boil, THEN start timing: 45 minutes for quarts, 35 for pints at 0–1,000 ft, plus the altitude increase. Turn off heat, wait 5 minutes, lift jars straight up, and cool undisturbed 12–24 hours. Confirm each seal, remove bands, label with the date, and store cool and dark.

Variations

• Whole or halved tomatoes packed in juice or water use a different tested process and time — switch to that NCHFP recipe rather than adapting this one.
• Vinegar instead of lemon/citric: 4 Tbsp of 5% vinegar per quart (2 Tbsp per pint) is the NCHFP-equivalent dose, but it flavors the tomatoes more — lemon juice or citric acid is usually preferred.
• Do not add onions, peppers, herbs, or extra low-acid vegetables to this process; those additions change the acidity and require a different (often pressure-canned) recipe.

Caution

Never cut the acid for taste, swap in fresh (variable) lemon juice, add low-acid vegetables, thicken with flour, or shorten the boil — every one of those raises pH or slows heat penetration and can let botulinum toxin form. Botulinum toxin is odorless and tasteless. If you cannot verify the finished pH at or below 4.6, do not water-bath can it; refrigerate or freeze instead. Plain (un-acidified) tomatoes are a low-acid food and require pressure canning, not this method. Cite and follow NCHFP.

See also

• Acidification — the tested acid doses and the 4.6 logic
• Water-bath canning — the boiling-water process in detail
• pH & safety calculator — confirm finished pH at or below 4.6
• Safety and botulism — why 4.6 is the absolute line
• Acidity and pH — what the line means
• NCHFP: crushed tomatoes and acidifying tomatoes