Ingredients — 4 jars of 500 ml
- 5 kg of ripe tomatoes
- Bottled lemon juice: 1 tablespoon (15 ml) per 500 ml jar, 2 tablespoons per 1 litre jar
- Salt, optional: half a teaspoon per 500 ml jar
Choose fleshy, fully ripe tomatoes without bruises. Paste varieties give a thick sauce faster.
Why add lemon juice?
A water bath at 100 °C is only safe for acidic foods. Many tomato varieties are close to the acidity limit below which the botulism bacterium can develop: lemon juice guarantees that margin. Use bottled lemon juice, whose acidity is standardized, unlike a fresh lemon. It barely changes the taste.
For the same reason, do not add onion, garlic, peppers or oil to the jar: they lower the acidity and the processing time would no longer be valid. Add them when you cook the sauce after opening.
Method
- Wash the tomatoes, remove the stem end and cut them into quarters.
- Cook them for about 20 minutes, then pass them through a food mill to remove skins and seeds.
- Simmer the purée uncovered, stirring often, until it reaches the thickness you like.
- Put the lemon juice (and the salt) at the bottom of each clean jar, then fill with the boiling sauce, leaving 1.5 cm of headspace.
- Wipe the rims, close the jars and process them in boiling water: 35 minutes for 500 ml jars, 40 minutes for 1 litre jars.
- Let the jars cool, then check the seal after 24 hours before storing them.
Start counting the processing time only once the water is boiling, and keep the jars covered by at least 3 cm of water. Above 300 m of altitude, add 5 minutes; above 900 m, add 10 minutes.
Storage
Kept in a cool, dark place, your tomato sauce keeps 12 to 18 months. Once opened, store the jar in the fridge and use it within a few days.
