- Prepare the lids and jars (see note).
- Using a small knife, remove the core from the tomatoes and make a small crisscross incision at the base of each tomato. Compost or discard the cores.
- In a large pot of boiling water, place one-third of the tomatoes at a time. Bring to a boil. Simmer just until the tomato skins start to split, about 5 minutes. Using a slotted spoon, remove the tomatoes from the pot and plunge into an ice water bath. Peel the tomatoes. Compost or discard the skins.
- Add 2 tbsp (30 ml) of the lemon juice and 1 tsp of the salt to each 4-cup (1 litre) jar.
- Divide the tomatoes among the warm jars, pressing and packing them down (the liquid will release from the tomatoes), leaving at least ½-inch (1 cm) space at the top. Remove any air bubbles with a non-metallic utensil and wipe the rims of the jars with a clean dishcloth.
- Centre the lids (discs) on the jars and tighten the rings until the point of resistance, without forcing.
- Place the jars upright on a support rack in a pot of hot water. Make sure the jars are covered by at least 1 inch (2.5 cm) of water. Cover the pot. Bring to a boil over high heat. Once the water comes to a boil, calculate 1 hour 25 minutes processing time.
- Remove the jars from the water.
Calculate about 3 lb (1.4 kg) tomatoes for each 4-cup (1 litre) jar.
In a small pot, place the lids and cover with cold water. Bring to a simmer, turn off the heat and leave the lids in the hot, but not boiling, water, in order to activate the rubber sealing band.
In a large pot, place the jars and cover with water. Bring to a simmer over medium heat. Adjust the heat to low and leave the jars in the pot while you prepare the recipe. Drain them just before filling with tomato sauce.