Choose the Right Tomatoes
While you can preserve any tomato, some varieties are better suited for the job. For sauces and pastes, look for meaty paste tomatoes like Roma, San Marzano, or Amish Paste. These types have less water content and fewer seeds, meaning they cook down into
a richer, thicker product. For canning whole or diced tomatoes, varieties like Ace 55 or Rutgers hold their shape and flavour well after processing. Regardless of the type, always select firm, ripe, and disease-free fruit. Avoid using tomatoes from dead or frost-killed vines, as they may have lower acidity, which is crucial for safe canning.
The Classic Method: Water Bath Canning
Water bath canning is a time-honoured technique ideal for high-acid foods, including properly acidified tomatoes. The process involves submerging sealed jars in boiling water for a specific amount of time. This heat processing kills spoilage microorganisms, removes oxygen from the jar, and creates a vacuum seal that keeps the contents shelf-stable for months. While other methods exist, boiling water or pressure canning are the only recommended safe methods for tomatoes; techniques like open-kettle or oven canning are considered unsafe. This guide will focus on the beginner-friendly water bath method.
Gather Your Equipment
Before you begin, gather your tools to make the process smooth and efficient. You will need a large, deep stockpot with a lid and a rack that fits inside—this will be your water bath canner. You’ll also need glass canning jars with new lids and screw bands, a jar lifter for safely moving hot jars, a funnel for clean filling, and a non-metallic spatula or chopstick to remove air bubbles. A separate large pot for blanching tomatoes and a bowl of ice water are essential for peeling.
Step 1: Prepare the Tomatoes
First, wash your tomatoes thoroughly. To easily remove the skins, you'll need to blanch them. Bring a large pot of water to a rolling boil. Cut a small 'X' on the bottom of each tomato and drop them into the boiling water for about 30 to 60 seconds, or until the skins start to split. Immediately transfer them to a bowl of ice water with a slotted spoon. This stops the cooking and makes the skins easy to peel off. Once peeled, you can leave them whole, halve them, or chop them as desired.
Step 2: Pack and Acidify the Jars
For safety, all home-canned tomatoes must be acidified, as modern varieties can be borderline low-acid. For each quart-sized jar, add two tablespoons of bottled lemon juice or a half-teaspoon of citric acid. For pint jars, use one tablespoon of lemon juice or a quarter-teaspoon of citric acid. It's crucial to use bottled, not fresh, lemon juice for its consistent acidity level. After adding the acid, you can add about a half-teaspoon of salt per pint for flavour, if desired. Pack the prepared tomatoes into the jars, pressing down gently to release juices and leaving a half-inch of headspace at the top. If needed, top off with boiling water, ensuring the tomatoes are covered but the headspace remains. Run a spatula around the inside of the jar to remove any trapped air bubbles.
Step 3: Process and Seal
Wipe the jar rims with a clean, damp cloth to ensure a good seal. Place the lids on top and screw on the bands until they are just fingertip-tight; do not overtighten. Place the filled jars onto the rack in your canner, which should be filled with hot water. The water should cover the jars by at least one inch. Cover the pot and bring the water to a rolling boil. Process pint jars for 40 minutes and quart jars for 45 minutes, adjusting for altitude if necessary. Once the time is up, turn off the heat, remove the canner lid, and let the jars stand in the hot water for another five minutes before removing them with a jar lifter. Place the hot jars on a towel on the counter and leave them undisturbed for 12 to 24 hours. You should hear the satisfying 'pop' of the lids sealing.
