Canning tomatoes is a great way to preserve their fresh flavor, but doing it safely requires precise temperatures to kill harmful bacteria (like Clostridium botulinum, which causes botulism*). Here’s exactly what you need to know about temperatures for water bath and pressure canning tomatoes.
Key Temperature Guidelines for Canning Tomatoes
1. Water Bath Canning (High-Acid Tomatoes)
- Minimum Safe Temperature: 212°F (100°C) – The boiling point of water at sea level.
- Processing Time: 40–85 minutes (varies by jar size and recipe).
- Why? Tomatoes are borderline acidic (pH 4.0–4.6). Adding lemon juice (1 tbsp per pint) or citric acid ensures safe acidity.
2. Pressure Canning (Low-Acid or Mixed Recipes)
- Minimum Safe Temperature: 240°F (116°C) – Requires 10–15 PSI (pressure depends on altitude).
- Processing Time: 15–25 minutes (for plain tomatoes).
- When Needed? If adding onions, peppers, or meat (raises pH).
Why Temperature Matters
- Below 212°F (Water Bath):
- May not kill botulism spores.
- Risk of spoiled or unsafe jars.
- 240°F (Pressure Canning):
- Destroys botulism-causing bacteria and spores.
Step-by-Step Canning Temperatures
1. Preparing Tomatoes
- Wash, core, and peel (optional).
- Simmer at 190–200°F (88–93°C) before packing jars.
2. Filling Jars
- Pack hot tomatoes into sterilized jars (kept warm at 180°F/82°C).
3. Processing
- Water Bath:
- Boil jars at 212°F (100°C) for 40–85 min (adjust for altitude).
- Pressure Canner:
- Process at 240°F (116°C) for 15–25 min (varies by recipe).
4. Cooling & Storage
- Let jars cool undisturbed for 12–24 hours.
- Store in a cool, dark place (50–70°F / 10–21°C).
Signs of Improper Canning
❌ Lid doesn’t seal → Reprocess or refrigerate.
❌ Cloudy liquid, bubbles, or foul smell → Discard (possible spoilage).
❌ Mold growth → Unsafe—do not eat!
Pro Tips for Safe Canning
✔ Use a tested recipe (USDA or Ball Blue Book).
✔ Check pH if adding other veggies (must stay below 4.6 for water bath).
✔ Preheat jars to prevent cracking.
✔ Vinegar-wipe jar rims for a better seal.
Final Thoughts
Tomatoes must reach 212°F in a water bath or 240°F in a pressure canner to be safely preserved. Always adjust for altitude and acidity to avoid risks.
