Canning Tomatoes Safely: Acid, Steps and Processing Times
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Tomatoes make a natural first canning project, and the acid is the one step you can't skip. Some tomato varieties sit slightly above pH 4.6, the line between acid and low-acid foods, so NCHFP's tested recipes add acid to every jar to make sure. Sugar can offset the sour taste if you want. In NCHFP's words: “do not leave acid out.”
How much acid
| Acid | Per pint | Per quart |
|---|---|---|
| Bottled lemon juice | 1 tablespoon | 2 tablespoons |
| Citric acid | 1/4 teaspoon | 1/2 teaspoon |
| 5% vinegar | 2 tablespoons | 4 tablespoons |
NCHFP notes vinegar works but may change the flavor. Use bottled lemon juice rather than fresh-squeezed, as the directions specify. And the acid is required whether you water bath or pressure can: NCHFP says the pressure options weren't developed for tomatoes without added acid.
Before you start
- Don't can tomatoes from dead or frost-killed vines, per NCHFP.
- Plan on about 22 pounds of tomatoes for a canner load of 7 quarts, or about 14 pounds for 9 pints (NCHFP's average for crushed tomatoes).
- Gear: a water bath canner or pressure canner, pint or quart jars, new lids, and a jar lifter.
Crushed tomatoes, step by step (NCHFP's tested method)
- Peel. Wash the tomatoes and dip them in boiling water for 30 to 60 seconds, until the skins split. Dip in cold water, slip off the skins and cut out the cores. Trim bruised spots and quarter them.
- Start the pot. Heat about one-sixth of the quarters quickly in a large pot, crushing them with a wooden spoon or mallet as they go in so they release juice.
- Add the rest. Once that's boiling, gradually add the remaining quarters, stirring constantly. They don't need crushing; they'll soften as they heat. Then boil gently for 5 minutes.
- Acidify the jars. Put the lemon juice or citric acid in each jar (amounts above). Add 1 teaspoon of salt per quart if you like.
- Fill hot. Fill jars right away with the hot tomatoes, leaving 1/2-inch headspace. Wipe rims and put on lids.
- Process using one of the tables below for your elevation.
Helpful gear
For juice and sauce (not crushed tomatoes), NCHFP's recipes have you press cooked tomatoes through a sieve or food mill to remove skins and seeds. A strainer like the Victorio VKP250 does that with a hand crank. More options in our food mill guide. Mrs. Wages' citric acid label gives 1/4 teaspoon per pint and 1/2 per quart, per the listing, the same as NCHFP.
Victorio VKP250 Johnny Apple Sauce Maker / Food Strainer
- Clamp-mount hand-crank strainer that separates skins and seeds, per the listing
- Includes apple/tomato screen (1.3 mm holes) and standard spiral; optional motor and screens
- Cast aluminum body, stainless screens; 5-year warranty
- Clamps to counters 3/4 to 2-1/8 inches thick
Mrs. Wages Citric Acid, 12 oz
- Label directions: 1/4 teaspoon per pint or 1/2 teaspoon per quart of tomatoes, per the listing
- 12 oz jar; kosher
Processing times for crushed tomatoes (hot pack)
Boiling-water canner
| Jar | 0–1,000 ft | 1,001–3,000 ft | 3,001–6,000 ft | Above 6,000 ft |
|---|---|---|---|---|
| Pints | 35 min | 40 min | 45 min | 50 min |
| Quarts | 45 min | 50 min | 55 min | 60 min |
Weighted-gauge pressure canner (pints or quarts)
| Time | 0–1,000 ft | Above 1,000 ft |
|---|---|---|
| 20 min | 5 lb | 10 lb |
| 15 min | 10 lb | 15 lb |
| 10 min | 15 lb | Not recommended |
Dial-gauge pressure canner (pints or quarts)
| Time | 0–2,000 ft | 2,001–4,000 ft | 4,001–6,000 ft | 6,001–8,000 ft |
|---|---|---|---|---|
| 20 min | 6 lb | 7 lb | 8 lb | 9 lb |
| 15 min | 11 lb | 12 lb | 13 lb | 14 lb |
Source: NCHFP's Crushed Tomatoes page, adapted from the USDA Complete Guide to Home Canning (2015). Whole, halved, juice and sauce have their own procedures and times on NCHFP's site; don't swap times between them.
FAQ
Do you have to add lemon juice?
Yes, or citric acid. Every jar.
Do I still need acid if I pressure can?
Yes. NCHFP is explicit about that.
Can I use tomatoes from frost-killed vines?
No, per NCHFP.