Do you need lemon juice to can tomatoes? Yes, in every jar. Here is how much

How to use the acid table

Find your jar size and pick one acid. That is all. You do not add lemon juice and citric acid together. You choose one.

The acid goes into the empty jar first, before the tomatoes. That way every jar gets its full share, and you don't forget one halfway through a batch.

The pint row has no vinegar amount because the book gives the vinegar figure only per quart. If you want to use vinegar in pints, take the amount from the tested recipe you are following.

The last row is the one people miss. A pressure canner does not let you skip the acid. NCHFP says its pressure options "were not developed for tomatoes without added acid."

After the acid, you still need the tested time. The book gives one example from NCHFP. Hot-packed crushed tomatoes at 0 to 1,000 feet take 35 minutes for pints and 45 minutes for quarts in a boiling-water canner. Higher up, the time goes up. Other styles of tomatoes have their own times in USDA Guide 3.

Why a tablespoon of lemon juice matters so much

Canning splits food into two groups. Acid foods have a pH of 4.6 or lower, and they can go in a boiling-water canner. Low-acid foods have a pH above 4.6, and they need a pressure canner.

Tomatoes used to sit safely on the acid side. Then the USDA found that some tomatoes "are now known to have pH values slightly above 4.6." Slightly is enough. A jar just over the line is a jar where botulism germs could grow.

The CDC is plain about why that matters: "You cannot see, smell, or taste the toxin that causes botulism." So the fix has to happen before the jar is sealed, not after.

A little lemon juice pulls every jar back to the acid side. It is the cheapest safety step in all of canning.

The tomato card that only says salt

Say you are standing at the counter in August. The kitchen is steamy, the tomatoes are peeled and the jars are hot. Your grandmother's card says one teaspoon of salt per quart. That's it.

You hesitate. She never used lemon juice. Her tomatoes were the best you ever ate.

Both things can be true. Her card matches the 1942 USDA bulletin, which also added salt only. She was following the rules of her time. The rule changed later, when the pH numbers came in.

So you keep her salt, her tomatoes and her method of packing. You add two tablespoons of bottled lemon juice to each quart. If it tastes a little sharp, NCHFP says you may add sugar to balance it.

Before you start, check the tomatoes too. NCHFP says not to can tomatoes from dead or frost-killed vines. Firm, healthy fruit only.

Where the book covers tomatoes

This is the problem The Lost Kitchen Skills, Checked was written for. Nancy Whitaker checks 42 old kitchen skills against current USDA, FDA, CDC and extension guidance and gives each one an honest badge.

Water-Bath Canning for High-Acid Food has the card for acidifying tomatoes. It carries an UPDATE IT badge, because the idea is sound and only the method changed. The card gives the amounts per pint and quart, the vinegar option, the sugar tip and what to watch for in a jar that looks wrong. The same chapter walks through water-bath canning start to finish.

The Pantry Workbook has the Grandma's Recipe Card, Checked worksheet. Its second question asks one thing: does the card add acid? Circle yes, no or not sure, then write down the tested recipe you will use instead.

If you plan to can at a higher elevation, our page on pressure canner altitude and dial gauges explains how times and pressures change as you go up.