How to Preserve Tomatoes

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Knowing how to preserve tomatoes depends on what you plan to do with them later. Canning in jars has the most rules, because tomatoes need added acid and a tested recipe before heat processing. Freezing is simpler, but thawed tomatoes lose their shape, so they suit cooking better than fresh use. This guide draws on the National Center for Home Food Preservation at the University of Georgia, Oregon State University Extension, Clemson Extension and NC State Extension, and it leaves out steps those sources do not state.

Quick answer

• Add acid to every jar before heat processing. Lemon juice or citric acid is the standard choice, and vinegar can change the flavor.
• Follow a tested recipe and the canner it names. Boiling water canners and pressure canners are both approved for tomatoes.
• Freeze tomatoes for cooking, not for fresh salads, because the texture softens when they thaw.
• Choose firm, ripe fruit from healthy vines. Do not can tomatoes from dead or frost-killed plants.

Choose tomatoes for the job

NC State Extension sorts tomatoes into slicing, paste and cherry types. Slicing tomatoes are large and juicy and are best eaten fresh. Paste types are fleshy and suit cooking, canning and drying. Cherry tomatoes are small and easy to grow, and they are not the usual choice for a canning batch. The same handbook lists intended use, meaning fresh eating versus canning, as one factor in picking a variety, next to disease resistance, space and flavor.

The National Center’s canning guide asks for disease-free fruit, preferably vine-ripened and firm. It also advises against canning tomatoes from dead or frost-killed vines. If you are still planning the bed that will grow the crop, see vegetables to plant in raised beds. For plant supports, see tomato cages.

Decide between canning and freezing

Canning in jars makes tomatoes shelf stable after heat processing, and it is the method with the strictest rules. Freezing keeps the fruit in the freezer and is much simpler, but the sources warn that frozen tomatoes change texture. Oregon State University Extension’s canning guide covers acidity, headspace, altitude and processing time in detail. The National Center’s freezing pages are shorter and center on preparation and packing.

Acidify every jar before canning

Tomatoes vary in acidity from variety to variety, so the acid step cannot be skipped. Oregon State’s guide states that acid must be added to all jars of canned tomatoes and tomato juice before processing to ensure safety. The acid can go into the jar before the tomatoes do, and the sources treat this as a fixed requirement rather than a flavor choice.

The National Center gives amounts per quart and per pint. For a quart of whole, crushed or juiced tomatoes, add two tablespoons of bottled lemon juice or half a teaspoon of citric acid. For a pint, add one tablespoon of lemon juice or a quarter teaspoon of citric acid. Oregon State’s table matches these amounts and adds bottled lime juice, which uses the same measures as lemon juice. Key lime juice should not be used in its place.

Vinegar is the other option. Oregon State lists five percent vinegar at two tablespoons per pint or four per quart, and warns that vinegar may change the flavor. Sugar can be added to mask sourness, at about a teaspoon per pint or two per quart, but it should never replace the acid. The National Center makes the same point: sugar is optional, and acid stays in the jar.

Follow a tested recipe for canning

Oregon State Extension explains that processing times are set by scientific testing, and that several factors affect them. Changing the amount or type of ingredients, or the way the tomatoes are prepared, can change the conditions the jar needs. That is why the guide insists on a tested recipe rather than a family adaptation.

Two canners are approved. A boiling water canner needs enough briskly boiling water to cover the jar tops by one to two inches, and the pot needs a rack that keeps jars off the bottom and a tight lid. A pressure canner must hold at least four quart jars, and it needs a dial gauge or weight to show the pressure. Oregon State says whole, halved and crushed tomatoes can be canned with either method, and the results are similar, so the choice comes down to preference.

Headspace also depends on the canner. Oregon State asks for half an inch of headspace for jars in a boiling water canner and one inch for jars in a pressure canner. Jars filled too full can let contents bubble out during processing, which can stop the jar from sealing.

Altitude changes the timing. Above 1,000 feet, water does not reach 212 degrees Fahrenheit, so the guide calls for longer boiling times, and it provides pressure adjustments for altitude in a separate table. Use the table for your own elevation, and do not guess from another city’s numbers.

Before each use, Oregon State asks for a pressure canner to be inspected. The petcock and safety valve must not be blocked, and they can be cleared with a string or pipe cleaner drawn through the openings. The cover gasket must fit tightly and be replaced when it is loose. A dial gauge should be checked for accuracy once a year, or more often if the canner gets heavy use or has been dropped, and a gauge that reads more than two pounds off should be replaced.

In a pressure canner, the guide says to vent steam for ten minutes before the weight or gauge is set. That step clears air from the canner, because trapped air heats the jars unevenly. Once the recommended pressure is reached, keep it steady. If the pressure falls below the required level, bring it back up and start the timer over from the beginning.

Peel, pack and fill the jars

Oregon State says to wash the fruit in cool running water. To remove skins, dip the tomatoes in boiling water for 30 to 60 seconds, until the skins split. Some cooks score the bottom of each tomato first to help the skin lift. After a cold dip, the skins slip off and the cores come out. Crushed, whole and halved tomatoes all start this way.

Packing has two styles. In a hot pack, the tomatoes are heated and packed while hot, then covered with the cooking liquid. In a raw pack, raw tomatoes go into the jars and boiling water or juice covers them. Oregon State also describes a raw-pack method with no added liquid for some styles. After filling, slide a plastic or other nonmetal tool around the inside of the jar to release trapped air, and adjust the headspace if needed.

Freezing tomatoes for cooking

The National Center’s raw freezing method starts with firm, ripe tomatoes with a deep red color. Dip them in boiling water for about 30 seconds to loosen the skins, then core and peel them. Freeze them whole or in pieces, pack them into containers with about an inch of headspace, seal and freeze.

The same page warns that the result is for cooking or seasoning, because tomatoes will not be solid when thawed. That warning matches the texture point at the top of this guide. The National Center also offers a juice method, which simmers quartered, firm, vine-ripened tomatoes for five to ten minutes, presses the pulp through a sieve and seasons it, if desired, at one teaspoon of salt per quart. A stewed method cooks peeled, quartered ripe tomatoes until tender, cools them in cold water, and packs them with headspace before freezing.

Clemson Extension’s general freezing guide takes a more cautious view. It says that when a frozen tomato is thawed, it turns into a pile of mush and liquid, and it notes that tomatoes are not usually frozen. The two sources agree that thawed tomatoes suit cooking, but they differ on whether freezing raw tomatoes is worth doing at all. This guide does not settle that question, so choose the method that fits your kitchen and your plan for the fruit.

Handle a spoiled jar with care

Oregon State tells home canners to discard any jar of spoiled food carefully, so that people and pets are not exposed to it. It also says that spoiled tomato products, or any tomato product that was not acidified before canning, should be treated as having produced botulinum toxin. The guide gives steps for handling suspect jars, and those steps should be read in full before anyone opens one.

The practical rule follows from the acid requirement. A jar of tomatoes that was canned without added acid is not a product to taste, even if it looks normal. Keep the recipe, the date and the method with each batch, so that any problem can be traced back.

Common mistakes to avoid

• Skipping the acid because the tomatoes taste ripe. The sources require acid in every jar because acidity varies between tomato varieties.
• Changing ingredient amounts in a tested recipe. Oregon State says those changes can alter the processing conditions.
• Expecting vinegar to taste like lemon juice. The guide warns that vinegar may change the flavor.
• Canning fruit from dead or frost-killed vines. The National Center advises against it.
• Using the sea-level time above 1,000 feet. The altitude adjustment is part of the method.
• Freezing tomatoes for fresh salads. Thawed tomatoes will not hold their shape, so they belong in cooked dishes.

How we chose

The sources were chosen because they are university or national extension guides with preservation rules that can be checked line by line. The National Center for Home Food Preservation, hosted by the University of Georgia, supplies the acid amounts and the freezing methods. Oregon State University Extension supplies the canner, headspace and altitude rules, and Clemson Extension and NC State Extension add freezing context and variety guidance. Each page was opened with curl on 2026-10-23. Where two sources disagree, both views are shown and the difference is named. No retail listing or product page was used, and no product is recommended.

What we could not verify

The guides are long, and this article covers only the rules that every method needs. It is not a substitute for the full recipe, the processing table or the canner manual, and the reader should open the source for the exact method before preserving any batch.

What the sources do not say

The pages opened do not give processing times in this article, because those times depend on the recipe, the jar size, the canner and the altitude. The NC State page names drying as a way to preserve paste tomatoes, but it gives no drying steps, so drying is outside what this guide can support. The pages opened do not give a storage time for frozen tomatoes specifically. Clemson Extension gives general ranges for frozen fruits and vegetables, and those ranges are not a tomato-specific rule. The sources also disagree about freezing raw tomatoes, and this guide does not resolve that disagreement.

Frequently asked questions

Can tomatoes be canned without lemon juice or citric acid?

No, not if you want the recipe to be safe. Oregon State says acid must go into every jar. The National Center gives the amounts for lemon juice and citric acid, and it lists vinegar as an option with a possible flavor change.

Is vinegar a good replacement for lemon juice?

It can be used, but it is not a flavor-neutral swap. Oregon State lists five percent vinegar at two tablespoons per pint or four per quart, and it warns about a change in flavor. Bottled lime juice is listed as an alternative to lemon juice in that same table.

Does canning tomatoes require a pressure canner?

No. Oregon State says whole, halved and crushed tomatoes can be canned in either a boiling water canner or a pressure canner. The results are similar, so the choice is a matter of preference, but altitude above 1,000 feet changes the required times for either method.

Can tomatoes be frozen whole?

The National Center describes freezing tomatoes whole or in pieces after dipping, coring and peeling them. Its guidance is for cooking or seasoning, since thawed tomatoes will not be solid. Clemson Extension raises the wider question of whether raw tomatoes should be frozen at all.

What should be done with a jar that looks spoiled?

Discard it carefully, following Oregon State’s handling steps. The guide says spoiled tomato products, and any product that was not acidified, should be treated as having produced botulinum toxin, so the jar should not be tasted.

Sources

• https://nchfp.uga.edu/how/can/how-do-i-can-tomatoes/canning-tomatoes-introduction/ (opened 2026-10-23)
• https://nchfp.uga.edu/how/can/how-do-i-can-tomatoes/tomato-acidification-directions/ (opened 2026-10-23)
• https://nchfp.uga.edu/how/freeze/vegetable/freezing-tomatoes/ (opened 2026-10-23)
• https://extension.oregonstate.edu/catalog/pnw-300-canning-tomatoes-tomato-products (opened 2026-10-23)
• https://hgic.clemson.edu/factsheet/freezing-fruits-vegetables/ (opened 2026-10-23)
• https://content.ces.ncsu.edu/growing-tomatoes-in-the-home-garden (opened 2026-10-23)