Sun-dried tomatoes packed in oil are a pantry staple in stores, but putting them up at home is not the same as canning tomatoes. There is no tested home-canning process for sealing sun-dried tomatoes in oil and storing the jars on a shelf. Oil keeps out oxygen, and any leftover moisture can let Clostridium botulinum spores grow and produce toxin. Current extension guidance treats oil as a cold-storage medium, not a canning liquid: dry the tomatoes fully, acid-dip them if you want a softer texture, cover them completely, and refrigerate or freeze.
Why oil packing is a botulism problem
Clostridium botulinum spores are common in soil and on produce. They do not grow in air, in food acidic enough to stay at or below pH 4.6, in food dry enough that water is unavailable, or at refrigerator temperatures that hold growth in check. They can grow when four conditions line up: moisture, low acid, no oxygen, and room temperature.
Oil supplies the oxygen-free part. A jar of tomatoes under oil is anaerobic even if the lid is only screwed on, not heat-processed. Fresh tomatoes sit near the acid boundary (often about pH 4.2 to 4.8). Drying concentrates acids and removes water, which is why fully dried tomatoes stored dry are a low-risk product. Putting those same pieces into oil reintroduces the risk if any pocket of moisture remains. The National Center for Home Food Preservation states that preserving tomatoes in oil is not currently recommended, in part because oil can shield organisms trapped in a droplet of water.
Garlic and fresh herbs make the problem worse. Garlic-in-oil mixtures are a documented cause of botulism when held at room temperature. Dried herbs and dried garlic still count as add-ins that change the safety rule under current Oregon State University guidance.
Why you should not water-bath or pressure can them in oil
Home canning works by heating food in a jar long enough, and hot enough, to destroy the organisms that can grow in that food. Timing charts assume a tested liquid—water, juice, syrup, or an acidified brine—that carries heat into the cold spot at the center of the jar.
Oil does not behave like those liquids. It transfers heat poorly, so a processing time copied from a tomato recipe cannot be assumed to reach every piece. Oil can also creep onto lid gaskets; at least one lid manufacturer advises against it, and a poor seal is both a quality and a safety failure. Iowa State University Extension, summarizing National Center for Home Food Preservation guidance, notes that there are no validated recipes for canning foods solely in oil, and that canning low-acid vegetables and herbs in oil is not recommended.
That rules out the methods people often improvise:
- Covering dried tomatoes with oil and processing in a boiling-water canner
- Pressure canning an oil pack using a vegetable timetable
- Oven “canning,” dishwasher sealing, or inversion sealing
- Re-canning commercial oil-packed tomatoes
None of those has a tested process for this product. A sealed lid is not proof of safety. Botulinum toxin can be present in a jar that looks, smells, and tastes normal.
What current guidance allows instead
Oregon State University’s publication SP 50-701, Herbs and Vegetables in Oil (revised January 2025), is the clearest current extension method for this product. It is refrigerated or frozen storage, not shelf-stable canning.
Dry until no moisture remains
Use firm, ripe tomatoes. Wash, core, and cut into halves, quarters, or slices no thicker than about 3/4 inch. Skins can be left on for dry storage, but pieces that will go into oil are safer and more evenly acidified if skins are removed or if pieces are thin enough for acid to reach the interior. Dry in a dehydrator, or in an oven that can hold a low temperature with the door cracked for airflow, until the pieces are leathery to crisp and show no beads of moisture when cooled and squeezed. Under-dried tomatoes are the main reason an oil pack becomes unsafe. Sun drying only works in hot, dry, low-humidity conditions with protection from insects; a dehydrator is more consistent.
Cool the tomatoes completely before packing. Warm pieces release moisture inside the jar.
Dip in bottled lemon or lime juice
For a softer result, dip the dried pieces briefly in bottled lemon juice or bottled lime juice, then drain. Bottled juice is used because its acidity is standardized. Do not substitute fresh-squeezed juice, water, wine, or a water-vinegar soak as the pretreatment. Those liquids can raise the pH or add moisture the drying step just removed. An older Oregon State Ask Extension reply (2020) described a shelf-stable version limited to skinless pieces no wider than 3/4 inch, dipped in bottled lemon juice, with no other ingredients. The revised 2025 fact sheet no longer treats room-temperature storage as the safe default. Follow the current publication: cold storage.
Cover completely and keep cold
Pack into a clean jar or food-grade container. Pour in oil until every piece is submerged. Olive oil is traditional; other vegetable oils work and may stay liquid longer in the fridge. Tap out air pockets. Leave a little headspace so the oil can expand if you freeze the jar.
Refrigerate for up to 6 months, or freeze for longer storage. Cold storage is required for safety and also slows rancidity. Oil turns cloudy and may solidify in the refrigerator. That is normal. Set the jar in a warm water bath for a few minutes before scooping, then return it to the fridge promptly. If the oil level drops and tomatoes sit above the surface, mold can grow on the exposed pieces. Top up with fresh oil or move the remainder to a smaller jar.
Label the jar with the pack date.
Garlic, herbs, and other add-ins
Unseasoned dried tomatoes in oil, acid-dipped and refrigerated, are the product the 2025 guidance allows for up to 6 months in the refrigerator.
If you add garlic or herbs—fresh or dried—the rule tightens. Oregon State University says dried-tomato mixtures seasoned with garlic and/or herbs must be refrigerated and used within 4 days, or frozen. The same 4-day refrigerated limit applies to garlic, fresh herbs, and pesto in oil. Freezing is the practical way to keep a flavored batch. Freeze in small jars or ice-cube trays, then bag the cubes. Thaw only what you will use.
Do not add fresh garlic, fresh basil, chili peppers, or cheese and leave the jar in a cupboard. Commercial jars that contain those ingredients were made under controls home kitchens do not have, and the label still usually says to refrigerate after opening.
How store-bought jars differ
Commercial sun-dried tomatoes in oil are produced with managed drying, often an acidification step, controlled water activity, and sometimes a heat treatment or approved preservative. The container, fill temperature, and shelf-life testing are part of that process. A home jar with the same ingredients has none of that documentation behind it. Treat commercial jars according to the label: many are shelf-stable until opened, then refrigerated. Do not assume a homemade jar can copy the unopened pantry life of a store jar.
Safer ways to keep the same tomatoes
If the goal is tomatoes that last without a botulism question, oil is optional.
- Dry and store dry. Fully dried tomatoes in an airtight container, in a cool dark place, keep for months. Refrigeration or freezing extends quality. Rehydrate in warm water, stock, or wine when you cook.
- Freeze dried or oil-packed pieces. Freezing stops the growth conditions that matter here. Pack plain dried tomatoes, or pack them in oil and freeze.
- Can fresh tomatoes with a tested recipe. Whole, halved, or crushed tomatoes can be boiling-water canned or pressure canned if you add the required bottled lemon juice or citric acid and use a current USDA or National Center for Home Food Preservation timetable. That is a different product from oil-packed dried tomatoes, and it is the method those charts were built for.
- Refrigerate a small oil batch and use it fast. For a dinner or a week of cooking, a jar in the fridge used within a few days is a low-stress option.
Using the oil and the tomatoes
Lift pieces out with a clean spoon so crumbs and moisture do not fall back into the jar. The tomatoes go on pizza, pasta, grain salads, omelets, and sandwiches. The flavored oil can go into a vinaigrette or a pan sauce once you are confident the jar has been cold and within date. Discard oil that smells like crayons, putty, or stale nuts. That is rancidity, not fermentation you can cook off.
Do not taste a jar that was held at room temperature, especially one with garlic or herbs, to “check if it is all right.” Botulinum toxin does not reliably change flavor. Heat destroys the toxin only if the food is boiled long enough—10 minutes below 1,000 feet, plus 1 minute per additional 1,000 feet—but boiling is a last-resort step for properly pressure-canned low-acid food, not a repair for an untested oil pack. When in doubt, throw it out without tasting.
When to discard a jar
Throw the container away, without tasting, if you see mold, bubbling, a bulging lid, leaking, cloudiness that is not from cold oil, or an off smell. Discard dried tomatoes that were packed before they were fully dry, or any oil pack that sat at room temperature with fresh garlic or fresh herbs. Do not feed suspect food to animals.
Frequently asked questions
Can I process the jars for 10 minutes in a water bath just to seal the lids? No. A short boil may vacuum-seal a lid, but it is not a tested process for tomatoes in oil, and a seal does not make an untested product safe on the shelf.
Are sun-dried tomatoes acidic enough to be safe in oil at room temperature? Drying lowers available water and concentrates acid, which is why some older extension notes allowed unseasoned, fully dried, acid-dipped pieces at room temperature. The National Center for Home Food Preservation still does not recommend preserving tomatoes in oil, and the revised 2025 Oregon State fact sheet requires refrigeration or freezing. Cold storage is the defensible home method.
Can I use wine, vinegar, or balsamic instead of lemon juice? Use bottled lemon or lime juice for the dip. Vinegar and wine add liquid and are not the pretreatment named in the current fact sheet. Do not pack the tomatoes in vinegar and call it the oil method.
How do I know the tomatoes are dry enough? Cool a piece and squeeze it. No moisture should appear. Pieces should bend leathery or snap crisp, depending on how thin you cut them. Flexible, cool, damp centers are not done.
Is freezing in oil safe? Yes. Freezing is the long-term option in the Oregon State guidance for both plain and seasoned dried tomatoes in oil. Leave headspace, thaw in the refrigerator, and use the thawed portion within a few days.