You did the sums before you started: a warm shelf, a few weeks of August sun, tomatoes halved and laid out to dry the way every recipe blog describes. Then a Scottish August delivered cloud by the day, a run of showers and humidity that never drops below "damp". The tomatoes went soft and started weeping juice rather than shrinking, and some grew a fuzz of mould at the cut edge before they'd lost half their moisture. That isn't a technique failure: it's a climate mismatch.
What true sun-drying requires
Traditional sun-dried tomatoes, made in Puglia or Andalusia for centuries, depend on several days of sustained heat, low humidity and near-constant airflow. Halved tomatoes are laid out in direct sun and turned regularly, and the process takes multiple days, not hours. Through all that time the fruit has to stay warm and dry enough that bacteria and mould can't take hold before the water content drops low enough to be safe. Traditional setups use fine mesh over the trays against flies and wasps, and any rain or heavy dew in the drying window can undo days of progress and restart the mould risk.
Scotland rarely gets that run of days. Even between June and August, the Met Office's 1991-2020 averages give Edinburgh about 32 rain days and Tiree about 42 (days with 1mm or more), so a reliable multi-day dry stretch isn't something you can plan a harvest around. Tomatoes left out too long in damp air don't dry, they rot, because the moisture doesn't leave fast enough to outpace bacterial growth before the next shower. An oven or dehydrator does the same job as the sun, driving off moisture faster than spoilage organisms can establish, but with heat you control rather than weather you're hoping for. A polytunnel or greenhouse on a warm, still day gets closer to sun-drying conditions than an open windowsill, since it traps heat and keeps rain and dew off the trays, but it can't be relied on for several consecutive warm days on demand.
Choosing tomatoes that dry well
Meaty, low-moisture varieties dry faster and shrink less disappointingly than watery ones. Roma and other plum types, and small varieties bred for sauce and paste, have thicker flesh and fewer seed cavities relative to their size. Principe Borghese, an Italian heirloom commonly grown for drying, is one of them. Large, juicy beefsteak types carry so much water that they take far longer to dry and tend to collapse into leather. Cherry and small salad tomatoes work too and need less prep, since they can often be dried in halves without seeding.
If your glut is the awkward kind, with end-of-season fruit still green when the first frost threatens, or fruit with an early touch of blight, green tomatoes won't dry down the same way, so ripen them indoors first: they're mostly water and haven't developed the concentrated sugars and flesh structure that make ripe fruit dry well. Cut away and discard any fruit with blight lesions rather than drying it: drying concentrates what's in the flesh and doesn't make damaged or diseased tissue safe to eat.
Preparing the tomatoes
Wash and dry the fruit, then halve them (or quarter larger ones). For tomatoes with a lot of seed jelly, scoop it out with a teaspoon, which speeds drying and reduces the wet pockets where mould can start later. Lay the pieces cut side up on the tray or dehydrator rack without touching, and a light sprinkle of salt helps draw out surface moisture as well as seasoning the result.
Oven versus dehydrator
There's no official UK figure for oven-drying tomatoes. The guidance that exists comes from US university food-science departments and broadly agrees on a low, steady heat held for several hours, with airflow to carry moisture away.
| Method | Temperature | Typical time | What to watch for |
|---|---|---|---|
| Oven | Roughly 60-65°C (140-150°F), the lowest a domestic oven will hold steady | Several hours, checked regularly; depends on tomato size and your oven’s real low-end temperature | Prop the door open slightly so moisture can escape; rotate trays for even drying; larger halves take considerably longer than a thin scatter of cherry tomatoes |
| Dehydrator | Around 60°C (140°F), within the appliance’s typical 30-70°C (85-160°F) range | Several hours to overnight, depending on size and thickness | Generally dries more evenly than an oven thanks to fan airflow, but check trays partway through and rotate if your model runs unevenly |
With a fan oven, err towards the cooler end of the range and check earlier than the timings suggest, since moving air dries the surface faster. Tomato size, water content and how thickly you've packed the tray change the real drying time more than any published figure can, and most gluts need more than one batch. A dehydrator run overnight on low uses less energy than an oven held on low for several hours.
How to tell they're done
Properly dried tomatoes are shrivelled and leathery, dry to the touch outside, and still pliable and chewy rather than snapping. Most dried vegetables are dried until brittle, at about 10% moisture, but tomatoes are traditionally left with more give, which means less margin for error in storage, so the checks below matter. Break a few pieces open and check the centre, not just the surface: thick pieces, or ones packed close together on the tray, can look dry outside and still be damp in the middle, and that trapped moisture has nowhere to go once the jar is sealed. If you're unsure, put the batch back in for longer.
Storing dried tomatoes safely
Cool the pieces completely before packing, since warm food sweats and the moisture can let mould grow. Pack them loosely in a clean, dry glass jar, where any moisture collecting on the inside is easy to see, and check the jar daily for condensation for the first week or so. If condensation appears, return the tomatoes to the oven or dehydrator. Then keep the jar in a cool, dark, dry place and check it from time to time.
Dried vegetables have about half the shelf life of dried fruit, which works out at roughly six months at about 15°C and nearer three months if the storage spot is warm (around 27°C), so a cool cupboard rather than one near the oven or a radiator extends a jar's life. That is mostly about quality fading, but leathery tomatoes leave less margin than brittle ones, so use the older jars first and keep checking them. Dried tomatoes without oil also freeze well and keep for months, which is an easy way to hold a big glut. A full tray of fresh fruit shrinks to a disappointingly small handful, so it's worth drying more than one batch if you've got a big glut to get through.
The safety issue is oil. Covering dried tomatoes in oil creates a low-oxygen environment, which is the condition Clostridium botulinum needs to grow and produce toxin. Some recipes, and the RHS, mention storing dried tomatoes in jars of oil, but food-safety extension guidance is more cautious, and home-prepared vegetables in oil are the usual source of reported botulism outbreaks. Refrigeration only slows the bacteria rather than guaranteeing safety, so the safe home approach is to keep oil-covered tomatoes in the fridge, use anything seasoned with garlic or herbs within about four days, and freeze rather than keep a jar longer. Don't leave a home-made jar in oil on a cupboard shelf, even though shop-bought ones sit unrefrigerated: commercial producers use controls a home kitchen doesn't have.
Using them
Rehydrate dried tomatoes by soaking in warm water or stock for twenty to thirty minutes before using them in sauces, stews or bread doughs, or chop them finely and stir them straight into slow-cooked dishes where they'll soften as they cook. Blitzed to a powder, thoroughly dried pieces make a concentrated flavour booster for soups and dressings through the winter.
Common questions
Can I dry tomatoes outdoors in Scotland if I catch a hot week?
In principle, if you get several consecutive dry, warm, low-humidity days, cover the trays with fine mesh against flies and wasps, and bring everything in at the first sign of rain or heavy dew. In practice that run of weather is unreliable enough here that most growers get more consistent, safer results from an oven or dehydrator.
My oven’s lowest setting is hotter than the guidance range. Is that a problem?
It will dry the tomatoes faster and with less control, and the outside may finish before the inside has lost enough moisture. Propping the door open a little further, checking more often and trusting the doneness test over any specific time are sensible ways to compensate.
Why do my dried tomatoes go mouldy in the jar after a few weeks even though they looked dry?
Almost always under-drying, usually in thicker pieces or ones packed close together on the tray so moisture couldn’t escape evenly. Break a few open before storing a whole batch and check the centre, not just the surface, and check the jar daily for condensation in the first week.
Is it safe to store my dried tomatoes in olive oil like the jars you buy in shops?
Not at room temperature. Oil creates a low-oxygen environment in which botulism bacteria can grow, and commercial producers use controls a home kitchen doesn’t have. At home, keep oil-covered tomatoes in the fridge, use them within about four days if they contain garlic or herbs, and freeze them for longer storage.
Do cherry tomatoes need less prep than larger varieties?
Yes. Halved cherry tomatoes have less seed jelly and flesh depth, so they can usually go straight onto the tray cut side up without scooping, and they dry noticeably faster than halved or quartered larger fruit.
Sources
Show the 7 sources
- RHS: What to do with a tomato glut: Drying cherry tomatoes cut side up with a little salt in a dehydrator or oven on low heat; mentions storing in jars of oil
- National Center for Home Food Preservation: Food dehydrators: Dehydrators dry food fast at 140°F; thermostat range 85-160°F; fan for air circulation
- National Center for Home Food Preservation: Packaging and storing dried foods: Vegetables have about half the shelf life of fruit (fruit 1 year at 60°F, 6 months at 80°F); cool, dry, dark places; check frequently; cool before packing; glass jars show moisture; vegetables dried until brittle
- University of Illinois Extension: Drying: Oven maintains 140-150°F with door slightly open and a fan; conditioning; check the container daily for condensation
- Oregon State University Extension: Herbs and vegetables in oil (SP 50-701): Dried tomatoes in oil with garlic or herbs refrigerated and used within four days or frozen; botulism risk of vegetables in oil
- Met Office: Edinburgh, Royal Botanic Garden long-term averages (1991-2020): Rain days of 1mm or more: June 10.4, July 11.5, August 10.4
- Met Office: Tiree long-term averages (1991-2020): Rain days of 1mm or more: June 12.1, July 14.3, August 15.4
A note on the numbers above: no UK body publishes an official oven temperature or time for drying tomatoes, so the specific figures in this piece come from US university food-science sources rather than a UK one. Treat them as a well-supported general range rather than an official single number, and prioritise the doneness checks in the text over the clock.