The Fine Details of Dehydrating Tomatoes

30 July 2015, written by Barbara Pleasant

This time of year you will hear a steady hum at my house, but it’s not the air conditioner. The food dehydrator’s little fan spins hour after hour, generating the sweet aroma of drying tomatoes. While I do can and freeze some tomatoes, every year I dry several batches, too. Compared to other storage methods, dried tomatoes take up much less space than frozen or even canned ones, and preparation goes fast – simply slice clean tomatoes and start dehydrating them.

I dehydrate tomatoes and lots of other food crops in an electric dehydrator, but if you live in an arid climate you can use a solar dehydrator instead. Tomatoes are around 93 percent water, so even in an electric dehydrator they take a long time to dry. Without a constant flow of forced warm air to hasten the drying process, tomato pieces can quickly become buttons of mould.

May we pause for a mini-rant? The ‘net is overflowing with recipes for sun-dried tomatoes that never see the sun, with claims that anyone can make them – in an oven! Sorry, but this is no way to actually dehydrate tomatoes. You can use the oven to slowly bake tomatoes until they collapse, and serve or freeze them as delicious "half-dried" tomatoes, but the oven cannot handle the second half of dehydrating tomatoes, in which they change from soft goo to richly coloured leathery pieces. For this, you need a proper electric or solar dehydrator, which bathes tomatoes in a gentle wind of warm, dry air.

Best Tomatoes for Drying

All types of tomatoes can be dried, and I think drying is the best way to preserve juicy cherry tomatoes and large slicing tomatoes that never found their way to a sandwich. These and other high-moisture tomatoes make a watery sauce that can be bitter if the seeds are not removed with a food mill or sieve, but they dehydrate into flavourful tidbits just right for adding to cooked dishes like pasta salad or chilli.

Comparatively dry-fleshed paste tomatoes can be dried, too, and they tend to dry faster than juicier types. I think paste tomatoes are at their best when diced and canned, but one of the great things about dehydrating tomatoes is that you can mix up different types – whatever is ripe that day can go into the dehydrator.

Preparing Tomatoes for Drying

Tomatoes for drying must be cut by hand, and for this you will need a sharp serrated knife that cuts clean and fast. Cut cherry tomatoes in half, and slice larger salad tomatoes into quarters. Bigger tomatoes are best sliced just under one-half inch (8-9 mm) thick. Thinner slices dry unevenly and are prone to turning dark as they dry. You can cut the slices in half to hasten drying.

You may also elect to first remove the tomatoes’ skins, by dipping them in boiling water for a few seconds, but I think the skins provide beneficial structure during the dehydration process. Besides, when you rehydrate dried tomatoes, or put them in a soup, the skins naturally float free and are easily fished out of the pot should you deem them to be excessive fibre.

Seed removal is optional, too. The gel and seeds contain flavour compounds and nutrients that I like to keep intact when drying tomatoes. Why not have raw, whole food with all its flavour features intact?

Dehydrating Tomatoes in Stages

Home food dehydrators circulate warm air continuously, but not uniformly. Some trays dry faster than others, so it is usually necessary to rotate the trays around every few hours to achieve even drying. This is important when dehydrating tomatoes, because you cannot move the pieces until the drying process is almost finished. Tomatoes go through a gooey stage as they dry, which starts 3-4 hours into the drying process and persists until they are almost done. If you try to pick them up during this period, they will tear apart. But if you are patient and wait until the tomatoes flatten into flakes or shrivel into tomato raisins, they are easy to peel from the trays in one piece. In my dehydrator, this takes between 8 and 10 hours.

Like other foods, dehydrated tomatoes benefit from a period of conditioning. I put the newly dried pieces in a big jar, screw on the lid, and keep it at room temperature for a day. Moisture levels equalize between the pieces, after which they almost always feel damp and sticky, which earns them another hour in the dehydrator, arranged in loose piles. Then they are ready to store in airtight containers in a cool, dark place, or in the freezer. They’ll last for six months at room temperature, but in the freezer, dehydrated tomatoes are still perfect after a year.

Dehydrating tomatoes is the best way I know to fit fifteen pounds of tomatoes in a one quart jar, with each piece in recipe-ready condition.

Barbara Pleasant