The tinned tomato test

Let's get the boring bit out of the way first, because it matters. Local and in season, together, is still the best combination going. A tomato grown up the road, picked when it's actually ready, hasn't been heated, cooled, flown, or coaxed into existence out of turn. Nothing beats that pairing. This isn't a blog arguing otherwise.

What it is about is what happens the moment you split "local" and "in season" apart. Because most of the year, in this country, you can't actually have both. And that's where people's instincts start leading them astray.

Picture two tomatoes

One's fresh, bright red, sat on the shelf in January looking like the height of summer. The other's been through a factory in Italy, sliced or crushed, sealed into a tin, and it's been sitting there since roughly last August.

Ask most people which one's better for the planet and they'll say the fresh one without pausing. Fresh sounds virtuous. Local sounds virtuous. Tinned sounds like the thing you reach for when you can't be bothered.

Except that fresh January tomato isn't local and in season. It's local and heavily out of season, which is a very different thing wearing the same word.

Why the fresh January tomato isn't what it looks like

That tomato didn't grow itself into existence in the middle of winter. Either it travelled a very long way, or it grew much closer to home in a greenhouse that had to be heavily heated to convince it that it was summer when it very much wasn't.

Researchers who've gone through the actual numbers found something that catches most people out. Heating a greenhouse to grow tomatoes out of season generates more emissions than shipping tomatoes in from somewhere naturally warm. In one study looking at tomatoes sold in Austria, tomatoes imported from Spain or Italy produced roughly half the greenhouse gas emissions of tomatoes grown locally in a heated greenhouse over the same winter months.

(Source: Environmental Footprint Literature Review: Tomatoes, Oregon DEQ)

So "local" on its own, once you've had to strip the season out to get it, stops being the trump card everyone assumes it is. Heating a British or Austrian greenhouse through winter takes a genuinely enormous amount of energy, more than a lorry driving up from southern Europe ever does.

Where the tin fits in

Tinned tomatoes are usually picked at peak ripeness, in season, somewhere naturally hot like Italy, then processed and canned almost immediately. No heated greenhouse, no refrigerated shipping to keep them looking fresh on a shelf for two weeks, no wastage from tomatoes going soft before anyone buys them. The same research found that tinned tomatoes from Italy came out with one of the lowest footprints of all the options tested, lower than both the local heated greenhouse tomato and the imported fresh one.

(Source: Environmental Footprint Literature Review: Tomatoes, Oregon DEQ)

Which means the tin sat quietly at the back of your cupboard, the one that feels like the boring, uninspired choice, is very possibly doing less damage than the good-looking one in the fresh aisle. Not because tinned beats fresh as a rule. Because that tin kept the "in season" half of the equation intact, and the fresh one gave it up.

The actual lesson here

It's not local versus tinned. It's that "local" only earns its reputation when it's also in season, and the two get separated far more often than people realise.

A fresh tomato grown in a UK greenhouse in January is local, but it's not remotely in season, and getting it to look fresh took a lot of gas to fake the conditions it needed. A tinned tomato from Italy travelled much further, but it grew in the sun it actually wanted and got processed straight away with almost nothing wasted. The tin didn't win because distance stopped mattering. It won because it kept the one thing that actually does the work.

What this actually means for your shopping

Not that you should avoid buying any fresh tomato and live exclusively out of tins. Fresh, in-season, UK-grown tomatoes in July are about as good as it gets, and there's a decent argument they taste better too. When local and in season line up, take it every time.

But come winter, when the choice is between a hothouse tomato coaxed into existence at real environmental cost, and a tin of something picked in the Italian sun back in August, don't assume the fresh one wins just because it's sitting closer to home. Check what season it's actually pretending to be first.