What makes this tomato

By James Vincent, a senior reporter who has covered AI, robotics, and more for eight years at The Verge.

Chances are you’ve seen this tomato-sorting machine before. Video footage of it goes viral on a semi-regular basis, as with this clip above, tweeted by @MachinePix this week. As mechanical contraptions go, it's impressively fast and unnervingly precise. It's sorting tomatoes, but it looks like the fingers of God flicking damned souls straight into hell.

It is also, according to Jim Frost, product manager at Tomra, the company that makes the thing, old hat. "We’ve been selling these machines for 25 years now," he tells The Verge in a phone interview. "This particular sorter is sort of the mother of all sorters. It's quite basic, and gets used out in the field."

Tomra (and lots of other companies) sell sorters like this around the world for all types of produce. They sort everything from peaches and potatoes to grapes and grains — some 60 percent of processed food gets sorted this way, guesses Frost. There's a line of optical sensors looking down onto the conveyor belt and a row of "rejectors" positioned like teeth on a comb just below. "We use the finger-type rejectors for larger produce, and air rejectors for smaller stuff," says Frost.

(A sorting machine using an air-rejection system on grapes made by rival firm Europress.)

Although machines like this look incredibly complex, Frost says that they’re actually pretty simple. The decision whether or not to reject a piece of produce (or stone, or clod of earth, as often happens) is a yes/no question that can be answered without much calculation. Likewise, because the rejectors are spread out in a line, it's just a matter of timing to pick the right one to knock out the offending article. And over the years the machines have gotten good.

"You’re talking about each and every one of those flickers working in a window of just 30 or 40 milliseconds," says Frost. "It has to get out there, reject the item, then tuck back in as fast as possible so as not to hit anything else."

The real engineering challenge for companies like Tomra is durability. Sorting machines like this are only deployed seasonally, but during that time they’re in constant use. When tomatoes ripen in California, for example, they’re harvested in a 12-week period that has sorters running round the clock, up to 24 hours a day, processing as much as 800 tonnes of vegetables an hour.

During this time farmers can't afford to have any stoppages. The tomatoes are ripe and need to be tinned or canned within 24 hours. Frost says this is why he actually prefers preserved tomatoes to ‘fresh’ ones. If they’ve been canned, he says, that means they were ripening in the sun until the very last minute and have more flavor because of it. "Canneries get a bad press, but it's one of the few foods that has as little additives in it as possible," he says. "There's salt, tomato juice, and tomatoes. That's it."

As for why clips like this go viral, Frost isn't surprised. He says most people just don't know how common technology like this is. "This particular footage impresses so many people," he says. "We have people come in — customers who we’ve been dealing with years — and they see the thing actually happening and they say ‘Oh my god that's unbelievable!’ and I tell them ‘We’ve been doing this for 20 years, where were you?’"

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