Why today’s tomatoes look great but don’t measure up in the taste department
Science learns why the taste disappeared
OTTAWA – Growing up in Alabama in the 1950s, Stuart Collins ate tomatoes his father grew. He can still remember the taste — powerful, sweet, and nothing like supermarket tomatoes today.
Collins now grows old-fashioned tomatoes commercially at Bryson Farms in Shawville, Que.
Farmers call them heirloom varieties, meaning they aren’t modern hybrids. They aren’t as pretty as modern varieties, but they taste like the old tomatoes from the 1950s.
Farmers have become more efficient at growing tomatoes. The fruit stands up to shipping across continents, lasts a long time in the refrigerator, and can fall off the table with barely a bruise.
But what happened to the taste?
A California food scientist knows. Ann Powell found that all that breeding and modernizing accidentally made one mutation, the tiniest change it’s possible to make in DNA, which changed the flavour of the tomato.
Her paper has a fancy title about transcription factors and chloroplasts, but Science magazine, the major research journal that published it, simplified it: “Why supermarket tomatoes taste like cardboard.”
Powell, a biochemist at the University of California at Davis, cringes at those words.
“I’m just a nerdy little scientist,” she said, and she didn’t want to be rocking boats in a major industry.
Still, she has some qualified good news. Growers can get the flavour back, one way or another. Powell has been working on how fruit ripen for more than 20 years, “so I’m interested in lots of aspects of what happens to tomatoes.”
And information on tomato genes has suddenly become available, with the completed decoding of the tomato genome, or full set of tomato DNA. That makes gene-hunting easier.
Genes work indirectly. Each one carries a code that creates a matching type of protein, which in turn does the actual work of making the cell develop one way or another.
The protein at the heart of the tomato story is called GLK2. It does two jobs: By helping with photosynthesis, or drawing energy from the sun, it helps the tomato produce the pigment called lycopene that makes the fruit red. It also helps the tomato produce sugar.
It was colour that had growers’ attention. Over the past 70 years, producers have crossbred tomatoes to create varieties that turn red all over at once, instead of the more natural tendency to turn red at the bottom while still green at the stem end.
The red-all-over tomato looks wonderful. It’s also much easier to judge when it is ready for harvest. Unfortunately, the breeding somehow disabled the GLK2 protein, and shut down much of the sugar production.
“It was bred out completely inadvertently,” she said.
“You can see the trait very easily when the fruit are green. It’s not easy to see when they are ripe. These are fruit that are uniformly light green,” whereas tomatoes without this mutation tend to have darker green “shoulders” near the stem.
Suddenly tomatoes were growing fat and red and tender and juicy, but lacking in sugar, the substance that’s crucial to the flavour of all fruits. (Tomatoes are technically fruits, not veggies.)
Flower researchers are trying to fix a similar problem with roses that are big and hardy but have less smell than a dandelion. They too blame overbreeding.
At Bryson Farms, Collins often introduces jaded shoppers to the old-fashioned tomato, which actually means about 300 varieties.
“Once they taste them they freak out,” he said. “I have elderly people who come to the booth (on Sundays at Brewer Park in Ottawa) and say ‘I remember my mother growing tomatoes that tasted this great.’ The fact is that they have bred out all the taste in place of uniform ripening, resistance during transportation. They never rot. They have all these wonderful characteristics for transportation but they have absolutely no taste.”
Among his older varieties, “some of them look horrible, some look ugly, some of them are black, every colour imaginable, even multi-coloured. And each variety has a different flavour.”
Yellow and oranges are generally sweeter. White tomatoes have no acid and are very sweet. Black and multicoloured varieties are the most popular.
“Years ago it was very difficult to get the seeds. Now they are becoming more popular. It’s no longer our best-kept secret.” This year Bryson Farms planted 40,000 tomato plants, about 10 acres.
The tomato has about 35,000 genes. Each gene has thousands or millions of individual “letters” of DNA code. The change that created the cardboard tomato came from just a single one of those millions of tiny pieces in just one gene, and although there are many varieties of commercial tomato, this mutation has crept into most of them.
But not into cherry tomatoes, Powell notes. Little tomatoes are grown and harvested in a very different way and were never subject to the same type of breeding. As a result, she says, they still have much of the natural tomato flavour.
“This is one of the reasons that probably contributes to the better flavour in cherry tomatoes ... It’s not the beall and end-all, but it’s one of them.”
It’s easy to put the original gene back in, she argues. “It’s in a lot of heirlooms. It’s in a lot of wild species” that are preserved as reservoirs of valuable genes.
But when a breeder shuffles the genetic deck, bad surprises can crop up as well. A big question is whether using heirloom tomatoes to breed back the flavour gene would also bring back traits that growers consider bad — smaller tomatoes that are harder to harvest on the massive scale of modern farming, for instance.