Sugar is not what makes tomatoes sweet, or anyway, not what makes people think they are sweet.
Which brings me back to our “market based” research on tomato flavor. Which is the sweetest tomato we grow? It depends. On many things, including the time of year and the daytime and nighttime temperatures. But mostly it depends on the person eating the tomato. You can offer three different people a taste of three different tomatoes at the peak of their season, and each person will choose a different tomato as “the sweetest”. It’s fairly amusing to do this experiment and watch people argue about their choices.
If tomatoes tasted like rock candy, there would really be no room for debate on this issue — the variety with the most sugar content would win. Luckily, nature prevents plant breeders from creating “Kotton Kandy” variety tomatoes because the biochemistry of tomato plants will not allow them to make that much sugar.
Instead, it turns out that tomatoes have dozens of other compounds that enhance their flavor and make you think they are sweeter — their own version of MSG. Tomatoes containing more of these compounds — many of which are heirloom varieties — taste sweeter. But they aren’t sweeter. And each tomato variety has a slightly different mix of the compounds. This is why one person might prefer the combination of aromatic flavors-enhancers in a Cherokee Purple that give it a tangy, smoky sweetness, while another might prefer the floral citrus-esque taste of a Marvel Stripe.
In my opinion, the most important characteristic of a tomato isn’t its flavor anyway, but rather its texture — the combination of juiciness, meatiness and satin that make it so sublime. It doesn’t matter how many great flavor genes a tomato has if it’s mealy. Tomatoes get mealy when they are harvested too green, or exposed to cold temperatures. And both things tend to happen when they are grown far away, shipped long distances and eaten out of season.
And so I have two pieces of advice for the plant breeders in Kentucky: Good luck getting consensus on which tomato tastes best. And good luck breeding a tomato that still tastes good when it is grown in Florida and trucked to New Jersey in the dead of winter. Until they figure this out, the best way to get a nice “sweet” tomato is to buy one locally, in season. It doesn’t even have to be an heirloom.