Is it healthier to leave tomatoes on the vine?

tomatoes (1)Living in Boston, we barely have room for counter space, never mind tomato plants. Luckily, my mother-in-law has a soil-worn emerald green thumb that she puts to great use in her circular garden just an hour north of us in New Hampshire.

Summer visits are the best, always ending with a goodie bag full of garden surplus for the city folk. This weekend’s bounty included three beefsteak tomatoes, fat with juice. They were more plump than their anemic grocery store counterparts, but they were all a yellowing-green. My mother-in-law reassured me the color didn’t matter.

“If I don’t pick them now, something else will.”

I’d thought the luxury of growing your own veggies was eating them the moment they ripened. But she was the expert, and the gardening blogs I read on the way home had a healthy supply of growers who did the same in their best attempt to beat birds, squirrels, and insects to their hard-earned harvests.

I’ve happily watched my beefsteaks kaleidoscope from green-yellow to yellow-orange to not-quite-red. Still, I couldn’t help wondering whether their vines would’ve delivered more flavor and — more importantly — more nutrients to the fruits.

So I finally dove head-first into a research hole to see what science had to say about it.

What Makes a Tomato Red

It seems to be simple chemistry. According to sources cited in an article in the Journal of Food Science (and pretty much every newspaper article and gardening blog you’ll find), tomatoes go from green to red when the fruits’ chlorophyll changes to lycopene.

In tomatoes, the pigment helps harvest light and protects the plant from sun damage. In humans, lycopene has been touted by natural foodies and even the NIH as an antioxidant with the potential to lower the risk of cancer and heart disease. And, as far as the evidence shows, you’ll get your dose of it if you ripen your tomato before biting in, regardless of whether its on the vine or the windowsill (lycopene or not, I’ll still be popping fried green tomatoes every chance I get).

When to Pick Tomatoes for the Most Nutrients

Tomatoes are brilliant little packets of antioxidants like vitamin C, vitamin E, beta-carotene, and our new friend lycopene. But do the levels of those healthful nutrients vary depending on when you pick the tomatoes?

A study in a Korean horticultural journal tested just that. The experimenters found tomatoes that were picked green had the most Total Antioxidant Activity (followed by vine-ripened, then tomatoes picked pink). That’s with the skin on. Apparently skinning the fruits reverses the order, meaning vine-ripened tomatoes have the highest antioxidant levels in their flesh alone.

Then there’s the raw vs. cooked debate. Some antioxidants like vitamin C break down with heat, while others like lycopene become more available when cell walls are damaged by cooking. Overall, science says you’ll get the highest Total Antioxidant Activity when you cook your tomatoes.

But What About the Taste?

If you know what you’re doing, picking green tomatoes shouldn’t affect flavor. The Cornell Vegetable Program recommends picking the fruit when it first starts to ripen (not before!) and finishing ripening at room temperature. And don’t even think about putting them in the fridge if you want them to taste good.

Side Note: Cornell also says sun exposure and soil fertility do not affect the ripening process. The optimum temperature for ripening tomatoes is 70-75F, and ripening can slow or even stop in temperatures ten degrees higher or lower than that range.

Is it healthier to leave tomatoes on the vine?

If you want to get the most antioxidants for your bite:
Pick your tomatoes just as they’re starting to ripen on the vine. Put them on the counter until they turn red, then cook them up in a tasty sauce, soup, or whatever tickles your tastebuds to release all the fruits’ lycopene (and flavor) potential.

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