By Kelly Murray, CNN
Editor's note: The Science Seat is a feature in which CNN Light Years sits down with movers and shakers from many different areas of scientific exploration. This is the fourth installment.
Ever wondered why some tomatoes taste great, and many others don’t?
Professor Harry Klee, a horticulturalist at the University of Florida in Gainesville, is on a mission to improve the taste and quality of supermarket tomatoes. He was elected to the National Academy of Sciences in 2012 for his efforts.
Klee presented his research in Boston recently at the American Association for the Advancement of Science annual meeting. CNN Light Years spoke with Klee before the conference. Here is an edited transcript:
CNN's Kelly Murray: I just want to be upfront. I hate tomatoes; I hate raw tomatoes.
Harry Klee: I don’t blame you. I don’t (like them) either!
CNN: I like cooked ones though.
Klee: Yeah, I’m pretty sick of tomatoes myself after sampling many thousands of them. I’m not a big fan of raw tomatoes either. Although I eat massive quantities of them cooked.
CNN: Tell me about what exactly your lab does. How do you study the flavor of tomatoes?
Klee: Over the last five years or so, we’ve probably grown over 300 different kinds of heirloom tomatoes. We take those tomatoes, and we grind them up to see what’s in them, and then we give samples of each of those to consumers, and we ask them how much they like them. We measure how much sugar is in there, how much acid is there, and we measure the volatile chemicals with a machine called a gas chromatograph. And you can use simple, statistical models to basically extract out a recipe for what is a good tomato.
CNN: How would a fruit like the banana differ from the tomato?
Klee: So that’s a really good question. Bananas tend to have very few chemicals that contribute to their aroma. There’s one chemical I can give you that if you smell you’ll say, "Oh, it’s a banana." But when you look at a tomato, there’s no single compound that you could smell and say, "Oh, that’s a tomato."
We estimate a tomato probably has 30 different volatile chemicals that all contribute to its unique smell and taste. So that is the main reason that working on the flavor of a tomato is so challenging because we can’t just go in and manipulate a couple of chemicals and make the tomato taste better. It’s really kind of a palette; it’s almost like a painting in your mouth of many different colors that, altogether, contribute to making a tomato taste like a tomato.
CNN: Is there another food to which you could compare the complex palette of a tomato?
Klee: Wine is probably the best comparison. And again coming back to how important smell is, I always tell people, the best way to really appreciate a wine is to hold your nose. If you hold your nose, you block the ability of those volatile chemicals to get to their receptors, and if you swirl a glass of wine around in your mouth while you’re holding your nose tightly, you get almost no perception. And then, just as you’re ready to swallow, if you release your nose, you’ll get this incredible release of the volatile chemicals that will just give you this really amazing, instantaneous taste that is the wine.
And it turns out that actually many of the volatile chemicals that contribute to the nose of wine are the very same chemicals that contribute to the flavor of tomato. A wine aroma is probably 20 or 30 different chemicals that all are mixing together to give the wine its complex taste – the same exact phenomenon with the tomato.
CNN: Do most people agree upon what is a good tomato?
Klee: I think everyone would agree on a very good tomato, but I don’t think people will agree on what their favorite tomato is. Tomato flavor, very simply, is three different kinds of compounds that are in the fruit: sugars, acids and volatiles. The sweeter the tomato is, generally the more people like it. You have to have acid to balance that sugar, so some people like a tomato that’s a little tarter than others. And then we get to the real complexity of the tomato, which is the volatile chemicals. Volatiles is just a fancy name for chemicals that you smell.
We’re going to ignore, for now, the texture and the visual appearance, as both things can influence how something tastes. Basically you have two different sensory systems that contribute the most flavor. Taste, which is the receptors on your tongue, where you get sweet, sour, salty and bitter. And smell is where you get all the flavor in my opinion. If you’ve ever had a cold, and you can’t taste anything, the cold is really blocking just the smell.
CNN: Which is people’s favorite tomato, based on your research?
Klee: It’s very clear that people like the heirloom tomatoes. We take a lot of questions when we recruit our consumers, and basically you can divide them out into the foodies and the non-foodies. There are people who live to eat and there are people who eat to live. And you find that they like slightly different tomatoes. Your basic non-foodie really likes sweet. When we look at the foodies, we find that they like a much more complex tomato with more volatile composition. Overall, a lot of the top ones are cherry tomatoes or fairly small tomatoes. Also, everybody who tastes Brandywine pretty much likes it. I think your average consumer is going to like a smaller tomato because it’s going to have more sugar in it.
CNN: Among your basic, commercial tomatoes in the grocery store, how, in your expert opinion, would people pick out a good-tasting tomato?
Klee: The problem with the tomatoes is they all look good. Also, many commercial tomatoes have been refrigerated. And the wholesalers refrigerate them, and then the supermarkets refrigerate them, which ruins the flavor.
CNN: So would you go to the farmers market to buy tomatoes?
Klee: Yeah, I would. But the problem is you can only get them in season. There are some varieties that sell for more on the supermarket shelves that have been picked when they’re ripe, and have in theory, not been refrigerated. A really good one is called Campari. Most supermarket chains carry them. They’re going to cost you twice as much as the typical bulk bin tomato, but it’s a very good product.
CNN: How about buying tomatoes ‘on the vine.’ Does that really influence the flavor of a tomato?
Klee: So the problem here is when you’re picking those tomatoes on the vine, you pick them up and you smell them and you do smell something. You’re actually smelling the vine and not the tomato itself, so it’s really a marketing gimmick. The good thing about those tomatoes that are picked on the vine is that generally they are picked when they’re ripe.
CNN: So a lot of the volatiles must develop very late in the ripening process, while the tomato’s still on the vine?
Klee: Yes, they do. Most of the important volatiles are synthesized by the fruit basically after it’s started to change color and before it is fully red. And so, basically, if you pick that tomato early when it’s still green, you’re disrupting the natural ripening process. It occurs, but it doesn’t occur quite the same way as when it’s attached to the plant.
CNN: People talk about heirloom tomatoes being closer to the “original” tomato. How is the heirloom tomato different from what we consider the modern, commercial American tomato?
Klee: There is no real definition of an heirloom tomato. Most people would classify heirlooms as being very old varieties. I would probably draw the line at maybe World War II. Most people would say heirlooms are what we call open-pollinated – that is, when you can save the seed. It breeds true.
Virtually all of the modern varieties are hybrids, so that means when you get seeds out of the fruit, they’re not going to breed true, they’re going to be different. Generally heirloom varieties are really hard to grow. You don’t get a lot of fruit, and sometimes the fruits have really short shelf lives. They crack easily and they’re really soft. Modern varieties are far, far superior in terms of yield, disease resistance and shelf life. But the big thing – at the heart of the difference – is heirlooms frequently do taste very good, and modern varieties frequently don’t taste very good.
CNN: I’d argue that the texture is not even that good. On a fast-food hamburger, you get a tomato, and it’s just soggy and flavorless and not even a pretty color.
Klee: You’re absolutely correct. And part of the texture is also related to the modern breeding for long shelf life and shipability. People are passionate about tomatoes, but a large majority of those people are really disappointed in what they can buy at the supermarket, and so they don’t buy them. But if I can make a tomato that really tastes like an heirloom tomato, that’s really good, would you really like it more?
And if you really liked it more, would you eat more of it? I think if we’re successful in understanding how to improve flavor, to bring back flavor to where it was 100 years ago, but maintain that in a package that the growers can still grow and make money at, you’ll make healthier dietary choices. What if we can make a peach that you can bite into that will taste just like a peach is supposed to taste like, like you just picked it off the tree, warm from the sun. Would you choose to eat that instead of a piece of cake? By and large, I think the answer to that is yes.