Few pleasures are simpler than sitting on your back step savoring the taste of summer’s first vine-ripe tomato. Yet if you look at it closely, few things are more complicated. Sure, a bite of a sweet, deeply flavored tomato is one of life’s more elemental joys. It’s a flavor we yearn for all through the cold months, an experience we remember from our childhoods. And yet in real life, that kind of juice-gushing taste explosion is something that happens all too rarely. Tomato flavor, or the lack thereof, is one of the biggest complaints in the produce world. And there is no easy fix.
In part this is because the taste of a tomato is a devilishly difficult thing to pin down. In the first place, as real tomato lovers know, all tomatoes don’t taste the same. Instead, there is a whole range of flavors, from almost citrusy to nearly meaty. But even if you’re just trying to describe that essential tomatoey flavor, the problem is incredibly complex.
Flavors and aromas are made up of chemicals, and although some fruits, such as the banana, can be identified by just one (3-methylbutyl acetate, if you’re curious), scientists who study flavor chemistry have identified more than four hundred compounds that go into the taste of a ripe tomato. And more than thirty of those are regarded as essential—detectable in amounts down to one part per billion. (Even this tiny bit may not be sufficient when you’re dealing with tomatoes. The human nose can detect some odors/flavors in parts per trillion.)
Furthermore, the science of flavor is much more complicated than simply putting a bunch of elements together in a chemistry set. When scientists talk about the chemical compounds that make up flavor, they don’t speak the same language we do. They disdain romantic descriptions such as “beefy” or “minty” or “flowery” and instead zero in on specific names: Z-3-hexenal, beta-damascenone, beta-ionone and 3-methylbutanal.
Those are hardly words to make a gourmet’s heart flutter, but they are the four flavor compounds found in the highest concentrations in a raw tomato. Z-3-hexenal is a fresh green fragrance often found in the aroma of cut grass (it also dissipates quickly, disappearing when heated). Beta-damascenone is generally described as fruity and sweet, while beta-ionone is fruity and woody. The last compound, 3-methylbutanal, is hard to describe; one source describes it as having “nutty-cocoa facets.” It is also found in Parmesan cheese.
But a high concentration of a compound does not necessarily mean that it is the most important element. Some chemicals found in tomato flavor are more distinctive than others, even though they may be found at far lower concentrations. Methyl salicylate, for example, makes the distinctive smell of wintergreen. Linalool is a sweet, floral scent found in coriander seed and oranges. Safrole—found in wintergreen, anise, vanilla and camphor—is often described as smelling like root beer. In fact, it was used as a chemical flavoring for the drink until it was found to be mildly carcinogenic.
Chemicals are perceived in different ways as well. There are “top note” flavors, which tend to be heat volatile, meaning they are released just from the warmth of your mouth and are immediately identifiable. And there are “bottom note” flavors, which are not so volatile and linger in the background. And you wondered why there is no such thing as a good artificial tomato flavoring?
All this chemical name-dropping is of more than academic interest. To get a handle on the problem of tomato flavor, scientists need to be able to quantify just what it is made of, where it comes from and how it can be measured. This is far more complicated than you might think. To begin with, the chemical nature of flavor is not static. The flavor compounds that are present in a whole tomato change when the cell structure of that tomato is altered.
Slice a tomato, and chemicals combine and react. Chew it, and the same thing happens. Even more elusive: when you eat a tomato, some flavor compounds are formed by the interaction of the tomato’s chemicals and your own—those enzymes found in saliva, for example.
The fruit is constantly changing, too. It doesn’t take slicing or chewing to start the flavor reactions. Cell walls soften during ripening, which allows the exchange and combination of chemicals. This process, in particular, is the key to much of what we regard as fine tomato flavor. As tomatoes ripen, all sorts of flavor-building events occur. The first and most obvious is that the color changes from dark green to brilliant red (well, in most cases). This is not simply a matter of decoration. That color change is caused by the development of coloring chemicals called carotenoids. And unlike some other pigments, these have flavor-causing chemicals attached to them.
At the same time, as the tomato ripens, the amount of sugars builds, and their composition changes. Green tomatoes don’t have much sugar, and what is there is mostly glucose. As the fruit ripens, the sugars that develop are much more heavily weighted to fructose, which is three times sweeter than glucose. The acids in the tomato change as well, from malic (such as that found in apples) to citric, which actually increases our perception of the sweetness of the glucose that remains. A whole host of aromatic chemical compounds are formed—hexanal (which is frequently described as “winey”), alanine and leucine (meaty) and valine (fruity). Furaneol, which has a characteristic pineapple aroma, is also created, as are some unusual aroma compounds that are not found in any other fresh fruits, but which are found in flowers. In addition, the sheer physical softening of the flesh that comes with ripening increases our perception of flavor.
This ripening doesn’t have to happen entirely on the vine. Tomatoes are climacteric fruits, like peaches and mangoes, and if grown to something approaching physiological maturity, they can be picked while still solid green and continue to ripen in storage. And as with other climacteric fruits, this process is encouraged by exposing the fruit to ethylene gas. In the trade, most of the tomatoes ripened this way are sold as “mature-green,” and they still make up the bulk of the standard tomatoes found in the market. Picked at just the right moment and ripened this way, a tomato can be adequate, but it will never be great. Picked a day or two too early, no matter how much gas is applied, it will never develop flavor, even though it may change color. This is particularly troublesome because it is nearly impossible to look at a whole green tomato in the field and tell whether it is mature enough to pick—the color is virtually identical to one that is still immature. The only way to tell for sure whether a green tomato is ready to pick is to cut it open and see whether the gel around the seeds has softened. Since the growers cut open only a few tomatoes to check and since tomatoes don’t mature uniformly, inevitably a significant percentage will be so immature that they will never develop any ripe flavors at all. Even so-called vine-ripe tomatoes are picked at a stage that most of us would consider green, when only the very first traces of a tan, yellow or pink “blush” appear on the tomato’s base.
The holy grails of tomato flavor study are techniques that would tell plant breeders which varieties have the best flavor, tell growers when tomatoes are ready to be picked and tell packers and shippers when the fruit is ripe enough to go to the store. Obviously, every tomato cannot be run through a sensory panel to determine its culinary worth. Just as obviously, taking apart a tomato’s chemical components to try to measure flavor is incredibly difficult. One of the latest attempts to understand and measure just what is going on when we eat a ripe tomato was developed by scientists in Florida, who actually waved chemical sensors under the noses of people who were chewing tomatoes. Fine-tuning tomato flavor at this level is something that could take forever.
Much more practical steps can be taken that would improve tomato taste a lot more quickly, but the research to discover them is just beginning. Most of the research up until now has been aimed at solving what seemed to growers and shippers to be more important flaws.
At its most basic, the biggest challenge with tomatoes is the same one faced by so much of agriculture—to produce a fragile, temperamental product on an industrial scale. By nature tomatoes are thin-skinned and late-maturing, to say nothing of being prone to a wide array of diseases and insects. That we have such an insatiable demand for them—cut up in salads, sliced onto hamburgers, chopped up in salsas—is a cruel irony. It would be a lot better for everyone involved if those culinary functions could be filled by, say, an orange or a zucchini, any fruit or vegetable that isn’t always poised on the edge of self-destruction.
But we must make do with the fruits and vegetables that we have, not the ones we may wish we had. And up to now, quite frankly, taste has been the least of anyone’s concerns. As a result, breeders have developed tomato strains that resist all manner of cankers and wilts, without paying much attention to choosing ones with great flavor. And farmers and shippers still insist on picking fruit at the very earliest signs of impending ripeness to ensure that the tomatoes survive the trip to the grocery store. There hasn’t even been any really reliable research that would clear up the most troublesome basic questions regarding tomato flavor: How much does it improve for every extra day the fruit is allowed to hang on the vine? How does this improvement work? Are there steps growers can take—such as using specific fertilizers or withholding water before harvest—that will make a difference in flavor?
One vital piece of the tomato quality puzzle involves steps you can take yourself. Cold temperatures wreak havoc with tomato flavor. The exact mechanism of how this works is still being studied, but without question it does happen. Temperatures below 60 degrees reduce the aroma-creating volatiles in the fruit. This change is quick and irreversible. If a case of tomatoes is even stacked next to a cooler for a day, that can be enough to ruin them. Tomato growers have been working diligently for the last several years to get that word out up and down the supply chain, but it is still not uncommon to walk into a grocery store and see tomatoes stored in the refrigerator. If this should happen to you, there is only one solution: turn right around and walk back out. That may not be much, but it is as close to a sure and simple fix as exists in the tomato world.
WHERE THEY’RE GROWN: Every year tomatoes are in a tight race with head lettuce as the biggest vegetable crop grown in the United States in terms of sheer dollar value. But whereas head lettuce is largely confined to one state (and, to an amazing extent, one region of one state), the tomato harvest is much more widespread: eighteen states grow commercially important amounts. Still, just two states—California and Florida—account for almost two thirds of the harvest. Florida dominates the winter market, while California rules in the summer. Tomatoes are one of the most heavily imported produce items. Roughly one third of our fresh tomatoes come from overseas, and Mexico produces as many tomatoes for the American market as either California or Florida. Oddly, Canada and the Netherlands are in second and third places, almost entirely with hothouse varieties.
HOW TO CHOOSE: Picking a terrific tomato is as much of an art as it is a science. Obviously, you should avoid any tomatoes with obvious flaws—dents, nicks or cuts. Also, you want tomatoes that are heavy for their size. You don’t want a tomato that shows a lot of green, but beyond that don’t pay so much attention to color, unless you’re looking for a tomato to eat right away. Actually, overripeness can be as big a problem as underripeness. Overripe tomatoes are mealy and have off flavors, and you can tell them by their slack skin. In the end, trust your nose. Tomato aroma is the best indicator of quality.
HOW TO STORE: Do not, ever, put a tomato in the refrigerator. That will kill the flavor faster than anything. Store tomatoes in a cool, dry place away from direct light. If they are slightly underripe, they’ll soften in a day or two.
HOW TO PREPARE: Tomatoes need to be peeled for cooked dishes. To do this, cut a shallow X in the blossom end and blanch it in boiling water until the skin begins to peel away. The time will vary according to the ripeness of the fruit—anywhere from 5 to 20 seconds. To seed tomatoes, cut them in half crosswise and squeeze out the seeds and pulp. Purists do this over a sieve, collecting the flavorful pulp in a bowl below.
ONE SIMPLE DISH: Dice seeded, unpeeled tomatoes as finely as you can. Dress them with a little olive oil, salt and freshly ground pepper. Taste them, and if they need a little red wine vinegar, add that. Place a log of fresh goat cheese on a plate and spoon the tomatoes around it. You may never go back to tomatoes and fresh mozzarella.