Last month, I provided some practical tips on tasting tomatoes. Now I’d like to delve a little deeper into the science of tomato flavor.

First, a quick refresher on how we taste our food. Our taste buds are capable of picking up five flavors: salty, sweet, bitter, sour and umami. Everything else that we experience and describe as flavor is a product of scent. This is because our senses of taste and smell are so closely linked.

Tomato flavor is based strongly on two of those basic flavors - sweet and sour. The sweetness comes from relatively high concentrations of fructose (25%*) and glucose (22%*). The sourness comes mainly from two acids - citric acid (9%*) and malic acid (4%*). Some tomatoes are sweeter than others (like Sun Golds and Super Sweet 100s) while others are distinctly acidic (Green Zebras).

Quantifying sweetness and acidity can be conveniently measured using a Brix Refractometer to gauge sugar content and a pH tester to gauge acidity.

But there is a lot more to tomato flavor than just sweetness and acidity. The extra elements that give a tomato it’s unique flavor are volatile organic compounds. These compounds sport indecipherable scientific names, such as 1-penten-3-one, 3-methylbutanol and trans-2-hexanal. What unites these compounds is that they are volatile, meaning they vaporize easily. Hence they drift from the tomato to your nose or enter the nose through the nasal cavity while you’re chewing your tomato.

Most volatile organic compounds have been shown to contribute positively to tomato flavor, such as furaneol, cis-3-hexenal, trans-2-hexenal, hexanal and 2-isobutylthiazole. However, not all compounds have a positive correlation with flavor. 2-isobutylthiazole has been described as contributing a “spoiled vine-like slightly horseradish-type flavor”** (although it can be tolerable at lower concentrations).  

These volatile organic compounds also are a big reason why ripe tomatoes taste so much better than unripe tomatoes. While the rate of formation varies by compound, there is a general pattern: VOCs form late in the ripening process. Try comparing the scent of a vine-ripened, freshly sliced homegrown tomato to a grocery store tomato sometime and I’m sure you’ll notice the difference...even if you can’t tell which scents come from cis-3-hexenal or 1-penten-3-one.

But what about the remaining 40% of a tomato? The other major constituents of a tomato are: protein (8%), minerals (8%, mainly potassium and phosphate), pectic substances (7%, natural gelling agents), cellulose (6%, structure for cell walls), and hemicellulose (4%, similar to cellulose). The remainder is made up of small concentrations of acids, sugars, amino acids, pigment and vitamins.

Finally, I wanted to offer one last observation after doing all this research. The bulk of the studies being done on tomato flavor comes from Florida, not exactly a hotbed of high-flavor tomatoes as Barry Estabrook noted in his book Tomatoland. Relatively little research seems to have come from the University of California despite the fact that the state’s farmers do nearly $400 million in fresh tomato sales each year. We at Farmscape would like to change that; any researchers interested in joining us?

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*Petro-Turza, M. 1987. Flavor of tomatoes and tomato products. Food Rev. Int. 2(3):309-351.
**Yilmaz, E. 2001. The Chemistry of Fresh Tomato Flavor. Turk J Agric For. 25:149-155.