Associate editor Tim Chin portions out samples of different formulas of ginger syrup as he experiments with compounds associated with spiciness for an upcoming article.
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Sweet Heat

A taste of science makes sweets that stay spicy forever.

One of the things we love about fresh ginger, besides its sweetly sharp fragrance, is its spicy kick. Like chile peppers, ginger contains particular molecules that cause a pleasingly pungent burn. Indeed, the compound gingerol, which gives that spicy edge to ginger, is a close chemical relative of capsaicin, which does the same in chiles.

How do gingerol and capsaicin make you feel that spicy burn? It all comes down to shape. Different molecules fit differently into receptors in our mouths and on our tongues. Like a lock and key, the taste of a spicy food depends on how well the molecules and receptors fit together. The TRPV1 receptor, first discovered in 1997, is a perfect fit with capsaicin molecules, stimulating that familiar sensation of heat and irritation that we perversely crave. The gingerol molecules from fresh ginger don’t fit quite as well. The more neatly the molecules fit into the receptor, the more powerful the sensation, which is why ginger’s burn is never as strong as a pepper’s.

Pepper flakes sit in the foreground ready to use as associate editor Tim Chin slices ginger. The spiciness of ginger dissipates over time so Tim is experimenting with ways to infuse heat back into a dish that relies on the root of this flowering plant.
Pepper flakes sit in the foreground ready to use as associate editor Tim Chin slices ginger. The spiciness of ginger dissipates over time so Tim is experimenting with ways to infuse heat back into a dish that relies on the root of this flowering plant.

There’s another important difference between gingerol and capsaicin that affects the cook as well: gingerol is much less stable. As soon as you heat fresh ginger, its gingerol starts to decompose. Each molecule splits in half. One half is zingerone, which fits very loosely into our mouth’s receptors, meaning we perceive it as much less spicy. The other half becomes an aroma molecule with a fruity, grassy odor.

This breakdown continues over time, so gingery dishes that are served shortly after cooking—say, a stir-fry—are still plenty pungent. But if a gingery delicacy is stored for a while before it’s eaten, the end result may be significantly less spicy than we might hope. This happens with ginger candy, ginger syrups and sodas, and ginger cookies. And the breakdown of gingerol happens fastest in a high-pH (basic) environment—for instance, in a cookie made with baking powder.

Sliced ginger with and without chili flakes sit ready to use as associate editor Tim Chin tests how to reintroduce some of the heat that is lost as the root ages.
Sliced ginger with and without chili flakes sit ready to use as Tim tests how to reintroduce some of the heat that is lost from dishes made with ginger as they sit.

Interestingly, when ginger is dried, gingerol sheds a water molecule and turns into a variant called shogaol, named for shoga, the Japanese word for ginger. Shogaol sockets into our spiciness receptors better than gingerol does, so, molecule-for-molecule, it tastes about twice as spicy. But, when dried ginger is rehydrated, shogaol starts to convert back into gingerol, and when it’s cooked, it loses its fire after a few days, in the same way that fresh ginger does.

To taste this change first hand, test cook Tim Chin made a ginger syrup with 100 grams of thinly sliced fresh ginger and 250 grams each water and sugar. After it had sat for a week he made an identical batch of fresh syrup and the Cook’s Science team tasted them blind, side-by-side. The fresh syrup was lively, spicy, and sinus clearing, while the week-old batch was mild, flat, boring.

Different formulas of ginger syrup sit ready to taste as associate editor Tim Chin experiments with compounds associated with spiciness for an upcoming article.
Different formulas of ginger syrup sit ready to taste.

An easy way to compensate for ginger’s fleeting kick? Spike gingery food with a little chile pepper. As anyone who’s eaten leftover five-alarm chili can attest, heat and time do little to tame capsaicin. And since it stimulates the same receptors in the mouth, it gives a similar bite as fresh ginger—even months later.

Back to the ginger syrup, Tim found through further testing that adding a small amount of crushed red pepper (1 percent of the weight of the ginger in the recipe, or ½ teaspoon per 3½ ounces thinly sliced ginger) to the syrup at the same time as the ginger yielded a syrup that was pleasantly spicy a week out. Pepper flakes can vary in spiciness so taste the syrup frequently while infusing to make sure it’s not getting too spicy. For recipes calling for dried ginger, like ginger snaps, a pinch of cayenne pepper works well.

Test kitchen photography by Kevin White.

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