Though peppermint and spearmint are both mint plants in the Mentha genus, peppermint (Mentha x piperita) is actually a hybrid of spearmint (Mentha spicata) and water mint (Mentha aquatica). When it comes to shared characteristics, peppermint and spearmint both have serrated leaves, produce pink or light purple flowers, spread via underground stems called stolons, and contain menthol—the chemical compound behind that familiar cooling sensation. However, there’s a pretty significant discrepancy between their levels of menthol, which helps explain the flavor differences between the two types.
While peppermint’s menthol content is a whopping 40 percent, spearmint contains just 0.5 percent. Therefore, as Taste of Home explains, peppermint is especially pungent and even spicy (hence the “pepper” in its name). Spearmint, on the other hand, contains a compound called carvone, which gives it a much subtler, sweeter flavor. Because peppermint has such a strong taste, it’s usually the main focus of whatever dish or drink it’s in—think candy canes or peppermint tea. If you’re cooking something savory with a variety of other herbs, you’re better off using spearmint, whose sweetness will offset the blend of flavors without overpowering them.
According to Spoon University, the two mints are similar enough that you can substitute one for another if your grocery store doesn’t happen to carry both. And, if you’re having trouble remembering which flavor goes with which mint, those colorful gum wrappers might help—peppermint’s icy coolness matches blue, while spearmint’s earthy sweetness goes with green.