The Real Difference Between Spearmint And Peppermint
Many people talk about them interchangeably, but spearmint and peppermint are actually two distinct plants (via Reluctant Gourmet). Peppermint is a hybrid of spearmint and watermint, a mint variety that we don't see so much. It occurs naturally near waterways, such as rivers and ponds (via Gardening Know How) in the United States and Europe and is intensely minty, which is why it's not particularly popular for culinary uses (via Spiceography).
Both plants are in the Mentha genus of plants, which contains just over a dozen varieties, though just two of them — peppermint and spearmint — see widespread culinary use (via Mental Floss). If you take a stroll down the candy and mint aisle at a grocery store, you'll notice that the majority of peppermints-flavored items are presented in a blue color, while spearmint is often green.
There's definitely a difference in their mintiness as well — while peppermint contains 40 percent menthol, the compound that gives mint its "oomph," spearmint has only 0.5 percent.
How spearmint stands apart from peppermint
Spearmint is sweeter because it contains a compound called carvone. As a result, things that are peppermint flavored have an intense mint flavor (think candy canes and mint tea), while products or dishes that contain spearmint are more subtle. As a result, spearmint is more often used for savory dishes (via Imperial Sugar).
While there are a number of differences between the two, you can use them interchangeably if you don't have the variety that a recipe calls for. In fact, when you see "mint" extract at the grocery store, it's likely a blend of the two mints, whereas peppermint extract is sourced solely from peppermint plants.
Both plants also grow tiny purple-pink leaves when they blossom (via Encyclopedia Brittanica). When it comes to identifying the two in a garden, you might have a very hard time differentiating between them. Both grow like weeds, and they both feature fuzzy, toothed leaves. Even the most experienced gardeners say the best way to determine which mint you have is to take a taste test.