Menthol is the chemical ingredient that creates that recognizable and much-loved cooling effect on the mouth. While peppermint’s menthol content is a whopping 40 per cent, spearmint contains just 0.5 per cent. Therefore 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 flavour.
Peppermint is a hybrid of spearmint and watermint, a mint variety that we don’t see so much. It occurs naturally near rivers and ponds and is intensely minty, which is why it is not particularly popular for culinary uses. On the other hand, fresh spearmint leaves contain a much lower level of menthol than other mint species, which makes it less pungent and more suited to health drinks and cooking.