When recipes call for mint not specifying spearmint or peppermint which type is the default ingredient that I should use?
Actually, there are more than 30 varieties of mint to choose from, but you're right, peppermint and spearmint are the leading contenders in any mint duel. We consider peppermint the more generic choice when the recipe doesn't specify, as it has a cleaner, purer flavor that, in our opinion, blends better with a broader range of other ingredients.
While spearmint's flavor is milder, its taste is a little more off-center, making it less compatible with other ingredients.
But, as with so many other flavor issues, it may come down to personal preference. Do you like spearmint better than peppermint? If so, you might prefer to make spearmint the default and turn only rarely to peppermint.