Whether you use Mediterranean or Mexican oregano can impact a recipe's taste.
Oregano is one of the few herbs that retains much of its flavor when dried, which is why we call for it in many recipes. Oregano's aroma compounds are less volatile than those of other herbs, meaning that more remain after the leaves are dried. There are two general categories of oregano: Mediterranean and Mexican, which come from different plants. Mediterranean oregano (Origanum vulgare) is a member of the mint family and a close relative of marjoram, while Mexican oregano (Lippia graveolens) is a member of the verbena family and a close relative of lemon verbena. Both plants contain a phenolic compound called carvacrol, which gives both herbs their distinctive, pungent flavor.
We tried both types in tomato sauce and mojo-marinated skirt steak and noticed minimal differences. The Mediterranean oregano was milder and faintly sweeter, while the Mexican type was stronger, with a hint of menthol.
As with other dried herbs, oregano's volatile compounds will eventually dissipate. Whichever kind you choose, be sure to store it in a cool, dry, dark place to preserve its flavor. Discard your oregano if it's faded in color or has lost its distinctive aroma.