San Marzano tomatoes are considered one of the best tomatoes in the world for sauce, as they are sweet with the right amount of acidity and a rich tomato flavor. However, you may not be buying real San Marzano tomatoes, even if the "DOP" or Denominazione d' Origine Protetta (Protected Designation of Origin) label verifies its status on the can.

While a can of ordinary tomatoes costs about $2, real San Marzano tomatoes run between $6 to $7 — yet despite this price tag, Alton Brown says that about 95% of the tomatoes sold in the United States labeled San Marzano are fake. The problem is that in the U.S., the DOP label is not regulated, and anyone can slap a DOP designation on the can.

To make sure you have real San Marzano tomatoes, know that they are always sold peeled and canned, never chopped, diced, or pureed. In addition to the DOP seal, a Consorzio San Marzano certification number should be stamped on the bottom of the can, along with the location where they were grown. If they were grown in the U.S., they are not true San Marzano tomatoes.