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If you've bought a can of San Marzano tomatoes recently from a grocery store, there's a good chance that the tomatoes you bought aren't the real deal.
San Marzanos are basically the only recognized name in canned tomato products, and are highly valued for their quality and flavor. In fact, Taste reports that authentic Napoletana pizza must use San Marzanos to be considered legit, and that the cans even require a special "DOP" label to be sold as San Marzano tomatoes in Italy. That label means that the tomatoes have met all of the growing and processing criteria necessary to be called a San Marzano (which includes being grown in the volcanic soils of Mt. Vesuvius, for example).
Unfortunately, those same labeling regulations do not apply in the United States. Anybody can slap a DOP label onto a can of tomatoes to make it look like they're San Marzano, and many companies do that to throw customers off and deceitfully elevate their selling prices. One importing company has been told by the president of the San Marzano labeling consortium in Italy that about 95% of the products called "San Marzano" tomatoes in the United States are actually knock-offs. That percentage is a low-ball estimate, as well, meaning an even higher percentage of San Marzano tomato products on U.S. shelves could be fakes.
Fortunately, there are ways to spot a fake San Marzano can out there. San Marzanos can only be sold as whole or filleted, peeled, and canned to be certified. Crushed or diced tomatoes are not legitimate certified products. You should also be on the lookout for a DOP seal and a seal from the labeling consortium, along with a certification number. Finally, true San Marzano tomatoes don't even have the name "San" on the label, and are instead labeled as “Pomodoro S. Marzano dell’Agro Sarnese-Nocerino.” Sounds like a mouthful, but it's a great way to differentiate from the industrial giants that use the name to throw consumers off.
If you really want to use the high-quality San Marzano tomatoes when cooking, follow those guidelines, and you should be good to go.
