Pig Fat. It’s all that (and more).
They can be used interchangeably in recipes. Both are made from pork belly and can be smoked or unsmoked but the difference is in the curing. Bacon is usually dry cured with salt and sometimes a little sugar, although it can also be brined and smoked afterward. Pancetta is cured flat or rolled with the addition of garlic and herbs, and sometimes also rubbed before with white wine (that sounds like a spa treatment to us). As a result, Pancetta is more complex than bacon and can be more delicate.
These two are not the only pig-fat flavor enhancers, however, so here are a few more to consider:
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