SCIENCE: How Acid “Cooks” Seafood
Citrus juices can render raw fish safer to eat, much like fish cooked with heat. But how does it actually work?
How does acid work to cook seafood?
When an acidic marinade encounters the myosin proteins that make up the muscle of the fish, those proteins coagulate, bonding together and making the muscle firmer in texture and opaque in appearance. The process is more gentle than heating, so the texture remains tender and moist, without the dryness that comes so easily to cooked fish.
Ceviche is a popular South American dish where small pieces of raw seafood are marinated in lemon or lime juice and seasonings. In ceviche that’s marinated for a short time, only the surfaces of the pieces of fish are transformed by the acidity, while the centers of the pieces are still translucent. A longer marination allows the acid to diffuse through the fish until it’s opaque all the way through, with a firmer texture that lacks the slightly tacky smoothness of raw fish. And while the appearance and texture of the fish is altered from this marination process, it does not affect the flavor of the seafood in the way it happens with high heat.
Is acid-marinated seafood like ceviche safe to eat?
While ceviche isn’t actually cooked, the short-term exposure to acid does have an antimicrobial effect—in other words, it can kill or slow the growth of microorganisms, including potential pathogens—but it’s not nearly as effective as heat is, especially when it comes to killing parasites.
For that reason, ceviche should be treated like raw fish: Buy the best, freshest, most delicious saltwater-species (not freshwater) fish you can from a fishmonger you trust, looking or asking for a “sushi-grade” label if possible. Serve it as soon as you can, and do not serve it to pregnant or immune-compromised persons.
