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Is Ceviche Really Safe? Ask Paul

And how does acid “cook” food?
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Published Aug. 31, 2022.

Emily asked: “Is ceviche really safe?”

The short answer: Ceviche is only as safe as the fish you start with, so you should only make ceviche with fish that you would be fully comfortable serving raw.

With really good fish, ceviche is one of the most delicious things you can make. All you have to do is cut the raw filleted fish into small, bite-size chunks; refrigerate it for a few minutes to a few hours in an acidic marinade (usually involving lime juice) to “cook” the fish; and then serve.

It is those quotation marks that always show up around “cook” that we are here to look at more closely today. What does the acid do exactly? Is it comparable to cooking the fish with heat?

How Does Ceviche Work?

When the acidic marinade encounters the myosin proteins that make up the muscle of the fish, those proteins coagulate, bonding together and making the muscle firmer and opaque. The process is more gentle than heating, so the texture remains tender and moist, without the dryness that comes so easily to cooked fish.

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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.

Four pieces of raw fish marinated for ceviche

Is Ceviche Really Safe?

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 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.

Ask Paul Adams, senior science research editor, about culinary ambiguities, terms of art, and useful distinctions: paul@americastestkitchen.com

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