Why You Should Never Marinate Your Tuna Steaks For Too Long

There's nothing more disappointing than having sourced a fantastic fresh ingredient, only to ruin it in the kitchen. Tuna steaks are popular for a number of reasons: They're versatile, they work with a broad array of flavors, and they're quick and easy to prepare. While some meats may benefit from a long marinade of up to 24 hours, tuna steaks require a different approach.

Why marinate a piece of meat or fish? The first reason is flavor. In this classic poke bowl, for example, the asian flavors of soy sauce, sesame oil, and rice vinegar derive entirely from the marinade. How long does the ahi tuna for the recipe marinate? Just 15 minutes is all it takes to perfectly infuse the tuna with flavor.

It's possible to have too much of a good thing, and that's particularly true for tuna steaks. What would happen if you extended that marinating time?

Meat and fish marinades add flavor and they're also frequently used to tenderize. Acid, often from citrus juice or vinegar, starts to break down your beautiful tuna steak, which is great — to a certain point. If you marinate your tuna steak too long, what happens? The acid in your marinade will cause your lovely translucent fish to turn opaque, which, not coincidentally, is the same color change that occurs when you cook your tuna (via Scientific American).

While a 15 to 20 minute marinade gives you flavor, an acid bath that's too long will actually "cook" your tuna steak, giving you tuna ceviche, per Edible. If you apply heat to tuna that's marinated too long, you're doubling down and your tuna steak will likely be tough and not very appetizing. Whether you plan to sear, grill, or serve your tuna steak raw, limiting the acid contact is vital. 

A brief marinade perfectly prepares your fish, while a lengthy marinade will ruin it.