Recipes engineered for perfection—what exactly does that mean? We take you inside Cook’s Illustrated’s science experiments.
We don’t like it when our perfectly cooked fillets of salmon get marked by amysterious foam that sometimes forms on the fish. So just what is this protein called albumin—and how can we avoid it?
When the muscle fibers in the fish are heated, they contract, pushing the moisture-filled albumin to the surface of the flesh. Once this protein reaches temperatures between 140 and 150 degrees, its moisture is squeezed out, and it congeals and turns white. Not only does the white albumin detract from the salmon’s appearance, but its formation indicates a loss of moisture in the fish.
We tried cooking two fillets of salmon at different temperatures: high and low. The results proved that the amount of albumin that appears on the fish is not an indication of overcooking, as even perfectly cooked fish exuded a few strands of this white material along the unseared sides. But we did notice that slightly more of this matter showed up on the fillets that we overcooked intentionally.
We turned to Donald Kramer, professor of seafood science at the University of Alaska, Fairbanks, for an explanation. According to Kramer, this “white curd” is composed of fish albumin—soluble proteins that are squeezed out onto the surface of the fish and coagulate once they denature during the cooking process. Most often, this curd is seen when salmon is canned, smoked, or poached. “There’s nothing harmful in it,” said Kramer. “There will always be a certain amount that comes out, and how the fish is cooked is probably not going to affect that.”
The best way to check for doneness is not to wait for albumin to appear on the surface but to peek inside the fillet with the tip of a paring knife. If the salmon is opaque all the way through, the fish is clearly overdone. A little translucency is a good sign. If the look of the albumin really bothers you, use a damp paper towel to gently blot it off.
We also recently discovered that brining fish can reduce the unsightly white layer of albumin that coagulates on the surface during cooking. Just 10 minutes in our standard 9 percent solution (1 tablespoon of salt per cup of water) is enough to minimize the effect. The salt partially dissolves the muscle fibers near the surface of the flesh, so that when cooked they congeal without contracting and squeezing out albumin. We tested the method on white fish (including cod and haddock) as well as on fattier salmon and saw a dramatic improvement in both. The brief soak also seasoned the fish’s exterior, making it unnecessary to salt it before cooking.