What Is the White Stuff That Comes Out of Salmon?

The white stuff that seeps out of salmon as it cooks is a protein usually called albumin. It's liquid from inside the muscle that gets squeezed to the surface as the fish heats, and the proteins dissolved in that liquid set into soft white curds when they hit the hot outside. It's completely safe to eat, but a lot of it is a sign the salmon was cooked too hot or too long, and that it has lost moisture it could have kept.

What exactly is salmon albumin?

Fish muscle contains three main groups of proteins. The biggest are the contractile proteins, myosin and actin, which form the long fibres you see as flakes. Then there's a small amount of connective-tissue protein, mostly collagen. And finally there are the sarcoplasmic proteins, which are dissolved in the fluid inside each muscle cell. This group includes enzymes, the red-orange pigment-binding proteins and a family of proteins similar to the albumin found in blood.

Cooks call the white goo "albumin," which is a handy shorthand. Strictly, it's a mixture of those water-soluble sarcoplasmic proteins, carried out of the muscle in the fish's own juice. It's the same basic idea as the grey scum on simmering stock or the white foam on boiling beans: dissolved proteins that have met heat and coagulated.

The orange colour of salmon comes from astaxanthin, a carotenoid pigment that the fish gets from its diet and stores in its muscle. The pigment is bound inside the muscle, which is why the albumin that seeps out is white rather than pink.

Why does salmon push out the white stuff?

It's a squeeze-and-set process, and it happens in a few steps.

1. The fibres contract. As salmon heats, its myosin starts to unravel and bond together from about 40°C (104°F), lower than in beef or chicken. That's because fish live in cold water and their proteins are built to work at cold temperatures, so they come apart sooner. As the fibres tighten, they squeeze fluid out of the cells.
2. The juice travels outward. That fluid, carrying dissolved sarcoplasmic proteins, moves along the gaps between fibres and between the flakes, finding its way to the surface and the cut sides.
3. The proteins set. When the juice reaches the hot outside of the fillet, the dissolved proteins undergo protein denaturation and coagulate into the soft white curds you see, much like egg white setting in a pan.

The faster and hotter you cook, the harder the outer fibres clench before the inside has warmed, and the more juice gets pushed out at once. That's why salmon blasted in a very hot oven or grilled over high flame often comes out wearing a white crust, while gently cooked salmon shows just a few specks.

Chef Fizz says: The white stuff is the salmon waving a little flag that says 'easy on the heat!'

Does white stuff mean the salmon is overcooked?

Often, but not always. A little albumin between the flakes is normal, even in perfectly cooked salmon. A thick layer coating the whole top of the fillet usually means the outside got too hot, too fast, or the fish was simply cooked too long.

Here's how salmon changes as the centre heats up:

Food safety agencies, including the US FDA and Health Canada, recommend cooking fish to 63°C (145°F), or until it's opaque and separates easily with a fork. That's the number to use if you're cooking for young children, older adults, pregnant people or anyone with weakened immunity. Many restaurants and home cooks serve salmon lower, around 50 to 55°C (122 to 131°F), because it's much more moist; that's a quality choice that carries more risk, especially with wild fish that has not been previously frozen, since freezing is what kills any parasites.

Thick fillets also keep cooking after you take them off the heat, so pull them a couple of degrees early. That's carryover cooking at work.

Why does salmon cook so fast, and dry out so easily?

Fish muscle is very different from beef or pork muscle. Its fibres are short and arranged in stacked blocks called myotomes, separated by thin sheets of connective tissue called myocommata. Those sheets are the white lines you see running across a raw salmon fillet, and they're also where the flakes split apart.

Fish has very little collagen compared with land animals, and the collagen it has turns to gelatin at much lower temperatures. That's why fish is tender after just a few minutes and why it flakes apart so easily. But it also means there's nothing to buffer overcooking. Unlike a braised beef shoulder, which turns rich and tender as its collagen melts, overcooked salmon simply gets drier and chalkier with every extra minute. A typical 2.5 cm (1 in) fillet can go from perfect to dry in about 2 minutes.

How do you cook salmon without the white stuff?

You can't eliminate albumin entirely, but you can cut it down dramatically.

Brine it briefly

A quick soak in salt water before cooking is surprisingly effective. Dissolve about 3 tablespoons of fine salt (around 50 g) in 1 litre (4 cups) of cold water, submerge the fillets, and refrigerate for 10 to 15 minutes. Then pat them very dry. The salt partially dissolves proteins at the surface, which then set into a fine mesh during cooking that holds the albumin in place, and it seasons the fish too. This works on the same principle as brining meat, just much faster because fillets are thin. Don't leave it longer than about 30 minutes, or the texture turns firm and ham-like.

Lower the heat

Gentle methods produce far less albumin:

• Slow-roasting: bake at 120 to 135°C (250 to 275°F) for 15 to 25 minutes, until the centre reaches your target. The fish cooks evenly from edge to centre with almost no white curds.
• Poaching: keep the liquid below a simmer, around 70 to 80°C (160 to 175°F).
• Pan-searing skin side down: start skin side down over medium heat and cook it mostly on that side. The skin acts as a shield, the flesh warms gently from below, and you get crisp skin. Flip for just the last 30 seconds or not at all.

Don't overcook it

Use an instant-read thermometer in the thickest part, or check by gently pressing a fork into the top: the flakes should just start to separate and the centre should still look slightly translucent if you're aiming below 63°C (145°F).

Start with good fish

Fish that's been frozen and thawed often leaks more juice because ice crystals damage cell walls. That doesn't make it bad, but it's another reason to cook it gently and use the brine trick.

The Cooking Scientist app has a short lesson on cooking fish gently, plus one on how proteins set in the heat, both with mini games.

Is the white stuff the same as salmon fat?

No. Salmon fat is a different thing entirely. Farmed Atlantic salmon in particular is quite fatty, with thick white bands of fat along the belly and between the muscle blocks. As it cooks, that fat melts into a clear, golden oil in the pan. The albumin is the opaque, slightly curdy white solid that appears on the surface and in the gaps between flakes. Fat looks glossy and liquid when hot; albumin looks like soft, set egg white.

Try it at home

Make the albumin visible and then beat it with two pieces of salmon.

1. Cut one salmon fillet, about 2.5 cm (1 in) thick, into two equal portions. Mark one with a toothpick so you can tell them apart.
2. Brine the marked piece for 15 minutes in 1 litre of cold water with 3 tablespoons (about 50 g) of fine salt, refrigerated. Leave the other piece in the fridge unsalted, then lightly salt it just before cooking.
3. Pat both dry and bake them together, skin side down, on a lined tray at 230°C (450°F) until the thickest part of each reaches 63°C (145°F), usually 10 to 12 minutes.

What you'll see: the unbrined piece is likely dotted with white curds, especially along the top and sides. The brined piece shows noticeably fewer and tastes evenly seasoned. Why: high heat made the fibres contract fast, squeezing juice and dissolved proteins to the surface. In the brined piece, salt had already loosened the surface proteins so they formed a tight mesh that held much of that liquid in. Next time, try a third piece slow-roasted at 135°C (275°F) and compare how little albumin appears.

Common mistakes

• Cooking salmon over very high heat. The outside clenches hard and squeezes juice out before the centre warms. Fix: use a moderate pan or a low oven, or cook mainly skin side down.
• Cooking it until it flakes everywhere. By then it's usually overcooked and dry. Fix: use a thermometer, and pull it a couple of degrees early to allow for carryover.
• Scraping off the albumin and assuming the fish is spoiled. It's harmless protein, not a sign of bad fish. Fix: eat it or wipe it away; focus on cooking gentler next time.
• Brining too long. More than about 30 minutes in salt water makes salmon firm and salty. Fix: 10 to 15 minutes, then pat dry.
• Putting cold, wet fish straight into the pan. Surface water stops the skin crisping and makes the fish stick. Fix: pat thoroughly dry and let the pan heat properly first.
• Flipping it over and over. Each flip disturbs the flakes and blasts the delicate flesh with direct heat. Fix: cook mostly on the skin side and flip once at most.