Why doesn't fish go well with red wine?
Quick answer
Red wine contains ferrous ions (Fe2+) that react with the unsaturated fatty acids in fish, creating an unpleasant metallic aftertaste. A 2009 study in the Journal of Agricultural and Food Chemistry proved that the more iron a wine contains, the stronger the metallic taste. Tannins make it worse by drying out your palate.
Detailed answer
The "no red wine with fish" rule is one of those food traditions that actually has hard science behind it. It's not just snobbery — there's chemistry happening on your tongue.
In 2009, researchers at Mercian Corporation in Japan cracked the code. They found that ferrous ions (Fe2+) in wine react with the polyunsaturated fatty acids in fish (the omega-3s and omega-6s). This reaction produces compounds called lipid peroxidation aldehydes, which taste and smell metallic. Red wines have significantly more iron than whites, which is why the problem is much worse with reds.
Tannins pile on the problem. They dry out your mouth, which amplifies the metallic sensation and kills the delicate texture of the fish. With a light, flaky fish like sole or sea bass, the effect is really noticeable.
But here are the exceptions that prove the rule. Meaty, protein-rich fish like tuna, swordfish, and even salmon can work with light, low-tannin reds. A light Pinot Noir with seared tuna is actually a well-respected pairing. The key is minimal tannins and minimal iron.
Also, if the fish is cooked in red wine (like a classic French matelote), then drinking the same red wine makes total sense. The cooking process changes the chemistry. So the rule isn't absolute — but for everyday fish dinners, white wine is your safest and tastiest bet.