Chemists have done chemical analysis and found that duck eggs are not only rich in protein, but also contain a lot of fat. In the whole duck egg, fat accounts for about 16%. Except for a little bit in protein, more than 99% of these fats are "live" in egg yolk. So for egg yolk, the fat content is as high as 3 1%. In other words, almost one third of the yolk of the whole duck egg is made up of fat.
Since the fat content in egg yolk is so high, why can't you see any oil and your tongue can't feel it? It turns out that this is a trick of protein and fat change.
Have you ever eaten cod liver oil emulsion? Cod liver oil is nutritious, but it smells like fish. Some people don't like it, so people add some sweet wort, water and some emulsifier to cod liver oil to make it into emulsion. Cod liver oil turned into emulsion and the oil suddenly disappeared. Of course, cod liver oil is still intact, but it is dispersed into very small oil droplets, and each oil droplet is covered with a layer of emulsifier and water film.
Besides fat, egg yolk is also rich in protein, isn't it? Protein is a clever emulsifier, which can disperse the fat in egg yolk into tiny oil droplets like cod liver oil emulsifier, thus deceiving our eyes and tongue.
However, why does the fat in the egg show its true colors when it is made into salted eggs?
It turns out that salt and protein are sworn enemies. Salt can reduce the solubility of protein in water and precipitate protein, which is called "salting out" by functional chemists. After protein was salted out as an emulsifier, the emulsion was destroyed, and those originally dispersed into tiny oil droplets gathered together and became big oil. Because the fat content in egg yolk is as high as 3 1%, once cooked, the whole egg yolk becomes oily and even overflows.