The egg yolk
Why are egg yolks yellow?
This is one puzzle that is easily solved: the color of the yolk reveals what the hen has been eating. The carotenoids in the henís feed make the yolks yellow. They are found throughout the natural world, in fruit and vegetables for example, and are easily recognized by their yellow to orange-red color. The greater the quantity of these colorful substances in the henís diet, the stronger the shade of the yolk is. The hen ingests yellow pigments in corn or grass, for instance. A golden yolk is produced by red carotenoids from red peppers or by canthaxanthin, a substance found widely in nature.
The hen - a truly high-performance production unit
In the ovaries of one hen, several thousand egg cells wait to start out on the path to a finished egg. The yolk matures within seven to eleven days. After ovulation the yolk enters the oviduct, where it is enveloped in several layers of egg white. A thin shell membrane forms in the part of the oviduct known as the isthmus. Finally, the egg enters the shell gland, where the shell itself develops. Just before the egg leaves the henís body it is covered with a thin protective coating called "bloom". Thus hygienically packaged, the little voyager sees the light of day. A hen egg takes about 24 hours to pass from a yolk to a finished egg. A hen lays about 280 to 300 eggs a year - a truly magnificent achievement.
» By the way: brown eggs take on their hue only in the final 5 hours of shell formation. «
Why we love yellow egg yolks
Our preference for golden yellow egg yolks is rooted in history. Pale yolks were always a sign of sick hens, worm infestation, or poor feed. Only healthy, well-nourished hens store carotenoids (preliminary forms of vitamin A) in their yolks. Bright golden-yellow yolks show that the hens are well supplied with essential carotenoids such as lutein or canthaxanthin. These protective substances are widely found in nature; they not only give the yolk its yellow color, but also prevent the oxidation and destruction of fragile, vital substances such as vitamins in the egg.
Europe is not unanimous
Where the color of egg yolks is concerned, Europeans are not unanimous. A real North-South divide can be observed. While the northerners prefer pale yellow yolks, the preference of consumers for golden-yellow yolks grows as we go further south. On the shores of the Mediterranean, only bright, orange-red yolks stand a chance of reaching the plate.
From chicken feed to yolk pigment
Not all carotenoids find their way into the yolk. The well-known beta-carotene, for example, is completely converted to vitamin A and metabolized by the hen. Beta-carotene has no effect on yolk color. Canthaxanthin, another carotenoid, is different: Birds only convert about 30 per cent of it into vitamin A. The rest is stored in the egg yolk as a protective substance, causing the yolk to take on a golden-yellow hue.