Mary Allen
The golden yellow color of the egg yolk, which is so popular with Swiss consumers, depends on the hen’s feeding and metabolism. If the latter does not work, the eggs can have an unloved taste.
The color of the yolk is strongest at the beginning of a new laying period and then slowly decreases. More than 50 years ago, Alfred Mehner wrote in a textbook on poultry farming that the color of the yolk is primarily based on feeding. The grass in the run as well as corn, carrots, tomatoes, or peppers give the yolk a rich yellow color. But the metabolism of the individual hen also influences the color. If there are no dyes in the feed, not every hen will react in the same way. Experiments have shown that acorns, canola, and other cruciferous vegetables make the yolk appear bronze or olive green. Red egg yolk is created by adding allspice pepper.
Pigments in the form of carotenoids are still added to laying hen feed today. These natural dyes provide a yellow to reddish color. Today, over 800 different carotenoids are known. In order for the egg yolk to get a nice color, the yellow and red pigments must be in a balanced ratio. In commercial poultry farming, the later use of the eggs plays a particularly important role. The pasta industry is looking for an egg with as many yellow pigments in the yolk as possible so that the pasta produces an intense yellow color. For edible eggs, the somewhat darker, yellow-orange colored yolks are preferred.
Food Can Affect Not Only the Color but Also the Taste
In Switzerland, natural pigment carriers are used as additives. The marigold flower provides a yellow color and paprika extracts give the egg yolk a reddish tint, as can be seen from the teaching material for the basic vocational training as a poultry specialist. There are also pigments that are identical to natural ones but have been produced synthetically. Apocarotene ester provides a lemon-yellow color and canthaxanthin or citranaxantine provides red pigments.
Feeding Feed with a low proportion of red pigments or those with poor pigment quality can result in light-colored yolks. Another reason could be food that has been stored for too long. The pigment degrades as a result of storage, and this degradation occurs more quickly, particularly at high temperatures. Another reason could be the high content of vitamin A in the feed. This vitamin competes with the absorption of the pigments in the intestine, because carotenoids are a precursor of vitamin A. Worm infestation could also be responsible for the pale color of the egg yolk. If one wants to influence a color change by adding pigments through feeding, the assessment of the yolk must be repeated after ten days. How long does it take for the color change to become apparent?
The taste of the chicken egg is also influenced by the feed. For example, the cause of the unpleasant “fishy smell” in eggs is in most cases a gas called trimethylamine, which has this smell. With a functioning metabolism, the hen uses an endogenous enzyme to convert this trimethylamine into an odorless form. However, if an animal has a metabolic disorder, the trimethylamine is not converted and this “fishy smell” develops in the eggs. In the past, this metabolic disorder was mostly found in brown hybrids and not in pedigree chickens. A high proportion of unsaturated fatty acids, spoiled feed, or feed that has been stored for too long can be the reason for odor problems in the eggs.
Fresh Eggs Can be Recognized by Their Density, Yolk, or Albumen
There are several ways to find out whether an egg is fresh or has been stored for several days. The specific gravity of fresh eggs is greater than that of water, which is why they sink if you put them in a glass of water, for example. In older eggs, the density is similar or less than that of water, which is why the eggs stand vertically in the water. If the eggs are inedible, they will even float. Egg weight depends on the size of the air chamber. While this is barely visible when fresh eggs are examined, the air chamber in poorly stored eggs is more than six millimeters in size.
Another indication of the freshness of eggs is the yolk. With fresh eggs, this is practically invisible when candling, with older eggs the shadow of the yolk becomes clear. The yolk is close to the shell and this is what makes the shadow visible. A similar effect is evident with boiled eggs. If the yolk is in the middle, the eggs are fresh. If the yolk is close to the shell, the egg has been stored for a long time. A final factor in determining the age of eggs is the albumen. A clearly visible, rather firm albumen around the yolk can only be seen in fresh eggs. If the albumen liquefies and becomes watery, the egg is older.
The albumen liquefies through biochemical processes during storage. The higher the storage temperature, the faster the albumen will liquefy. Because the egg white reacts so sensitively to the storage temperature, it is used as a quality criterion in the international egg trade. Samples are taken there to determine whether the eggs have been stored correctly. However, not only the storage is responsible for the consistency of the egg white. The age of the laying hens also has an influence on the egg white density. The older a hen is, the lower the egg white density and the less fresh an egg would look according to this goods inspection. This random sample is still valid in commercial poultry breeding because all hens are only about one year old and they have more in common in terms of breeding direction than the different breeds of hobby breeders.