The weight of an average egg yolk is 18 grams, approximately 30 percent of the total weight of the egg. The thick, clear white part of the egg, called albumen, makes up 60 percent of an egg's weight.
The color of an egg yolk is dependent upon a hen's diet. The United States Department of Agriculture has developed a grading system for eggs, which takes into account an egg's shell, yolk and weight. An egg yolk is rich in fat and a great source of vitamins and minerals. Fresh yolks are rich in color and stand upright with little spreading.