Saturday, June 25, 2022

Egg Yolk Color Can be Synthetic, Shell Color is Genetic

Egg shell color is genetic by breed. If you want brown shells, own Rhode Island Reds. Interestingly (and mysteriously), brown is the preferred shell color in New England, whereas the rest of the U.S. prefers white. The color decision is not absolute – in New England roughly 50% of consumer-bought eggs have brown shells, dropping to 11% in the mid-Atlantic states, and lower in the rest of the country. In general, white eggs are preferred in South America and the Middle East, whereas brown is preferred in Africa, Europe, China and Japan.

The process of assembling an egg is interesting. Yolks, surrounded by a membrane, increase in size in the ovary, and are then released into the oviduct. Egg white, contained inside a membrane, surrounds the yolk. That process takes about four hours. Next, the egg enters the shell gland. Adding a shell – layering hour after hour – takes about 20 hours.

Range of eggshell colors
Shell pigment is added last. The amount, translating to darkness of brown color, appears to be constant per egg. Given that as laying hens get older, they lay larger eggs, those shells will be less brown than when the same hen was younger. Shell thickness averages 0.30 millimeters, and decreases with age. Shells are made almost entirely of calcium carbonate crystals. A laying hen in good health needs 4-5 grams of calcium per day, typically provided as crushed oyster shells. (By way of comparison, the Estimated Average Requirement for adult humans is about one gram.) Hens tend to start laying eggs at 18 weeks of age. Productivity peaks at about one year, on the order of 250 eggs per year. By year three, approximately 70% of peak, by year four, 60% of peak. Hens will live 8-10 years, but egg production is not expected after year six.

“Pigment last” is not really last. As each egg leaves the oviduct, it is covered in a protein and lipid layer referred to as bloom or cuticle. Before this has time to dry, the egg will be sticky to the touch. The purpose of bloom is to prevent bacterial access to the eggshell contents. In the U.S. commercially sold eggs are washed, removing the bloom. For this reason, eggs must be refrigerated. In the European Union, eggs are not washed, and can be packaged, displayed and sold at room temperatures. In the U.S., people who raise their own chickens for eggs can do either, depending on state regulations. Unrefrigerated eggs last only about 21 days, whereas refrigerated eggs last about 50 days.

Egg yolk color depends on what the laying hens eat. Caged, and fed a diet of predominately corn will result in a pale yellow yolk. Hens with access to an area that has wild plants and insects will lay eggs with a yellow-orange yolk. This comes from carotenoids compounds being passed to the yolk. The orange hue does not mean healthier chicks if eggs are allowed to hatch, nor healthier for humans who consume those eggs. However, eggs from “free range” chickens are perceived as healthier, and priced higher, accordingly.

Egg yolk color choices offered by DSM, a Dutch-based
multinational corporation that acquired the vitamin
division of Roche in 2003
“Money is the necessity of invention.” The classic version of this belief is “Necessity is the mother of invention.” But as egg farmers consider money a necessity, the first version holds true, too. Pasture-raised hens are eating seeds and insects that contribute natural color compounds – carotenoids – will lay eggs with an orange tint to the yolks. Chrysanthemum or rose flower petals, also red bell peppers or chili pepper, can donate a darker hue. However, as an alternative to these natural methods or affected yolk color, chicken feed companies publish a yolk color chart which allows egg production companies to pick a yolk color derived from amounts of synthetic carotenoids added to the feed. The only downside to using synthetic carotenoids is that the eggs cannot be labeled organic.

While talking chicken, lets dip into “Free Range.” FR usually defined as the laying hens being outside at least six hours per day, but only requiring two square feet of outdoor space per bird. A typical set-up for the outside space is concrete, covered in sand, shredded bark and straw. The covering material is removed on a regular basis so the concrete can be hosed clean. While still a higher density habitat than most people image FR means, it is still a huge improvement over the factory farm conditions still dominant in the U.S. “Battery cages” are a few feet square. Between four and ten birds are held in each cage. Industry guidelines recommend each bird having floor space roughly the size of a piece of printer paper. This is where they live for years. Several states, including Massachusetts, have banned caged hen practices.

Trivia: Ostrich eggs are about 2.0 mm thick. Shells from the extinct elephant birds of Madagascar were about 4.0 mm thick. These flightless birds could approach ten feet in height and exceed 1,000 pounds in weight.