My supermarket sells eggs that are guaranteed to have double yolks, but this is surely a random process. What are the chances of a double yolk, and how do egg producers ensure there are enough to fill their boxes? Can they engineer them via artificial means? My local supermarket always seems to have a plentiful supply so presumably it鈥檚 easy enough to find or generate them.
鈥� The process is not as random as it first seems; the most common cause of double-yolked eggs is when two ovules are produced so close together that the hen鈥檚 oviduct processes both yolks into the same shell. The tendency to produce more than one ovule at a time is influenced by genetics, so some breeds of chicken produce far more double yolks than others.
Certain cross-breeds ovulate rapidly, so that most eggs are double-yolked (and incidentally only rarely produce chicks). Some people prefer double-yolked eggs, regarding them as lucky, rather like four-leaf clovers. This is also reasonable from a nutritional point of view because most of the value of the egg is in the yolk, despite its high cholesterol level.
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鈥淪ome people prefer double-yolked eggs, regarding them as lucky, like four-leaf clovers鈥�
However, in some regions people prefer single yolks. This offers an incentive to market single or double-yolked eggs at a premium on the basis of regional tastes. This is aided by 鈥� you can shine a light through the eggshells to tell whether they are internally unusual, containing blood spots, double yolks or the like, and then sell them according to consumer preferences.
Jon Richfield, Somerset West, South Africa
鈥� When young hens begin to lay eggs, their ovulation is irregular and it is not uncommon for them to shed two yolks so close together that these get wrapped up in the same shell, giving a double-yolked egg. These are obviously larger than normal eggs and will be filtered out when the eggs are graded. Inspecting them over a bright light will confirm the double yolk.
When the birds settle into a regular laying cycle, such eggs become rare. Your questioner鈥檚 supermarket presumably purchases its eggs from a large producer that always has a proportion of young birds.
J. Allen, Grantham, Lincolnshire, UK