As a professional pastry chef, I crack lots of eggs. My job requires me to separate many eggs too; whites go to the kitchen for egg white omelettes and the yolks go into the many different desserts I make. On a day where I was separating a large amount of eggs, I encountered a dozen double yolk eggs. They occur regularly, but usually just one or two at a time and not every day. Even less common than double yolks are bloody eggs, thankfully. All of this got me to thinking about just what causes these two things to happen.
A quick internet search turned up some facts on double yolks. First of all, they are not rare and there is about one double yolk egg in every thousand laid. The main cause for this is an ovulation that occurs too quickly or a reproductive system that is not synchronized. However, some hens lay double yolk eggs because they have inherited the trait. At the same time, it is possible for the hens to lay eggs without a shell leaving the membrane that lines the shell to hold it all together. And then there are “wind” eggs or eggs without a yolk. These eggs are also called dwarf or fart eggs. In all of my years of baking, never have I encountered an egg without a shell or a yolk but once I did crack an egg with three very small yolks.
Since hens do not need a rooster to be able to lay an egg, how do they end up bloody? That has always perplexed me. Apparently though it is common among older hens. When the yolk is released from the ovary to begin its journey, blood vessels in the ovary can break and cause spots on the yolk and a bloody tint to the white. Although it is rather unappetizing, it is harmless and the offending spots can be removed with the tip of a knife and the red portion of the white can be scooped up and discarded as well.
With all of the headlines about salmonella in recent weeks, it is important to handle eggs carefully. Always throw away a cracked or broken egg. While the contents may be sterile when the egg is layed, once the shell is cracked, it provides an opportunity for bacteria present on the shell to contaminate the contents. Consider purchasing pastuerized eggs if you have health issues, are pregnant or may have a compromised immune system. Otherwise, always keep your eggs refrigerated until needed and be sure to check the expiration date on the carton. Finally, have clean hands, clean utensils and cook eggs thoroughly to prevent illness.
For more information on ingredients and baking, click on the subscribe button above. To read more about eggs, egg safety and methods of cooking eggs, check out the following websites:
The incredible edible egg
Whats cooking America
My source for much of the facts given above: