What exactly is “bloom” and what is it for?
In short, it’s a coating, courtesy of the hen herself, deposited on the outer surface of the shell, which helps protect the contents of the egg from contamination.
Another name for it is “cuticle.” It is a protein, a mucous secretion of the hen’s cackleberry chute, to get scientific.
It’s necessary because eggshell is permeable, with about 80,000 microscopic pores on the surface of one egg. Bloom blocks bacteria, etc., from entering the egg and keeps the egg fresh longer.
Factory eggs, among their other issues, have been washed to make them palatable for the public and this removes the bloom. A coating of mineral oil is substituted to prolong their shelf-life. Like most man-made interferences, it is unequal to nature’s own.
Now our own homegrown hens’ eggs get dirty sometimes and need to be washed, which leaves us with a sort of Catch-22: leave the bloom and the surface contaminants can’t penetrate the egg, but they are still there on the outside, looking gross, getting into the egg when you crack it open, getting on your hands when you handle it, and looking really not cool at all sitting on your counter or in the fridge. Heaven forbid one should present a poopy egg to a friend, family member, or customer.
But, see, the bloom is there, protecting the egg inside . . . You explain and point and nod authoritatively but no, the horror is still frozen on their faces. And understandably so.
What to do?
The general consensus is that washing dirty eggs is indeed fine. Best to do it soon before using the eggs to take advantage of the natural protection of bloom for as long as you can, but a washed egg is a lovely egg as well, and much more presentable to the general population.
Use water that is 20 degrees F. warmer than the temperature of the egg itself. This will prevent thermal cracks from developing in the shell which would shorten the fresh life of the egg. A vinegar solution or a mild soap followed by a dry towel is fine. You’re really not trying to get an absolutely aseptic shell, just remove the exterior contaminants that gross people out and might fly into your food when you crack the egg.
Speaking of cracking, chefs and foodies recommend cracking eggs on a flat (or nearly flat) surface for the best, most shell-free result.
Prevention is even better. Collect eggs soon after they are laid if possible. Maintain clean bedding and make it nice and deep. Straw is one good one. Keep roosting areas up and away from the nesting sites.
And remember, if in doubt, place a suspect egg in a glass of water. If it floats, it’s past its prime. If it sinks, it’s likely a good’n.