I have seen more arguments about this than about anything else over the years. Here’s what I have worked out based on numerous scientific studies that I have read, several books, and discussions with several incubation experts.

  1. My opinion is: always wash all eggs before setting. Eggs that look clean will still harbour bacteria, and are likely to spoil an entire hatch if only the dirty eggs are washed.
  2. Don’t set really dirty eggs–bin them. You are OK with partial contamination, if it is not too heavy. You can remove some mud with a knife or sandpaper, but perhaps those are eggs which should not be set (I have successfully incubated dirty eggs, but I have also found that if I do set a REALLY dirty egg then not only does it not hatch, the eggs adjacent to it often fail also).
  3. Always use water which is hotter than the eggs. I use water which is about as hot as my hands can stand. As the water cools, gets bits in it, or turns cloudy, change it for clean.
  4. Wash your cleanest eggs first and work your way to the dirtier ones.
  5. Use a good egg sanitant: I use F10, or Virkon, or Brinsea’s own brand, but I have heard lots of people recommend Tek-Trol, which Michael Mason uses. Make sure you dilute it properly, as instructed. You can also use most pet-safe disinfectants, like Genie (another UK brand name! Sorry).
  6. Once your eggs are clean, keep them that way by sanitising your candler each time you use it and by wearing sterile gloves to handle them (OK, I don’t do that one, but I do wash my hands very well first). Don’t hatch in the same incubator that you are incubating in if not all of your eggs are due to hatch at the same time: this will infect all your remaining carefully-sanitised eggs.
  7. Treat all eggs the same: so if you dip some eggs in to clean them, do that with all of them. If you use a cloth, do that on all of them. This is because abrasion removes the cuticle, which (as Michael Mason has implied) will lead to faster weight-loss during incubation. So you need them all to do the same.

I have a friend who is a “professional” incubator, and she is horrified that people would set unsanitised eggs: it makes such a difference to the hatch-rate, and also to the survival rate of the chicks which you get. Those ones which die for no apparent reason often have yolk infections, due to unsanitised eggs. So it is well worth doing. She estimates that people incubating at home would have 15-20% more chicks at 8 weeks old if they just sanitised all their eggs properly.

In my opinion, the research which suggests that eggs for incubating should not be washed is outdated and inaccurate.

For eating, though, there is no need to wash eggs, so long as you don’t drop the dirty eggshell into the cracked egg. The shells of boiled eggs get sterilised when you cook them, anyway. If we have any eggs which are very dirty, we give them to the dogs, but any that are medium-dirty I scrape the filth off and eat them within a day or two. Perfectly clean eggs we stick in the fridge or give away.

Eggs which are freshly laid have a cuticle on them, a waxy layer which helps to slow down evaporation of moisture from the egg. It does help prevent the ingress of bacteria through the shell, but only a little: when an egg is sat on by a mummy bird, the oils from her feathers rub off onto the eggshell too, and it is these natural oils which are antiseptic and do the most of the protecting.

When we incubate eggs artificially, our eggs don’t get the benefit of those natural oils, as the hen just does not sit on the eggs. So any bacteria which are present on the eggs, even if they look perfectly clean, will grow and penetrate the shell, and infect the contents of the egg on which they sit AND the contents of the eggs adjacent to them. As the conditions in an incubator are perfect for growing bacteria as well as eggs (think of how path labs culture bacteria, in incubators just like ours), it is essential that we remove as much of that bacteria as we can prior to incubation, by washing the eggs. Study after study has shown that egg washing prior to incubation not only increases the number of eggs which hatch, it also results in stronger, healthier chicks. The studies which prove otherwise were all done quite a long time ago, before the science of it was properly understood, and before good egg sanitants were available.

Egg washing has to be done properly, for reasons already explained. Cold water causes the egg contents to shrink, allowing the water AND the bacteria it contains to be pulled into the egg. Warm (or even hot) water makes the egg contents expand and press against the shell (I always picture this like a balloon being blown up inside a sieve), thus preventing the bacteria from entering the pores of the egg. And after washing, eggs should only be handled with clean hands (or even sterile gloves).

You should wash them as soon as possible after collection, then set them into clean trays until you are ready to incubate. However, most home incubator people seem to wait until they are ready to set the eggs before they wash them. I think it depends on where and how you store the eggs.

If you choose not to wash your eggs:

by Misty Johnson

Again, do not incubate very dirty eggs. If they are only a little dirty you can gently (emphasis on gently) wipe them off with a paper towel. If that doesn’t get the dirt off, you can try very fine-grained sandpaper. You’ll want to use as little force as possible for as short a time as possible. Both of these methods can wipe away the protective coating of the egg, leaving the possibility of germs entering the egg.

Every time you handle the eggs, you are adding germs to the surface. Always wash your hands with anti-bacterial soap before handling eggs. No matter if you are collecting, turning, or moving to another location; if your hands are going to come in contact with the egg surface, completely wash, rinse, and dry your hands first. If you do not wish to wash your hands so often, an alternative is non-powdered disposable gloves.

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