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Should I refrigerate my eggs or keep them out on the counter? This depends on where you live, and what egg practices your country follows.

Hosted by: Hank Green
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Sources:
http://www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation/ucm207507.htm
https://www.gov.uk/guidance/eggs-trade-regulations
http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6976.2008.00161.x/abstract
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2271858/pdf/epidinfect00027-0066.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870917/
http://www.latimes.com/food/dailydish/la-dd-heres-why-we-need-to-refrigerate-eggs-20140714-story.html
http://www.forbes.com/sites/nadiaarumugam/2012/10/25/why-american-eggs-would-be-illegal-in-a-british-supermarket-and-vice-versa/3/#37688e90f0da
http://io9.gizmodo.com/americans-why-do-you-keep-refrigerating-your-eggs-1465309529
http://www.sciencedirect.com/science/article/pii/S0956713515001103
Images:
Salmonella: https://commons.wikimedia.org/wiki/File:SalmonellaNIAID.jpg
Vaccination: https://commons.wikimedia.org/wiki/File:Chicken_vaccination.jpg
[SciShow intro plays]

Hank: Where do you keep your eggs? In the refrigerator? On the kitchen counter? Or in the little basket you use to bring them in from the coop? Well, if you live in the US and you get your eggs from a grocery store, odds are you keep them in the fridge. But if you live pretty much anywhere else, you probably don’t refrigerate your eggs — and you might think it’s a little weird that Americans do.

There is a good reason for it though: we in America wash and refrigerate our eggs to avoid getting salmonella. Salmonella bacteria can be transmitted to an egg in two different ways: from an infected hen, or from manure. Chicken poop, is what I mean. Here in the US, we wash and dry the eggs as soon as possible to prevent contamination from infected chicken poop. But there are downsides to washing eggs.

See, when an egg comes out of a chicken, the shell is coated with a protective layer of proteins and other molecules called the cuticle. Cuticles are designed to keep bacteria like salmonella from getting through the porous eggshell, and setting up shop inside. And washing eggs gets rid of any dirt and the protective cuticle.

In other places, like Europe, they do the opposite: egg washing is banned. Instead, they try to keep the eggs from getting dirty in the first place, and rely on the cuticles to keep out bacteria. They also vaccinate their hens against salmonella, to keep eggs from getting infected while they’re forming.

Basically, it’s more likely that American hens will be contaminated with salmonella, so we have to constantly refrigerate those eggs, from farms to our homes, to slow bacterial growth. Studies have shown that if an egg is contaminated with salmonella, on the surface or inside, the bacteria will reach dangerous levels after about 3 weeks at room temperature. If you refrigerate the egg, though, the bacteria will hardly grow at all — even after 6 weeks.

But if the hens are vaccinated against salmonella and the eggs aren’t washed — so they have cuticles to protect them — it’s probably better to keep them at room temperature. See, when you take an egg out of the fridge, condensation can build up on the shell. All that moisture encourages bacterial growth, and eventually the bacteria might find a way in through the cuticle and the porous shell.

So if you don’t live in the US, or a couple other countries where you buy your eggs in the refrigerated section, keep your eggs at room temperature. But if your eggs are pre-washed, keep them in the fridge... unless you just really want to get salmonella.

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