Do Eggs Need to Be Refrigerated?

Hey, welcome to sign Stuff, a production of iHeartRadio, I'm Hoar hit Cham and today we're cracking open a question that humans have been asking for over a century. Do eggs need to be refrigerated? We're gonna unscramble this mystery by taking a deep dive into the signs of eggs, answering questions like what does it mean for an egg to be Grade A or B? How does salmonella get inside an egg? And is it okay to eat raw eggs?

Enjoy? Hey? Everyone?

Okay, if you're someone who eats eggs every day or only occasionally, you're not alone. According to the US Department of Agriculture, the average American eats about two hundred and ninety eggs a year. The average European eats two hundred and seventeen eggs per year, although it varies by country. For example, in Greece, the average person eats one hundred and forty one eggs a year, but in Denmark they

Worldwide per year.

Purely, eggs are a big part of our diet, and for good reason. Eggs are full of nutrients and they're relatively cheap. According to historians, humans have been farming eggs for thousands of years. The first chicken is said to have been domesticated around ten thousand years ago, and throughout all that time we didn't refrigerate the eggs. Refrigerators were invented in the eighteen hundreds, with the first home fridge

Them when we bring them home.

But if you talk to anyone with backguard chickens, or if you travel abroad a lot, you might have noticed some people just leave their eggs out, which also makes sense. Keeping eggs cool makes moving and storing eggs more complicated and expensive and they take up space in your fridge. So do we have to refrigerate eggs? To help answer this question, it reached out to a bonafide expert, Professor

I teach at the University of athlet in Australia and I also practice of thetan Areas a Poultrybaateinaria. Microsearch group has been researching on eggs and Salmanala for the last several years.

So he tell us what are the current laws or guidelines or customs about storing eggs in different regions of the world.

Interestingly, the rules and the regulations around egg storage or refrigerations they do vary from country to country. The US, for example, stipulates the eggs they must be stored or held in transported at the temperature no greater than seven point two degrees that is not more than forty five degrees fahrenheit. In the UK, eggs must be held at the constant temperature that can range between five to twenty

Do you know how what it is in other parts of the world like Asia, or.

When I visit a number of farms in India, for example, those eggs are not stored at a refrigeration temperature on the farm or during transport. In a big supermarkets in India they are stored sometimes in the refrigerator, but not always so.

Laws and regulations around refrigerating eggs are different depending on the country. For example, in Latin America, there are also no regulations about egg storage. In Brazil, which produces about ninety three billion eggs a year, it's only suggested that you put your eggs in the fridge after you buy them. Now, when I heard this, I thought it was odd that different parts of the world have different requirements by refrigerating eggs.

Why is that?

Is it optional? Does it depend on the egg or the culture of each region. Well, it turns out a big reason is a word that should be familiar to anyone who does any regular cooking with chicken products, and the word is salmonilla. But the main concern seems to be about bacteria.

Is that right?

For eggs? Yes, so a name of vectory is called salmonella. Some of you may have heard about it in the audience, but that's a predominant concern across the world in terms of food safety.

Can you tell us what salmonilla is?

It's a bacteria. People may have heard its name in two contexts. So when it's salmonala typhee, which is called a typhotole salmonella, it results because of the the hicle or contamination typically what we call human to human transmission when it comes to eggs and chicken may to some degree. We are talking about the salmonella which falls into a category of non typhoid or salmonella, so it does not cause typhoid, it causes food poisoning. So there are two

Wow, there, but not all.

Of them are as nasty as some of them, like Typhanirum and introduce, and there are some others as well.

These are all bacterias. They're all called salmonilla, but they're just different kinds of species of bacteria.

There are different kinds of species of bacteria within salmonilla.

Okay.

The first thing to know about salmonilla is that there are many different kinds of salmonilla. As like your chul Salker says, there are over twenty five hundred different serophars or strains of salmonilla. Some cause typhoid fever and are transmitted from humans to humans by poop, and some cause food poisoning and are transmitted from animals to humans by

Birds themselves do not show any clinical signs or symptoms. They don't get sick because of salmonilla. So as a veterinarian, there is no way to find out whether chickens are carrying salmonilla or not until we really test those samples, and it's expensive testing is not cheap. It's expensive to.

Test the chicken to see if they have salmonilla.

If they have.

Salmonilla, Okay, here's the thing about salmonilla. It's kind of impossible to tell if a chicken has it or not. The bacteria can live happily inside the chicken's guts and you might never know. First of all, it doesn't affect the chickens. They don't get sick from it. And second, it doesn't really come out of their food unless the chicken is stressed.

So they have to test their poop. And birds often don't shed that in their faces. It can become a normal part of their gastro in personal microflora and can live happily in the gut of the birds. So if you keep your birds happy and comfortable, they tend not to shed it. When birds are stressed, they tend to shed it. Then the bacteria tends to replicate in the higher number and contaminate the eggshell. Okay, So to recap

But it's out there. Some chickens have it.

Sometimes out some chickens have an unfortunately only way to find that out is when people get sick. Chickaus don't get.

Sick, all right, So some chickens have salmonilla, and sometimes that salmonilla can be the kind that gives you food poisoning. Now the question is how does that bacteria get on the eggs. We're going to get into the nitty gritty of chicken anatomy and egg production after the break. Stay with us. You're listening to sign stuff and we're back.

Okay.

We're answering the question of whether eggs need to be refrigerated, and the answer seems to involve a bacteria called salmonilla. We learned some kinds of salmonilla can live inside the cuts of chickens, and some of those can give you food poisoning through the eggs. Now, the question is how does the bacteria get on the eggs. Here's what our expert, doctor Joe scar said. Now, how did they sell many like kid on the eggs?

Not a lot of people who are not farm in background understands where egg comes from. It comes from a backside of a chicken. And the literally one hole there where the poop and the egg comes out from.

It's the same hole.

Egg comes from, the same hole where the poop comes from. Okay, he just.

Give me the anatomy of a chicken. Like the egg forms in the same tract as the poop.

So there is one part of chicken's body it's called as a reproductive tract. We call that oviduct. That's where the formation of egg takes place. There is a different part where which is a gastro intestinal tract. That's where the poop is formed. There is another part where it connected to kidneys. That's where the urine comes from. But all of those openings they open in the part called kloa and so that's the common opening. That's where the

Hey guess what chicken butt is where both chicken poop and eggs come out of the chicken. This opening called the cloaca is how salmonilla can get on the egg, specifically the egg shell. But here's a shaker. There are also ways for salmonilla to get inside the egg.

Some types of salmonella can contaminate egg from outside, and you can have some types of salmonella that can contaminate egg content from inside. The good example is Salmonella introdude to this that has a potential to multiply in the orbituct, which is an egg forming organ or the reproductive organ. So what happens is once the bacteria is lodged in the reproductive organ, it can contaminate the inside of an

WHOA Okay, how often does the bacteria get in the yolk? Is that common or rare?

It's not very common, at least in Australia. It is not very common unless you really stuff up egg in the kitchen and store it. Barrio mishandling eggs. Most of the commercial eggs produced in the countries like the UK, Australia, also in the US. They are produced in a very highly regulated environment. They are vaccinated against salmonella, so the chances are low that you will get a type of some bacteria in yolk during the formation of egg.

I see, But if they are Baccia.

Chickens, it's very difficult to see how those eggs are collected, how they are kept, and how they're refrigerated, and how people handle them, so it's difficult to tell that I see.

So salmonella can get inside the egg directly during the formation of the egg. Egg scientists called this vertical transmission of salmonilla, but it's very rare, at least for commercial eggs like the kind you get in stores. More concerning is what scientists called horizontal transmission of salmonilla.

That means the bacteria is in the book or is on the shelf because of the contamination buffaces or the dust that can be in the shed and through the shell, the bacteria can migrate inside an egg.

Okay, you're probably thinking, but forehead, the whole point of having a hard egg shell is to protect the egg. How does some manilla that might be in the chicken poop or dirt get inside the egg.

Well.

One easy way is for there to be cracked in the egg shell. The egg gets bumped or dropped, there could be cracks for bacteria to come into the egg. So if you see a cracked egg, you may want to not eat that one or all. The other way bacteria can go in is by getting sucked in. How does it get through the egg shell?

If you look at the body temperature of birds are hotter than humans. Their body temperature is around thirty nine degrees to forty one degrees, so around three to four degrees higher than us.

Wow.

Because they are fully feathered, birds don't have sweat lands, so they can't release sweat. So one of their thermoregulatory mechanism that is patting, and so in the shed there has to be an air movement. So these birds, they are kept in a farm environment where temperature is set at twenty one to twenty three degrees, So hot birds in a cool farm. And that's why those temperatures in the shed are set at that temperature to keep chickens

Right.

So now egg is cooling down from third thirty nine to twenty three degrees and during that cooling down period, there can be a negative pressure that can be developed inside and egg which can suck bacteria from the shell. Wa and so those bacterias get sucked into the pores.

Oh okay, let me see. The egg comes out hot, but it comes out into cool a shed and as it cools, I guess the inside shrinks because it's cooling, that's right.

That's right.

That tends to suck things from the outside of the egg.

That's right. So to give you quite an example, if you have a kind of a warm or hot water in the water plastic water bottle, it kill cools down, it shrinks, the bottle shrinks, right, right. The same thing would happen with an egg. But because egg shell is porous, then that bacteria can get sucked in inside the shell pores. So that's the starting point. That's how bacteria gets in.

Yeah, eggs can suck bacteria in if they come out warm out of the chicken into a cool chicken coop or cage. The shrinking egg white and yolk can pull bacteria in. And this is something I did in know before egg shells have pores. I see, I guess I didn't know that egg shells had pores, Like, why doesn't the stuff come out then? If it has holes in it?

Hual is very porous. And going back to the structure of an egg, the moder nature has designed that egg for development of chicken embryo. So when embryo develops, it also needs to undergo a process we called as embryo metabolism. So it breathes and it also excretes the waste material and so for excretion of that waste material, it has to come out through pores. And that's why it has actual pores.

What even as the embryo grows inside, it's breathing through the egg shell and it's excreting through the axel too.

So embryo takes twenty one days to hatch. And as embryo grows, it produces lot of heat. So those shell pores actually help to remove that heat from the egg, so you can say embryo is breathing, although technically it's not breathing through just through egg shell, but it helps to remove all the heat and the metabolized water through shell shell portes.

Oh fascinating is that how eggs also get fertilized through the pores?

No, so it's the egg gets fertilized in the part of oviduct or birds called as infundibulum. So that's a funnel shaped structure which is right next to the ovary of birds.

I guess I had another birds in the bees of chickens.

Yeah, yeah, that would be another session to talk about how our domating and our fertilusion takes place. Quite a lot of interesting science behind that as well.

Yeah, let's not get into how baby chickens are made. But the point is that egg shells have tiny little holes or pores because eggs are made to grow embryos inside, and as embryos grow, they need those pores to pass oxygen in CO two and water vapor to support their metabolism. According to reports, a typical egg has thousands of pores on their egg shell and up to twenty liters of gases can pass through these pores throughout the life of

It's not that easy. When we come.

Back, we'll find out why washing your eggs is not such an egg sele the idea stick around.

We'll be right back. Welcome back.

Okay, we floored that big motivation for refrigerating eggs is salmonilla, which mostly ends up on the outside of the egg on the shell. So now the question here is I guess a naive question would be why don't we just wash the eggs when they come out of the chicken?

Egg Washing is a whole lot lot of science. So again if you look at different laws of regulation in different countries and the US, egg washing is mandatory for all eggs that are commercially produced and sold. In Europe, egg washing is not allowed. And in Australia are the large proportion of eggs sold commercially are washed. Not all of them are washed, large proportion of them are washed.

When you say washed, what does that mean like rinse with water or actual soilp and chemicals or disinfectant.

Yeah, so that are.

Different and different different ways people do it. Some people they wash and sanitize, other people just wash. So it depends on what procedures or the farms are following. So egg washing machine, egg goes into a washer so where the brushes are set to remove the visible fickle material from the eggshell. Then they are sanitized with flordinated water or food grade sanitizer and then they're dried. So that's step. But again there's a whole lot of signs behind how

I think I read some ra that washing can also damage either the lining or the inside of the egg. Is that true. Yes.

When you talked about protective mechanism, it's called as cuticle, also referred as bloom on the eggs shell. That's another barrier or defense mechanism of an eggshell which prohibits or which stops bacteria from migration into shell. But one of the limitations of the cuticle is that it is not

Which makes the egg more vulnerable to bacteria getting in that can.

But after washing and after drying, those eggs are oiled to see the pores so the bacteria doesn't get in when the posts are sealed, and that is done to replace the job of cuticle because critical is damaged during washing.

Oh, fascinating. So when you say they're washed commercially, they're usually washed and sealed, washed and oiled and oil the porste Yeah, so that's fascinating. So if I go to Europe and I'm in Europe, then I'm not allowed to wash eggs. But if I cross over to the US.

In the US, yes, in Australia, majority of them are washed.

All right, you can wash eggs, but it's best to leave it to the professionals. Okay, I decided to ask that thertial saltcar directly whether eggs should be refrigerated. Here's what he said. Okay, so something that I can get into the egg vertically horizontally, is that then the reason to refrigerate eggs?

Yeah. Look, the migration of bacteria across the shell or through horizontal way of transmission is also driven by temperature. When eggs are stored at a room temperature, when they are not a refrigerator or not cooled, then the rate of penetration could be higher across the eggshell.

Why is that?

Because that temperature is helpful for bacteria to survive and also penetrate across the shell. That a number of different organs or bacteria that get switched on at that temperature. That a lot of the bacterial genome. People have looked at how the gene expressions of the bacteria look like at that temperature when they migrate or when they penetrate across the shell.

WHOA, So, then refrigeration, how does that help prevents the bacteria from going inside?

Look, it slows down the activity of bacteria overall. As soon as you lower the temperature. It does not kill the bacteria, so it just slows down the growth and it can slow down the multiplication of the bacteria as well. If the egg internal contents are contaminated, that's the important thing to remember. And also remember that if eggs are stored inside the cool temperature refrigerator temperature, that lowers the risk of the footbone illness overall.

So then do eggs need to be refrigerated.

I would recommend yes, refrigeration of egg that if you have eggs at home, I'll definitely recommend to keep them in the fridge. Don't leave them on the bench because if you leave eggs on the bench, the egg white, which is inside an egg, it tends to deteriorate. That means it tends to go more runny. So you might remember the old method of testing if eggs are fresh or stale, because the fresh eggs would sink, can stale

Interesting what your Chou Socar is saying here is that refrigerating eggs also helps keep eggs fresh studies have found that the quality of the egg goes down over time. Egg whites get runnier and less acidic, and they also lose weight over time. If you crack an egg on a plate and measure the height of the blob of egg white, that height, also called the hot unit, is a measure of the quality or grade.

Of an egg.

Great AA is the tallest, followed by A, B, and C. That height also decreases with time. But if you refrigerate the egg, all these processes slow down, so the eggs need to be refrigerated.

The answer is.

Really an egg can last just fine if you leave it on the counter for days, but putting it under fridge does lower the risk of salmonilla getting in the egg, and it keeps the egg fresher. This explains why different countries and regions have such different rules and regulations. And what does that depend on what a country decides to do.

I think it depends on the risk and the prevalence means to the extent to which the bacteria are present in the population on the flock. Also depends on the type of bacteria that is in the country. For example, for many many years, salmonella in treated was not endemic

I see, so then it makes more sense for them to be more careful.

Yeah, in general, industry has always been quite careful because it affects the business. Food safety is an important element for egg business. Egg farmers, they do lots of good things to produce a very safe product for humans, and so it all boils down to how that egg is handled in the kitchen environment. So we just had to be very careful on how we prepare dishes metal from eggs. People don't always wash their hands in the kitchen after

What happens?

Since you are essentially cross contaminating things in the kitchen.

The saveest thing is to assume that the outside of the egg probably has some manilla on it, and that the inside could also have some manilla inside of it.

Yeah, so there is a possibility of bacteria being there on the shell. There is a low possibility of bacteria being in satin egg. It's not zero, it's low. So just wash your hands after you are handling eggs and cook eggs properly.

All right, thanks for joining us. We hope you had a shell over time. And if you don't like egg puns, I'm sorry for all the bad yolks. See you next time. You've been listening to Science Stuff production of iHeartRadio Bring the produced by Me or Hm hedited by Rose Seguda, executive producer Jerry Rowland, audio engineer and mixer Casey Pegrom and you can follow me on social media.

Just search for.

PhD Comics and the name of your favorite platform. Be sure to subscribe to Sign Stuff on the iHeartRadio, app, Apple podcasts or wherever you get your podcasts, and please tell your friends we'll be back next Wednesday with another episode.