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A Bad Egg

By Brian Geiger, contributor

January 22nd, 2010

Kitchen Mysteries is a weekly exploration of oddities surrounding cooking and food. They could be recipes that fail when they shouldn't, conflicting advice from different sources, or just plain weirdness. If it happens in a kitchen, and you're not sure why, send a tweet to The Food Geek or email to brian@thefoodgeek.com to find out what's happening.

On January 13th, Kellie Lyn asked:

Hi, Kellie,

First of all, there's no reason to feel dumb about this. Almost every type of food these days proclaims that it's best to eat or drink it before a certain date. This does two things. The first is to make people wonder how bad it is if it's just not at its best. The second is to stop people from thinking about why food goes bad and how and instead to just look at the date. The second consequence was probably not intentional, but it happened all the same.

Now, there are those I know who will throw things out when the food is near or past that date, and there are those I know who will use something waaaaaay past the date because, really, it's not that bad, right? Sometimes that results in a muffin that doesn't rise very much, and sometimes that results in a trip to the hospital.

In general, knowing how to tell if your food is good or bad is a better idea than trusting a date on the side of the package. Although sometimes it's a matter of what will make you sick, many times it's a matter of whether the food will taste good. And, depending on whether your goal is to make something taste as good as it can or just to make something that will be filling and not make you sick, you will have different interpretations of bad.

Fortunately, eggs are a relatively forgiving on the "going bad" front. People are afraid of eggs because of the whole "salmonella" thing, but the things about salmonella are that it lives on the outside of the egg and cooks away nicely. You see, the egg has this handy shell, plus a couple of layers of membranes that are designed to keep things like bacteria and viruses out of the egg. After all, an egg isn't about protecting your food, it's about protecting a chicken-to-be, so it's quite serious about what it does.

As an egg ages, it loses water out of the shell, so it becomes less dense. The white becomes less white and more clear, and the yolk starts to become watered down, so an older egg isn't going to be as tasty as a fresh egg, but it won't kill you. If an egg goes rotten, it's going to smell like sulphur (or, as many would say, it will smell like rotten eggs). This is unmistakable, and if your main goal in life is to avoid that smell, then you aren't going to want to open eggs that you suspect are rotten.

So, aside from the date on the carton, what can you do about knowing if an egg is aged or not? The easiest and most popular test is to put the egg into water. Remember how I told you that an egg loses water as it ages? Since the egg shell stays the same size, but the mass decreases, this means that it becomes less dense. A fresh egg is a little more dense than water, so it sinks. An old egg is less dense than water, so it floats. 

posted in: Blogs, food geek, egg, yolk, salmonella, shell, egg white, age
Comments (8)

dioclaus writes: Met an old trick that works very well Posted: 11:43 pm on April 18th

Snapbean writes: I thought older eggs were easier to peel after hard boiling. Posted: 8:28 am on February 5th

dirtball140 writes: I spoke to the poultry specialist at the Vt Tunbridge Fair about this one year as the feed store where I worked sold eggs off the counter. His response was that moving eggs from in, to out of your fridge does more than anything to cause the breakdown of the egg. All of the above comments are true, but I've had eggs that were months old that hadn't rotten. The were fine to whip and use as a wash on baked goods, or in quiches etc. They can loose enough body in time that you may need another egg, however. If they're really questionable I scramble them for my cats. they don't seem to mind. Posted: 8:20 am on February 4th

LRinOakland writes: Actually, in response to Dani H above, maybe it is a difference in terminology. Older eggs lay flat - from the side view you will see a very flat white and a yolk...in part due to the moisture loss the writer was discussing and the slow process of the breakdown of the cells/proteins. On a really fresh egg the white has more resilience and from the side the white rises to encompass the yoke much more/better than on an old egg.....the fresher white still has the resilience that enables it to perform its function well. The proteins/moisture haven't degraded - of which flatnees is a result. Posted: 8:54 pm on February 3rd

jcwell writes: I've always heard that the reason it floats is because it is producing gas inside the shell as it starts to go bad, hence the sulfur smell as you mention. It seems the sulfur smell is a gas which causes it to be lighter than water and float rather than a loss of water. Regardless the trick works but the science behind it seems debatable. Gas inside the egg makes more sense to me but I don't know the true answer. Posted: 5:34 pm on February 3rd

Dani_H writes: To simplify:
If the egg lies flat on bottom of bowl, it's fresh. The more it "stands up" the older it is, and best used in baking, quiche, and the like rather than on it's own. If it floats, throw it away.
Eggs are usually good for two to four weeks after the "best by" date. Posted: 6:57 pm on January 25th

TheFoodGeek writes: That is great to hear. I am all for ending domestic disharmony. You are quite welcome. Posted: 8:52 pm on January 24th

TheNaptimeChef writes: You've successfully ended a debate in our household - thank you! Posted: 2:12 pm on January 23rd

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