How to tell if an egg is fresh

You can put a flashlight right next to the eggshell to light up the insides, but historically, a piece of cardboard with a small hole in it was used, with a light source behind it and the egg in front.

The above method will let you see the air space and mold, but it's really a difficult technique to get down.

Above you can see a fresh egg (little air space, slightly visible yolk), a slightly old egg (larger air space, slightly darker yolk), a nearly bad egg (really dark yolk, spotty), and a spoiled egg (mixed in yolk, lots of dark), lit up using the candling technique. If you want to see inside your eggs more often, try out this LED egg candle light — it's made to check if an egg is fertilized if you're into that.

If you don't need the shell intact, you can also crack the egg onto a plate or other flat surface to test how fresh it is. If it's fresh, the yolk should be bright yellow or orange, and the white shouldn't spread much. If you're not sure, give it a good sniff: fresh eggs shouldn't have much of a smell at all.

The yolk will be flatter and the white will be much runnier in an older egg. An egg that spreads out when cracked isn't necessarily bad, though, just older (and again, good for hard-boiled eggs). If it's gone bad, you probably won't even needto do the sniff test—even slightly rotten eggs will have a very strong, distinct smell you'll notice right away.

Got a bunch of eggs that are going to go bad before you can use them? Hard-boil them and throw them in a jar with a beet brine to make tangy, delicious, and beautifully purple pickled eggs.

Looking for more eggy tips? Learn everything you need to know about cooking eggs from The Ultimate Guide To Cooking Eggs, by D and P Gramp.

There are also lots of things you can do with those discarded eggshells, like make your teapot super clean, fertilize soil, and make sidewalk chalk. And don't forget about those leftover egg cartons, which make good seed and fire starters, bird feeders, and candle-making molds.