Whenever you’re cooking or baking with eggs, good food safety practices are of the utmost importance. Sometimes, though, laziness wins: At one point or another, most of us have set a spent eggshell back in the carton rather than finding a more appropriate receptacle. Even if you’ve never sent anybody to the hospital with this move, it’s still a bad habit that you should break immediately.
As you almost certainly know by now, eggs can be contaminated with Salmonella bacteria, which can cause severe food poisoning. We mostly think of raw and undercooked eggs as the main risk factor, but it’s important to remember that eggshells can get contaminated, too. Thankfully, this is rarely a big deal: Industrial sanitizing procedures take care of the vast majority of surface contamination, so as long as all the eggs are intact, the carton environment is typically the least of your worries.
All that changes when you put empty shells back in the carton. You’re suddenly introducing another potential source of bacteria — raw egg residue — into the place where you store your eggs. If you think that any remaining eggs are safe just because their shells are intact, think again. Eggshells aren’t Fort Knox; Salmonella can penetrate them, which makes cross-contamination a serious possibility. Even if you just set the shells in the carton for a minute while you finish cracking the rest, they’re bound to leave behind some residue, which could be enough to colonise the whole carton. Refrigeration doesn’t kill bacteria — it just slows them down.
The bottom line: Storing empty shells and whole, raw eggs in the same container gives Salmonella even more chances to multiply and potentially make someone very sick, so don’t do it. Instead, collect your eggshells in a bowl as you go and dispose of them right away. It does require you to remember to pull a bowl out before you start cracking, but that sure beats food poisoning.