葛美玲

Some hard-boiled eggs have a gray or green ring of discoloration between the white and the yolk，which might prompt you to wonder if the chicken in question had some exotic disease or whether the egg is safe to consume.

Good news：It is. The gray coloring appears due to a chemical reaction when boiling the egg. Proteins in the egg are held together by sulfur，which breaks down in heat and becomes hydrogen sulfide. Iron in the egg yolk can alter it further so it becomes ferrous（iron）sulfide on the surface. Too much iron in your water can produce a similar result.

What does this have to do with the color？It’s the iron sulfide that creates the gray（or green）rings around the egg，and that’s usually a result of overcooking it. According to Sauder’s Eggs，a crumbly，dry yolk takes about 14 minutes in boiling water. One way to avoid overcooking is to dip the cooked eggs in an ice bath immediately afterward.

If you do wind up overheating them，the eggs might be a little firmer than you’d like，but there’s nothing about the color that indicates any food safety issue. The same holds for eggs that have speckling（brown spots）or bumps on the shells. So long as you use store-bought eggs within three weeks of purchase and cook the yolks until they’re firm，you’ll be good to go.

一些煮老了的雞蛋蛋黃和蛋白相接觸的一層表面會成灰色或綠色，有人可能會因此懷疑母雞得病了，或者雞蛋是否可以安全食用。

好消息是可以吃。煮雞蛋時，蛋黃表面由于化學反應而呈現灰色。雞蛋的蛋白質中含有硫元素，高溫下蛋白質分解形成硫化氫。蛋黃中的鐵元素會進一步與之發(fā)生反應，使其表面形成硫化亞鐵。水中含鐵過多也會導致類似的結果。

那這和蛋黃表面的顏色有什么關系呢？正是硫化亞鐵讓蛋黃表面呈現灰（綠）色，這通常是因為雞蛋煮老了。據“索德雞蛋”公司稱，一個易碎的干蛋黃在沸水中大約需要煮14分鐘。為避免過度烹煮，可以將煮熟的雞蛋立即浸泡在冰水中。

如果雞蛋煮老了，口感可能會比你想得更硬一點，但是顏色并不能說明任何食品安全問題。蛋殼上有斑點（棕色斑點）或凸起的蛋也是如此。只要你的雞蛋購買回來的時間不超過三周，并將蛋黃煮至變硬，就可以放心食用。