What’s That Gray Ring You Sometimes See Around Hard-Boiled Eggs?

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黄和蛋白相接触的一层表面会成灰色或绿色，有人可能会因此怀疑母鸡得病了，或者鸡蛋是否可以安全食用。

好消息是可以吃。煮鸡蛋时，蛋黄表面由于化学反应而呈现灰色。鸡蛋的蛋白质中含有硫元素，高温下蛋白质分解形成硫化氢。蛋黄中的铁元素会进一步与之发生反应，使其表面形成硫化亚铁。水中含铁过多也会导致类似的结果。

那这和蛋黄表面的颜色有什么关系呢？正是硫化亚铁让蛋黄表面呈现灰（绿）色，这通常是因为鸡蛋煮老了。据“索德鸡蛋”公司称，一个易碎的干蛋黄在沸水中大约需要煮14分钟。为避免过度烹煮，可以将煮熟的鸡蛋立即浸泡在冰水中。

如果鸡蛋煮老了，口感可能会比你想得更硬一点，但是颜色并不能说明任何食品安全问题。蛋壳上有斑点（棕色斑点）或凸起的蛋也是如此。只要你的鸡蛋购买回来的时间不超过三周，并将蛋黄煮至变硬，就可以放心食用。