Why does egg yolk turn grey

Two solutions here — use older eggs or add a little bicarb soda to the cooking water to increase the pH. If you boil an egg for five or 10 minutes, it becomes firm and cooked. If you boil it for hours, it becomes rubbery and overcooked. When scrambled eggs sit for a while, they tend to turn green or gray. This is a chemical reaction that happens as hydrogen sulfide in the egg white reacts with the iron in the yolk to form iron sulfide.

The eggs are perfectly safe to eat like this, the problem is, they look unappetizing. If you let your backyard chickens free-range even a little bit, they are more likely to have darker yolks and better quality eggs. A dark orange or orange egg yolk likely has better nutritional qualities than a yellow egg yolk.

As for the nutritional value of the yolks, darker, more colorful yolks have the same amount of protein and fat than lighter yolks. Some studies have shown, however, that eggs from pasture-raised hens can have more omega-3s and vitamins but less cholesterol due to healthier, more natural feed.

Black—or green or red—inside of an egg is a bright neon sign of infection. This can be explained easily. For the grey colour to occur, both components from the egg white and from the egg yolk have to interact. This is a great example of food chemistry, a chemical reaction occurs here! The two components involved in this reaction are sulfur in the egg white and iron in the egg yolk.

One of these minerals is actually the iron that plays a role in this reaction. When the proteins in the egg yolk heat and unfold, the iron gets free, free to react. The sulphur component of this reaction is present in both the egg white and yolk. By heating the egg white it comes loose in the form of a gaseous component, hydrogen sulfide and is able to react with the iron. This reaction only happens under the influence of heat, which is why it happens only when boiling an egg.

Indeed, cooling your egg properly after boiling it and not boiling it for too long will prevent it from occuring. The discolouration of the egg yolk only starts when enough iron and sulfur have come free to react. For that to occur temperature has to be high enough and the heating has to be long enough, which is why it only happens after a certain time of boiling.

Another factor into play is the acidity of an egg. The higher the pH thus the less acid the egg , the faster the sulphur is released and thus the more prone the egg is to colouring blue or grey. As a matter of fact, during storage the pH of an egg slowly increases , this is part of the ageing process.

Never realized that chemistry is so much fun and can be found all around you? Let's talk about hard boiled eggs for a minute. They're an excellent source of protein that will actually keep me full all morning. They're a great make-ahead option to guarantee I have breakfast on lock all week--and they even come in their own protective travel case i. They're the perfect topping for an Instagram-worthy toast with all that golden yolk glory. Some of my colleagues would argue they're not exactly the most "office-friendly" breakfast selection in terms of aroma.

Sometimes I lose half of my breakfast when attempting to separate it from the protective travel case. And sometimes And I end up with a dull yellow yolk surrounded by a questionable ring of greenish gray. It's incredibly disappointing.