Understanding egg yolk discolouration

When boiling hard-boiled eggs, some of us have noticed an unsightly greenish-grey ring around the yolk. At first glance, this might seem worrying, but in reality, it's the result of a chemical reaction. When an egg is boiled for too long, the sulphur in the yolk reacts with iron present in the white, forming iron sulfide. This compound is responsible for the characteristic dark colour of the ring.

Overcooking eggs is the main cause of the greenish-grey ring. If an egg stays in hot water for longer than 10-12 minutes, the risk of this effect appearing greatly increases. Therefore, it's essential to monitor the cooking time to avoid unsightly changes and nutritional loss. It is believed that an egg boiled longer than 7 minutes loses half of its vitamins and minerals.

Many of us wonder whether an egg with a greenish-grey ring is safe to eat. The answer is simple: yes, it is safe. The colour change is an aesthetic defect and does not affect the taste of the egg. You can eat an egg with a greenish-grey ring without worry, as it is not a sign of spoilage, but we must be aware that it has significantly fewer nutritional values.

1. Soft or hard boiling: Boiled eggs are considered one of the healthiest ways to consume them. Boiling doesn't require added fat, which helps maintain a low-calorie count. Soft-boiled eggs, with liquid yolks, are particularly recommended because they retain more vitamins and minerals.
2. Poached eggs: This is another healthy option that doesn't require the use of fat. Poached eggs are delicate and low in calories, making them an ideal choice for those watching their weight.
3. Baking: Baked eggs, for example, in the form of shakshuka, are a great way to combine eggs with vegetables, further enriching the meal with vitamins and minerals.
4. Frying eggs: Frying eggs, especially in a large amount of fat, can lead to the loss of valuable nutrients and increase the calorie content of the dish. Fried eggs may contain more oxidised fats, which are less beneficial to health. If you decide to fry, use a minimal amount of fat with a high smoke point, such as coconut oil or clarified butter.

In conclusion, the healthiest are soft-boiled or poached eggs, which retain the most nutrients and are low in calories. Frying, especially with a lot of fat, should be limited to enjoy the full health benefits of eggs.