Everyday phenomena explained scientifically: “Why does an egg harden?”

Everyday phenomena explained scientifically: “Why does an egg harden?”

© orinoco-art, GettyImages

Everyone knows it: Boiling in water for too long and the egg has become too hard. On the other hand, if it is in the water for too short a time or if the temperature is too low, the egg will remain liquid. But what processes take place in the egg and how can I know when my egg has the perfect consistency? With modern technology and science, this process becomes transparent. A novel invention – the Golden Egg – clearly demonstrates the phenomena that occur in our everyday lives and how we can use science to obtain the ideal breakfast egg.

Why does an egg harden?

When cooking, physical processes take place inside the egg that cannot be reversed. Many reactions can be reversed, but it is not possible to return a boiled egg to its original state. The increase in temperature leads to denaturation of the protein in the egg. This process begins at around 61.5 degrees Celsius. The higher the temperature rises, the more changes occur. If the egg is hard-boiled, it has reached a temperature of 84.5 degrees Celsius. Other chemical processes take place during the cooking process. Iron is released from the egg yolk during prolonged cooking. The egg white releases hydrogen sulfide when exposed to heat. At the border between egg yolk and egg white, both substances react to form iron sulfide, which is a… Discoloration inside the egg You can tell if the eggs are cooked for a particularly long time. The egg is still edible, even if the changed color seems unusual at first glance.

Golden egg
Golden Egg, the thermal egg timer for cooking with you. © Media Service Konradin GmbH

The Golden Egg – using practical science to create the perfect breakfast egg

The singing one Egg timer looks like a real egg – but is plated with 24-carat gold and has impressive technology inside. Placed in the water bath together with the chicken eggs, the egg timer shows by playing different melodies whether the real eggs inside are soft-boiled, medium-boiled or hard-boiled. But how does the Golden Egg work? What technical processes are hidden behind the modern shape of the egg timer?

How does the egg timer work?

The egg registers the water temperature and uses the data to calculate the internal temperature of the eggs. For this purpose, the egg timer uses a differential equation. As soon as the inside of the eggs reaches a temperature of 62 degrees Celsius, a melody starts, indicating that the eggs are as soft as wax. The temperature calculated by the egg timer serves as an indicator of the assumed temperature in the real eggs and thus as an indicator of the cooking status of the eggs. If the melody “Killing me softly” can be heard, the eggs are soft. If you hear the melody “I wish I were a chicken,” then the eggs are medium. When the melody “Triumphal March” sounds, the egg is hard. Many other egg timers measure the time that has passed. The developers of these models assume that eggs need a certain cooking time to develop the desired strength. However, in reality, the cooking behavior of eggs depends on numerous factors, such as the actual temperature of the water, which in turn depends on the ambient air pressure.

The relationship between air pressure and the boiling temperature of water

An extreme example: On the Mount Everest boils water already at 71 degrees Celsius. In the home kitchen, however, the boiling temperature of water is 100 degrees Celsius. The reason for the changed behavior of the water is the air pressure. At high altitudes, air pressure drops, causing liquids to boil more quickly. Although no one will probably boil water on Mount Everest, the differences in cooking behavior can also be seen at lower altitudes.

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