Boiled egg

Boiled eggs are a versatile food item made primarily from chicken eggs. The cooking process usually involves immersing the eggs in boiling water while the shells remain unbroken. This simple method can produce very different results depending on the time spent in the heat. Hard-boiled eggs are cooked until both the white and the yolk are completely solid. Soft-boiled eggs are cooked for a shorter duration, leaving the yolk partially or fully liquid.

This culinary staple is a popular breakfast food across many different global cultures.

The science of boiling an egg is based on the behavior of proteins. Inside the egg, proteins in the white, called albumin, and proteins in the yolk undergo a process called denaturation. This process causes the proteins to unfold and then bond together, a stage known as coagulation. As the proteins coagulate, they solidify the liquid contents. The egg white begins to coagulate at a lower temperature range than the yolk. The yolk requires a slightly higher temperature to thicken and eventually solidify.

Because the albumin surrounds the yolk, heat must travel through the white to reach the center. This makes it difficult to achieve a perfectly solid white alongside a runny yolk.

There are several distinct ways to categorize boiled eggs based on their texture. Hard-boiled eggs are typically cooked for about 10 minutes. These are often used as ingredients in dishes like egg salad, Cobb salad, or Scotch eggs. They can also be prepared as deviled eggs. Soft-boiled eggs offer a different experience with a creamy, sweet, and umami-rich yolk. In the United Kingdom and Australia, people eat soft-boiled eggs with toast strips called "soldiers."

In Southeast Asia, a variation called half-boiled eggs is served in a bowl with soy sauce and pepper.

History shows that humans have used eggs for a very long time. The history of eating eggs follows the history of the domestic chicken. We find recipes for boiled eggs in *De re coquinaria*, which is the first known cookbook. This ancient text even includes a recipe using preserved boiled eggs. The poet Alexander Pope once recommended cooking eggs over the embers or ashes of an open fire.

These historical methods highlight how central eggs have been to human nutrition for centuries.

Different regions have developed unique methods to change the flavor or appearance of boiled eggs. In Japan, eggs are often served in ramen after being steeped in a mixture of soy sauce, mirin, and water. This process gives the eggs a distinctive brown color.

In the Ōwakudani region of Japan, eggs are boiled in mineral-rich hot spring water to create *Kuro-tamago*. These eggs are famous for their characteristic black shells. In China, duck eggs may be preserved in salt or brine for 20 to 50 days before being boiled. These salted eggs represent a specific method of food preservation.

Precision in cooking can prevent common issues like discoloration. If an egg is overcooked, a thin green iron(II) sulfide coating may form on the yolk. This happens more quickly in older eggs because their whites are more alkaline. To prevent this, cooks often rinse or immerse the eggs in cold water immediately after boiling. This "shocking" process halts the cooking.

For those who want a specific shape, machines can produce "long eggs." These are eggs where the yolk and white are separated and poured into a cylindrical mold. This method was first introduced in 1974 and is used commercially in Denmark and Japan.

Boiled eggs also connect to broader topics like food safety and chemistry. To destroy harmful bacteria like *Salmonella*, the egg must reach a specific temperature. While some believe complete coagulation is the only way to ensure safety, temperature is the most critical factor. Additionally, the ease of peeling an egg is tied to its chemical makeup. As an egg ages, it loses carbon dioxide through its pores, making the pH of the white more basic. This higher pH makes the egg less likely to stick to the shell, making it easier to peel.