Egg white, also known as albumen, is a complex aqueous solution of proteins and water. Its chemical identity plays a significant role in its function both within the egg and in culinary applications. Understanding the acidity or alkalinity of this protein-rich liquid requires a grasp of the pH scale. This chemical context determines everything from the egg’s freshness to how it behaves when whipped into a meringue.
Defining the pH Scale
The acidity or alkalinity of any solution is measured using the pH scale, which is an inverse logarithmic scale ranging from 0 to 14. This scale quantifies the concentration of hydrogen ions present in a solution.
A solution is classified as acidic if its pH value is less than 7.0, and basic (or alkaline) if the pH is greater than 7.0. The neutral point on the scale is exactly 7.0, which is the pH of pure water. Highly acidic substances like lemon juice register at the low end, while highly alkaline substances like lye are found at the high end.
The Alkaline Nature of Egg White
The egg white is an alkaline substance. When an egg is freshly laid, the albumen starts with a slightly alkaline pH, typically falling in the range of 7.6 to 7.9.
This pH begins to change immediately after the egg is laid due to the loss of dissolved carbon dioxide (CO2) through the porous eggshell. CO2 dissolves in the egg white to form carbonic acid, which keeps the fresh egg’s pH lower.
As this gas escapes into the atmosphere, the carbonic acid concentration decreases, causing the solution to become progressively more alkaline. Within a few days of storage, the pH of the egg white can climb significantly, often reaching 9.0 or even higher.
How pH Influences Culinary Use and Storage
Culinary Effects
The increasing alkalinity of the egg white has consequences for its use in the kitchen. In older eggs with a higher pH, the proteins begin to degrade, making the white less viscous and causing it to spread out when cracked.
This higher alkalinity also affects the egg’s foaming ability, which is crucial for meringues and soufflés. While older, more alkaline egg whites may whip up faster, the resulting foam is less stable.
Chefs often add a small amount of acid, such as cream of tartar or lemon juice, to egg whites to lower the pH, which creates a more stable, longer-lasting foam. The high pH of older eggs also influences flavor, sometimes contributing to a sulfurous taste.
Storage and Peeling
One practical benefit of a higher pH is seen when peeling hard-boiled eggs. The alkaline environment weakens the bond between the egg white and the inner shell membrane, making older eggs easier to peel cleanly.
Storing eggs in the refrigerator is the most effective way to slow down the escape of carbon dioxide, thereby minimizing the pH increase and preserving the quality of the egg white.