Why apples go brown when boiled?

When apples are boiled, the heat causes the enzymes in the apple to break down, releasing polyphenols. These polyphenols react with oxygen in the air, causing the apple to turn brown. This process is called oxidation.

The rate at which apples brown depends on several factors, including the temperature of the water, the acidity of the water, and the type of apple. Apples that are boiled in acidic water will brown more slowly than apples that are boiled in neutral or basic water. This is because the acid helps to inhibit the activity of the enzymes that cause browning.

Some varieties of apples are more prone to browning than others. For example, Granny Smith apples hold up well to cooking, retaining their shape and color, while McIntosh apples tend to become soft and brown when cooked.

To prevent apples from browning when boiling, you can add a few drops of lemon juice or a pinch of ascorbic acid (vitamin C) to the water. You can also cook the apples in a covered pot, which will help to reduce the amount of oxygen that comes into contact with the apples.