What makes meat shrink when heat is applied to it?

When meat is heated, several physiological and chemical processes contribute to its shrinkage. Here are the main factors:

**Protein Denaturation**: Heat causes proteins in meat, such as collagen and myosin, to denature. This means that their molecular structure changes, causing them to unfold and lose their original shape. As proteins denature, they exude moisture, which can lead to shrinkage.

**Collagen Breakdown**: In tougher cuts of meat, collagen (a fibrous protein found in connective tissues) breaks down into gelatin when subjected to heat for extended periods. While this process can lead to tenderness, it also contributes to the overall contraction of the meat fibers.

**Moisture Loss**: As meat is cooked, water vaporizes and escapes from the meat as steam. Since a significant portion of meat is composed of water, the loss of moisture during cooking causes the meat to become smaller and firmer.

**Fat Rendering**: Fats within the meat can render (melt) when exposed to heat. This process not only reduces the fat content of the meat but also contributes to shrinkage as the fat is lost.

**Muscle Fiber Contraction**: When heated, muscle fibers contract. This contraction can be responsible for a noticeable decrease in size, especially in lean meat cuts.

These elements combined explain why meat shrinks when cooked, leading to changes in texture, moisture content, and overall size.