Why does a roux separate?

A roux can separate due to overcooking or improper incorporation of fat and flour. If the fat is too hot or if the roux is cooked too long, it can break down, causing the fat to separate from the flour. Additionally, if liquid is added too quickly or in an incorrect ratio, it can destabilize the emulsion, leading to separation. Proper technique and attention to temperature and ratiOS can help maintain a smooth consistency.