How did cooling white sauce uncovered affect its appearance?

Cooling white sauce uncovered will have several effects on its appearance:

1. Skin Formation: The most noticeable change is the formation of a skin on the surface of the sauce. This happens due to the evaporation of water from the sauce, leaving behind a layer of concentrated protein and fat. This skin will be a thicker, more opaque layer than the rest of the sauce.

2. Color Change: The white sauce may appear slightly yellowed or slightly brown due to the Maillard reaction, which is a chemical reaction that occurs when sugars and amino acids are heated. The more the sauce is exposed to air, the more likely it is to brown.

3. Texture Change: The sauce will become thicker and more viscous as it cools and the water evaporates. It may also appear less smooth due to the formation of the skin.

4. Flavor Changes: The taste of the sauce can become more concentrated and less fresh due to the evaporation of water and the Maillard reaction.

In short, cooling white sauce uncovered will make it appear less appealing due to the formation of a skin, color changes, and a thicker, less smooth texture.

To prevent these changes, it's best to cover the white sauce with plastic wrap or a lid to keep it moist and prevent air exposure.