A cook that does not understand this process or its importance ends up with a less than desirable sauce full of impurities and fat.
Any sauce that has been thickened with a roux must be depoulled.
Depouillage as it is applied to sauces, is the removal of all fat and impurities from the flour and stock in the sauce. To successfully depouille a sauce you must first use a ratio of only 10 to 13 percent roux per weight of the sauce. This ratio will allow for enough stock to make the roux a liquid thereby allowing the impurities to rise during the reduction process.
Follow this process
This process is a must when working with a roux sauce to have a fully finished sauce.
Straining of the sauce also improves the texture and increases the luster or sheen. Straining will also blend the liquid ingredients together. Use the finest mesh available for the best results.