Why does one need more roux if it was made the “fast way”?
-A fast roux is made in about 20-30 minutes (Prudhomme and Besh)
-A slow roux takes closer to an hour (home cooks)
-When a roux is made the “fast way”, the molecules of flour deform and can only expand to hold 2-3 times their weight
-When a roux is made the “slow way”, the molecules of flour hold their structure and can hold many times their own weight
-Thus, you need much more “fast roux” to thicken the same amount of liquid than a “slow roux”
-Taste is not compromised no matter which method you choose.