I am interested in my extraction yields for different conditions of preinfusion. I recall reading that you can simply weigh the puck before and after so I dump the grinds into a small bowl, distribute them, and leave them on the warming tray for a day. They seem thoroughly dry when I weigh them. I get yields in the 21-22% range from medium roast beans. This is from grinding fine, performing drip preinfusion (just boiler pressure for about 20 sec), and then brewing for about 33 sec 22g in, 54 g out. These shots tend to be smooth and exhibit less acid than shots ground a bit coarser and without preinfusion. Clearly, drip preinfusion has a repeatable effect so I am encouraged to try some lighter roasts.
Does anyone know of a standard method for calculating extraction yield by weight? I suspect I am doing something wrong.