“discard the heads and tails”
How do you know how much to discard? 1/2 the batch? 1/4 the batch? 2 tablespoons?
How do you know?
A simple rule of thumb for this is to throw away the first 50 mL (reflux still) you collect (per 20 L mash There are books that give more details. I haven't thought about it in a long time personally.