It surprises me that they loose that much weight.
That would be 33 pounds of tomatoes for each gallon of finished sauce. If the finished sauce weighs around 8 pounds, that means that you are loosing around 75% of the weight.
Half of that weight loss would be from the cook down, but still your loosing 37.5% at the mill. I'm guessing at least half of that must be water.
That must be a nice thick sauce, as you said.
