Don Marcotte wrote:

>So, is it basically that the industrial processes don't
 totally remove whey proteins (and lactose) when
they try to isolate casein, or does casein contain lactose?<

Yes, sorta, to the former, and no to the latter, Don.

Lactose is an entirely separate component of milk
from the proteins. It is dissolved in the liquid portion 
of milk (which is simply water).

Because everything else is also dissolved (or technically 
in colloidal suspension) in the liquid, processors have to work 
hard to make sure they separate out all the lactose.

A cheese curd starts out liquid and traps some water,
including lactose, inside the curd. Aging almost 
literally squeezes the water and lactose out.

Industrial processing is more sophisticated, but 
the principle is the same.

It can be done, and I believe that processors in general 
are doing a better job than in the past.

Best,
Steve Carper