Compressed Yeast

Does anyone know how compressed yeast (in a cake form and bought fresh from
a refrigerated cabinet) is made?

The reason why I am asking is that a lot of the old books dating from the
19th C and the early 20th C which I own, give recipes that describe boiling
unpeeled potatoes with hops as a way of making yeast. I am curious if that
old method of making yeast is/was in any way similar to how modern
compressed fresh yeast is made.

I've tried doing a google search but failed miserably to turn up anything
informative ont he subject.