How do you get gelatin from rendering cow fat?
I beg to differ with most of the responses. In my personal experience, rendering of fat - not simply suet - from 'general meat' produced a great deal of gelatin. I am using some as a base for tonight's stew at this very moment.

No, suet would not render out significant gelatin, but I have just now rendered about 3kg of fat from beef/fat leftovers from a butcher. I used a food processor to turn the fat/beef mistress to a chunky paste, then boiled the paste over water. I was left with approximately 25% hard tallow and approximately 70% meat. In the process of cooling the tallow atop the same water used for rendering, I found that the water gelled. I separated the tallow from the gel, then boiled down the latter, leaving myself with a gelatin - rich base for tonight's stew.