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.

When I render fat scraps (usually taken from brisket and shoulder roast), there is usually a significant amount of connective tissue mixed in (although I try to trim away all of the meat). Thus, after rendering the tallow and letting it cool, the liquid below the tallow is quite gelatinous. It is a whitish color. It is thicker than a typical stock, although not quite as thick as calf's foot jelly. I save this and use it to thicken broths and soups (although it doesn't have much flavor, so I don't use it by itself).

you cant render beef fat to produce gelatin, the main reason for rendering fat is to remove impurities ie to clarify remove the "scum" and other byproducts water ect. in butter very similar removing milk solids/salts ect

I just got plain old beef fat from butcher shop.

Fat scraps I put in a pot filled with water to just above the fat at just boiling point not any longer than not to burn the fat. Do not boil to long to prevent evaporation of any of the oil. Let cool at room temperature until the oil rises to the top and hardens and then removed. Return the fat with adding water to just above boiling point and cooked again the same as the first with after it has cooked awhile use something in both cooking to scoop out the oil; a tablespoon will work against the pot. If the second time scooping out the oil, if the fat seems to be falling apart you should not worry with it.

This is how the gelatin or jelly is made: finish cooking as the first and cool at room temperature when you take the wax off after removing you should have a pot full gelatine or jelly. If you want your tallow for soap you clarify it. It is simple: heat the fat, drain through a strainer and let set. Let anything else settle to the bottom of pot and then drain off the fat leaving the settled material left at the bottom. This is clean oil. What ever you do, don't scorch your oil it can smell funny.

I'm a butcher and just got done rendering about 15 lbs. of beef fat(mostly from strip loin and tri-tip). You will get a 1/4 to a 1/3 of gelatin depending on how much you let the water boil off.