Hack mine please.
Two large-ish beef straight leg bones, no joints, roasted at 400F for 30 minutes with some tallow. Both ends of both bones exposed marrow. Very little meat on one of the bones.
Into the slow cooker with ~4 quarts of filtered water, 1 T. vinegar, 1 t. salt and 1 peeled garlic clove. Put the cooker on High and it took nearly 4 hours to get up to a boil- then turned it to low where it slowly simmered for ~6.5 hours. By that time it was time for bed, so I turned it off but left it overnight at room temp.
The next morning, turned it on High again- took 2.5 hours to boil (warm vs. cold water), turned it to Low. Added some finely minced onion and carrot, a bay leaf, and the leafy celery tops. Simmered for 4 hours. Added a couple cups finely chopped roast beef and a celery stalk, simmered another hour, and then turned it off and took the lid off to help it cool. Fished out bay leaf and celery tops. Once coolish, put into glass mason jars. Got 2.5 quarts "soup".
The bones were hollow- most of the marrow (but not all of it) had dissolved, and the remaining marrow was a big glop floating on top. Bones were not soft. I reserved the bones and marrow glop in case I can use it again.
Stuck it in the fridge overnight. Next morning had a great thick layer of fat on top of each jar which I chipped off, but definitely not gelatinous whatsoever. Tastes okay, and I will mess with the flavoring- but not gelatinous, which is what I'm going for.
Total simmer time- 10 hours, plus the 7 hours of heating, and the overnight (approx 9 hours) cooling. What else can I do-- hotter temp? Faster to bring to boil? Longer simmering? More vinegar, less water, more bones?!
Edit: Can I use the hollow bones and "marrow glop" for another batch? Might not gel up but I should get more out of the bones yet with some vinegar, right?