Go get some beef feet, the whole thing or slices, and throw it in your pot. 1 foot, 1 chunk marrow bone, simmering for 1.5 days, not turned off over night. Marrow bone for all the minerals in the bone, and the great marrow taste, and the foot provides all the collagen you could ever want, it will be solid, thick jello if you add a foot, I promise. Tastes better too. I don't add spices until about an hour before I turn it off, then I let it cool until I can handle it. Seems to work best that way, I can fish out the chunks of basil and parsley before they fall apart like they will if they've been in there for a day. But that's just how I do it. Add more feet. Chicken or turkey feet if you can't find beef feet, they don't need to be in nearly as long as beef feet, 8 hours or so will do them pretty well.

I get very little gel action from the straight bones, so started buying knuckle bones from US Wellness. I toss one in with my roasted marrow bones, some lemon juice or ACV, keep the water level as low as you can while still covering the bones -- this part is hard because of course we want MOAR BROTH but even a little too much water will dilute the gelatin, in my experience. I only toss in a few bay leaves, saving the bone broth from too much more moisture added by the vegetables. Also, for what it's worth, I apparently cook mine longer than everyone else -- usually upwards of three days on very low. Once I get a broth with a nice firm set, then I'll start part two with veggies and whatnot if I want a stock or a soup.

Marrow is mostly fat, theres like perhaps 10-15% protein. Altho it is the superfat. Best fat on animal par brains or something similar. Straight leg marrow bones are not so good for stock. Whole beef knuckle is what you want. It will have tendons etc. Best for stock. Ask from your butcher. Neck bones are great as well but they might be unavailble due to the bse scare.

Crack a beef knuckle open with a chisel and hammer. Boil. Gelatin.

Sometimes it takes longer than just overnight in the fridge for my broth to gel up, like halfway though the next day. I use marrow bones with the ends of the bone still attached.

I've never gotton my marrow beef broth to go gelatinous--only my chicken and turkey broth does. Maybe I'm going something wrong too. I cook for 48 hours at low in a 7 quart slow cooker. Also...I save all the fat to cook with but it's hard as a rock so you have to soften each time.

Stupid question, I know, but I'll start with you can't judge the consistency until the broth's been in the fridge for a long time such as overnight. Mine certainly isn't firm when I first put it in the fridge but it's like firm jello the next day.

I'm further guessing that the removal of marrow and/or tallow is a partial cause of watery broth because if meat is all that's in it you don't get real broth. I also agree you need a mix of marrow and joint bones for best consistency. I just made a batch that is like firm jello, so here's what I did for comparison.

I started with raw bones at about 10 in the morning. Like you, I had them on High for about 2 hours--I didn't roast them first. I then switched to Low and left them simmering on that setting until about 10 the next morning. The bones came out "clean" and I removed ONLY the clean bones. I put the clean bones in a bowl and even rinsed them with a little fresh water and then poured that "broth" back into the slow-cooker, discarding only the clean bones.

I added vegetables and cooked the broth and the veggies for another 4-5 hours when we dug into the pot.

I think the suggestion I'd make is don't remove the marrow from the broth for possible re-use; it's a key component of firmness as it continues to dissolve into the broth. Yes, a layer coats the upper surface but I believe other portions of the marrow and cartilage remain in solution and create the firm broth.

More vinegar should help... I would (and do) use 2 TBSP with that much water. It's not enough to make the broth taste "vinegary."

No matter what kind of broth I'm making, I always, always, always throw at least 1 chicken foot in. It's how my mom always made her beef, chicken, and turkey stock, and those guys are little gelatinous gold mines. Just buy a really big pack of them from the grocery store, and throw them all in the freezer. Every time you are going to make some broth, grab a handful and add them in.

I bought something labeled "marrow bones" only once. The target market is dog owners. Waste of money. Get soup bones, or at least bones that show well-delineated marrow lines on the ends, and look like they contain marrow all the way through (hard to describe the look, but you catch on quickly).