Fat sinking to bottom of stock So I've made stock a couple of times in the last couple of months - one batch of chicken stock and one of beef neckbone stock - and I've come across a problem I've never seen before.

After cooling, the majority of the fat in both batches sunk to the bottom of the containers they were in. It's definitely at least mostly fat, since there was almost no fat layer to speak of on top (as there should be.)

The thought crossed my mind that it could be the storage containers, since I used regular mouth Mason jars for the beef stock, but I store my chicken stock in a big pitcher since I use it so often, and the same thing happened there.

Two different sized pots, as well: the chicken was the same 20-qt aluminum pot I always use, and the beef in a heavier stainless pot that's only 8-qt or so. Therefore, I wouldn't imagine it was the pot.

The only thing different was the butcher for the beef: our butcher where I live now is MUCH higher quality than what I used to have access to.

As a side note, while thickened, the fat did not solidify as per usual, which suggests it wasn't saturated fat (right?), but with beef...?

Does anyone have any idea what may have caused this weirdness, and how can I prevent it?
Gelatin. All bones and connective have gelatin and collagen. When you cook bones slowly and gently for a long time, the gelatin leaches out in the water. Being heavier, it sinks. It isn't marrow. Marrow will stay in the beef bone until you spoon it out (lucky you). If it did fall out, it would stay in one piece. But I believe the substance you found in the bottom of your soup pot is the natural gelatin from the bones in your stock!