Bone broth - marrow isn't dissolving.

[amcal]

I've had a pot of beef bone broth on the stove for almost 24 hours and the marrow in the bones isn't dissolving.  It's still rock solid in the bone.  

I used large, flat marrow bones, filtered water and a tablespoon of apple cider vinegar.  I simmered it for hours yesterday, turned it off overnight, simmered it again all day today and the marrow is still in the bones.  

Usually, when I use the smaller, tube style bones, the marrow dissolves in the broth.  But, these were flat cut, very large bones and nothing is dissolving.  Any ideas? 

[BubblingBrooks]

Rib bones? Not going to get marrow out of those.

[amcal]

No,  they're not rib bones.  They are large, flat marrow bones.  

My store sells 2 kinds - the round, tube like ones and the large flat ones that are like a cross section of a very large bone.   I'm using the large flat ones.

[keevelish]

Well, I have to simmer (think a blip blip blip) chicken bones for 48 hours in order to get them soft enough to crumble, so I'm betting that hard beef bones would require a minimum of 48 hours. 

Just try an extra day or two and see what happens.