I have a bunch of oxtails I've been braising for hours in an adobo sauce and they remain awfully tough. What I'd love to see happen is for that abundant connective tissue to melt away and coat each fiber of meat with succulent its succulent juices, but that collagen just does not want to budge.
This makes me wonder what is causing the conversion to fail (or just take so long). I'm sure the fact that we're dealing with oxtail is a factor--and older piece of meat simply is more tightly bound. But I suspect there may be more going on here as well. For example, the braising liquid is relatively acidic--would the pH of the medium affect the conversion rate? Or water hardness, perhaps? I've checked the collagen references in "On Food and Cooking" but didn't find anything that seemed relevant.
So, generally speaking what factors will affect the rate and effectiveness of collagen to gelatin conversion?