Veal stock is lauded as culinary gold in French cooking, chicken feet are common in Chinese stocks, and pig feet are the secret weapon to many pots of split pea soup. What do all of these culinary weapons have in common? When cooked for a long time, they release lots of gelatin.
Hervé This in Molecular Gastronomy discusses the affects of gelatin on volatile odorant molecules:
“Cooks can slow down the evaporation of volatile molecules by putting them in the presence of larger molecules, with which they bond…. More general, in water solution, the amylose warps around hydrophobic molecules, many of which are odorant molecules….Gelatin does the same thing, hence its usefulness in sauces.”
“In the mouth these molecules are released in different ways, so that the flavor…lasts longer.”
In other words, gelatin makes meat stocks taste so good because it traps the flavor that might otherwise escape into the air while cooking.
Logan's Kitchen 