pork in water, and then clarifying the liquid twice with batches of finely chopped chicken meat, which are gently simmered for 10 minutes and then carefully strained off Manufacturers now also produce more conventional sauce bases with their gelatin intact These are often sold in the form of demi-glace or glace de viande Cooks can improve the flavor of commercial meat extracts and canned broths by cooking them briefly with herbs and/or diced aromatic vegetables This fills out the extract’s aroma, which is generically meaty to begin with and depleted during the concentration process Fish and Shellfish Stocks and Sauces Like mammals and birds, fish have bones and skin rich in connective tissue But thanks to the cold environment in which fish bodies function (p 189), their collagen differs from mammal and bird collagens Fish collagen is less cross-linked, and so melts and dissolves at much lower temperatures The collagen and gelatin of warm-water fish like tilapia melt at around 77ºF/25ºC, that of cold-water cod around 50ºF/10ºC So we can extract fish gelatin at cooking temperatures far below the boil, and in relatively short times The collagen of squid and octopus is more crosslinked than fish collagen, so these molluscs require more prolonged heating at 180ºF/80ºC to give up much of their gelatin Most cooks recommend cooking fish stocks for less than an hour so as to avoid making the stock cloudy and chalky with calcium salts from the dis-integrating bones Another reason for short and gentle extractions is that fish gelatins are relatively fragile and more readily break down into small pieces when cooked And because they associate more loosely with ... an hour so as to avoid making the stock cloudy and chalky with calcium salts from the dis-integrating bones Another reason for short and gentle extractions is that fish gelatins are relatively fragile and more readily... boil, and in relatively short times The collagen of squid and octopus is more crosslinked than fish collagen, so these molluscs require more prolonged heating at 180ºF/80ºC to give up much of their gelatin.. .the cold environment in which fish bodies function (p 189), their collagen differs from mammal and bird collagens Fish collagen is less cross-linked, and so melts and dissolves