Hot dogs, also called frankfurters, were first created in Frankfurt, Germany, in 1852. At its heart, a frankfurter is a sausage. Hot dogs are now made by hundreds of companies all across the globe, and each company has its own secret recipe. In general, however, hot dogs contain:
Marshall Brain's mother has a recipe that contains 1.5 pounds of pork, 0.75 pounds of pork fat, 0.25 cups of bread crumbs, an egg white, a little water, salt, pepper, onion and garlic to taste. Note that this recipe leaves out the preservatives, coloring and sodium nitrate that you find in store-bought hot dogs. Many brands leave out the bread crumbs and say "no cereal fillers" on the label. Cereal fillers got a bad name because some manufacturers got greedy and started using more filler than meat.
These ingredients are blended together in a meat grinder or a food processor, and then they are stuffed into sausage casings. Most of the hot dogs you get in the store are stuffed into synthetic collagen casings, but if you are making them at home you can use natural casings (see the first link below).
Once the hot dogs are stuffed, you pre-cook them (you can boil them in water for 15 minutes) and then refrigerate or freeze them. All hot dogs bought at the store are pre-cooked. When you are ready to eat one, you cook it again by boiling, microwaving, frying or grilling it.