What makes a hot dog a hot dog?

Hot dogs are a an example indigenous to North America of a class of sausages called emulsified sausages. The meat and fat are ground so finely that they emulsify together into a smooth paste. Other sausages of this type include German Frankfurter Würstchen (of which the hot dog is a descendant) and Italian Mortadella (which is also the pre-cursor of the American Bologna sausage).

Hot dogs are cured, and typically hot smoked and sold fully cooked.

They can be made from a variety of meats, but beef and pork (or a mixture thereof) are the most common.

Hot dogs require a careful balance of lean (for the protein myosin, which provides the binding and structure to the sausage), fat, and water (usually added in the form of ice during the manufacture ring process, to help keep the nascent emulsion from breaking by keeping the mixture cool.)

There is no binding agent as such in hot dogs: the myosin in the meet forms a matrix that provides the structure and chew of the sausage. A hot dog without enough meat (or some other protein source) would not hold together. This is much akin to the way a pâté is made--in some sense, a hot dog is a pâté stuffed into a casing, and hot smoked.

While it is possible to add fillers (and emulsify in additional water), it is not necessary and high quality manufacturers do so in moderation or not at all.

The major flavor elements in a New York style hot dog (where they originated) are typically the cured meat itself, salt, pepper, garlic, and paprika, as well as the smoky flavor. Around the world, emulsified sausages are flavored with a wide variety of spices, especially warm spices, but these would not be typical in a hot dog.

You can find a recipe and slideshow with detailed pictures of the hot dog making process at Serious Eats. It shows all of the key steps: selection of ingredients with a careful balance of lean and fat, initial grinding, emulsification, stuffing, and smoking.

Now you made the edit, it is clearer to me what you ask. Here the answers to your two questions:

2) They don't need any agents. Protein acts as a glue when heated. Protein is almost the only food type which will actually "glue" things together - try making gluten-free pancakes with non-protein flour like almond flour and you will notice what I mean. (You can "cheat" and use hydrocolloids like xanthan which make a mass so viscous that it sticks together, but that's another topic). In other, rougher sausages, you can notice the difference between the lumps of stuff, because the lumps are bigger. Some rough sausages can also be likely to fall apart, but that is because they are not cooked, they are cured raw. Hot dog sausages are made from animal protein, animal fat, flavor agents (not too many), and fillers. The amount of meat is enough to cause the mass to curdle in a tight sausage, just like the proteins in the egg yolk are enough to cause a creme brulee to curdle in a holds-its-own-shape custard. You can cook your own sausages at home, and they will bind without any additives.

The cohesiveness of a hot dog can be achieved with a relatively low amount of meat when compared to the fat and the possible fillers (like bread). If a producer decides to use yet more fillers, he can use transglutaminase to get the tight texture even when there is less meat than normal in the sausage. I don't know whether producers actually do this or don't, I suspect that at least some do it. It is possible that in some jurisdictions, they are not allowed to.

1) As I already mentioned: the hot dog is made from meat, fat and a few fillers. It doesn't contain much seasoning. The meat used for it is low-quality meat, pure uniform protein from young animals, mostly pigs or chickens. And it is boiled, not exposed to direct high heat. Therefore, the aroma component of the flavor is almost completely missing. Other meats you eat have their own aroma, depending on the animal and developing with age (have you tried eating old goat?). They also get that lovely seared aroma from caramelization and Maillard reactions at temperatures which aren't achieved through boiling. Both are missing from a hot dog. (The second is missing from other sausages too, but good sausages such as cured salami or lukanka are made from aged beef or donkey, and they use generous additions of herbs and spices, often also smoke). You just get a faint aroma of uniform, underdeveloped protein.

The taste component of the flavor doesn't contain much either. There is salt from the seasoning, and there is some umami from the meat (but not much, this being young meat). Don't forget that while most people like umami, it is more known for enhancing the aroma of the food than for being a consciously pleasant flavor on itself the way sweetness is. Parmesan, tomatoes, meat - they are tasty because of the aroma they have, not just because of the umami per se. Pure MSG is very umami, but very disappointing if you try to eat it by itself. The fat in the sausage acts similarly as a flavor enhancer. Both the umami taste of pure protein and the fat would be great if they had something to enhance, but there isn't anything in the hot dog to be enhanced, so the flavor stays bland and uniform.

The veggie hot dog producers can use this well. Almost-pure soy protein is not that different from almost-pure chicken or pig protein where taste is concerned. The texture is different, but processing both to a fine paste with the right amount of moisture takes care of that. Neutral fat can be added for mouthfeel without changing the taste. In theory, the protein of the soy should be able to bind the sausage upon curdling. In practice, I suspect that the extraction process which purifies the soy protein from the bean-tasting plant matter curdles the protein and they use some kind of additives to "glue" the sausage afterwards. (At least the pure soy protein I have had as meat substitute was already curdled. Maybe there are other processes which don't require that).

So what is a hot dog sausage? Meat processed to the point where it is almost pure protein, fat processed to the point where it tastes neutral, salt. Some starch to improve texture. Everything cooked together in a sausage shape. Doesn't sound too appetizing, but it is cheap, filling, and the taste attack of mustard and ketchup is so strong, that any better sausage would be wasted in a hot dog sandwich.

klypos,

From what I recall (!), the filling of a meat hot dog sausage is typically soft, moist, homogeneous and without a particularly strong flavour, at least compared to other sausages. Rather bland-tasting, to some.

The Tesco brand sausages to which you refer is based on soy and wheat proteins http://www.mysupermarket.co.uk/#/tesco-price-comparison/frozen_vegetarian/tesco_vegetarian_hot_dog_sausages_10_per_pack_300g.html

In my opinion, most basic soy-based vegetarian sausages tend to mimic the texture and flavour of the filling in a budget meat hot dog sausage. Despite being a somewhat bland and uninteresting sausage (in my opinion!), they work well as a substitute for a meat sausage in a hot dog. Perhaps this is because the filling in a meat hot dog sausage tends to be highly processed see e.g. http://en.wikipedia.org/wiki/Mechanically_separated_poultry. As such, the rather homogeneous texture from a soy-based vegetarian sausage hits pretty close to the mark.

However, I do not know how the flavour of a vegetarian sausage is made to approximate the meat filling. I have been impressed at how close in taste a vegetarian substitute can be made to the meat it is aiming to replace. This is particularly true when the context of the meal is taken into account. Here is a thing that looks like a sausage inna bun (thanks Terry Pratchett!), slathered with tomato sauce and mustard. I bought it cheaply off a street vendor. I expect the sausage filling to be dubiously bland paste. Is it meat based or soy based? Not sure, can't really tell in context. Compare this with an attempt to replicate a high quality meat sausage with a vegetarian substitute.

Does this bring us close to an answer for you? Do you need meat in your sausage filling to call the bun-wrapped article a "hot dog"? I would argue that the amount of meat in a budget hot dog sausage is minimal and so cut down with fillers that the basic soy-based sausages make a good replacement.

The other day I made a vegetable stock of what was left in the fridge. It was primarily celery, onions and garlic. I simmered it all day. Yesterday I made a lentil soup out of it. My wife is not eating pork or beef for lent so I simmered some bacon on the side of the lentils in a cup of the stock so that I could put the pieces in my own bowl of soup as an addition. My wife came downstairs and asked, "Are you cooking hot dogs". I said no, it must be the bacon and the stock. I tasted the stock in the bacon water and it indeed tasted exactly like a hot dog, an intense "hot dog" flavor.

I therefore suspect that the classic hot dog flavor is primarily celery, onions, garlic and salt pork with some smoke flavor (bacon is smoked).

What is the flavor of hot dogs? The answer is hardwood smoke, salt, paprika, onion, nutmeg and celery powder. You only have to look at the label of all-natural hot dogs in health food stores to find out.

The original, 100+ year-old flavor of hot dogs came from a handful of simple ingredients, and believe it or not, the generic Tesco hot dogs derive from that very same century-old recipe and are not magic, despite being filled with mysterious ingredients. All of these so-called natural flavorings, MSG etc, mimic the original hot dog recipe flavor. All-natural hot dogs achieve the same result using only the original ingredients.