What are bologna and hotdogs really made of? I am hoping this question isn't off-topic as it's mainly about what a specific type of food is made of rather than how to make it. Of course, I could always reframe the question as "How do I make hotdogs and bologna from scratch exactly as it's done by mainstream companies?"

So I want to know how to find out what, exactly, supermarket bologna and hotdogs are made of. When I was young, I was told that all the leftover parts -- organs included -- went into the slurry before being formed into the final product. Later, I was told that it was only the trimmings. I see trimmings as the more undesirable cuts of meat such as the parts I trim off myself before prepping. This includes fatty tissue, sinew, etc. I do not, however, consider organs to be trimmings.

I know that some brands -- perhaps the lower-shelf, bargain brands -- might use literally every leftover part, but what about mid- to top-shelf brands? In the middle, there are brands like Kahn's, Oscar Mayer, and Ballpark. Near the top of the shelf you have Hebrew National, Nathan's, and others. How can I tell which brands use organs and other unsavory leftovers and which use actual trimmings?

Also, is there a difference between the beef variety vs. the kind made with chicken and pork with beef added other than the type of animal they come from? Does the type of animal have an impact on what part of the animal goes into the mix? Is the beef variety more "premium" or do they all contain the same tier of meat trimmings?
I doubt you will find a specific ingredient list that identifies particular cuts or parts of meat.

As an example, here is the ingredients for Oscar Mayer bologna: Mechanically Separated Chicken, Pork, Water, Corn Syrup, Contains Less Than 2% of Salt, Sodium Lactate, Flavor, Sodium Phosphates, Autolyzed Yeast, Sodium Diacetate, Sodium Ascorbate, Sodium Nitrite, Dextrose, Extractives of Paprika, Potassium Phosphate, Sugar, Potassium Chloride.

Similarly, you can probably look up the ingredient lists for other brands and products.

Making an emulsified sausage (hot dogs, kielbasa, bologna, mortadella, etc.) from scratch is not that difficult.  You would probably not want to make it exactly like these companies do.  They are mass producing and need to ensure shelf life, as well as safety.  There are a lot of things on that ingredient list above, for example, that you would not need if making this at home. Additionally, these companies weigh quality against cost efficiency.  At home, you would likely use higher quality ingredients.  Although, there is an argument to be made about the parts of the animal that are desirable vs. not.  This could just be your preference.  I'm not sure how you are defining "premium."  I assume that in general, the parts of the pig, cow, and chicken, that can be sold at higher prices are not used to create emulsified sausages.

In the end, you probably get what you pay for in terms of quality.