Q. Why when I fry my bacon do I end up with a pan of horrible, white froth?
A. A lot of large, commercial producers cure their bacon using phosphates (or similar products) to encourage the absorption of water which boosts the weight of the bacon. There's your froth!
Traditional bacon can wet or dry cured without injecting phosphates. It tastes better and is less salty.
Sausages can be made with any kind of meat, but pork is the most common. A sausage should contain at least 40% meat, but in some cheap, catering sausages this may include fat and connective tissue (ligaments etc.), so check out the ingredients before you buy!
A good quality sausage should contain quality pork/beef/lamb/game, some fat, seasoning, bread and that's about it!
A good quality burger will contain at least 80% meat of which 65% must be lean meat. A low quality burger will contain much lesser percentage. Burgers can be made from beef, pork, or a combination of the two. Fat can be added as well as cereal.