Homemade sausages

One of the great benefits of eating food you have cooked from scratch is that you know what you are eating.  The ideal is that you buy all the raw ingredients, then you add what you want to add.  But what happens when you buy things like sausages?  They're raw, but what's in them?  Who would know.  In Australia, sausage, by law, must contain 50 percent meat - but that meat may come from any part