JerBear, I double grind for a couple of reasons. First, I get less smear; and second, I get better grinding.
BriCan is getting very fresh pork. Those of us getting pork more than about 48 hours after slaughter, or from a store, might benefit from adding a little liquid. I add about 1 oz per pound, depending on the freshness of the pork, and how much liquid it has retained. My pork is not injected, so there is are no saline or phosphates added before it comes to me. I use the liquid to better distribute the salt, and I do find that I get a more uniform result, and I think it also feeds through the stuffer a little easier. I do not add water to chicken sausages. I think the chicken is wet enough, as is, and doesn't require additional liquid for rapid/uniform distribution of the salt.
Here's what I do in my home, generally:
I trim the lean from the fat to assess and adjust fat content. I slice the shoulders into 1" slabs and par-freeze for about 80 minutes before cubing into large cubes (1" or 1 1/2" cubes). If it is a warm day, I'll put the cubes back in the freezer to keep them par-frozen for better grinding (another 30-60 minutes, depending on the day - wish I had a cold room, at home). Then, I run them through the primary grind (1/2" plate). At this point, I add the salted water, if needed, or just the salt, and seasonings. The coarse grind makes it easy to mix the seasonings throughout the meat, and because I'm using minimal liquid, and the coarse ground meat presents a large surface area, the meat takes up the water/liquid, readily and quickly. After brief mixing, the meat has usually warmed up enough that I prefer to return the meat to chill, so the fat stays good and cold. It also improves resistance and grinding when I run the meat through final grind, and I get less smear, less mashing of the meat, and better feeding through the grinder. Also, my spices are thoroughly mixed through the meat and uniform. Myosin and actin activity have already started, and I can immediately stuff into casing with a great texture.
Were I able to keep the meat in a commercial cooler, and work in a cold room, I wouldn't have to repeatedly chill the meat to keep it good and cold, but my reality is that I'm working in a residential kitchen with residential equipment, in central Virginia, where the summers are hot and humid. It does take longer to do the double grind, but in my experience, and based on my consumer feedback, it is well worth it.
I know it's not truly commercial, yet, but that's my take.
Don't tell me the odds.
You have the power to donate life