justpassingthru
If you do use nonfat dry milk use the old fashioned type , not the very light instant type.My only problem with the non fat dry milk is that it CAN live a slightly sour taste that you may not like.In mettwurst that would work well. Even in ring bologna , that very slightly tartness can be good.And you could probably mask it with a little brown sugar.
As far as the soy protein concentrate goes there are many suppliers on line and in catalogs. Also one can purchase soy flour at most places that call themselves bulk food. I have bought it at a local Kroger superstore. Much less expensive than the SPC bought thru mail. If the only way you can buy it is thru the mail , I would bite the expense bullet and see if it makes enough of a difference for you.
I will offer a couple of other possibilities. One can bind sausage with unflavored gelaton. Just be sure it is well mixed .It addes no salt , no calories , no carbs , some protein and supposedly is good for the joints .
There are also food grade phosphates that cause moisture to be retained in product. You wouldnt use that for products that are intended to be dried.I have not used them but i noticed a lot of store bought products contain them. I want to study the health effects more.If the only problem would be the amount of sodium , I would just cut down on the sodium in the original recipe.
And finally , again , the temperature plays a vital role in moisture retention. Moisture being , water , fat and even the lean part of the meat.Happy Sausage making. Weisswurst