My main question would be the amount of non-deer trimmings or fat I should add in to make the summer sausage. I'm going to stick to the sausage kit recipe for the most part but I don't recall it saying adding fat (but surely I would).
Oh, got you. Between 20%-30% fat is ideal. 20% is minimum for sausage. Keep in mind that once you tip the scales at somewhere around 40% fat, your sausage will no longer taste like venison.
For a fat source, I prefer fatback for most sausages, but pork shoulder as well as trimmings will work fine, too. Get the highest quality pork shoulder or fat that you can find/afford/get your hands on. I highly suggest pasture raised, heritage pork if you can find it in your area.
Regardless of the instructions on your mix, follow these steps:
1. Cube the venison to grinder size cuts and place in the freezer for ~20 minutes.
2. Dice your fat with a cleaver, return it to the freezer for ~20 minutes.
3. Remove the Venison from the freezer and grind it. Return it to the freezer.
4. Remove the fat from the freezer and grind it. Return it to the freezer.
At this point, you will likely be adding your cure and season. Mix together and return the meat to the freezer for ~20 minutes.
5. Grind the venison and fat together.
By following this program, your venison and fat will bind together. It may seem like a lot of steps, but it will make a significant difference. The above sequence is the difference between amateur and professional quality sausage. Michael Ruhlman even goes so far to suggest that you the bowls you grind into be placed in larger bowls containing ice. Basically, you need to keep everything COLD. If you were in a butcher shop, you would be doing this entire process in a cold room.