Homemade Sausage Making

I purchased a very lean and dry frozen turkey and after roasting a portion decided to grind the rest with 50-50 pork trim and make Hot Smoked Polish sausage. It was a good call.

Ross that sausage looks really good! But how did you manage to get that blackened look on the casings? Does not look over cooked/baked.

The casings are mahogany fiber casing. Smoked over oak and finished in the oven.