@kking Did you follow the bratwurst process where you grind through 3/16 plate and then mix in the seasoning without getting protein extraction? The reason I ask is that you wouldn’t normally cook bratwurst like that. Bratwurst is a fresh product so that means that no cure has been added and by keeping it at that lower temp for that length of time you might have grown some bacteria and microorganisms in there that could throw off the taste and texture of the meat. I’m not sure if this would have affected the casing but it is a natural product.
So if you did make a bratwurst and then smoked it like you would a smoked sausage, then what MIGHT have happened is that the fat rendered out of the product and started “cooking” the casing basically in the fat. This doesn’t happen when you are making smoked sausage because the protein extraction will keep the meat, fat, water and other additives all bound up together.
I will say I prefer using collagen casings because I think the natural casings do get a little bit rubbery when they are smoked, so that could be what it is. Have you smoked other sausages with natural casings in the past and been okay with them?
Other things it could possibly have been:
Not soaking the casings long enough
Poor Casings or Old Casings (Unlikely but I am running out of thoughts here!)
Im hoping someone else has a better idea because other than the fat rendering out I don’t think any of my suggestions were the likely cause. Does anyone have some possibility that I missed?