I did snack sticks this Christmas and ran out of the new casings/from Waltons and use some I had left over from last year/ Lem brand. After stuffing with the old snack stick casings, it left a slight corrugated texture like an esophagus, these were stored in my refrigerator for the past year. After smoking they were substantially wrinkly and the newer/fresh casing I stuffed, looked perfect. Next time, I won’t waste my time doing this, using old collagen casings.