Agree, that is a liner. i just picked up 4 food grade barrels that held cranberry juice concentrate and it had the liner. At first i thought, hmmm no liner thinking it would be plastic or something and that the inside was painted/powder coated red. then i read what colonel00 posted about it being a polymer,etc and saw pix online somewhere and realized i have the liner. My son in law sand blasted them out for me at the body shop he works at, cost me $55 for the material. well worth it, and it may save your having to repaint the outside if you go the burn it out way. Just my 2 cents. best of luck.
Al - CG SuperPro w/SFB and Outlaw w/SFB, 18" WSM, 22.5" WSM