Post Barrel Burn Out Crusties

I'm building my second UDS and this barrel was not as clean as my first one. I was told it contained cooking oil but can't be sure as I bought it from a recycling center. Whatever it is, it had congealed onto the inside surface. Washed it out with a hose (after borrowing two non-operational pressure washers) and burned it out. Now I'm left with crusties on the inside surface of the barrel.

I'm thinking I should go at it with a wire wheel and repeat the burn process. Am I on the right track?