I think I saw the video of it, they did it by holding a blow torch to it.

But many videos like that are misleading because the person filming it doesn't know how blow torches work. They always hold the torch RIGHT up against the thing they're trying to burn, but you barely get any heat when you use it like that. You have to hold it a few inches back, right at the tip of the inner jet. That's where the hottest point is.