When I adopted Squeek, I was told she sometimes got chin acne, and to dab it with q-tip (cotton swab) soaked in alcohol. She hasn't had it since we've had her though, so I've no real experience. We assume she got it from the stress of the foster environment - too many cats in too little space.
I've also read it can be caused by bacteria lurking in plastic water / food dishes. Anything porous can start to harbour bacteria and be difficult to get fully clean. By 'cane' do you perhaps mean bamboo? I'm not sure how anti-macrobial that is, I would imagin similar to wood? I use porcelain / ceramic bowls and we have one stainless steel water bowl for the upstairs, and they all get washed on occasion.
Have you tried switching back to the old food, albeit temporarily, to see if the problem goes away? At least then you can start to identify the cause by a process of elimination.