Are you talking about cooked cobs? The cobs break down slower, but my worms love them. I've found that worms use the ridges of the cob to help remove the egg capsules from their body. If your balcony gets allot of son, I wouldn't suggest you place your bin there. Black absorbs the suns heat more than other colors.

alawys chop up coarse materials like cobs and shucks as much as you reasonably can ... and lean a piece of plywood against the bin to shade it

Bill