You either have to light the background separately like Kirk said or you can put a layer mask on it in CO and push it's exposure until you get what you want. But, it depends on where your exposure is. Again, I would recommend lighting separately for the background, this is the easiest and far superior way of doing it. Have a look on youtube for lighting wine bottles, there are a lot of videos to help you out. Also look for phase one tutorials to learn what it can do for you regarding layer masks.