I am planning on brewing up a batch of Dusseldorf Altbier, I want to try and do as traditional as I can. Of course that means a double or triple decoction, cold open fermenting and lagering. My big concern is the cool open fermentation issue. What I am thinking is using a freezer (of course it will have a temperature controller) and sanitizing the crap out it. Then place the open top primary bucket in it with a couple layers of cheesecloth just to make sure nothing falls in. I even had a wild idea of put a HEPA filter on a fan to create air movement and a little positive pressure inside the freezer. Does anyone have any other ideas or advice?