I have been doing some Bier Tourismus in Germany. Currently I am Bräuerie Eck in Böbrach Niederbayern. They were brewing yesterday, and said stop in the brewery as we had a brewing experience there last year. A couple things were discussed with the degrees Brewer. I had a rough recipe of my Dunkel on paper, and we went over the grain bill. I had 1% Carafa II for color. He recommended adding that to the mash at Vorlauf, so you don't get the sharp flavors. I said that technique had been discussed in American Homebrewing and I have done it, which he liked.
The Keller at the end of the summer was all the way up to 3.5C. It was 3 C last Dec. All natural, no forced cooling. Deep in the rocks, at some altitude, with trees and a Barn over the Keller help it stay cool.
I did bring up O2 in the brewing. He said that it is known that some breweries have a house flavor from O2, and their beer is not shelf stable. He talked a little about modern systems, and how they fill the mash tuns fro the bottom, rather than mixing and dropping down like his 1971 system. He does make some fine beers, and wins a fair amount of awards for the Dunkel.