Franconian Beer Message Board

 

I don't know precisely about Mahrs but I can tell you about Spezial. They (like most small breweries I've visited in Germany) use horizontal lager tanks rather than the vertical conical ones.At the top is a valve connected to a tube. The valve starts out open and the end of the tube is in some water and this basically acts as an airlock. The amount of fermentation can be judged by the bubbles in the water. At some point the brewer closes the valve and any residual fermentation carbonates the beer. If the valve is left open, it is then an "ungespundetes bier" (the valve is called a spund) The lager tank is not open in the way the primary fermenter is. It is essentially closed.

You can see some kinds of tanks in Fred's photo essay on his trip around Spezial but they aren't what I think of as horizontal.  The method above reminds me of an scaled up version of my homebrewing, as I use a water-filled airlock.  The bubbles stopping is the signal for the end of primary fermentation, which with top fermentation is a matter of days (sometimes a couple of weeks) rather than the 8 weeks for bottom fermentation.

Must be a trick of the light but that is a very pale Rauchbier!