Copy and pasted from here:http://forums.tripwireinteractive.com/showthread.php?p=1288226#post1288226
"First of all, we at Tripwire Interactive hope everybody had a great December (a time many of us spend with family and friends) and wish all of you all a Happy New Year!
One of our favorite things about the new year is Brewing! No, not that one (with a special shout out to Putz with his King Tiger home brew). What I am talking about is a new system (which we are calling "Brewing") that replaces the cooking system of Unreal Engine 3.
Like cooking, it will optimize game content, but without any of the random non deterministic aspects that the old system used. In short, this should allow us to do smaller updates to the game, may reduce custom map size, and best of all, should allow custom content to continue working between game patches.
Maps should only need to be brewed and then they should work for the life of the game. Even some older maps (from previous builds) may work, but we can't guarantee it.
We feel that Brewing has now matured enough that it is ready for a public test. That is why later this week (or possibly early next week) we will be updating the Rising Storm beta to be a Brewed build with the new map Maggot Hill also making its debut for public testing!"