It’s like a mini-mash that is scaled up to full all-grain volumes, and requires far less equipment than normal all-grain brewing (all you really need is a ~10 [some say 15] gallon kettle for full-volume boils and a very large mesh bag). I do worry when people talk about getting greater than 80% efficiency (and using too fine a grind) because of the increased potential for tannin extraction, but that should be easily remedied.

I’ve looked into it a bit and have found several links to help anyone interested out:

• A Guide to All-Grain Brewing in a Bag: From the Aussie forums that seem to have started it all. Includes a handy PDF booklet and some other links to a FAQ and some other resources. You’ll need to register there for access to the files.
• The Brewing Network Forums: A nice post describing how to brew in a bag, along with a lot of discussion on the topic.
• Brew in a Bag All Grain Brewing Method: A good blog post with pictures describing the method for BIAB.
• BIAB at BeerSmith: A post on the BeerSmith website that discusses BIAB and includes information about how to set your equipment up in their software.

I’m very interested in this brewing method, in part because I am lazy and I’m open to trying something faster and easier, and in part because it looks like people are getting better efficiency than most all-grain brewing gets. And, because it’s still pretty experimental.