False Bottom,
Here is a reply i received back from Wes Smith who runs Maltcraft.
They did a talk a couple of months ago at our homebrew club meeting.
Hi Ken,
The "optimum" is a bit of a moving target depending on which style of
brewing you subscribe to. Assuming you are going to drill your own false
bottom or "lauter platten", then think about 12% open area for traditional
German lager brewing, or the compromise we find works very well at 23% open
area using a perforated stainless sheet with 1mm holes on 2mm centres. If
you are going to drill out your own plate, then calculate the required open
area and go to it. Dont forget to countersink the holes from the back. And
dont go over 1.5mm in diameter.
The material we use is available from Perforated Stainless Products (I
think) in Sydney
Wes.