Mash Tun false bottom placement

[carloski44]

I been brewing for about 2 years now with keggles, and a Ice chest with a copper manifold for a mash tun. I am going to build a mash tun with a 100 qt, aluminum pot, and i have some questions for those of you with false bottom experience. Is there some rules to go by in the placement of the false bottom? I plan on a bottom drain and using a HERMS type system with a pump recirculating the mash. Its a 21 inch diameter pot, and would seem the closer to the bottom the better. Do you actually need the dead space at the bottom for a reason? It is alot of surface area, would half an inch off the bottom provide the pump enough return to prevent cavitation? Does the distance really matter, as long as the grain is covered during mashing?

 

[Catt22]

Ideally, you want the FB to be as close to the bottom as possible or practical. The limiting factor is usually the kettle outlet port. The FB must be above this port if you want to avoid having to use a pickup tube (siphon tube). You will need some dead space below the false bottom in order to allow the wort to flow down through the grain bed. The wort has to have somewhere to go and that somewhere is the dead space. I would say that a minimum of 1/2" of dead space below the false bottom would be a good place to start. Mine has about 1-1/2" and it works just fine. The term "dead space" is somewhat misleading as there is really nothing "dead" about it. The space will be filled with wort, but not with grain. There will be enzymes present and active in this space during the saccharification process. When using a pickup tube (siphon tube), some clearance between the kettle bottom and the end of the tube will be required and the FB must be above the lower end of the tube, so there is another physical limitation on how low the FB can be positioned. So, the bottom line is to have the FB as low as possible while still accommodating the dip tube or drain port as the case may be. Personally, I prefer to avoid the pickup tube and just have a straight drain port. Obviously, a very large volume below the FB is not ideal as it would necessitate a higher water to grain ratio to achieve the desired mash consistency. A space of 1" to 2" is tyically what is used with most false bottoms.