Or mash tun aspect ratio, if you like. Tall and skinny, or short and wide? I know a deeper grain bed (tall and skinny) will be better for lautering purposes, but will a flatter grain bed (short and wide) be better in any way? I've read mixed reviews online, but thought I'd solicit some opinions here.
I'm batch sparging now, but will likely move to fly sparging in the future.
John Palmer says
Deeper grainbeds have more uniform rinsing, all else being equal.
An more uniform rinsing can mean increased yield, so then shape does have some impact. As Denny says, taller is better since there is more chance for the water to rinse the grains when fly sparging. (But, up to a point, if the grain bed is very deep then it might become compacted, which leads to stuck sparge or increased channeling further down the grain bed.)
Previously, I used a 70qt cooler for 5 and 10 gallon batches, batch sparged, and typically got 65% extraction, and usually 70% for 10 gallon batches. I'm now using a blichmann 20 gallon kettle and false bottom, and got 90%-92% on each of 10 brews so far.
I don't think the change in efficiency is entirely due to the shape, but I always felt the cooler was far too large for the batch size, making it difficult to get an even temperature. As well as the different MLT shape, the improvement in extraction is probably also due to these other changes in brewing process:
I'm not adding fly sparging to this list because I really don't know if that improves efficiency - I've not done a batch sparge to directly compare. Will batch sparge the next brew and I'll update this answer with the result.
For batch sparging, it doesn't matter. For fly sparging, taller is a bit better.
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