Do Mash Tun Dimensions Matter?

So far, I have been mashing in my kettle on my electric stove. It works, but I have to tinker with the temp to keep it “steady.” Plus…I tinker with the mash (frequent stirring), which - given my high efficiency issues I may start to cut back on.

I do, however, have a Yeti cooler that I could use as a mash tun (modified out-flow and strainer, obviously). So…

Question: Does the shape and size of the mash tun matter? Should mash be “contained” in a more “upright” orientation and more “consolidated,” or can it be more flat, and “spread out” across the bottom of a rectangular cooler?

I know that folks USE rectangular coolers, but what I am wondering is how BIG of a rectangular cooler can be used? …an extreme example would be: could the mash be 1" thick and spread out over a large area, or should it be at least “X” depth for proper conversion???

This is for 5 gal batches…


Tun geometry has a huge effect - if you are fly sparging. If you batch sparge or do BIAG, geometry is a minor issue, pretty much limited to how well the cooler keeps the mash in a “block”, which keeps temperature a bit better than if it is spread out like a flat sheet. Though cooler insulation is a bigger factor for that then geometry. How do you sparge?

I BIAB, so in the past I have sparged/rinsed the grain in another kettle with the remainder of the batch water. …however, my efficiency has been extremely high lately, so I will probably NOT sparge on this next go round and see how I do. Hence my question - if I don’t have to sparge/rinse the grain, then I “should” be able to do like others and use the cooler as my mash tun. But I was just curious as to how geometry affects things; obviously temperatures being equal.

No, no effect. For BIAB, the only advantage to using a cooler for a tun is that it will hold temperature better. But whatever size fits you batch size is fine, and any shape should work equally well. You might want to make sure there is a drain on it to make emptying the wort easier.

Assuming you have no mash tun, and want to buy one; the most significant advantage of a cooler is the price. Coolers are cheaper and always have a drain. Even assuming you replace the drain the cooler comes with, you’re still cheaper than adding a valve to a pot.