Round Igloo beverage coolers are commonly used for mash tuns, and they work great. You heat some water to about 165° or 170° F, then pour in your grains and stir. Adding the grains brings the water temp down to a good mash range, between 150° and 160°, but beyond that there isn’t much control.
You can’t beat the convenience of the kettle and steamer insert. The insert serves as a false bottom to contain the grains and also provides a buffer between the heat source and grain to prevent scorching. The grain brewing can be stirred regularly and the temperature can be monitored and adjusted as needed.
I clip on a stainless steel thermometer to regulate the mash temp (you know those long stem thermometers, like this one), and can leave the lid off to stir the grains. I mash up to about 5 pounds of grain using about 1.25 quarts of water per pound. Combine that in with a 3.3 lb. can of extract and we end up with enough fermentable sugars to produce a good ale.
What I do is heat water in the steamer pot, put the steamer insert in there too, once my water is a little above my desired mashing temp, say about 10 degrees or so, I pour my milled grain into the water.
Regularly stir the grain and check the temp of the grain bed in random areas to make sure your keeping them at a consistent temperature throughout.
8 quart brew pot with steamer insert.
After an hour at your maintained temperature you’re ready to transfer the mash water to the brew kettle. You might need a little help with this. What I do is raise the grain basket and let it drain as much as possible, then I hang it on my brew pot, as shown in the photo to the left. It will continue to drain there.
Now, pour the mash water over the grain bed so it drains into the brew pot. This will help filter the mash water.
Once your mash kettle is empty, use it to heat your sparge water. You’ll want to heat enough water to bring your brew pot to the final boil volume. So if you brew a concentrate you’ll want about 2.25 gallons of water collected in your brew pot. I’ve marked my brew pot on the outside, at the 2 gallon level for reference.
You will lose some water as steam during your boil, and any extracts you use will displace the water as well, so use about 1 gallon less than your brew pot will handle. The remainder is added (cold) to your fermenter.
I usually boil 2.25 and put 3.25 gallons of cold water in the fermenter. Remember, you’ll be losing another quart or so of water in the trub at the bottom of the fermenter as it settles.
Once your sparge water is up to temp begin pouring it over the grain bed. It will rise into the grains and once you finish pouring you will have to raise the grain basket so it can drain fully into the brew pot. You may have to hold it there for a few minutes.
That’s it! Now that you’ve collected your mash water you can begin your boil and brew as usual.