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I have a 10 gallon mash tun (chest cooler) and I've been brewing with pre-made kits. I want to start making my own recipes but I want to do half-batches (2.5 gallons) until I get the hang of things so I don't waste a bunch of grain and bottling time.

Is my current mash tun too big for the 2.5 gallon batches? Should I just suck it up and do full 5 gallon batches?

Here is my process: I do a single step mash, heating the water on a propane burner and adding it to the cooler then waiting the appropriate amount of time. I then do a two step batch sparge.

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The smaller the volume of grain the harder it is to maintain a consistent mash temp, so it depends on how you are heating it. I'm guessing since its a chest cooler you don't apply heat directly? What is your process right now? I assume since you tagged this "all-grain" that is what you're trying to accomplish? –  thanby Feb 18 '13 at 15:23
    
I do a single step mash, heating the water on a propane burner and adding it to the cooler then waiting the appropriate amount of time. I then do a two step batch sparge. –  bdowden Feb 18 '13 at 15:30

3 Answers 3

I do a single step mash, heating the water on a propane burner and adding it to the cooler then waiting the appropriate amount of time. I then do a two step batch sparge.

In this case the size of the mash tun will simply make it more difficult to maintain the mash temperature, but it's still do-able. Coolers tend to hold their temp very well, but the increased air volume from the decreased mash volume means the air will leach off more of the temperature from the mash. You can adjust for this by simply heating the water a bit more before dough-in. Exactly how much depends on the cooler itself and how efficient it is, so you'll just have to experiment with a good thermometer. I'm guessing it won't need much more than an extra 5 degrees F though.

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That size will be fine, especially if you batch sparge. If you fly sparge, you may find the grain bed depth a bit shallow, which could negatively impact your efficiency. If you batch sparge, you don't have that problem. Holding temp shouldn't be too big a problem and if it is you can wrap your cooler in a blanket or sleeping bag to help hold the temp.

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I actually brewed outside during a cold CT day, high winds (probably 25*F), and the mash tun only lost 2* during the 60 minute mash. I'll give it a shot and see if the larger air volume will have an effect, like thanby is saying. –  bdowden Feb 18 '13 at 15:49
    
Won't batch sparge have the same issue with the grain bed tickness? Aren't the problems related to grain particles getting into the boil? –  Cleber Goncalves Feb 18 '13 at 16:21
    
I used to do 5 gallon batches in a 15+ gallon chiller. Sure, some flour and maybe the odd husk may make it into the boil, but they quickly fall out, and don't make it into the final beer. Even less so if you use a pump to recirc. I pretty much always batch sparged. –  mdma Feb 18 '13 at 16:50
    
Cleber, the issue is channeling when you fly sparge, not grain particles. –  Denny Conn Feb 18 '13 at 19:51

I've recently been asking much the same question and the consensus seems to be that for smaller batches, its better to just do Brew In A Bag rather than use a larger mash tun.

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