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Old 09-13-2010, 03:20 PM   #1
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Default Using an aquarium air pump to stir the HLT -- surprisingly it works!

This topic came up in a thread that I was asking about the best way to automate the stirring of an HLT. Specifically I was asking about paddles and planning on using a cheap harbor freight drill or the guts of an old cordless drill. Each had their own problems, but someone suggested that I use an aquarium air pump.

The theory was that the stream of bubbles creates enough agitation in the water to help mix it. I ran one ill-fated test last week, but I tried again this weekend with a new digital thermometer. It works...really well actually.

I was surprised by the results, but I figured I'd share them.

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Old 09-13-2010, 03:35 PM   #2
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I've often wondered why more were not doing it this way. It's basically the same principle used to circulate water in an aquarium. Might work even better if you put the air stone inside of a lift tube. The bubbles in the water column effectively reduce it's density and water of higher density will displace it. Confining the water column within a tube enhances this effect as the displaced water cannot diffuse until it reaches the top of the tube. I like this approach much better than using pumps or paddle mixers.

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Old 09-13-2010, 03:53 PM   #3
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I originally got the air pump and the diffuser stone to aerate my beer, but I've found that shaking the hell out of it does just as well for me. Therefore I already had the hardware sitting around.

I took the diffuser stone off of it and just ran a tube down to the bottom of my keggle. I would think that you'd want as much air and as many large bubbles as possible. Taking the stone off decreases the pressure that the air pump sees and allows it to produce a larger volume of air flow.

I think I may hard-plumb a port at the bottom of my keggle for this so that I don't have to worry about something dangling in the pot that might hit my heater element. It's an impressively simple solution though.

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Old 09-13-2010, 05:14 PM   #4
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Quote:
Originally Posted by bblack7489 View Post
I originally got the air pump and the diffuser stone to aerate my beer, but I've found that shaking the hell out of it does just as well for me. Therefore I already had the hardware sitting around.

I took the diffuser stone off of it and just ran a tube down to the bottom of my keggle. I would think that you'd want as much air and as many large bubbles as possible. Taking the stone off decreases the pressure that the air pump sees and allows it to produce a larger volume of air flow.

I think I may hard-plumb a port at the bottom of my keggle for this so that I don't have to worry about something dangling in the pot that might hit my heater element. It's an impressively simple solution though.
IIRC, small bubbles displace more water. That's why an air stone is used in an aquarium. You have a valid point on the air volume though. The restriction caused by the air stone could reduce the air flow volume substantially, so you may well be right on that. I don't really know one way or the other for certain, but that's the main reason that an air stone is used on an aquarium. It is an amazingly simple method and cheap to implement as well.
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Old 09-13-2010, 05:23 PM   #5
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at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?

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Old 09-13-2010, 05:38 PM   #6
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at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?
I don't think that there's anything to worry about when aerating the water. Heated water won't retain much, if any, oxygen IIRC. I'm guessing on this one, so YMMV. It may warrant further investigation.
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Old 09-13-2010, 05:39 PM   #7
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IIRC, small bubbles displace more water. That's why an air stone is used in an aquarium.
I'm pretty sure that's incorrect. At least with respect to brewing, the reason you use an air stone is to create small bubbles because that increases the surface area which in turn increases the absorption of oxygen into the liquid. If there is a constant flow rate, the displaced volume will be relatively independent of bubble size (to an extent). Either way there's such a large pressure drop across the air stone that it significantly restricts air flow. I completely agree with you that bubble size is a moot point.

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at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?
Yah, no need for a sanitary air source since it's pre-boil. However, in general hot side aeration is a bad idea, so maybe that's why people don't do this more often?
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Old 09-13-2010, 05:54 PM   #8
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Yah, no need for a sanitary air source since it's pre-boil. However, in general hot side aeration is a bad idea, so maybe that's why people don't do this more often?
I thought this was being used to mix the HLT water, not the wort. Did I miss something? HSA should only be an issue with hot wort.
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Old 09-13-2010, 06:02 PM   #9
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I thought this was being used to mix the HLT water, not the wort. Did I miss something? HSA should only be an issue with hot wort.
Well, it drains directly from the HLT onto a pile of grain and quickly becomes wort. So if there's any residual oxygen in the water that flows out of the HLT, then that quickly becomes residual oxygen in the wort. The amount of oxygen dissolved in the water quickly approaches 0 as the temp gets closer to 100C, so it may not be an issue. However, there are people out there that scream and yell that any splashing whatsoever of the wort will ruin your beer. Those people might complain about any remaining oxygen in their strike water. I'm not one of those people, so it doesn't bother me.
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Old 09-13-2010, 06:04 PM   #10
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On the small bubble thing, I think that it depends on whether the objective is to aerate or move the liquid. In the aquarium example, the objective is to expose all of the water to the surface where the majority of the gas exchange with the atmosphere occurs. This is completely different than trying to infuse a pure gas like Oxygen or CO2.

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