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.

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.

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.

bblack7489 said:

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.

Click to expand...

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.

at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?

Atl300zx said:

at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?

Click to expand...

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.

Catt22 said:

IIRC, small bubbles displace more water. That's why an air stone is used in an aquarium.

Click to expand...

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.

Atl300zx said:

at this point i assume filtering the air isnt neccessary. any negatives to aerating the water ?

Click to expand...

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?

bblack7489 said:

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?

Click to expand...

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.

Catt22 said:

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.

Click to expand...

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.

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.

bblack7489 said:

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.

Click to expand...

Agreed, but there will be air (and oxygen) in the grain as well, so any slight residual amount in the strike/sparge water would likely be relatively insignificant. I try to minimize splashing too, but it's near impossible to prevent exposure somewhere along the line. I have not noticed any oxidation problems with my beer though, so I don't worry about it.

Why is it so important to stir the hlt? What's the big deal if the top of the water is cooler than the bottom? If you run a copper coil through it the wort temp will even out, won't it?

wildwest450 said:

Why is it so important to stir the hlt? What's the big deal if the top of the water is cooler than the bottom? If you run a copper coil through it the wort temp will even out, won't it?

Click to expand...

No, the water will tend to stratify with the warmer water accumulated near the top and the cooler water near the bottom. Furthermore, you want to keep the water moving past the coil for best performance. It's very similar to what happens with an immersion chiller. Only the wort or water actually touching the surface of the coil is cooled, or mostly so anyway. Stirring or otherwise keeping it mixed up helps tremendously with this. I learned this early on with my first IC. I thought I could just stick it in the BK and run the cooling water. The cooling was very slow doing it that way. Moving the IC around helped a lot and you could easily feel the difference in the temperature of the water coming out of the chiller.

Catt22 said:

Moving the IC around helped a lot and you could easily feel the difference in the temperature of the water coming out of the chiller.

Click to expand...

Essentially, the concept for a CFC or plate chiller - two fluids in constant motion.

wildwest450 said:

Why is it so important to stir the hlt? What's the big deal if the top of the water is cooler than the bottom? If you run a copper coil through it the wort temp will even out, won't it?

Click to expand...

I'm not building a heat exchanger in my HLT at this point in time, and I don't want to recirculate it with a pump. It's just an electric vessel to get water to the proper temperature and hold it at that temperature before the strike / sparge. If there's no agitation in the vessel, it stratifies and it doesn't heat evenly. That in turn makes the control basically useless not to mention the fact that my drain from the keggle is in the bottom (cold) section of the water column.

And to answer the second question, yes the wort temp will be even, but the water in the HLT will not necessarily be even. The copper coil / heat exchanger will help generate convection in the tank, but it still may not mix completely. On top of that, your heat exchanger's efficiency will increase dramatically if you stir the HLT.

Interesting that this is working for you. I read the other thread and honestly had my doubts.

Did you find any difference in temp between the top and your outlet temperature? Does it have to "stir" for any length of time to mix well or when it hits your set temp is it ready to go?

I already have a pump for this purpose but if that ever fails I may go this route.

I haven't checked for stratification in my HLT, but it seems to me that since my element and probe are toward the bottom, the heated water will be displaced by the cooler water until it reaches equilibrium within a degree or two. I guess I could check, but I haven't had issues with controlling my mash temps, so I never have.

HLT stratifies SIGNIFICANTLY. At least with an electric keggle, there is no question here.

Push air down a sight gauge. This will circulate the water just like in an aquarium.

[Will post pics eventually].

lschiavo said:

Did you find any difference in temp between the top and your outlet temperature? Does it have to "stir" for any length of time to mix well or when it hits your set temp is it ready to go?

Click to expand...

Yah, there was a significant difference between the top and bottom, but the first time that I noticed it was when I was testing my new eHLT. I had a digital thermometer in it that was set to go off at my strike temp. When it went off, I noticed that the bottom part of the keggle (below the heating element) was still cool to the touch while the top part was steaming. I stirred the pot and watched the temp drop from 168 to 140. So the water below the element was cold, and there was enough of it that mixing it fully dropped the overall temp by nearly 30F.

I don't know how long it takes to mix with the aquarium air pump. I just turn it on when I turn on my heater and leave it on until I'm done.

klyph said:

I haven't checked for stratification in my HLT, but it seems to me that since my element and probe are toward the bottom, the heated water will be displaced by the cooler water until it reaches equilibrium within a degree or two.

Click to expand...

Absolutely. That principle is called natural convection and means that as the hot liquid rises the cooler liquid fills in and it all stays well mixed. That works perfectly above the heating element, but it doesn't cause the entire HLT to circulate. The cold water at the bottom of the kettle (below the element) just sits there and never gets mixed in.

bblack7489 said:

Yah, there was a significant difference between the top and bottom, but the first time that I noticed it was when I was testing my new eHLT. I had a digital thermometer in it that was set to go off at my strike temp. When it went off, I noticed that the bottom part of the keggle (below the heating element) was still cool to the touch while the top part was steaming. I stirred the pot and watched the temp drop from 168 to 140. So the water below the element was cold, and there was enough of it that mixing it fully dropped the overall temp by nearly 30F.

I don't know how long it takes to mix with the aquarium air pump. I just turn it on when I turn on my heater and leave it on until I'm done.

Click to expand...

I understand what the original problem was (had the same thing myself). I was just curious if you followed up after using the air pump with temp measurements from the top and bottom. I know with mine (using a pump) and a bottom outlet, I get exactly the temp I have my controller set for. Just wondering how yours compares.

lschiavo said:

I understand what the original problem was (had the same thing myself). I was just curious if you followed up after using the air pump with temp measurements from the top and bottom. I know with mine (using a pump) and a bottom outlet, I get exactly the temp I have my controller set for. Just wondering how yours compares.

Click to expand...

Oh, sorry. I apparently answered a question that you weren't asking.

So I didn't measure the temperature in multiple places, and the bottom of the keggle was definitely hot enough that I didn't want to do the touch test again. Instead I measured the temperature in one spot, after my temp controller hit the commanded temp. I then stirred the crap out of it with a paddle and took the temperature again. If there had been pockets of cool water like there were before, then the temp would have dropped after I stirred it. However when I stirred it, the temp stayed the same. That was definitive enough proof for me (and arguably more definitive than taking the temp at multiple locations inside of your kettle).

bblack7489 said:

Oh, sorry. I apparently answered a question that you weren't asking.

So I didn't measure the temperature in multiple places, and the bottom of the keggle was definitely hot enough that I didn't want to do the touch test again. Instead I measured the temperature in one spot, after my temp controller hit the commanded temp. I then stirred the crap out of it with a paddle and took the temperature again. If there had been pockets of cool water like there were before, then the temp would have dropped after I stirred it. However when I stirred it, the temp stayed the same. That was definitive enough proof for me (and arguably more definitive than taking the temp at multiple locations inside of your kettle).

Click to expand...

Cool...sounds like its working fine to me then. This is just one of those small aquarium pumps that you hook up like a 1/4-in line to right?

passedpawn said:

HLT stratifies SIGNIFICANTLY. At least with an electric keggle, there is no question here.

Push air down a sight gauge. This will circulate the water just like in an aquarium.

[Will post pics eventually].

Click to expand...

Even with the element and probe at the bottom?

bblack7489 said:

Absolutely. That principle is called natural convection and means that as the hot liquid rises the cooler liquid fills in and it all stays well mixed. That works perfectly above the heating element, but it doesn't cause the entire HLT to circulate. The cold water at the bottom of the kettle (below the element) just sits there and never gets mixed in.

Click to expand...

I'm having a tough time envisioning the water below my element having any significantly temperature differential.





Maybe it does, I haven't measured it, but we're talking like 3" from the bottom of the dome to the element.

klyph said:

Even with the element and probe at the bottom?

Click to expand...

My element is horizontal and at about the 3 gallon mark, and the temp gradients are significant there. I have no reason to make this up. I have a 4-channel logging thermometer that I'll use to do a test this weekend (maybe).

Your element appears to be lower than mine. I'm imagining you taking that picture.

passedpawn said:

I'm imagining you taking that picture.

Click to expand...

It was a lot like that.

klyph said:

It was a lot like that.

Click to expand...

I remember that movie. White blood cells attacking. Now that's some old-school sci-fi!

klyph said:

I'm having a tough time envisioning the water below my element having any significantly temperature differential.

Click to expand...

I would guess you're still getting a temp difference. One quick way to find out is to get some water up to temp, draw a cup out of your spigot and and make sure it's the right temperature. Or if you're brave, you could always just feel the bottom of your kettle. Water is a surprisingly good insulator, so unless there's mixing going on, then you're probably getting cold spots.

bblack7489 said:

so unless there's mixing going on

Click to expand...

That's the thing, when the 5500W element pulses on, a stream of bubbles go up to the top, and I can see ripples on the surface.

Next brew session, I'll try to remember to measure at varying points to check for stratification.

I recently built an EHLT in a cooler. I mounted my element parallel to the bottom and as close to the bottom as I could get. I mounted my outlet on the opposite side away from the element.

Now I'm sure that I've read somewhere that the heat will rise creating an upward current and, over time, will create it's own stirring effect. The hot water on one side of the cooler rises and the cooler water on the other side fills the void creating a slight upward and downward current. This effect may not occur if the element is mounted in the center from the bottom, but I don't see why it wouldn't.

I don't know if it's true or not but while my water was heating decided to conduct an experiment. I took temperature readings near the top of the water on the opposite side from the heating element. Then, I stirred the water with a spoon, taking care to avoid touching the element, (Metal spoon) and the temps remained exactly the same with or without stirring.

So, until I learn something different, I'm not going to bother with any type of stirring mechanism.

I have an e-HLT built in a 10g rubbermaid cooler. The element is mounted vertically from the bottom. I have noticed significant stratification in my last few batches. Actually, it wasn't until I read this thread that I figured it out. I've been missing my mash temps by at least 5 degrees in the last 3 batches (which never happened before) and my mash out failed to raise the temp of the grain bed. These also happen to be the batches where i didn't use my stirrer. I set my controller to 170 and use this water to mash in and I got mash temps of only 145-148. When I use the stirrer I get a mash temp of 13-15 degrees below my strike temp (155-157). That's all the justification I need to hook that stirrer back up.

It really depends how you draw your water off. If you draw from under the element with no stirring, try a temp reading and see if it matches your setpoint.

Bump to revive a dead thread.

What kind of aquarium pump does one need to stir a keggle eHLT?

TIA

stlbeer said:

Bump to revive a dead thread.

What kind of aquarium pump does one need to stir a keggle eHLT?

TIA

Click to expand...

Any pump will do, push the air down through the sight glass tube if you use one

And if you go by the sight glass, in a kettle, youll have to install some fittings to go to the bottom of the kettle, under the element. A bit like the fitting i got for my dip tube. If i choose to do that, i will use a straight barb and a longer lenght of silicone tubing to go under the element in the middle of the kettle.

Im not sure yet if i go this way or if i install a recirculating port to the top of the kettle. Im leaning towards the latter.