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Home Brew Forums > Home Brewing Beer > Equipment/Sanitation > Is there something to limiting grainmill rpms?
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Old 02-23-2009, 05:30 PM   #1
Joe Camel
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Default Is there something to limiting grainmill rpms?

Or is this another mantra that is repeated because it was read somewhere?

It used to be said that the gap should be 0.040 or you risk tannin extraction, but now people are going tighter for more efficiency and no reports of tannins.

It used to be that the hottest water used for sparging was 170, batch or fly, or you risk tannin extraction, but now we know that batch sparging can go much hotter.

Is this another one of those? or is there something to it? I'm not proposing they be run at 1500 rpm off a direct drive of a furnace motor, but my crappy cordless drill probably runs the mill at 600 rpm with the trigger pinned.

Cheers

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Old 02-23-2009, 05:37 PM   #2
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There is something to it.

Your drill prolly runs more like 800-1000 rpm with the trigger pinned depending on whether it's set to drill or driver. Of course, you can look up the drill to verify.

A slower crush improves the rollers ability to crack the grain without ripping up the husk. Ideally, you want to just split the husk open as you crack the innards of the grain.

At a higher rpm the risk of shattering the innard and reducing the husk to what equates as shrapnel increases. Speaking all scientifically of course.

As for the tannin bit with batch vs fly. That has to do with the ratio of sugars in the mix. During a fly sparge the potential for tannin extraction does increase as the solution of sugars decreases BUT, this condition has a LOT more to do with the pH of the sparge water than it does the actual temperature. The citation of 170*F is more of a safe haven for those uf us sparging at an unknown pH.

FWIW, AIUI

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Old 02-23-2009, 05:47 PM   #3
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Originally Posted by Joe Camel View Post
It used to be that the hottest water used for sparging was 170, batch or fly, or you risk tannin extraction, but now we know that batch sparging can go much hotter.Cheers
Hottest water or grain temp?
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Old 02-23-2009, 08:43 PM   #4
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Originally Posted by GilaMinumBeer View Post
There is something to it.

Your drill prolly runs more like 800-1000 rpm with the trigger pinned depending on whether it's set to drill or driver. Of course, you can look up the drill to verify.

A slower crush improves the rollers ability to crack the grain without ripping up the husk. Ideally, you want to just split the husk open as you crack the innards of the grain.

At a higher rpm the risk of shattering the innard and reducing the husk to what equates as shrapnel increases. Speaking all scientifically of course.

As for the tannin bit with batch vs fly. That has to do with the ratio of sugars in the mix. During a fly sparge the potential for tannin extraction does increase as the solution of sugars decreases BUT, this condition has a LOT more to do with the pH of the sparge water than it does the actual temperature. The citation of 170*F is more of a safe haven for those uf us sparging at an unknown pH.

FWIW, AIUI
The "high torque" FWIW setting on my firestorm maxes at 750, but under the load of milling, it seems to be much lower than that, so I spitballed it at around 600. It just seems that the drill is happier running at full speed rather than holding the trigger halfway.

I do notice more flour is produced, but I haven't really paid attention to whether the husks are shredded or not, I'll have to compare. I don't seem to have any trouble with stuck sparges or the like, but my tongue isn't really calibrated for tannins to know if that's an issue. Maybe it's another one of those things that causes different effects if you batch sparge as opposed to fly.

Does tightening the gap lead to shredding as well? a lot of people on this board talk about having their gaps tightened down to where they would get a stuck sparge if any tighter.

Cheers
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Old 02-23-2009, 08:45 PM   #5
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Hottest water or grain temp?
The earlier information discussed this in terms of water temperature, as usually a mashout was involved.

With the changing information out there, most people now seem to discuss it in terms of grain bed temp.

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Old 02-23-2009, 08:48 PM   #6
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The earlier information discussed this in terms of water temperature, as usually a mashout was involved.

With the changing information out there, most people now seem to discuss it in terms of grain bed temp.
That's because most of the earlier literature was only dealing with continuous sparging.
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Old 02-23-2009, 08:52 PM   #7
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Originally Posted by Joe Camel View Post
The "high torque" FWIW setting on my firestorm maxes at 750, but under the load of milling, it seems to be much lower than that, so I spitballed it at around 600. It just seems that the drill is happier running at full speed rather than holding the trigger halfway.

I do notice more flour is produced, but I haven't really paid attention to whether the husks are shredded or not, I'll have to compare. I don't seem to have any trouble with stuck sparges or the like, but my tongue isn't really calibrated for tannins to know if that's an issue. Maybe it's another one of those things that causes different effects if you batch sparge as opposed to fly.

Does tightening the gap lead to shredding as well? a lot of people on this board talk about having their gaps tightened down to where they would get a stuck sparge if any tighter.

Cheers
If it doesn't like to run at slower speeds then the drill doesn't have enough torque. I have the Bosch 24 volt cordless 1/2 inch drill. I have to be careful with it when I am drilling when the bit gets stuck it will twist my arm to the point that my wrist hurts a lot. On the driver setting I can bring it down to a crawl on the BC. I think I am somewhere in the 300-400 range though most of the time. I tried full bore and it did seem tpo make more flour and less intact hulls
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Old 02-25-2009, 07:19 PM   #8
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Does any one have a recommendation for a good grain mill motor? I tried using an AC gearmotor from mcmaster carr but it doesn't have enough torque.

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