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Brews & Views Bulletin Board Service * Brews and Views Archive 2006 * Archive through November 14, 2006 * Magnetic stirplate speed? < Previous Next >

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Paul Edwards
Senior Member
Username: Pedwards

Post Number: 1095
Registered: 03-2003
Posted From: 70.236.18.203
Posted on Friday, October 27, 2006 - 05:00 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I just got a nice magnetic stirplate I bought on eBay for $20. Seems to work just fine, even with a 3/4 full 1 gallon jug sitting on it. (it has a 6-1/2 inch diameter platform)

I may try to pick up a second one, as I usually split a 10 gallon batch and pitch a different yeast into each 5 gallon half-batch.

Question is, what sort of speed should I set the stirplate to? I'm assuming fairly low, but then I'm only guessing, since I've never used one before. This particular unit has a speed range of 100 to 1200 rpm.
 

Graham Cox
Advanced Member
Username: T2driver

Post Number: 710
Registered: 11-2004
Posted From: 172.130.69.5
Posted on Friday, October 27, 2006 - 06:54 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Two schools of thought, Paul.

1) The yeast need oxygen to reproduce, and lots of it. Turn it up high until you generate a vortex and thus continually suck air down into the wort for them.

2) High speeds create hydrodynamic shear forces in the wort and damage the yeast. The yeast should be oxygenated up front with the stir plate off, then the stir plate should be started a few hours later on very low speed, just fast enough to keep the yeast in suspension.

The speed you use is also dependent on the size of your stir bar - longer bars need less RPM to do the same amount of work.

FWIW, I use school of thought #2.
 

Paul Edwards
Senior Member
Username: Pedwards

Post Number: 1096
Registered: 03-2003
Posted From: 70.229.30.192
Posted on Saturday, October 28, 2006 - 12:57 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Thanks, Graham.

I think I'll give the second option a test drive. I have been giving my starters a shot of O2 lately anyway.

Since I only have one stirplate right now, I can do a side by side comparision to see what I get.
 

Richard Nye
Senior Member
Username: Yeasty_boy

Post Number: 1725
Registered: 01-2004
Posted From: 68.4.202.69
Posted on Saturday, October 28, 2006 - 01:52 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Paul, here are my thoughts.

The yeast are so small I wouldn't worry about hydrodynamic forces, etc. I think that's a bunch of hooey. I turn mine up until I see quite a few small bubbles being churned in the wort. I uses higher speeds at first to get more air/O2 into solution. I also have the stirplate on when I oxygenate to make sure I get maximum saturatation.

My best ferments are when I grow yeast up from a small test tube to 2+ quarts (for 10 gallons) on my stirplate. That way I know I've got lots of healthy yeast.
 

Graham Cox
Advanced Member
Username: T2driver

Post Number: 713
Registered: 11-2004
Posted From: 68.32.249.201
Posted on Saturday, October 28, 2006 - 02:10 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Here's a germane but lengthy discussion on this topic: http://hbd.org/discus/messages/26895/30258.html

Richard, it seems to me that running the stir plate while oxygenating, or shortly after oxygenating, would only agitate the oxygen you put in right back out of solution. Not being an oxygen molecule myself, I couldn't say first-hand.
 

Richard Nye
Senior Member
Username: Yeasty_boy

Post Number: 1728
Registered: 01-2004
Posted From: 68.4.202.69
Posted on Saturday, October 28, 2006 - 04:40 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Graham, OTOH, when you oxygenate you fill the flask up with O2 as well so you stir the gaseous O2 into the wort.
 

FrostyTheBeerMan
New Member
Username: Frostythebeerman

Post Number: 1
Registered: 11-2006
Posted From: 70.82.220.183
Posted on Thursday, November 02, 2006 - 04:47 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Something I heard on one of Jamil's brewcasts, last week, was that when you have your stirplate going, you are producing / reproducing yeast, and not producing alcohol.

( I hope I understood him correctly )

This was something I was not aware of and thought it was rather interesting. So as long as the stirplate is running, the production of alcohol is very low, or nil, and yeast production is at its greatest. Anyway, just something I thought I would share.

Mark
 

Richard Nye
Senior Member
Username: Yeasty_boy

Post Number: 1741
Registered: 01-2004
Posted From: 68.4.202.69
Posted on Thursday, November 02, 2006 - 05:36 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Frosty, I'm no expert at this, but I believe yeast have 2 metabolic states, aerobic and anaerobic. They produce alcohol under the anaerobic state, but very little alcohol under the aerobic state. So if the wort has oxygen in it that the yeast can metabolize they don't produce much alcohol.
 

FrostyTheBeerMan
New Member
Username: Frostythebeerman

Post Number: 2
Registered: 11-2006
Posted From: 70.82.220.183
Posted on Thursday, November 02, 2006 - 05:52 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Hi Richard,

Thanks for explaining that for me. I think it's a really interesting topic. I had no clue this happened, but glad I know this now.

I recently bought a stirplate, but now wish to build another one, as at times I'll make 2 flasks of starter, and so one will sit on the counter, while the other stirs on the stirplate machine.

I went to a local place last week and bought 2 rare earth magnets ( 60 cents each ) and so I am slowly on my way to build another one.

All I can say is - amazing !, eventhough these magnets are so small, they are like nothing I have ever experienced before - they are so so powerful. I put one of them on my stove top to show my wife, and could hardly get it off, very impressive.

Thanks again for the info Richard.

Mark
 

Denny Conn
Senior Member
Username: Denny

Post Number: 5980
Registered: 01-2001
Posted From: 140.211.82.4
Posted on Thursday, November 02, 2006 - 06:06 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Yeah, but doesn't the Crabtree effect kinda negate that?
LIfe begins at 60...1.060, that is.
 

FrostyTheBeerMan
New Member
Username: Frostythebeerman

Post Number: 3
Registered: 11-2006
Posted From: 70.82.220.183
Posted on Friday, November 03, 2006 - 06:56 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Hmm hi guys,

I just logged in now to see if there were any new posts, and sure enough I see one.

How come I didn't get an email alert ? is there somewhere, where I can turn this feature "on" like on other boards ?

thanks in advance for any info.