Author Topic: Right RPM for stir plate?  (Read 15763 times)

Offline klickitat jim

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Re: Right RPM for stir plate?
« Reply #75 on: January 16, 2015, 02:51:15 AM »
What's the right RPM for stir plate?

I turn mine up just enough so that the wort is rotating, which sometimes results in a small dimple on the surface.  To my eyes, this is less agitation than occurs in the fermentor during peak fermentation.

I used to not oxygenate my starters, I do now

I've started doing this as well.  How long of a blast of O2 are you hitting them with?
For a 2L starter, enough to give it a decent layer of froth on top but not over flowing the flask. Maybe 10 seconds

Offline Philbrew

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Re: Right RPM for stir plate?
« Reply #76 on: January 16, 2015, 02:57:12 AM »
"spinner flask" (price sensitive brewers should expect to experience major sticker shock if purchasing new). 
Ha!  Now there's some hi quality internet snarc right there.  I love it!  Let's be honest, we all enjoy it.  And no, there's no way I'm EVEN going to look up the price of one of those "spinner" puppies.
Many of us would be on a strict liquid diet if it weren't for pretzels.

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Re: Right RPM for stir plate?
« Reply #77 on: January 16, 2015, 03:13:31 AM »
Correct me if i'm wrong
Yeast has 3 phases:
1. anaerobic - reproduce
2. aerobic - eat
3. cold – sleep


No, yeast cells normally go through three major phases.  The first phase is the called the lag phase.  During the lag phase, the yeast cells adapt to their new environment and prepare to bud.  The next phase is called the log or exponential phase.  During the exponential phase, yeast cells are budding (multiplying) like crazy.  The final phase is called the stationary phase.  Depending on whose work one reads, each of the major phases has one or more sub-phases.

The thing that confuses most people is that yeast cells have two separate metabolic pathways. The first metabolic pathway is called the respirative (aerobic) metabolic pathway.  The respirative metabolic pathway is extremely efficient. It basically converts sugar to water and carbon dioxide gas.  The second metabolic pathway is called the fermentative (anaerobic) metabolic pathway. It is the pathway through which sugar is converted primarily to ethanol (which is a carbon-based compound) and carbon dioxide gas.  The fermentative metabolic pathway is not anywhere near as efficient as the respirative metabolic pathway.   

Many older home brewing texts erroneously refer to the growth phase as respiration.   Brewing yeast cells do not respire in beer wort due to something known as the Crabtree Effect.  The Crabtree Effect states that yeast cells will favor fermentation over respiration when subjected to dissolved glucose levels above the Crabtree threshold, and they will do so even in the presence of dissolved oxygen (O2).  The Crabtree threshold is around 0.3% weight/volume (w/v). 

To put things into context, the extract from the average mash contains roughly 14% glucose, which means that wort with a specific gravity above 1.008 contains a glucose level above the Crabtree threshold.

Here's the math:

A 1.008 solution is a 2% sugar weight/weight (w/w) solution, which is the same thing as w/v when dealing with a solute dissolved into water because 1ml of water weighs one gram.  Of that 2%, only 14% is glucose; hence, 0.02 x 0.14 = 0.0028, or 0.28% glucose w/v, which is below the Crabtree threshold.

As all beer and batch yeast propagation worts have specific gravities above 1.008, yeast biomass growth in brewing is fermentative.  Now, the metabolic pathways in yeast cells are a little on the leaky side.  What yeast cells do while there is still O2 in solution is shunt a small percentage of the glucose being consumed to the respirative metabolic pathway for the synthesization of ergosterol and unsaturated fatty acids (UFA).   These compounds make cell membranes more pliable, which, in turn, make passage of nutrients and waste products in and out of the cells easier.

Quote
With this knowledge, it's better to keep a yeast starter barely covered to stop contamination, but allow breathing.
I've seen a lot of people use airlocks on their flasks

RIGHT?

I am sorry to inform you, but the no airlock argument is also for the most part home brewer pseudo-science.   CO2 is heavier than air.  Plus, the culture is under positive pressure; hence, little to no O2 makes it into solution from the atmosphere after CO2 production begins, especially in an Erlenmeyer flask.  The only way to ensure that a culture receives a continuous supply of O2 is to use forced aeration throughout propagation. 

With that said, there is a way to propagate yeast respiratively, but it requires a hi-tech piece of equipment known as a bioreactor.  This type of propagation differs from how brewers propagate yeast.  Brewers use batch propagation.  Respirative propagation is a continuous process in which nutrient and O2 are continuously added to the medium while yeast cells are continuously drawn off.   A bioreactor makes this process possible because it can hold the dissolved glucose level in a steady state below the Crabtree threshold.  Lallemand and Lesaffre (the parent company of Fermentis) use this type of propagation to produce dry yeast cultures.  Respirative growth is more efficient than fermentative growth; hence, more yeast cells can be produced using the same amount of carbon (sugar is basically carbon bound to water).  Respirative growth also has the added advantage of continuous ergosterol and UFA production; hence, the yeast cells that are produced via the process do not need to undergo ergosterol and UFA replenishment after being pitched.  As mentioned above, yeast cells use the O2 that is solution at the beginning of fermentation to synthesize ergosterol and UFAs via the respirative metabolic pathway.  Pitching fully-charged yeast cells basically eliminates the need to aerate one’s wort.

For anyone who is interested in learning more about Lallemand’s yeast propagation process.  Here’s a link a to short paper that describes how they propagate baker’s yeast in layman's terms.   Baker’s yeast and brewer’s yeast are the same yeast species; namely, Saccharomyces cerevisiae (S. cerevisiae).  The strains only differ in the application at which they excel.

http://www.lallemand.com/BakerYeastNA/eng/PDFs/LBU%20PDF%20FILES/1_9YPROD.PDF

“Growing via respiration is important because it is about eighteen times as efficient as fermentation at converting sugar into yeast. The tendency of yeast to grow via respiration when large amounts of oxygen are present is known as the Pasteur effect. The tendency of yeast to grow via fermentation when high levels of sugar are present is known as the Crabtree effect.  The combination of Pasteur and Crabtree effects in Saccharomyces cerevisiae is the reason commercial bakers yeast fermentations use high aeration and incremental feeding to maintain high oxygen and low sugar levels throughout the process.”


Offline narcout

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Re: Right RPM for stir plate?
« Reply #78 on: January 16, 2015, 03:08:33 PM »
For a 2L starter, enough to give it a decent layer of froth on top but not over flowing the flask. Maybe 10 seconds

10 seconds is about what I've been using as well.  Have you noticed much of a difference?  I don't know that I can say it definitively, but it seems like my oxygenated starters take off more quickly.
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Offline Wort-H.O.G.

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Re: Right RPM for stir plate?
« Reply #79 on: January 16, 2015, 03:20:43 PM »
For a 2L starter, enough to give it a decent layer of froth on top but not over flowing the flask. Maybe 10 seconds

10 seconds is about what I've been using as well.  Have you noticed much of a difference?  I don't know that I can say it definitively, but it seems like my oxygenated starters take off more quickly.
i give a shot of o2 also. if in fact very little o2 is added during stir plate activity, makes sense to me to add o2 to starters just like I do making full batch.
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Offline Stevie

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Re: Right RPM for stir plate?
« Reply #80 on: January 16, 2015, 03:46:01 PM »
My whole issue is that both whitelabs and wyeast promote the use of stir plates. If they were voodoo, I think wyeast and whitelabs would call it out allowing them to sell more yeast.

Offline klickitat jim

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Re: Right RPM for stir plate?
« Reply #81 on: January 16, 2015, 04:05:02 PM »
My whole issue is that both whitelabs and wyeast promote the use of stir plates. If they were voodoo, I think wyeast and whitelabs would call it out allowing them to sell more yeast.
I think stirplates are great. The point is that they dont add enough O2, probably.

Offline klickitat jim

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Re: Right RPM for stir plate?
« Reply #82 on: January 16, 2015, 04:11:28 PM »
For a 2L starter, enough to give it a decent layer of froth on top but not over flowing the flask. Maybe 10 seconds

10 seconds is about what I've been using as well.  Have you noticed much of a difference?  I don't know that I can say it definitively, but it seems like my oxygenated starters take off more quickly.
In my change to adding O2, I also made up a fresh couple of cases of starter wort, and its half gallon pressure canned 1.030 extra light DME and each jar got canned with wyeast nutrients inside.

So for me two changes. O2 and nutrient. My starters are clearly bigger and healthier.

Offline denny

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Re: Right RPM for stir plate?
« Reply #83 on: January 16, 2015, 04:48:15 PM »
cool thought. however i'm sure i'm not the only one who will say the following: many award winning, top quality, great tasting home brew beers have been made and will continue to be made with starters and stir plates...many of them i'd rate better than several commercial beers.  hows that song go..."must be doing something right".

at the end of the day, if what i make or what i drink tastes and smells like what I consider to be a good, great, or exceptional beer.... then in that, I trust.

THIS^^^^  I'll change my methods when I don't get great results with my current method.
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Offline JT

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Re: Right RPM for stir plate?
« Reply #84 on: January 16, 2015, 06:00:56 PM »
cool thought. however i'm sure i'm not the only one who will say the following: many award winning, top quality, great tasting home brew beers have been made and will continue to be made with starters and stir plates...many of them i'd rate better than several commercial beers.  hows that song go..."must be doing something right".

at the end of the day, if what i make or what i drink tastes and smells like what I consider to be a good, great, or exceptional beer.... then in that, I trust.

THIS^^^^  I'll change my methods when I don't get great results with my current method.
Depends.  Even if I'm getting good results, I'll try something new in a heartbeat just to see if I like the results even better - as long as it doesn't require a bunch of extra effort or cash. 

Offline denny

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Re: Right RPM for stir plate?
« Reply #85 on: January 16, 2015, 06:48:27 PM »
Depends.  Even if I'm getting good results, I'll try something new in a heartbeat just to see if I like the results even better - as long as it doesn't require a bunch of extra effort or cash.

Me, too, which is how I arrived at my current method.
Life begins at 60.....1.060, that is!

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Offline Wort-H.O.G.

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Re: Right RPM for stir plate?
« Reply #86 on: January 16, 2015, 07:06:05 PM »
I'm just happy the documented trial and errors of the  Brewers that have been brewing 20-30+ years are easily accessible on the web- made life learning to brew much easier. Imagine when you needed some guidance or an answer , and no web, forums, Google. 
Ken- Chagrin Falls, OH
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https://www.facebook.com/pages/Harveys-Brewhaus/405092862905115

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Vienna IPA          O'Fest
Dort
Mead                 
Cider                         
Ger'merican Blonde
Amber Ale
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Offline JT

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Re: Right RPM for stir plate?
« Reply #87 on: January 16, 2015, 07:10:45 PM »
I'm just happy the documented trial and errors of the  Brewers that have been brewing 20-30+ years are easily accessible on the web- made life learning to brew much easier. Imagine when you needed some guidance or an answer , and no web, forums, Google.
I was just thinking this the other day!  Things we take for granted...

Offline HoosierBrew

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Re: Right RPM for stir plate?
« Reply #88 on: January 16, 2015, 07:12:47 PM »
Imagine when you needed some guidance or an answer , and no web, forums, Google. 

I resemble that  :D     If nothing else, I learned the value of the split batch - it was a good way to get extra info quicker. That and taking a hell of a lot of notes !
Jon H.

Offline archstanton

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Re: Right RPM for stir plate?
« Reply #89 on: January 16, 2015, 07:45:13 PM »
Imagine when you needed some guidance or an answer , and no web, forums, Google. 

I resemble that  :D     If nothing else, I learned the value of the split batch - it was a good way to get extra info quicker. That and taking a hell of a lot of notes !

No software either. That's how I learned to brew, a few books and learned experience. I find the internet to be a great place to learn tricks and develop gadgets and streamline processes.  I do feel that something learned through personal experience is much harder to let go of than something learned form a book. A difference between knowledge and education maybe???