Author Topic: Stater without a stir plate  (Read 1478 times)

S. cerevisiae

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Re: Stater without a stir plate
« Reply #15 on: August 30, 2015, 05:41:10 PM »
I do not see how my method would not work with 1450.  I used it many times when the culture was known as CL-50. 

My method is yeast strain agnostic.  Pitching at high krausen makes a significant difference in the number of viable cells that need to be pitched due to the fact that one is not pitching quiescent cells with low or darn near depleted ergosterol and unsaturated fatty acid (UFA) reserves.

With respect to a stir plate producing more viable cells, that's completely bunk.  Maximum cell density is maximum cell density.  A starter that is stirred and allowed to ferment to completion will contain more cells than a non-stirred starter that is pitched at high krausen, but it will not contain a significantly higher number of viable cells than a starter that is pitched at high krausen, and high krausen cells are in better health; therefore, they experience a shorter lag phase.

The cold hard truth is that stir plates were not designed for, nor are they used in yeast culturing outside of the home brewing community (orbital shakers are used in labs).  Their use in home brewing is based on "brewing by buddy," that is, my brewing friend uses a stir plate; therefore, it must be the way to do it.  This behavior is no different than "management by magazine" or "management by golf course" in the corporate world.

Yeast cultures grow at a rate of 2N, where N is the amount of time in minutes that have elapsed since the end of the lag phase divided the replication period (approximately 90 minutes for ales), which is why the growth phase is known as the exponential or log phase.  Any method that does not increase the viable yeast cell count by a factor of at least two is insignificant.  I have yet to see a repeatable published study using a stir plate that produces a two-fold increase in viable cell count over a well-aerated culture. 

The reason why a well-shaken starter works as well as it does for being such a low-tech method is because it takes advantage of physics and chemistry.  A gas dissolves into a liquid at the interface between the gas and the liquid; hence, surface area is critical to O2 pickup.  A gas-liquid foam has a very high specific surface area.  By shaking the medium until it is almost all foam, we create an amount of surface area that is impossible to replicate with a stir plate and an Erlenmeyer flask, and we do it at the beginning of fermentation when the O2 load on the medium is highest due ergosterol and UFA synthesis.  Bubbling a gas through a liquid with tiny bubbles creates the same kind of effect, but much less efficiently.   

The gas-liquid interface shrinks in an Erlenmeyer flask as the volume of media increases.  Stirring the culture fast enough to create a vortex increases the size of the interface between the liquid and the gas as well as creates a vacuum that helps to overcome the geometry of an Erlenmeyer flask, but it does so by increasing the amount of shear stress placed on the cells.  That's why stirred starters smell off when compared with non-stirred starters.  A lot of home brewers mistakenly equate the odor with continuous aeration, but no O2 is entering the flask after the culture starts to outgas. The geometry of an Erlenmeyer flask almost guarantees it, and  CO2 dissolves more readily in a liquid than O2.
« Last Edit: August 30, 2015, 07:42:35 PM by S. cerevisiae »

Offline denny

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Re: Stater without a stir plate
« Reply #16 on: August 30, 2015, 06:00:46 PM »
I was being a bit facetious...imagine that!  ;)  I have no doubt that your method worked great for you.  But I've tried it both ways and I know what works better for me.  Now, that may be at odds with the science.  I don't really know how to explain that.  But I do know what my results are and I get better results with a stir plate.
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Offline johnnyb

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Re: Stater without a stir plate
« Reply #17 on: August 30, 2015, 11:32:54 PM »
I do not see how my method would not work with 1450.  I used it many times when the culture was known as CL-50. 

My method is yeast strain agnostic.  Pitching at high krausen makes a significant difference in the number of viable cells that need to be pitched due to the fact that one is not pitching quiescent cells with low or darn near depleted ergosterol and unsaturated fatty acid (UFA) reserves.

With respect to a stir plate producing more viable cells, that's completely bunk.  Maximum cell density is maximum cell density.  A starter that is stirred and allowed to ferment to completion will contain more cells than a non-stirred starter that is pitched at high krausen, but it will not contain a significantly higher number of viable cells than a starter that is pitched at high krausen, and high krausen cells are in better health; therefore, they experience a shorter lag phase.

The cold hard truth is that stir plates were not designed for, nor are they used in yeast culturing outside of the home brewing community (orbital shakers are used in labs).  Their use in home brewing is based on "brewing by buddy," that is, my brewing friend uses a stir plate; therefore, it must be the way to do it.  This behavior is no different than "management by magazine" or "management by golf course" in the corporate world.

Yeast cultures grow at a rate of 2N, where N is the amount of time in minutes that have elapsed since the end of the lag phase divided the replication period (approximately 90 minutes for ales), which is why the growth phase is known as the exponential or log phase.  Any method that does not increase the viable yeast cell count by a factor of at least two is insignificant.  I have yet to see a repeatable published study using a stir plate that produces a two-fold increase in viable cell count over a well-aerated culture. 

The reason why a well-shaken starter works as well as it does for being such a low-tech method is because it takes advantage of physics and chemistry.  A gas dissolves into a liquid at the interface between the gas and the liquid; hence, surface area is critical to O2 pickup.  A gas-liquid foam has a very high specific surface area.  By shaking the medium until it is almost all foam, we create an amount of surface area that is impossible to replicate with a stir plate and an Erlenmeyer flask, and we do it at the beginning of fermentation when the O2 load on the medium is highest due ergosterol and UFA synthesis.  Bubbling a gas through a liquid with tiny bubbles creates the same kind of effect, but much less efficiently.   

The gas-liquid interface shrinks in an Erlenmeyer flask as the volume of media increases.  Stirring the culture fast enough to create a vortex increases the size of the interface between the liquid and the gas as well as creates a vacuum that helps to overcome the geometry of an Erlenmeyer flask, but it does so by increasing the amount of shear stress placed on the cells.  That's why stirred starters smell off when compared with non-stirred starters.  A lot of home brewers mistakenly equate the odor with continuous aeration, but no O2 is entering the flask after the culture starts to outgas. The geometry of an Erlenmeyer flask almost guarantees it, and  CO2 dissolves more readily in a liquid than O2.


I was wondering about the bolded because some people recommend periodically shaking. Once the culture is kicking off CO2 wouldn't shaking just put CO2 into solution?

I've been using 15 seconds of pure O2 just prior to pitching -- then leaving it alone -- and having great results. My starters are reaching high krausen in 5 to 7 hours, and I'm seeing fermentation activity within hours of pitching into the wort.

« Last Edit: August 30, 2015, 11:34:34 PM by johnnyb »