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Author Topic: Orbital Shaker  (Read 9684 times)

S. cerevisiae

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Re: Orbital Shaker
« Reply #15 on: June 29, 2015, 12:41:31 pm »
If the shaker continually aerates the starter, will you still pitch the entire thing rather than chilling and decanting the supernatant?

Neither a shaker, nor a stirrer continuously aerates a culture.  Very little to no O2 enters a flask after a culture starts to produce CO2.  CO2 heavier than air, and the culture is under positive pressure; therefore, air is not entering the flask.

With that said, I do not plan to use the shaker in continuous mode.  I plan to experiment to see if there is a difference between a starter made with my method and one that is shaken for a period of time and left to incubate.

« Last Edit: June 29, 2015, 09:05:05 pm by S. cerevisiae »

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Re: Orbital Shaker
« Reply #16 on: June 29, 2015, 05:21:22 pm »
Very little to no O2 enters a flask after a culture starts to produce CO2.  CO2 heavier than air, and the culture is under positive pressure; therefore, air is not entering the flask.

So the increased cell count from an unstirred to a stirred starter is entirely (or almost entirely) due to agitation of the yeast?
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S. cerevisiae

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Re: Orbital Shaker
« Reply #17 on: June 29, 2015, 09:26:54 pm »
So the increased cell count from an unstirred to a stirred starter is entirely (or almost entirely) due to agitation of the yeast?

I have seen no professional-level peer-reviewed publication that proves that an agitated starter produces more viable cells than a well-aerated starter that is not agitated.  Most of the home brewer tests compare a non-aerated starter to a stirred starter.  If one were shake an Erlenmeyer flask like I do a media bottle, there would be wort all over the room.  That's why I use a screw cap media bottle.  The best that one can do with an non-screw cap Erlenmeyer flask is a vigorous side-to-side rocking motion.  That's not well-shaken in my book.

With that said, I am not the only home brewer who has reached the conclusion that agitation with brewing yeast is overrated.  I discovered that Steven Deeds was becoming skeptical of stir plate results around the same time that I started to believe that stir plates were modern snake oil.  He recently published results of a test that he ran, which are linked below.  I do not agree with all of his results, but I do agree that stir plates produce no more viable cells than a well-aerated starter that is not agitated.

http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html

Offline jjflash

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Re: Orbital Shaker
« Reply #18 on: June 29, 2015, 09:45:15 pm »
Thought I would show pictures of my twins.

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Offline jjflash

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Re: Orbital Shaker
« Reply #19 on: June 29, 2015, 09:48:01 pm »
---JJ---

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S. cerevisiae

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Re: Orbital Shaker
« Reply #20 on: June 29, 2015, 09:51:02 pm »
Do you experience any over-foaming problems with your Fernbach flasks?

S. cerevisiae

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Re: Orbital Shaker
« Reply #21 on: June 29, 2015, 10:00:16 pm »
I just looked that model up.  It appears to be a well-built orbital shaker for the price, even if it is made in Taiwan.  DOTMED is selling the Gemmy VRN-360 new for $330.00.  That's still a lot of money for a home brewery, but it's a lot cheaper than the U.S. and European-made orbital shakers.

Offline narcout

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Re: Orbital Shaker
« Reply #22 on: June 30, 2015, 09:42:13 am »
Thought I would show pictures of my twins.

Cool. 

Can you describe your process (do you oxygenate or aerate the starters prior to using the shaker, how vigorous is the agitation, do you decant the supernatant, etc.)?
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Offline narcout

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Re: Orbital Shaker
« Reply #23 on: June 30, 2015, 10:16:19 am »
I found something interesting re agitation (though perhaps not conclusive): http://www.academia.edu/3890122/Factors_affecting_the_growth_of_Saccharomyces_cerevisiae_in_batch_culture_and_in_solid_state_fermentation

"As can be seen from Fig. 1, the increase in agitation speed from 50 to 250 rpm led to an increase in biomass production (Fig. 1). This paralleled with the increase in the specific growth rate, sugar and nitrogen consumption and pH reduction (Fig. 2). However, the effect of increased mechanical agitation on the viability of Saccharomyces cerevisiae appears to be negative, with higher levels of dead cells present at the end of the cultures (Fig. 3).

Previous works [20] on the effect of mechanical agitation on the viability of yeast cells did not report cell damage at agitation speeds values higher than the maximum value used in the present study. Since in this work, the nutrients (carbon and nitrogen) consumption increased with increased agitation intensity (Fig1), this last variable is unlikely to have a physical effect on the growth of Saccharomyces cerevisiae.

Thus, the loss of viability observed at the end of the cultures could be due to the depletion of both carbon and nitrogen sources (Fig. 2) rather than to fluid-mechanical stresses caused by agitation [20]. However, the combination of both effects with the production of toxic metabolite (such as ethanol) may cause higher loss of viability than each factor alone."
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narvin

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Re: Orbital Shaker
« Reply #24 on: June 30, 2015, 01:11:58 pm »
I found something interesting re agitation (though perhaps not conclusive):

If I read this right, the culture that they're stirring it sucrose plus yeast nutrient, inoculated at 2 million cells / ml at 86 degrees F.  That's approximately 2% of a homebrew yeast vial in a liter.  Not sure if this is really applicable to the way homebrewers make starters.

Offline AmandaK

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Re: Orbital Shaker
« Reply #25 on: June 30, 2015, 02:11:30 pm »
Thus, the loss of viability observed at the end of the cultures could be due to the depletion of both carbon and nitrogen sources (Fig. 2) rather than to fluid-mechanical stresses caused by agitation [20]. However, the combination of both effects with the production of toxic metabolite (such as ethanol) may cause higher loss of viability than each factor alone."

With all this discussion about shakers/stirrers/hand shaking/etc, this is what I'm really curious about.
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S. cerevisiae

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Re: Orbital Shaker
« Reply #26 on: June 30, 2015, 02:34:20 pm »
If I read this right, the culture that they're stirring it sucrose plus yeast nutrient, inoculated at 2 million cells / ml at 86 degrees F.  That's approximately 2% of a homebrew yeast vial in a liter.  Not sure if this is really applicable to the way homebrewers make starters.

It depends on who you are counting as a home brewer.  The first-level culture that I grow from slant is 40ml in volume.  I routinely pitch the yeast from a 40ml first-level starter into 1L of 10% wort.   If manage to reach maximum cell density in that 40ml, I am still only pitching 8 million cells per milliliter, which is less than 1/12th of the pitching rate of someone who is pitching a White Labs vial.

As strange as it may sound, sucrose is the primary carbon source on which dry yeast is grown.

S. cerevisiae

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Re: Orbital Shaker
« Reply #27 on: June 30, 2015, 02:46:13 pm »
However, the effect of increased mechanical agitation on the viability of Saccharomyces cerevisiae appears to be negative, with higher levels of dead cells present at the end of the cultures (Fig. 3).

This finding correlates with what I have been saying about stir rate and shear stress.  Spinning the bar fast enough to aerate a culture results in shear stress being placed on the cells.  In essence, one achieves a higher cell count with a higher stir rate, but the cells are less healthy; therefore, nullifying the effect.

Here's a paper on shear rate in stirred tank and bubble column bioreactors: http://www.massey.ac.nz/~ychisti/ShearRate.pdf

Quote
1) shear rate influences the average apparent viscosity of non-
Newtonian fluids and hence affects power absorption, mixing
characteristics and mass transfer phenomena[1] ; (2) microor-
ganisms, bioflocs and other suspended solids are susceptible to
damage that is dependent on the prevailing shear rate and asso-
ciated shear stress
[2,3].



Offline jjflash

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Re: Orbital Shaker
« Reply #28 on: June 30, 2015, 08:03:48 pm »
Do you experience any over-foaming problems with your Fernbach flasks?

Never had over-foam issues with these Fernbach flasks.  I use them for the first and second step propagation so my max volume in 2.8L flask is only one quart.  I can wort starters in quart jars so that is the max volume used in these flasks.  Third step up is in the 5L Erlenmeyer flask which uses a portion of the wort from the intended beer.
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Offline jjflash

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Re: Orbital Shaker
« Reply #29 on: June 30, 2015, 08:12:32 pm »
I just looked that model up.  It appears to be a well-built orbital shaker for the price, even if it is made in Taiwan.  DOTMED is selling the Gemmy VRN-360 new for $330.00.  That's still a lot of money for a home brewery, but it's a lot cheaper than the U.S. and European-made orbital shakers.

They look great on the outside.  Adjustable RPM with gauge.  Bought mine used and disassembled to clean them up.  Look rather whimpy inside, small motor in big housing.  Runs the Fernbach's with ease for 48 hours.  The 5L Ernlenmyer I fill to max 3L, which are quite heavy.  Loads the motors but still running strong and yet to burn one out.  Will see what kind of mileage I get out of these. 
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