Author Topic: Stir Plate  (Read 659 times)

Offline flbrewer

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Stir Plate
« on: April 25, 2015, 06:36:14 PM »
I've never used one and my starters have always been great. What am I missing?

Offline Wort-H.O.G.

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Re: Stir Plate
« Reply #1 on: April 25, 2015, 06:43:48 PM »
seek the truth, and you shall find your answer  ::)
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Online brewday

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Re: Stir Plate
« Reply #2 on: April 25, 2015, 06:45:09 PM »
I've been using Mark's shaken (well, injected) not stirred method for a few months now.  I think my StirStarter is about to go on ebay.
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Offline erockrph

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Re: Stir Plate
« Reply #3 on: April 25, 2015, 08:02:26 PM »
I've never used one and my starters have always been great. What am I missing?
You answered you own question. If you're happy with how your starters and beers have been turning out, then you aren't missing anything. I've never used one, and I've never had a problem from not doing so.
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Offline denny

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Re: Stir Plate
« Reply #4 on: April 25, 2015, 08:16:32 PM »
I've never used one and my starters have always been great. What am I missing?

Not a lot.  I brewed for 15 years making starters without a stir plate.  I still wouldn't have one if someone hadn't given me one.  I can make starters in less time now, but that's about it.
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Offline Steve Ruch

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Re: Stir Plate
« Reply #5 on: April 26, 2015, 03:17:12 PM »
I've never used one and my starters have always been great. What am I missing?

Not a lot.  I brewed for 15 years making starters without a stir plate.  I still wouldn't have one if someone hadn't given me one.  I can make starters in less time now, but that's about it.

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Re: Stir Plate
« Reply #6 on: April 29, 2015, 04:46:14 PM »
The time savings, if any, that is achieved from using a stir plate only materializes if one is waiting for a starter to reach quiescence before pitching.  Waiting for a starter to reach quiescence is a less than optimal propagation practice because it increases the dissolved O2 demand and the length of lag period upon pitching.  Quiescent yeast cells have low to fully depleted ergosterol and unsaturated fatty acid (UFA) reserves.  These reserves have to be replenished before fermentation can proceed in earnest, and that process places a load on dissolved O2.

Ergosterol and UFAs make the cell plasma membrane more pliable, which, in turn, makes it possible for nutrients to enter the cell and waste products to exit the cell.  Additionally, pliability is critical to high gravity fermentation and ethanol tolerance.  High gravity wort provides an environment with high osmotic pressure (i.e., it is a hypertonic solution).  Osmotic pressure causes water to migrate across a semi-permeable membrane toward the side which has the higher solute content, which in this case is the wort.  This phenomenon results in cell shrinkage and the loss of turgor pressure.  Turgor pressure is the internal cell pressure that holds the cell plasma membrane against the cell wall. Ethanol is hygoscopic; therefore, it also draws water out of the cell, resulting in the loss of turgor pressure.  Cells that go into fermentation with healthy cell membranes are better able to withstand the effects of the high osmotic pressure and high ethanol levels encountered in high gravity brewing.

In synopsis, the health of the yeast cells that are pitched is more critical than the absolute number of cells that are pitched, that is, as long as the delta between the cells counts is within a few multiples.  Given two starters, one with 150 billion healthy cells that are pitched at high krausen and one with 250 billion cells that have reached quiescence, the 150 billion cell culture will outperform the 250 billion cell culture almost every time.