Author Topic: Maximum volume for a stir plate starter  (Read 4602 times)

Offline bmetzger

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Maximum volume for a stir plate starter
« on: December 15, 2011, 08:32:27 PM »
I have a recipe with a SG of 1.043, which dictates that I use 367 billion cells in a 6 gallon batch. I am planning on growing up Wyeast California lager. I only purchased 1 yeast packet and by adjusting the volume of starter in BS I can only achieve 335 billion with a stir plate.

When I increase the volume of starter in Beer Smith beyond 1.7 L the number of yeast cells won't exceed 335 billion?

Can't I pitch into a larger volume of starter wort (2L) and achieve the 367 billion recommended, or do I need to pitch into 1.7L decant and add another volume of wort to achieve the 367 billion recommendation?

Offline Neild5

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Re: Maximum volume for a stir plate starter
« Reply #1 on: December 15, 2011, 08:53:12 PM »
I have not taken the big step towards being a beer geek and actually counting yeast cells, some times I will do the calculations.  If I was brewing that light a beer and had fresh yeast I would think about skipping the starter.  The 1.080 batch I brewed with a 2.5L starter on a stir plate had CO2 bubbling at 2 hours after pitching.   
Currently my largest flask is a 2.8L Fernbach and typically I will only put 1.5L of starter to take advantage of the huge surface area and the stir-bar to really get the O2 levels up.

Offline tom_hampton

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Re: Maximum volume for a stir plate starter
« Reply #2 on: December 20, 2011, 08:27:48 AM »
The "yeast growth factor" parameter on the options page limits the amount of cells you can grow.  So, if your growth factor is 3.0 and you start with 100 billion cells it won't grow beyond 300 billion no matter what you do.  Beersmith seems to have an internal limit on the growth factor of 6.0.

These limits are artificial.  In real life, you will grown yeast cells as long as you increase your starter wort volume.  The only real limiting factor is the maximum cell concentration in the starter (~220 B/liter).
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Offline dharalson

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Re: Maximum volume for a stir plate starter
« Reply #3 on: December 21, 2011, 08:11:52 PM »
I personally think that the "yeast experts" have been pulling the wool over our eyes.  Yeast grow and grow and grow.  The size of the starter, the inoculation rate are not really growth factors, but rather growth limiters.  Yeast multiple by splitting into two cells and each cell will split about every 2-3 the right environment.  Meaning you have to have enough food and oxygen.  In the presence of oxygen (aerobic) yeast consume the starches and sugars and generate CO2 and water.  Without oxygen (anaerobic) yeast will produce CO2 and alcohol.  Alcohol is bad for yeast growth.  The benefit of the stir plate is to keep the yeast off of the bottom, expel the CO2 and to bring in air (oxygen). 

As Tom put it, the limit of growth is about a cell concentration of 220 M/ml or 220B/liter.  At this concentration, the yeast will pollute their environment to the point of stopping their growth.  All of the "yeast grow" is based on a very limit set of test conducted by Chris White.  The growth limit of 6 is because that is where he stopped in tests and that is based on 100B cells pitched into 5 gallon wort to make beer.  Beer is one of the worst environments if yeast growth is the goal.  You can make good beer or you can grow lots of yeast, but not both.
I would suggest splitting your starting yeast into to two pitches.  Store half in the refrigeration and make a starter with the other half.  That half (100 B) will grow up to the limit of your starter size; if you use the 1.5L your will get about 300B+. And you should only take about a day, maybe a bit longer.  Now switch, store the first starter and pitch your second batch.  In the end you should have about 600 B cells; or pitch 1/3, grow to about 300B then add the 2/3 (130 B) saved for a total of 430B. 

I am testing my theory now.  I pitch a very small amount of yeast; about a match head size (~500M cells) into 500ml.  I am letting the yeast settle out now to get an estimate of the growth.  I am expecting the original 0.06ml of yeast to yield around 5-10 ml of yeast.  That will be about 50 - 150 growth factor.  Since yeast growth is exponential  (ie 2n) that only represents 7 generations at the top end  (27 = 128 x the original count.

The other thing you should consider is using oxygen in the wort and pitching a bit on the higher temperature side for 12 hours or so.  In this environment the yeast will grow rapidly until they consume all of the oxygen.  At this point lower the temperature to the normal lager temperature.


Offline Ghosttrain

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Re: Maximum volume for a stir plate starter
« Reply #4 on: December 31, 2011, 03:29:32 PM »
Be careful pitching warm with a small and light lager.    You will get the growth, but also the by products from the growth.   If you want a cleaner beer pitch at your fermentation temperature and pitch enough yeast.   You can do a diacetyl rest near the end of fermentation for the yeast to consume the diacetyl, but other by products  from the yeast growth will still reside.  If you are flask limited, make two starters as suggested above to ensure you have enough yeast to pitch.

If you decant the excess starter put it in a glass and so you can smell and taste it.   Yuck!   As someone above said you can make the yeast grow or you can make beer, but the two are somewhat exclusive.   After a few tastes I have decided to always decant my excess starter "beer"