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Old 07-26-2009, 10:40 PM   #1
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Default Cell count from yeast starter

I'm curious about the cell count in a yeast starter compared to the cell count if the yeast were to reproduce after pitched into wort. For example, lets say I create a starter with x amount of yeast and the starter ends up with 4x cell count. Now lets say I pitch x amount of yeast into fermenter without a starter, will there eventually be 4x amount of yeast also or less? The 4 I'm using is a completely random guess, really I just want to be able to compare how much yeast there is with a starter vs no starter.

The reason I ask is this: I did a 2.5 gallon batch a few weeks ago and used WLP008. I didn't do a starter and should have only used 1/2 the vial, but accidentally used 3/4. So now I have 1/4 vial that I don't know what to do with. If i do a starter for my next 2.5 gallon batch will it build up a high enough cell count? If not I guess I'll just have to trash the rest of this vial.

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Old 07-26-2009, 10:49 PM   #2
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Use a multistep starter. Make a 1000mL starter, then bump it up to 2000mL by adding more wort to it. More yeast never hurts.

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Old 07-26-2009, 10:58 PM   #3
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I would pitch the whole vial on the 2.5 gallon batch, then use the yeast from that for a 5 gallon batch. Once I open a vial, I use the whole thing, once you've had air in it, or anything else, you don't know whats going on inside that vial anymore. A brand new, sealed vial is a pure culture.

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Old 07-27-2009, 03:51 AM   #4
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Thanks guys, more questions though...

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Use a multistep starter. Make a 1000mL starter, then bump it up to 2000mL by adding more wort to it. More yeast never hurts.
What type of container is typically used for a starter this size? A 1 gallon glass bottle?

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I would pitch the whole vial on the 2.5 gallon batch, then use the yeast from that for a 5 gallon batch. Once I open a vial, I use the whole thing, once you've had air in it, or anything else, you don't know whats going on inside that vial anymore. A brand new, sealed vial is a pure culture.
How about making 2 starters from a vial. The one I don't use I could put it in the fridge after a few days and then reprime it a couple days ahead of time with a bit more wort?

And I assume I need to keep the starter around 65 - 70 degrees while its active?
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Old 07-27-2009, 12:25 PM   #5
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I usually use a 1/2 gallon bottle or a 2000mL Erlynmeyer flask.

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Old 07-27-2009, 02:44 PM   #6
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Yeast reproduce to a certain concentration after which fermentation starts. The max concentration of yeast achieved is bound by the gravity of the wort, amount of available oxygen, and amount of available nutrients such as free nitrogen, zinc, or amino acids. Pitching without a starter may or may not yield the same number of yeast cells before fermentation begins depending on whether there is sufficient oxygen and nutrients available to support the number of generations that need to be produced.

A starter with unlimited oxygen (eg. on a stir plate) and plenty of available nutrients presents ideal conditions for yeast growth, and should yield between 10M and 15M cells per mL/*P of wort. For a 1.040 wort and a 1L starter that means you would get 100B to 150B of cells regardless of the amount pitched into the starter. The drawback of starting from fewer cells is that you will have more generations, and each generation depending on the strain can take between 1 and 3 hours to reproduce. Longer lag times means a higher percentage of unwanted nasties will end up in the starter and eventually your beer, since these guys (bacteria) can reproduce as frequently as once every 15 minutes or so. Once fermentation begins bacteria growth in inhibited, and once alcohol concentration reaches 2% or greater most bacteria die. This is the main reason why it is recommended to only step up by a factor of 10 or so in cell counts. For instance, I'll pitch a slant (which probably has 1M viable cells on it) into 250mL of *sterile* wort on the stir plate, wait 24 hours, and then pitch that into 1-2L of wort on the stir plate. After 24 more hours my starter is ready to pitch into 5 gallons with 150B-300B active yeast cells.

Wort doesn't present good conditions for yeast growth, unless you are making a 1.040 beer and you use an O2 stone to saturate the wort with oxygen before pitching. Even so I would still make a starter unless the yeast in question is very fresh, since yeast stored for long periods tends to have a long lag time increasing your chances of developing an unwanted infection. The recommended pitching rate is .75-1M cells/mL/*P for ales, and 1.5-2M cells/mL/*P for lagers. I typically aim for the upper end of the range for beers over 1.070 starting gravity, since the high sugar concentration both stresses the yeast and reduces the amount of oxygen I can introduce into the wort. Jamil's pitching calc
(Mr Malty Pitching Rate Calculator) will give you the .75M or 1.5M numbers depending on whether you select ale or lager.

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Old 07-28-2009, 11:37 PM   #7
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This is exactly what I needed, but I'm having a hard time working through the numbers. Help me figure out what I'm doing wrong here...

You say 1L starter of 1.040 wort will give 100 - 150 billion cells. So 1L = 1000mL and 1.040 = 10P. From this I get that I should have 10M to 15M cells per (1000/10) = 10 to 15M per (100). 10,000,000 * 100 is only 1 billion, how did you get 100 billion?

Also not sure where you get the .75M that mr malty uses for ales. I typed in 2.5 gallon batch with 1.06 OG, it says I need 104B cells. 2.5 gallon as liters is 3.8 * 2.5 = 9.5L, or 9500mL. 1.060 is close enough to 15P. So 750,000 per 9500/15 = 475M, not 104B.

What am I missing?

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Old 07-29-2009, 02:16 PM   #8
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It's 10M to 15M cells per mL per degree plato, so you have to multiply not divide by 10.

1000 (mL) * 10 (Plato) * 10M cells/(mL *P) = 100B cells.

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Old 07-29-2009, 09:48 PM   #9
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Saccharomyces, Thank you for the response in post #6.

David

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Old 07-30-2009, 02:45 AM   #10
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Doh, figured I was doing something dumb. Thanks

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