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Old 12-08-2010, 02:45 PM   #1
c-note
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Default Multi-step starter

I have a question about yeast starters. I've been doing 10-gallon lager batches lately and have been doing about a 2-gallon starter for the 10 gallons. I originally had only one 5L (~1 gallon) flask so I would do a 1 gallon starter, let it ferment completely and settle out, decant the liquid, and then pitch another 1 gallon of wort onto the yeast cake. That is a total of 2 gallons but done in two steps.

My understanding of yeast is that they multiply until they reach some critical density and then reproduce no more, but do continue to ferment.

If that is true, then in the above process when I pitch the second gallon of wort on the yeast cake, won't the yeast simply ferment the wort without much reproduction - since the yeast will already be at the critical density? So the amount of yeast before pitching the second gallon of wort is about the same as after the second gallon has been fermented? I know that not all yeast settle out once fermentation is complete - this question is more qualitative than quantitative.

What I am currently doing is using two 5L flasks. I'll ferment the first gallon as described above, then split it between the two 5L flasks, and then split another gallon of wort between them.

Do the two processes described above produce the same amount of yeast? Or does the second method produce more yeast?



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Old 12-08-2010, 06:19 PM   #2
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Quote:
Originally Posted by c-note View Post
I have a question about yeast starters. I've been doing 10-gallon lager batches lately and have been doing about a 2-gallon starter for the 10 gallons. I originally had only one 5L (~1 gallon) flask so I would do a 1 gallon starter, let it ferment completely and settle out, decant the liquid, and then pitch another 1 gallon of wort onto the yeast cake. That is a total of 2 gallons but done in two steps.

My understanding of yeast is that they multiply until they reach some critical density and then reproduce no more, but do continue to ferment.

If that is true, then in the above process when I pitch the second gallon of wort on the yeast cake, won't the yeast simply ferment the wort without much reproduction - since the yeast will already be at the critical density? So the amount of yeast before pitching the second gallon of wort is about the same as after the second gallon has been fermented? I know that not all yeast settle out once fermentation is complete - this question is more qualitative than quantitative.

What I am currently doing is using two 5L flasks. I'll ferment the first gallon as described above, then split it between the two 5L flasks, and then split another gallon of wort between them.

Do the two processes described above produce the same amount of yeast? Or does the second method produce more yeast?
I think you understand that you are not growing your 2nd pitch of 1 gallon by a heck of a lot. There is a good video out there on steppnig up a starter, search this forum for it. I do not think splitting your 2nd pitch does anything different. What I do, is I start with 1 gallon, then add 2, etc to get high growth. Check the video....


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Old 12-08-2010, 06:47 PM   #3
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Why not just make a 5 gallon batch of beer (with the 1 gal starter if the yeast is fresh) and then use the cake to make 10 gallons

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Old 12-08-2010, 06:49 PM   #4
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Here is the link to the video I think the above poster was talking about:
Step up video

But according to the chart from JZ new book you would end up with about 300 billion yeast cells after first step, then after 2nd step you will end up with about 550 billion yeast cells.

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Old 12-08-2010, 06:49 PM   #5
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You're exactly right that the second 1gallon step isn't doing too much. Have you ever looked at Wyeast's pitch rate calculator? It can help you figure out multisteps.

http://www.wyeastlab.com/hb_pitchrate.cfm

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Old 12-08-2010, 06:59 PM   #6
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Ok guys -thanks for the info.

coypoo - After reading Bob's thread about pitching on yeast cakes I don't do that anymore. I also rarely do 5-gallon batches but I do understand your suggestion and it would be useful in some cases.

kanzimonson - Thanks for the link, I'll play around with the calculator. It doesn't take into account decanting between steps but that doesn't seem to be a good idea and I'm not going to do that anymore anyway.

jjones17 - Thanks for the feedback although we might disagree. I think splitting and adding an additional gallon is ok. I'm essentially starting with one gallon, fermenting that, then adding another gallon. I don't think splitting into two vessels changes anything, but I may be mistaken.

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Old 12-08-2010, 07:06 PM   #7
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One more thing. I do a lot of reharvesting my yeast, but frequently I'll choose to split the yeast into lots of mason jars rather than just a couple. This always results in me having less than enough slurry in one jar for a batch, unless I make a starter. So how do you figure out what size starter to make when you have X mL of slurry? Here's the method I use (reposted from somewhere else). You might be able to use the info:

Let's say I'm making a 1.060 ale, pitching 5.5 gallons. I have a jar of reharvested slurry that is exactly four weeks old from today, and the yeast is very compacted into a 50mL puck. I go to Mr Malty, set the parameters of my beer, set the age of the yeast, go to the "Reharvesting" tab, set the Yeast Concentration to 4.0, set the Non Yeast Percentage to 15.

Mr Malty says that I need 229billion healthy yeast cells, which would be 134mL of my yeast in its current state. I have 50mL, or 37% of what I need (50/134). If you multiply 37% by 229billion cells, you find that I have about 84billion healthy cells.

Here's where things get fuzzy. As I understand it, the Mr. Malty calculator works such that a vial of yeast with 100% viability has 100billion cells. So if I have 84 billion cells, this is the equivalent of having one vial of yeast at 84% viability, right? So then I flip to the Liquid Yeast tab, manually set my viability to 84%, set the Growth Factor so that it says I need 1 vial. Doing this, it says I need to make a 1.23L starter with a stir plate



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