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Old 02-13-2012, 05:19 AM   #1
orcus332
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Default Yeast starter: volume size, yeast numbers

I'm going to be making a starter for a bells two hearted clone soon. I'm harvesting the yeast from bottles of Bells amber ale.
My calculated OG is 1.062 and a batch size of 5.5g. Using mr.malty it looks like i'll need around 1.5L of starter to get my yeast numbers up to a sufficient pitching amount.

The more I think about stepping up a starter, the more i'm confused about the final number i'm shooting for (1.5L) and I'm hoping someone can spell this out for me.

It's my understanding that If I just make a 1.5L starter out of an arbitrary amount of DME, say 12 oz I will end up with X amount of yeast (this is without stepping up at all).

Now say, i step up, and i go from 2oz, 4oz, 8oz, 12 oz of DME with my last step up of 12 oz going into 1.5L. The total DME i've used for this would be 26oz compared to the no-step up where i used 12 oz.
I would think the the step up would have higher yeast numbers than the non-step up method because they've gotten more "food" (dme). However, the final volume is still the same (1.5L).

This is where I am confused. Does the final volume of starter even really matter, or is it more about the amount of DME that you use that will influence how many yeast you end up with?
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Old 02-13-2012, 08:23 AM   #2
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Originally Posted by orcus332 View Post
This is where I am confused. Does the final volume of starter even really matter, or is it more about the amount of DME that you use that will influence how many yeast you end up with?
If you're not lost yet, congrats, i owe you a beer.
Well, neither, really. What's important is the cell count that you pitch.
The idea behind a starter is to take a particular amount of cells (say 100Billion, which is what you get in a single vial) and propagate the yeast until you get the right amount for your particular wort. On the way you are also proving cell viability, and improving cell condition so that the yeast can get right to work on your wort.

The amount of cell growth is nonlinear, and is a function of inoculation rate (how much yeast did you put in the starter) and starter size. Mr. Malty figures out the inoculation rate based on what kind of yeast you are pitching (vial, slurry, etc) and how old it is. Using that, and the numbers for your wort, it solves for the starter size you'd need.

In your particular case, since you are propagating yeast from a bottle, you are going to start with very little yeast, and it will be in very poor health (compared to if you had a full vial of healthy yeast). Therefore, you should treat it carefully and let it gather strength slowly. This means that you should definitely use a step up starter, and further more, that you should step up not only the volume but also the gravity.

I would suggest starting with a 50-100ml 1.025 starter, stepped up to 250-350, 1.035 and finally 1.5L 1.040 as Mr Malty suggests. This way your yeast gets a chance to work on wort that has lower osmotic pressure first, and propagate healthy cells first, before it is called upon to work on the "real" starter.
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Old 02-14-2012, 06:32 AM   #3
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Thanks boist. I'm working on my 3rd amber ale right now. Had to take three for the team in the name of science. I started with 50mls of 1.020 wort and will likely step it up as you outlined. Cheers.

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Old 02-14-2012, 10:19 AM   #4
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Thanks boist. I'm working on my 3rd amber ale right now. Had to take three for the team in the name of science. I started with 50mls of 1.020 wort and will likely step it up as you outlined. Cheers.
Check this out too. Bell's Amber Harvest
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