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Old 01-12-2010, 06:12 PM   #1
chrisedjohn
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Default Help pitching the right amount for lager

I'm planning on brewing this Saturday and will make a starter in the next few days. It's my first lager and I want to make sure I pitch the right amount. The yeast I will use came from a friend who works at a local brewery. They brewed back in December - so it's about 1.5 months old. When I first got it, I washed with sterilized water and put into a few mason jars, about 6 grams slurry in each. The calc from Mr. Malty tells me that with a harvest date of early december, I'd need 387 billion cells, or 614 ml of yeast.

If I just make a big 2 liter starter a few days before from one of these jars, do you guys think that'll do it? Should I start with several jars into the starter? Is there any way for me to approximate how many billions of yeast cells I'd have if I made an X sized starter?

My volume will be about 5.75 gal of 1.048 wort to ferment at 50 F for 3 weeks before lagering in the 30s for 3 more.

Thanks for any experience you can share with me!

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Old 01-12-2010, 07:06 PM   #2
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The calc from Mr. Malty tells me that with a harvest date of early december, I'd need 387 billion cells, or 614 ml of yeast.
That number of cells you need is independant of yeast viability. You'll need 387B cells regardless of viability. Yeast viability just tells the calculator about how many cells you actually start with.

If you click the 'Repitching from slurry' tab you'll see that a thin slurry is approx. 1B cells per ml and a thick slurry is 4.5B cells per mL. You can approximate your starting yeast count by multiplying your slurry volume (in mL) by 4.5B (this is settled yeast in a jar).

When I put December 1st in the liquid yeast 'Production Date' box, it says the viabilty is 67%. So multiply the result you got above by .67 and that should tell you about how much yeast you are starting with. It's a gross approximation but it's about all we can do.

In the liquid yeast tab, the yeast viabilty percent is actually telling you how many billions of yeast cells you are starting with (this is because a fresh vial/Activator pack is ~100B cells, so 67% is 67B cells and 150% is 150B cells). Yes, you can enter a percentage greater than 100.

So now you can just enter the billions of yeast cells in the 'viability' box, make sure the '# vials or packs needed with starter' is 1 (if not, slide the Growth Factor bar all the way to the right), enter all the other info for your beer, and it should tell you how big of a starter you need.

Wow, that got long and it looks way more complicated than it really is.

EDIT: If you didn't get all that, if you could post the approximate volume of your yeast slurry in mL (that's settled yeast in a jar) then I'll go through the entire example with your numbers.
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Last edited by SpanishCastleAle; 01-12-2010 at 07:11 PM.
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Old 01-12-2010, 07:28 PM   #3
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Wow - you're very helpful, thank you. I have quite a bit on my hands that I could use - half a mayonaise jar full of solid, settled yeast. It sounds like all I'd need is to pitch 5 oz of settled yeast - just over a half cup - which I do have and then some. So my options now are whether I make a small starter to "wake" them with or just pitch enough of that after I let it rise to temp. It sure would be convienient to just pitch enough of that slurry at 50-55F w/o having to make a starter - what do you guys think of that? Any significant downsides?

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Old 01-13-2010, 01:40 AM   #4
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You could just use a slurry or you could use the pitch rate calculator to figure out how much yeast you'd need to make one of your typical starters. Like if a typical starter size for you was 2L, you could calculate how much yeast slurry you should start with to get your 387B cells in a 2L starter. Depends on how long you want to stretch out that yeast.

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