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Yeast Starter Calculation


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#1 Hoser

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Posted 09 March 2011 - 10:58 PM

So I've been trying to use liquid yeasts properly and am still learning. But based upon what I've read in How to Brew and seen on Mr. Malty, I will need a yeast starter for a Wyeast Activator pack if my OG is above 1048. I'm about to make a porter that will include all 3kg LME, 600g steeped grains, 500g molasses/brown sugar, 500g dextrose in a 19L batch. I expect this will yield approx 1076 OG assuming 36ppg on LME and steeped grains and 46ppg on sugar. Sorry new to this so not sure if I've calculated that correctly.

Anyhoo, assuming 1076 OG which equates to 19 degrees Plato, I calculated my yeast needs as 270 Billion cells. If I make a 2L yeast starter with Wyeast Activator, I should have 200 Billion cells from the original 100 billion cell packet.

So how do I go from 200 billion to 270 billion? Making a new 2L starter of the 2L starter will result in 400 billion cells won't it?

Or does it matter? Will underpitching around 200 billion cells be ok?

I think I had the math right. Just not sure how to now make the correct starter size. Hoping some of you homebrew gurus can help!

Thanks!

Edited by Hoser, 09 March 2011 - 11:00 PM.


#2 pimpsqueak

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Posted 09 March 2011 - 11:16 PM

Hey dude. Check out this post on stepped starters... http://www.aussiehom...showtopic=52586

I think that has the info you're after.

#3 felten

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Posted 09 March 2011 - 11:31 PM

You mention mr. malty but it sounds like you're working this stuff out without the aid of any software. Try plugging your numbers into this http://www.mrmalty.com/calc/calc.html for your yeast starter. Unless you're limited to a 2L starter size, you just increase the amount of wort to get more growth.

There's also a ton of programs and web based apps that you can plug your ingredients & batch size into to get a proper gravity estimate.

#4 Wolfy

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Posted 10 March 2011 - 12:21 AM

Use Beersmith, or one of the free/online beer-tools type programs, plug your ingredients in, and it will calculate the OG for you correctly.

Then take that number to MrMalty, but assuming your 19l @ 1.076 you are looking at 270billion yeast cells (so you got that right).
Now select the type of starter (I presume intermittent shaking) and then adjust the 'growth factor' slider until you the 'vials or packs needed' says 1.
The end result will be a starter size a bit over 5l (or 3.5l with a stir plate).

However, as you suggested, if you were to pitch a pack int a 2l starter then step that up to a 4l starter you'd end up with closer to 4billion cells, so one option may be to pitch the pack into a 2l starter then splitting that into 2x 2l starters.
Having said all that, it seems like alot of work for an extra 70billion cells in what is always a rough guessing game, so I'm not sure if it's worth the effort.

One more thing to consider is that one way to grow enough yeast cells for a high gravity beer is to make a lower gravity beer first and then repitch the yeast from that.

#5 felten

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Posted 10 March 2011 - 12:42 AM

The end result will be a starter size a bit over 5l (or 3.5l with a stir plate).

Your viability % must be pretty low to get that, It's a little over 2L with a fresh pack.

#6 Wolfy

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Posted 10 March 2011 - 01:09 AM

Your viability % must be pretty low to get that, It's a little over 2L with a fresh pack.

I assumed a 2 month old pack (guessed to fit with the info in the OP) - but yeah, that's one area where there is heaps of guess work involved.

#7 Hoser

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Posted 10 March 2011 - 09:21 PM

Thanks guys. I struggled with what a few of the things on Mr Malty meant in the calculator but I think I get it now. It's an Activator Yeast that's got a December 6'10 manufacture date so 3mths old. Assuming I'll have a look at beersmith to confirm my OG and then try plugging it into Mr Malty again. Do you have to purchase the beersmith calculator?

Guessing the older date on the yeast significantly reduces viability meaning I need another packet for my starter. Starts to get trickier with an old packet and a new packet though when using Mr Malty to calculate. Any ideas how to overcome that?

#8 Hoser

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Posted 10 March 2011 - 09:25 PM

Just noticed the beersmith calculator is only available in Windows. Anyone know a calculator for Mac's?

#9 pmash

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Posted 10 March 2011 - 09:33 PM

Just noticed the beersmith calculator is only available in Windows. Anyone know a calculator for Mac's?

Have a look at beer tools pro, mac based

Cheers

#10 felten

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Posted 10 March 2011 - 10:10 PM

Guessing the older date on the yeast significantly reduces viability meaning I need another packet for my starter. Starts to get trickier with an old packet and a new packet though when using Mr Malty to calculate. Any ideas how to overcome that?

hmm say your old packet is 30% and your new packet is 100%, that's 130 billion cells, which is equiv to 2 packets at 65%?

#11 Wolfy

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Posted 10 March 2011 - 11:57 PM

Do you have to purchase the beersmith calculator?

Guessing the older date on the yeast significantly reduces viability meaning I need another packet for my starter. Starts to get trickier with an old packet and a new packet though when using Mr Malty to calculate. Any ideas how to overcome that?

There are a number of free web-based software solutions, you could easily use one of those.

If you are going to make a starter, and can make a stepped starter, there is no need for a second fresh pack of yeast.
By using two steps, the production date (and hence the viability) is less relevant because the yeast will reproduce enough in the first step to ensure you have more than ample to propagate into the second step (think of the first step as a brand new pack with ~60-120billion cells that were born in your starter yesterday).
Hence if you pitch the single old pack into 2l of wort, shake/stir for a day or so, then pitch that starter into 4l and you should be close to the expected cell density of around 100million cells per ml (or 400billion cells in your 4l) - adjust down for a shaken starter and you'll be pretty close to your target value. :)

Edited by Wolfy, 10 March 2011 - 11:58 PM.


#12 Hoser

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Posted 11 March 2011 - 04:13 PM

Found an online calculator that confirmed estimate of 1070. Thanks Wolfy makes sense. I'll make a 2L starter of my current pack and then after a day pitch that to a 4L starter.

When you make a starter of a starter do you pitch the full 2L of fermented wort into another 2L of unfermented wort? Or do you drain off the top beer and just pitch the yeast at the bottom?

Cheers!

#13 Wolfy

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Posted 11 March 2011 - 04:29 PM

When you make a starter of a starter do you pitch the full 2L of fermented wort into another 2L of unfermented wort? Or do you drain off the top beer and just pitch the yeast at the bottom?

When making a starter I simply add the new wort without letting the yeast settle out.
However, when its time to pitch the yeast into your batch of beer, I prefer give the yeast some more time to settle out, decant the spent wort and pitch only the yeast.

#14 Hoser

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Posted 11 March 2011 - 04:49 PM

Ok makes sense. So how do I calculate how many cells I have at the end of the first starter and then at the end of the second starter. I cheated on Mr Malty by playing with the OG number to show that a yeast packet with 6 Dec'10 date will yield 130 Billion cells in a 2L starter.

But then how do I calculate how big the yeast cell count will be when I double the starter size to 4L? Struggling to understand how you calculate that...

#15 Hoser

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Posted 11 March 2011 - 05:05 PM

Just tried playing with Mr Malty calc. If I say 100% viability it tells me that I need a 1.7L starter for 240 billion cells (what I require for a 1070 OG / 19L wort volume). If I make a 1.1 L starter with 30% viability (6th Dec date), it yields 100 billion cells. This would be the same end result as a 100% viability pack wouldn't it?

Assuming that I have 100 billion cells in a 1.1 L starter, if I then add 1.7L wort will that arrive at 240 billion cells?

I did all these calcs on Mr Malty at intermittent shaking.

Is that making sense?

#16 Wolfy

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Posted 11 March 2011 - 06:48 PM

Is that making sense?

MrMalty is not setup to deal with stepped-starters, it can only calculate what will happen if you pitch a pack of yeast directly into a starter before pitching that into your beer.
To get some estimate, I'd assume that the first step of your starter (2l) would have about as many cells as a fresh pack, then use MrMalty with 100% viability - however you already have a 2l starter so add another 2l (or 1.7 according to what you said MrMalty said) and you will be close to what you want.
Which is also close to what you'd get by simply assuming an expected cell density of around 100million cells per ml.

#17 Hoser

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Posted 11 March 2011 - 07:10 PM

ok thanks makes sense. Hey so should I use yeast nutrient in both starters? On that, is it good to also put yeast nutrient into the boil?

#18 raven19

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Posted 11 March 2011 - 08:08 PM

I use yeast nutrient in the boil for sure, however previous AG batches without it have not suffered in terms of attenuation thus far for me.

A little extra nutrient in the starter cannot be a bad thing imo.

#19 Hoser

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Posted 11 March 2011 - 08:50 PM

Cool thanks - ready to get it going tomorrow!