Author Topic: Determining yeast numbers?  (Read 3464 times)

Offline anje

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Determining yeast numbers?
« on: March 01, 2012, 01:22:19 PM »
I've only made a few batches of beer so far (first was quite good, second's still conditioning but seems promising, third's still fermenting), all with dry yeast. From reading here, it seems like one of the modifications I'm going to want to make soonest is to make yeast starters and start pitching them in larger quantities.

So I keep reading that it's important to pitch the correct amount of yeast for a good flavor profile, and I see calculators.  But how do you determine how much yeast you have? I don't have a spectrophotometer in my kitchen, and by the time I'd done plate counts the numbers would change significantly, even if I had the patience and equipment.  Surely numbers vary substantially based with the gravity of the starter wort and any limiting yeast nutrients, so we can't go by volume of a stationary phase culture when the yeast have flocculated, can we?
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Offline narvin

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Re: Determining yeast numbers?
« Reply #1 on: March 01, 2012, 01:26:28 PM »
I've only made a few batches of beer so far (first was quite good, second's still conditioning but seems promising, third's still fermenting), all with dry yeast. From reading here, it seems like one of the modifications I'm going to want to make soonest is to make yeast starters and start pitching them in larger quantities.

So I keep reading that it's important to pitch the correct amount of yeast for a good flavor profile, and I see calculators.  But how do you determine how much yeast you have? I don't have a spectrophotometer in my kitchen, and by the time I'd done plate counts the numbers would change significantly, even if I had the patience and equipment.  Surely numbers vary substantially based with the gravity of the starter wort and any limiting yeast nutrients, so we can't go by volume of a stationary phase culture when the yeast have flocculated, can we?

For cell counts, you'd use a microscope and a hemacytomer -- basically a slide that holds a known volume and has a grid etched into it for counting.  It's not all that expensive, but most of the time unnecessary.  Other people have done the work and made it pretty easy to estimate your cell count by starter size or slurry volume.  Obviously, you're still just estimating, and not taking into account things like the viability, but it's a repeatable process that you can use to get results you like over and over again.  Check out mrmalty.com for Jamil's calculator.
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Offline anje

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Re: Determining yeast numbers?
« Reply #2 on: March 01, 2012, 01:53:53 PM »
True, there are direct counts, though acquiring a respectable microscope seems easily as costly as a (basically indestructible) Spectronic 20. Slightly less bulky, though.
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Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #3 on: March 01, 2012, 11:53:21 PM »
True, there are direct counts, though acquiring a respectable microscope seems easily as costly as a (basically indestructible) Spectronic 20. Slightly less bulky, though.
I should get one of those, maybe they have one at UW surplus, a spec is way faster. :)

If you're going to stick with dry yeast, I think it is better to just buy an extra pack than to make a starter.  If it's not cheaper (and it might be) it is way easier and not worth it to save a little money.

If you're going to use liquid though, since that is more expensive, it makes more sense.  The online calcs are fine, but if you have access to a spec at work you can always take some samples of your finished starter in and measure them.  Once you have a feel for how your starters are performing you won't need to take samples any more.
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Offline thcipriani

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Re: Determining yeast numbers?
« Reply #4 on: March 02, 2012, 10:55:26 PM »
Any good links to resources for using a spec in brewing?
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Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #5 on: March 03, 2012, 01:07:18 AM »
Any good links to resources for using a spec in brewing?
I've got a sheet somewhere that correlates the spec reading with the density of the culture and thus cell counts.  It is not necessarily that accurate, but it will get you in the ballpark and if you want you can dial it in better for a specific strain by doing some plating and staining/scope work at the same time.  The sheet I have was generated for a common lab strain (S288C) and is good enough for a lot of lab work.  It's probably good enough for pitching, but I'd probably test it.

The only other use I can think of for a spec is determining beer color.  It's the ASBC standard method last time I looked.
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Offline thcipriani

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Re: Determining yeast numbers?
« Reply #6 on: March 03, 2012, 08:18:12 AM »
The other application that I think would be really awesome is determining FAN content for meads.

Looks like you could also do IBU: http://beersensoryscience.wordpress.com/2011/04/05/the-ibu-assay/

Also, looks like, could be used for carbon-filtered water chlorine, diacetyl, etc http://www.probrewer.com/vbulletin/archive/index.php/t-18167.html

I have to say that the lab part is one of my favorite parts of the process – almost as addictive as the brewing   ;)
Tyler Cipriani
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Offline dimik

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Re: Determining yeast numbers?
« Reply #7 on: March 03, 2012, 11:10:27 AM »
I would trust microscope with hemocytometer rather than specs or plates.
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Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #8 on: March 03, 2012, 04:00:54 PM »
The other application that I think would be really awesome is determining FAN content for meads.

Looks like you could also do IBU: http://beersensoryscience.wordpress.com/2011/04/05/the-ibu-assay/

Also, looks like, could be used for carbon-filtered water chlorine, diacetyl, etc http://www.probrewer.com/vbulletin/archive/index.php/t-18167.html

I have to say that the lab part is one of my favorite parts of the process – almost as addictive as the brewing   ;)
Good points, I was thinking about things you could do that didn't require hard to find or expensive reagents.  The need for iso-octane and octanol makes IBU determination a pain.  I don't know what might be required for the other assays.
Tom Schmidlin

Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #9 on: March 03, 2012, 04:02:00 PM »
I would trust microscope with hemocytometer rather than specs or plates.
Sure, it will be more accurate.  But it takes a long time, and the spec should be accurate enough while only taking a few seconds.
Tom Schmidlin

Offline anje

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Re: Determining yeast numbers?
« Reply #10 on: March 03, 2012, 08:39:09 PM »
I would trust microscope with hemocytometer rather than specs or plates.
Plate counts would be the most accurate, since they'd give a viable count. However, you have to have decent technique (change pipettes/tips at each point or your numbers end up completely screwed up, and good ways to accurately measure volumes) and plenty of plates. Easy enough for me to manage in my lab with lots of micropipettes and access to an autoclave, but I'd hate to attempt it in the tiny kitchen in my apartment.  In an ideal world you do growth curves correlating the optical density (probably at 600nm) with the plate counts in a growing sample -- again, this requires lots and lots of plates and seems like a hassle for someone like me who lacks dedicated space and equipment to do work with food organisms.
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Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #11 on: March 03, 2012, 09:18:21 PM »
I would trust microscope with hemocytometer rather than specs or plates.
Plate counts would be the most accurate, since they'd give a viable count. However, you have to have decent technique (change pipettes/tips at each point or your numbers end up completely screwed up, and good ways to accurately measure volumes) and plenty of plates. Easy enough for me to manage in my lab with lots of micropipettes and access to an autoclave, but I'd hate to attempt it in the tiny kitchen in my apartment.  In an ideal world you do growth curves correlating the optical density (probably at 600nm) with the plate counts in a growing sample -- again, this requires lots and lots of plates and seems like a hassle for someone like me who lacks dedicated space and equipment to do work with food organisms.
Not to mention that for a plate viability assay you've got to let the plates go overnight at a minimum, in order for the colonies to get big enough to see.  It's easier to count if you wait another night though.
Tom Schmidlin

Offline dimik

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Re: Determining yeast numbers?
« Reply #12 on: March 03, 2012, 10:16:15 PM »
Yeah but if you screw up your dilutions, there goes your count. And the time it takes... I'd just go trypan blue + hemocytometer route or just count and reduce to 80% as a general rule. If you're really into yeast counting and ranching you'll have to invest in a microscope any way you look at it. I don't think that a few seconds you might save with OD, if any at all since you have to calibrate with the same pre-fermentation starter, is worth sacrificing the accuracy.
« Last Edit: March 03, 2012, 10:18:30 PM by dimik »
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Offline tschmidlin

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Re: Determining yeast numbers?
« Reply #13 on: March 04, 2012, 12:01:12 AM »
Yeah but if you screw up your dilutions, there goes your count. And the time it takes... I'd just go trypan blue + hemocytometer route or just count and reduce to 80% as a general rule. If you're really into yeast counting and ranching you'll have to invest in a microscope any way you look at it. I don't think that a few seconds you might save with OD, if any at all since you have to calibrate with the same pre-fermentation starter, is worth sacrificing the accuracy.
Few seconds?  How fast can you count with a hemocytometer?  A lot faster than me apparently. :)

Running two samples on a spec will take less than a minute.  Besides that, if you can't dilute it without messing it up then your hemocytometer counts will be off anyway.

I think you can totally get by without a microscope.  Once you eliminate counting what do you really need it for?  That's not to say it's not awesome to have one, but you really don't have to have one for yeast ranching.
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Offline dimik

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Re: Determining yeast numbers?
« Reply #14 on: March 04, 2012, 12:22:58 AM »
Meh, maybe so. I've been counting cells for a long time and it's really easy after a while. You just count 40 and then directly convert by 0.1 into E6.
But on the other hand, would you really get a spec just to count cells? I mean I can see a use for a scope to look at stuff at home, but a spec? I guess you could use it for gravity measurements after playing around with it...
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