[mabrungard]

Last night, I attended a seminar in Indy presented by one of the Omega Yeast founders, Lance Shaner. There was one aspect of the presentation that caught my attention. He contends that its not truly applicable to target Cell Count as our metric for yeast starters. He said that the diameters of various yeast variants differ substantially and the amount of mass that those cells contain, also varies. For example, he said that Weizen yeast has much larger diameter and cell mass than something like a Saison yeast.

He went on to state that yeast growth calculators aren't necessarily accurate at predicting starter cell counts due to the differing individual cell mass. However, he did say that their research shows that for a given starter size and gravity, the total biomass produced is relatively consistent...regardless of the cell mass differences between yeast variants. So you might get a far lower cell count when growing a Weizen starter compared to the same size Saison starter, but the sum of yeast mass in each starter is going to be quite similar.

That was surprising to me, but its not when you figure that the yeast are probably utilizing the wort and growing biomass at the same rate, but putting it in different places. One makes fewer, but bigger cells and another makes more numerous, but smaller cells. He did say that pitching rate calculators are flawed do to these factors, they are still reasonably valid for sizing starters.

The final aspect that surprised me was that it is the amount of yeast biomass added to your batch that matters, not cell count. That also translates to a volume of high-viability yeast slurry that should be added to your batch. When he was pinned down, Lance did say that a typical gravity 5-gallon batch would need about 50 mL of high-viability yeast slurry. As I recall, the old clear White Labs yeast tubes probably held about that much slurry. That sounds like an easy to remember guideline for how much yeast slurry we should really be pitching into our batches if you're repitching slurry. Overpitching or pitching directly on a yeast cake may not be best for fermentation.

Give this some thought!

[denny]

I'm not surprised.  It's basically the idea behind the SNS starter. I haven't done anything else for over 2 years.

[ynotbrusum]

Lance is a good guy - he gave a talk to our club a year or so ago.  I wonder if he would suggest a slightly bigger volume for lagers than ales (as is the conventional wisdom)?

[dmtaylor]

This makes a lot of sense.  Elegant in its simplicity.  Or something.

Now we can all put our microscopes and counter grids away.  Yay!

For the record, I have never ever counted yeast cells.  Ever.  However I do own two microscopes, which I haven't used at all since I was a teen. 

[denny]

This makes a lot of sense.  Elegant in its simplicity.  Or something.

Now we can all put our microscopes and counter grids away.  Yay!

For the record, I have never ever counted yeast cells.  Ever.  However I do own two microscopes, which I haven't used at all since I was a teen. 

Dude, it's been so long since I've used a stir plate, I don't even know where it is any more.  In our talk at HBC, I said "Stop using yeast calculators and throw away your stir plate!".

[dmtaylor]

This makes a lot of sense.  Elegant in its simplicity.  Or something.

Now we can all put our microscopes and counter grids away.  Yay!

For the record, I have never ever counted yeast cells.  Ever.  However I do own two microscopes, which I haven't used at all since I was a teen. 

Dude, it's been so long since I've used a stir plate, I don't even know where it is any more.  In our talk at HBC, I said "Stop using yeast calculators and throw away your stir plate!".

Great to hear, Denny.

For the record, I also do not own a stirplate, never owned a stirplate, and never will use one.

Okay, gents, I did a little mathematics to make better sense of all this........

There are 5 mL in a teaspoon.  Therefore if we need 50 mL / 5 gallons, that's 10 teaspoons / 5 gallons, or 3.33 Tablespoons per 5 gallons, or 2 teaspoons/gallon.....

Or for my oddball 1.67-gallon batches, I need roughly 1 Tablespoon.  Yay.  But of course, since I mostly use dried yeast these days, I'll just continue to use a gram or two per batch.   

[denny]

I think yer gonna love our next book.

[Robert]

That 10 mL/gal biomass assumes 100% viability, right?

I go by volume, because that's all I can do.  When I repitch, my SOP is to let the yeast pack down hard in the jar,  rouse it into the liquid for a total volume 2x that of the yeast layer, and pitch 6 oz of that (so 3 oz of the slurry) to 6 gal.  Experience says that's about right.   I suppose that volume of slurry might well contain about 10 mL/gal of viable yeast.

Seems to jibe with the recommendation here.

FWIW I increase the volume by about 1/3 to 1/2 for lager yeast if I'm pitching around 50°F.  Seems to work right.  I would think that lager yeast is just yeast, and if pitched at say 60°F, it would not need an increase, but would grow sufficiently.  Would be nice to hear from the expert.

[dmtaylor]

I think yer gonna love our next book.

Lemme know if you guys need any help.      

[denny]

I think yer gonna love our next book.

Lemme know if you guys need any help.      

Too late..turned in final revisions yesterday!

[dmtaylor]

I think yer gonna love our next book.

Lemme know if you guys need any help.      

Too late..turned in final revisions yesterday!

I'll look forward to the final published copy. 

[Todd H.]

Fermentis talks in terms of biomass too rather than cell numbers.

[denny]

Fermentis talks in terms of biomass too rather than cell numbers.

As does Clayton Cone of Lallemand.

[Saccharomyces]

Lager yeast cells also tend to be smaller than ale yeast cells.  That is why I have always prefaced maximum cell density with the word "approximately." Maximum cell density is based on the space between cells while the culture is in suspension, not count.  A smaller cell size results in a higher cell count before maximum cell density is reached.

Amateur brewers get far too wrapped around the axle when it comes to yeast cell counts.  Yeast cultures are truly like nuclear weapons in that close with healthy cells (i.e., cells with good plasma membrane health) is more than good enough because a culture grows exponentially until maximum cells density is reached or the medium is spent.

The reason why high gravity beer requires a larger biomass is because it is more difficult to dissolve O2 in high gravity wort and osmotic pressure is high.  Osmotic pressure occurs when the solution on the outside of the cells has a higher solute (what is dissolved in the solution) level than the fluid inside of the cells.  Water is drawn to the side of the plasma membrane with the higher solute level, which is the wort.  The migration of fluid from inside of the cell to the wort causes the cells to shrink and the cell membrane to lose turgor pressure (turgor pressure holds the cell membrane up against the cell wall), which can result in cell implosion.   That is why it is a good practice to pitch at high krausen instead of waiting for a culture to ferment out.  Pitching at high krausen yields the maximum viable biomass while ensuring that the cells still have strong and pliable plasma membranes due to having good ergosterol and unsaturated fatty acid reserves (UFA).  Waiting until the cells have reached quiescence (fermented out) before pitching results in a brewer pitching cells that have lower ergosterol and UFA reserves; thus, weaker and less pliable cell membranes.  That is why I tell people to ditch the stir plate until quiescence is reached approach that has become fashionable in the last decade or so.  A stir plate does not buy a brewer much when growing yeast biomass because brewing cultures tend to stay in suspension until the sugars that a culture can break down to glucose becomes limiting. What is important is dissolved O2 when the culture is pitched because O2 is used synthesize ergosterol and UFAs during the lag phase.  Anyone who has used pure O2 or the poor man's O2 bottle (a.k.a. SNS) to aerate the medium before pitching understands this fundamental.

[Saccharomyces]

FWIW I increase the volume by about 1/3 to 1/2 for lager yeast if I'm pitching around 50°F.  Seems to work right.  I would think that lager yeast is just yeast, and if pitched at say 60°F, it would not need an increase, but would grow sufficiently.  Would be nice to hear from the expert.

Pitching a larger culture with a lager fementation reduces the time to high krausen because yeast cells replicate slower at lower temperatures due to reduced metabolic rate.   The beauty of lager fermentation and why it made industrial brewing possible is because lager yeast can function at lower temperatures than bacteria and other spoilage microflora that are often found in breweries.