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Brews & Views Bulletin Board Service * Brews and Views Archive 2003 * September 2, 2003 * Yeast cell propagation and starters < Previous Next >

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Jim O'Conner (
Posted on Saturday, August 16, 2003 - 07:31 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

By what per cent do yeast multiply when using a starter under optimal conditions?

Fredrik (
Posted on Saturday, August 16, 2003 - 09:22 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

As far as I currently understand the percentage or multiplication factor depends on the initial cell count as well as nutritions and oxygen in wort, but also inital nutrition pools of the cells.

I read somewhere that 15% biomass yield could be attained in a good starter(or I even think I read 30% somewhere?) (15% or the fermentable sugar converted into cellmass, the rest ethanol and CO2) I did a test some days ago and seemed to get about 10%. (with a multiplication factor of 1.5)

For 1 litre of 10 plato wort with 80% fermentable DME, this would mean you can expect at most about 12g cellmass, probably around 250 billion cells. It would depend on the average mass of the cell. According to some article I found someone had estimated that 1g dry mass is approx 20 billion cells? This may probably vary though.

If the initial yeast mass is 125 billion cells, they would only have to multiplicate once. This would probably not be a problem even if the starter was very low on nutritions provided that the initial cells had their pools full.

But if the initial yeast mass is only 1 billion cells the required multiplication is so large that the nutritions contents of the wort is mostly limiting along with oxygen. Therefore I doubt the maximum yieled of some 15% may be attained in a single step unless nutrition is added?

I hope to make some experiments on this later. It is interesting!

From some very interesting responses from the HBD list I have revised some ideas about the starter. I will from now on add nutritions in the starter. I will try to use terminated dry yeast.


Bill Pierce (
Posted on Saturday, August 16, 2003 - 04:48 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Under optimal conditions the yeast population can multiply as many as 20 times in a starter. This requires such measures such as continuous agitation and continuous aeration used by commercial yeast propagators. A multiplication factor of 10 is considered a more normal rule of thumb.

Jim O'Conner (
Posted on Saturday, August 16, 2003 - 05:55 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

In Daniel's book, "Designing Great Beers" it is mentioned that the optimal pitching rate for a 5 gallon batch of beer would be 200-400 billion yeast cells. The 125ML Wyeast Smack Paks contain 45-60 billion yeast cells when fully active. I had these two thing in mind when I posted my question to determine if it is possible to reach the 200-400 billion cell mark using a starter. I've emailed Wyeast with this same question, and am waiting for a response.

Bill Pierce (
Posted on Saturday, August 16, 2003 - 06:08 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I wouldn't expect Wyeast (or White Labs, for that matter) to be entirely forthcoming in their reply. They have to balance the biology against marketing considerations. If homebrewers realized that even the so-called "pitchable" tubes and vials constitute less than the optimum population to pitch into a 5 gallon batch of normal gravity beer they might be less likely to purchase these products. The price of a truly sufficient quantity of yeast would deter most homebrewers from using them.

The truth is that a making starter is recommended in the majority of cases despite the reluctance of the yeast suppliers to advertise this fact. Of course, as has been repeated on this forum hundreds of time over the years, many homebrewers still manage to produce decent beer even if they underpitch. It's just that making a starter increases the odds in your favor.

Fredrik (
Posted on Saturday, August 16, 2003 - 09:53 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I though I'd add some recent cool microscope pics :)


I made a 800ml 10 plato starter yesterday. Check out the pics 24 hours in between. I haven't made any repetability testing yet, and I have no hemacytometer but I think the roughly the order of multiplication can be determined.

Intially there was 11g dry yeast.
I haven't counted the cells yet, but the first peak seems to indicate a good growth. More than my last test. I belive I aerated more this time. Also the last time I measure the count after 12 hours. Now 24 hours has passed. (The reason I make staters out of dry yeast is an experiement.)


Jim O'Conner (
Posted on Sunday, August 17, 2003 - 08:04 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Bill or Fredrik, forgive my poor math skills, but how many times would I have to add fresh wort to the starter (after decanting the spent wort ) to increase the yeast cell count from 45 billion to 200 billion?

By the way, if Wyeast should be forthcoming with the info, I'll pass it on.

Fredrik (
Posted on Sunday, August 17, 2003 - 09:55 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Obviously you should listen to Bill because I am just trying to understand this myself :) so maybe I am just screwing things up.. but..

From my current calculations, I think in theory some 620ml 10 plato starter may do it. But that is provided you do have an optimal starter and that you attain the maximum yield, with stirring and enough nutritions. I would like to know the exact answer too. This weekend I am preparing a new batch of beer but later on I hope to do some testing.

Assuming 80% fermentable DME, 15% biomass yield, and that 1 g yeast ~ 20 billion cells

620 x 10% x 1,040 x 80% x 15% x 20 billion
= 155 billion new cells

+ the origial 45 = 200 billion

I think what one can affect is the yield. Less oxygen and less nutritions will give a lower yield. I am not sure but I think regardless of wether you just shake or use oxygen, oxyentaion/aeration only in the beginning is not sufficent for max yield?? I think I read that in a normal full size batch the typical biomass yield is some 2-5%? Clearly not optimal if you wanted to grow yeast, but then that's not what you want either.

If I were you I would try and uSe 1 pint 10 plato starter. And put the starter in at least a gallon size container, or bigger to make sure it's easy to aerate with lots of excess air. My last starter I shaked for about 10 seconds at very least once an hour for about 12-24 hours, expect for when I was asleep.( Shaking only once at the beginning is I think not enough.) Then when it has been going at good krausen a while, perhaps you could add a few grams of boiled terminated dry yeast to make sure it doesn't run out of nutritons. By guess that if you do it like this you may get pretty close to the target (if not better)?

I will try to do a similar experient next to this batch, one with added terminated yeast and one without, so see awhat the difference is.

But then I am just messing with modelling so beware I may be wrong about the calculations in case I missed something.


Bill Pierce (
Posted on Sunday, August 17, 2003 - 12:41 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I think Fredrik's calculations (based on his model) are in the ballpark. You don't need to be quite so exact for homebrew situations. Using the rule of thumb that assumes a 10-fold volume and population increase for each step of a starter, 45 billion cells (roughly the population of a so-called pitchable vial or tube) could be increased to about 400 billion in a 1.5-2 liter starter. The population in the tube or vial is more concentrated than in a typical starter because the yeast propagators use measures such as continuous agitation and continuous aeration. The yeast is also centrifuged to increase the concentration.

At any rate, 400 billion cells pitched into a 5 gallon batch should be more than sufficient for most gravities. The truth is that I sometimes use this size starter for a 10 gallon batch of low to moderate gravity ale even if it technically constitutes underpitching. It's not rocket science.

RonJeremy4Pres (
Posted on Sunday, August 17, 2003 - 02:53 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Bill & others, does a stir plate provide continuous aeration or just agitation, provided it is covered in aluminum foil, not sealed with an airlock? (I remember a few years back there was an awesome thread about stir plates and yeast propigation but can't remember what it said.)

Also, could I conclude, all other things being "normal/equal/ideal", that after a 2000mL starters-worth of slurry per 5 gal., additional yeast is simply an insurance policy against infection and will not add any desireable characteristics to the beer? Sorry if this is ignorant, but I am trying to draw conclusions about my brewing from what I read here.

Ken Anderson (
Posted on Sunday, August 17, 2003 - 04:42 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

What I'm wondering, is if you aerate like a mad man, does that automatically mean you can't pitch at high starter krausen anymore due to funk? Do you now have to decant? And if so, do you cool at high krausen, then decant, or let it finish, settle, then decant?

Fredrik (
Posted on Sunday, August 17, 2003 - 08:05 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I have done two step starters, wether it's needed for cell counts or not. The first step, I aerate like mad at room temp, as often as I can, let it finish and settle naturally and decant the liquid.

The next step I aerate like mad also, however I try to keep this starter at the fermentation temp from the beginning to reduce excessive fuesels and esters. Then I pitch it all at high krausen as usual.


Fredrik (
Posted on Monday, August 18, 2003 - 08:28 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I tried to estimate the requirement of oxygen. And it seems it doesn't take alot actaully. This gave me second thoughts again(!) and makes me think that the reason you ideally may need to add oxygen more than once is do maintain the rate of oxygen uptake? Oxygen is transported in the cells via diffusion through the cell wall. And the rate should be proportional to the level of oxygen. And if the rate of oxygen uptake is slower than the oxygen requirement due to the budding rate, oxygen will become limiting although there is in fact still some ppm's O2 left in there?? So the last few ppm's may not be utilized quick enough.

I have found and assumed that dry cellmass ideally consists of 1% sterol by mass.

Squalene is the precursor or ergosterol.
Squalene contains 0% oxygen.
Ergosterol contains 4% oxygen.

Assuming no oxygen is lost ot other processes.
And assuming for simplicity that all the sterols are ergosterol.

Thus using such a very crude estimate the O2 requirement for cell propagation would be

0.04% of the biomass

This means that assuming 100% utilization which may not be realistic? 5 gallons of 1.040, 10ppm O2 wort in theory would be enough for 490g new healthy biomass, which seems more than sufficent.

Or perhaps the need for oxygenating several times may increase the effiecent a bit, but is not as significant as I thought?

Or are there other processes competing for oxygen in the wort that explains this?

This remains to find out. This is confusing me.


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