Ask The Brewmasters

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Hi Steven this may be due to "underpitching" from the onset of your fermentation.  You could also be pitching a disproportionate amount of young daughter cells to mother cells.  Young daughter cells typically floc less than mother cells and will remain in suspension longer.  Do you happen to perform cell counts on your initial pitches for both the homebrew prop as well as your supplier yeast?  Dialing in your propped cell/ml could remedy this issue.   

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

I do monitor the cell growth rate over a 30 hour period.  I typically take 3 to 4 samples/counts and plot the results based on strain.  I am trying to establish a base line so I can predict how long the prop should take.  So I have been taking a final count before I pitch and then based on an assumed homogeneous slurry I calculate the volume of slurry to pitch base on population of cells and desired pitch rate.  That being said I never thought about the daughter cells being an issue, if I am pitching to soon in the cell in slurry life cycle I may have a large number of buds.  Should I be waiting till I see some signs of flocculation before I pitch to assure the cell reproduction is slowing? Thoughts?

Hi Steven this may be due to "underpitching" from the onset of your fermentation.  You could also be pitching a disproportionate amount of young daughter cells to mother cells.  Young daughter cells typically floc less than mother cells and will remain in suspension longer.  Do you happen to perform cell counts on your initial pitches for both the homebrew prop as well as your supplier yeast?  Dialing in your propped cell/ml could remedy this issue.   

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

I do monitor the cell growth rate over a 30 hour period.  I typically take 3 to 4 samples/counts and plot the results based on strain.  I am trying to establish a base line so I can predict how long the prop should take.  So I have been taking a final count before I pitch and then based on an assumed homogeneous slurry I calculate the volume of slurry to pitch base on population of cells and desired pitch rate.  That being said I never thought about the daughter cells being an issue, if I am pitching to soon in the cell in slurry life cycle I may have a large number of buds.  Should I be waiting till I see some signs of flocculation before I pitch to assure the cell reproduction is slowing? Thoughts?

Hi Steven this may be due to "underpitching" from the onset of your fermentation.  You could also be pitching a disproportionate amount of young daughter cells to mother cells.  Young daughter cells typically floc less than mother cells and will remain in suspension longer.  Do you happen to perform cell counts on your initial pitches for both the homebrew prop as well as your supplier yeast?  Dialing in your propped cell/ml could remedy this issue.   

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Is this something you are noticing across the board with your propped yeast or is it strain/beer-dependent?  Different strains have variable diauxic phases that could increase the length of your "exponential growth phase" leading to more young cells and longer prop times.  Also, do these beers eventually clear up after some time at TG?  Is this occurring past Gen 0?  Also, I agree with Michael and think you should wait for some signs of flocculation, if not entirely, and decant the supernatant beer, pitching only the slurry.  While it's in the similar percentage range to what we recommend for prop scaling, you are still on the smaller end size-wise, so there is a potential for off-flavor detection.   

I do monitor the cell growth rate over a 30 hour period.  I typically take 3 to 4 samples/counts and plot the results based on strain.  I am trying to establish a base line so I can predict how long the prop should take.  So I have been taking a final count before I pitch and then based on an assumed homogeneous slurry I calculate the volume of slurry to pitch base on population of cells and desired pitch rate.  That being said I never thought about the daughter cells being an issue, if I am pitching to soon in the cell in slurry life cycle I may have a large number of buds.  Should I be waiting till I see some signs of flocculation before I pitch to assure the cell reproduction is slowing? Thoughts?

Hi Steven this may be due to "underpitching" from the onset of your fermentation.  You could also be pitching a disproportionate amount of young daughter cells to mother cells.  Young daughter cells typically floc less than mother cells and will remain in suspension longer.  Do you happen to perform cell counts on your initial pitches for both the homebrew prop as well as your supplier yeast?  Dialing in your propped cell/ml could remedy this issue.   

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Thanks Nassim! so here is what I do:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• I generally pitch 1 for Ales into 12L of DME, and  2 into 18L of DME
• What is the gravity of your starter?
• OG of the DME is 1.045.  I boil the appropriate amount of water then add DME to hit this target. Based on my research between 10 to 12 P is where I want my started to be at, so 1.045 hits that range (sorry about switching up units of measure)
• What is the final gravity of your starter after fermentation?
• I actually have not tested FG
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• No, as I am only pitching into 2 bbls, I am able to get enough cells to pitch just from the carboy.
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• I have been pitching the between 24 to 30 hours after starting the pitching the Homebrew pack into the starter slurry.
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• I have not been waiting, do not crash and do not decant, just pitch the entire content, beer and cells, into the wort.
• What is a typical starting gravity of the wort that the yeast is pitched into?
• It depends but it is generally 1.045 to 1.058

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Thank you for answering all my questions! I don't have a definitive answer, but based on the info you've provided I believe that you might be under pitching (but not definitely), that the starters simply need more time, or both.  

Let me go step by step to how I got to that thought. Forgive me if this stuff is super basic, this is just how I like to organize my thoughts!

• First off, I calculated your yeast needs using the ale calculation from Yeast by White and Zainasheff: 750,000 cells/ml x (mL of wort) x (°P). 
  • On the lower end, you're pitching into 2 bbl, which is 234700 milliliters.
  • For gravity, I used the middle point: 1.052 ≅ 12.9 °P
  • That leads to a total yeast pitch size of 2.23 trillion cells.
• Next, I tried to figure out how many cells you would get from 1 homebrew pitch into 5 gal of wort. To find an answer I consulted a chart that can be found somewhere between pages 140 and 142 in Yeast by White and Zainasheff. That chart shows the yeast growth of 1 homebrew pack (containing 100 billion cells) in different starter volumes without aeration or stirring:
  • 1 L starter leads to a total of 152 billion cells
  • 2 L starter leads to 205 billion cells
  • 4 L starter leads to 276 billion cells
  • 8 L starter leads to 400 billion cells
  • The point here is that doubling the starter volume does not lead to double the cells. In fact, even though the total number of cells goes up, the gains come at a decreasing rate. 
• Your starter is 5 gallons of wort = 18.9 liters
  • Even if we assumed that 18.9 liters of starter gave you double what 8 liters would give, you're still only at 800 billion cells-far off from what your needs are

Here's where things go somewhat beyond my knowledge. You're stirring and aerating the starter and that will definitely lead to more cells. The question I can't answer is "how many more cells?" One paper I found says "almost two times higher" but I'm curious what @Jasper Akerboom's thoughts are.

So if we assume that you would have had 800 billion cells without constant aeration (which is likely too high) and that constant aeration will give you 2x the cells, you're going to end up with about 1.6 trillion cells with constant aeration. 1.6 trillion cells is close to the goal, but still somewhat low and relies on a generous estimate of what you would have had without aeration.

One other point: so far we're assuming that the yeast in the homebrew pack is not only in good health but also that there is a low % of dead cells. Ultimately, it's unlikely the homebrew pack is in perfect health and has 0% dead cells, and so that estimate of 1.6 trillion is likely high.

Even so, if you do indeed have 1.6 trillion then you're close, but still on the low end of the spectrum which might be close enough but also might be low. Close enough that you should probably be fine, but low enough that it could lead to problems (I want to emphasize, tho, that I don't know that for certain). I tend to err on the side of over-pitching, but that's just me. (Having said that, if we change the formula above to be "500,000 cells/ml" instead of "750,000 cells/ml", the cells needed becomes 1.5 trillion, meaning you would be right on the money.

Either way, I want to emphasize once more that this estimate is itself based on an overly generous extrapolation and on an assumption that the homebrew pack is at peak vitality and viability. If either of those is off in a meaningful way, it could lead to an estimated cell count that is well below what you need.

It's also worth highlighting that these estimates are strain dependent: some weizen strains can be severely under-pitched and still perform well and fully attenuate a beer. And so, once again, you might actually be fine with the number of cells you have.

With all of that in mind, the other aspect that jumps out to me is the prop being re-pitched just 24 hours later. It's my understanding that cell growth is typically done after ~24 hours, but I can't help but wonder if cell growth is taking longer in your starters and that waiting an additional 24 hours might help. In that same paper I mentioned above, the starters that received 1 L per hr and 3 L per hr of O2 didn't see meaningful yeast growth until after the 24 hour mark. If I were prepping a starter, I would give it 36-48 hours but, again, that's just me. If possible, grabbing an FG on the starter after 24 hours would give you an idea of how fermentation has come along and give you an idea of whether or not it needs more time. 

One follow up question: are you using any yeast nutrient in your starter? Are you using any yeast nutrient in your beer?

Thanks Nassim! so here is what I do:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• I generally pitch 1 for Ales into 12L of DME, and  2 into 18L of DME
• What is the gravity of your starter?
• OG of the DME is 1.045.  I boil the appropriate amount of water then add DME to hit this target. Based on my research between 10 to 12 P is where I want my started to be at, so 1.045 hits that range (sorry about switching up units of measure)
• What is the final gravity of your starter after fermentation?
• I actually have not tested FG
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• No, as I am only pitching into 2 bbls, I am able to get enough cells to pitch just from the carboy.
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• I have been pitching the between 24 to 30 hours after starting the pitching the Homebrew pack into the starter slurry.
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• I have not been waiting, do not crash and do not decant, just pitch the entire content, beer and cells, into the wort.
• What is a typical starting gravity of the wort that the yeast is pitched into?
• It depends but it is generally 1.045 to 1.058

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Hi Nassim, thanks for looping me in the thread. A lot of information and guidance has already been given, my suggestions might be a little mustard after your meal so to speak and I do not want to over-complicate things.

Hi Steven, You are using DME to propagate, which is by itself not very nutrient rich to grow cells. Your cells might be low on certain nutrients. I am also curious about your pitch rate, 24 hrs seems quite short. Not to say you cannot reach proper pitch rate after 24 hrs. From 200 billion(?) to ~2 trillion that is a tenfold increase, assuming all cells are participating.  A final gravity and cell count would be helpful. Do you have some numbers for us? 1.045 is on the high end for propagation in my honest opinion.

Thank you for answering all my questions! I don't have a definitive answer, but based on the info you've provided I believe that you might be under pitching (but not definitely), that the starters simply need more time, or both.  

Let me go step by step to how I got to that thought. Forgive me if this stuff is super basic, this is just how I like to organize my thoughts!

• First off, I calculated your yeast needs using the ale calculation from Yeast by White and Zainasheff: 750,000 cells/ml x (mL of wort) x (°P). 
  • On the lower end, you're pitching into 2 bbl, which is 234700 milliliters.
  • For gravity, I used the middle point: 1.052 ≅ 12.9 °P
  • That leads to a total yeast pitch size of 2.23 trillion cells.
• Next, I tried to figure out how many cells you would get from 1 homebrew pitch into 5 gal of wort. To find an answer I consulted a chart that can be found somewhere between pages 140 and 142 in Yeast by White and Zainasheff. That chart shows the yeast growth of 1 homebrew pack (containing 100 billion cells) in different starter volumes without aeration or stirring:
  • 1 L starter leads to a total of 152 billion cells
  • 2 L starter leads to 205 billion cells
  • 4 L starter leads to 276 billion cells
  • 8 L starter leads to 400 billion cells
  • The point here is that doubling the starter volume does not lead to double the cells. In fact, even though the total number of cells goes up, the gains come at a decreasing rate. 
• Your starter is 5 gallons of wort = 18.9 liters
  • Even if we assumed that 18.9 liters of starter gave you double what 8 liters would give, you're still only at 800 billion cells-far off from what your needs are

Here's where things go somewhat beyond my knowledge. You're stirring and aerating the starter and that will definitely lead to more cells. The question I can't answer is "how many more cells?" One paper I found says "almost two times higher" but I'm curious what @Jasper Akerboom's thoughts are.

So if we assume that you would have had 800 billion cells without constant aeration (which is likely too high) and that constant aeration will give you 2x the cells, you're going to end up with about 1.6 trillion cells with constant aeration. 1.6 trillion cells is close to the goal, but still somewhat low and relies on a generous estimate of what you would have had without aeration.

One other point: so far we're assuming that the yeast in the homebrew pack is not only in good health but also that there is a low % of dead cells. Ultimately, it's unlikely the homebrew pack is in perfect health and has 0% dead cells, and so that estimate of 1.6 trillion is likely high.

Even so, if you do indeed have 1.6 trillion then you're close, but still on the low end of the spectrum which might be close enough but also might be low. Close enough that you should probably be fine, but low enough that it could lead to problems (I want to emphasize, tho, that I don't know that for certain). I tend to err on the side of over-pitching, but that's just me. (Having said that, if we change the formula above to be "500,000 cells/ml" instead of "750,000 cells/ml", the cells needed becomes 1.5 trillion, meaning you would be right on the money.

Either way, I want to emphasize once more that this estimate is itself based on an overly generous extrapolation and on an assumption that the homebrew pack is at peak vitality and viability. If either of those is off in a meaningful way, it could lead to an estimated cell count that is well below what you need.

It's also worth highlighting that these estimates are strain dependent: some weizen strains can be severely under-pitched and still perform well and fully attenuate a beer. And so, once again, you might actually be fine with the number of cells you have.

With all of that in mind, the other aspect that jumps out to me is the prop being re-pitched just 24 hours later. It's my understanding that cell growth is typically done after ~24 hours, but I can't help but wonder if cell growth is taking longer in your starters and that waiting an additional 24 hours might help. In that same paper I mentioned above, the starters that received 1 L per hr and 3 L per hr of O2 didn't see meaningful yeast growth until after the 24 hour mark. If I were prepping a starter, I would give it 36-48 hours but, again, that's just me. If possible, grabbing an FG on the starter after 24 hours would give you an idea of how fermentation has come along and give you an idea of whether or not it needs more time. 

One follow up question: are you using any yeast nutrient in your starter? Are you using any yeast nutrient in your beer?

Thanks Nassim! so here is what I do:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• I generally pitch 1 for Ales into 12L of DME, and  2 into 18L of DME
• What is the gravity of your starter?
• OG of the DME is 1.045.  I boil the appropriate amount of water then add DME to hit this target. Based on my research between 10 to 12 P is where I want my started to be at, so 1.045 hits that range (sorry about switching up units of measure)
• What is the final gravity of your starter after fermentation?
• I actually have not tested FG
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• No, as I am only pitching into 2 bbls, I am able to get enough cells to pitch just from the carboy.
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• I have been pitching the between 24 to 30 hours after starting the pitching the Homebrew pack into the starter slurry.
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• I have not been waiting, do not crash and do not decant, just pitch the entire content, beer and cells, into the wort.
• What is a typical starting gravity of the wort that the yeast is pitched into?
• It depends but it is generally 1.045 to 1.058

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Thanks Nassim and Jasper, ye over complicating things can sometime cloud what needs to be done, but then again I am the king of over complicating things so the responses have each provided me a little more insight as to what I could be doing wrong, so the more details the better. 

So Jasper, I have used both wort and DME to perform my props in the past, and the wort may have performed better in growing the cells but my brew schedule has been non-consistent latly so the reason I decided to use DME as a prop medium.    One thing I have not done, but should have, is adding in yeast nutrient to improve the yeast cell health and you comment confirmed I should have probably been doing that all along.   

I have been tracking yeast cell grown throughout the first 30 hours, usually 3 to 4 times, to get an idea of the growth rate of differing strains.  Generally, with in 30 hours I am reaching my target pitch count.  With what Nassim provided I need to review my numbers to assure what I am calculating this correctly.  I am doing a propagation this week so will provide a fresh look at the results.  The 1.045 came from a couple of article I have read on yeast propagation, but yes its certainly worth looking at and experimenting with lowering.

Hi Nassim, thanks for looping me in the thread. A lot of information and guidance has already been given, my suggestions might be a little mustard after your meal so to speak and I do not want to over-complicate things.

Hi Steven, You are using DME to propagate, which is by itself not very nutrient rich to grow cells. Your cells might be low on certain nutrients. I am also curious about your pitch rate, 24 hrs seems quite short. Not to say you cannot reach proper pitch rate after 24 hrs. From 200 billion(?) to ~2 trillion that is a tenfold increase, assuming all cells are participating.  A final gravity and cell count would be helpful. Do you have some numbers for us? 1.045 is on the high end for propagation in my honest opinion.

Thank you for answering all my questions! I don't have a definitive answer, but based on the info you've provided I believe that you might be under pitching (but not definitely), that the starters simply need more time, or both.  

Let me go step by step to how I got to that thought. Forgive me if this stuff is super basic, this is just how I like to organize my thoughts!

• First off, I calculated your yeast needs using the ale calculation from Yeast by White and Zainasheff: 750,000 cells/ml x (mL of wort) x (°P). 
  • On the lower end, you're pitching into 2 bbl, which is 234700 milliliters.
  • For gravity, I used the middle point: 1.052 ≅ 12.9 °P
  • That leads to a total yeast pitch size of 2.23 trillion cells.
• Next, I tried to figure out how many cells you would get from 1 homebrew pitch into 5 gal of wort. To find an answer I consulted a chart that can be found somewhere between pages 140 and 142 in Yeast by White and Zainasheff. That chart shows the yeast growth of 1 homebrew pack (containing 100 billion cells) in different starter volumes without aeration or stirring:
  • 1 L starter leads to a total of 152 billion cells
  • 2 L starter leads to 205 billion cells
  • 4 L starter leads to 276 billion cells
  • 8 L starter leads to 400 billion cells
  • The point here is that doubling the starter volume does not lead to double the cells. In fact, even though the total number of cells goes up, the gains come at a decreasing rate. 
• Your starter is 5 gallons of wort = 18.9 liters
  • Even if we assumed that 18.9 liters of starter gave you double what 8 liters would give, you're still only at 800 billion cells-far off from what your needs are

Here's where things go somewhat beyond my knowledge. You're stirring and aerating the starter and that will definitely lead to more cells. The question I can't answer is "how many more cells?" One paper I found says "almost two times higher" but I'm curious what @Jasper Akerboom's thoughts are.

So if we assume that you would have had 800 billion cells without constant aeration (which is likely too high) and that constant aeration will give you 2x the cells, you're going to end up with about 1.6 trillion cells with constant aeration. 1.6 trillion cells is close to the goal, but still somewhat low and relies on a generous estimate of what you would have had without aeration.

One other point: so far we're assuming that the yeast in the homebrew pack is not only in good health but also that there is a low % of dead cells. Ultimately, it's unlikely the homebrew pack is in perfect health and has 0% dead cells, and so that estimate of 1.6 trillion is likely high.

Even so, if you do indeed have 1.6 trillion then you're close, but still on the low end of the spectrum which might be close enough but also might be low. Close enough that you should probably be fine, but low enough that it could lead to problems (I want to emphasize, tho, that I don't know that for certain). I tend to err on the side of over-pitching, but that's just me. (Having said that, if we change the formula above to be "500,000 cells/ml" instead of "750,000 cells/ml", the cells needed becomes 1.5 trillion, meaning you would be right on the money.

Either way, I want to emphasize once more that this estimate is itself based on an overly generous extrapolation and on an assumption that the homebrew pack is at peak vitality and viability. If either of those is off in a meaningful way, it could lead to an estimated cell count that is well below what you need.

It's also worth highlighting that these estimates are strain dependent: some weizen strains can be severely under-pitched and still perform well and fully attenuate a beer. And so, once again, you might actually be fine with the number of cells you have.

With all of that in mind, the other aspect that jumps out to me is the prop being re-pitched just 24 hours later. It's my understanding that cell growth is typically done after ~24 hours, but I can't help but wonder if cell growth is taking longer in your starters and that waiting an additional 24 hours might help. In that same paper I mentioned above, the starters that received 1 L per hr and 3 L per hr of O2 didn't see meaningful yeast growth until after the 24 hour mark. If I were prepping a starter, I would give it 36-48 hours but, again, that's just me. If possible, grabbing an FG on the starter after 24 hours would give you an idea of how fermentation has come along and give you an idea of whether or not it needs more time. 

One follow up question: are you using any yeast nutrient in your starter? Are you using any yeast nutrient in your beer?

Thanks Nassim! so here is what I do:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• I generally pitch 1 for Ales into 12L of DME, and  2 into 18L of DME
• What is the gravity of your starter?
• OG of the DME is 1.045.  I boil the appropriate amount of water then add DME to hit this target. Based on my research between 10 to 12 P is where I want my started to be at, so 1.045 hits that range (sorry about switching up units of measure)
• What is the final gravity of your starter after fermentation?
• I actually have not tested FG
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• No, as I am only pitching into 2 bbls, I am able to get enough cells to pitch just from the carboy.
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• I have been pitching the between 24 to 30 hours after starting the pitching the Homebrew pack into the starter slurry.
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• I have not been waiting, do not crash and do not decant, just pitch the entire content, beer and cells, into the wort.
• What is a typical starting gravity of the wort that the yeast is pitched into?
• It depends but it is generally 1.045 to 1.058

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?

Hi Steven,

Growing yeast in the presence of zinc improves flocculation.  That's an easy thing to try.

Cheers,

Ashton

Thanks Nassim and Jasper, ye over complicating things can sometime cloud what needs to be done, but then again I am the king of over complicating things so the responses have each provided me a little more insight as to what I could be doing wrong, so the more details the better. 

So Jasper, I have used both wort and DME to perform my props in the past, and the wort may have performed better in growing the cells but my brew schedule has been non-consistent latly so the reason I decided to use DME as a prop medium.    One thing I have not done, but should have, is adding in yeast nutrient to improve the yeast cell health and you comment confirmed I should have probably been doing that all along.   

I have been tracking yeast cell grown throughout the first 30 hours, usually 3 to 4 times, to get an idea of the growth rate of differing strains.  Generally, with in 30 hours I am reaching my target pitch count.  With what Nassim provided I need to review my numbers to assure what I am calculating this correctly.  I am doing a propagation this week so will provide a fresh look at the results.  The 1.045 came from a couple of article I have read on yeast propagation, but yes its certainly worth looking at and experimenting with lowering.

Hi Nassim, thanks for looping me in the thread. A lot of information and guidance has already been given, my suggestions might be a little mustard after your meal so to speak and I do not want to over-complicate things.

Hi Steven, You are using DME to propagate, which is by itself not very nutrient rich to grow cells. Your cells might be low on certain nutrients. I am also curious about your pitch rate, 24 hrs seems quite short. Not to say you cannot reach proper pitch rate after 24 hrs. From 200 billion(?) to ~2 trillion that is a tenfold increase, assuming all cells are participating.  A final gravity and cell count would be helpful. Do you have some numbers for us? 1.045 is on the high end for propagation in my honest opinion.

Thank you for answering all my questions! I don't have a definitive answer, but based on the info you've provided I believe that you might be under pitching (but not definitely), that the starters simply need more time, or both.  

Let me go step by step to how I got to that thought. Forgive me if this stuff is super basic, this is just how I like to organize my thoughts!

• First off, I calculated your yeast needs using the ale calculation from Yeast by White and Zainasheff: 750,000 cells/ml x (mL of wort) x (°P). 
  • On the lower end, you're pitching into 2 bbl, which is 234700 milliliters.
  • For gravity, I used the middle point: 1.052 ≅ 12.9 °P
  • That leads to a total yeast pitch size of 2.23 trillion cells.
• Next, I tried to figure out how many cells you would get from 1 homebrew pitch into 5 gal of wort. To find an answer I consulted a chart that can be found somewhere between pages 140 and 142 in Yeast by White and Zainasheff. That chart shows the yeast growth of 1 homebrew pack (containing 100 billion cells) in different starter volumes without aeration or stirring:
  • 1 L starter leads to a total of 152 billion cells
  • 2 L starter leads to 205 billion cells
  • 4 L starter leads to 276 billion cells
  • 8 L starter leads to 400 billion cells
  • The point here is that doubling the starter volume does not lead to double the cells. In fact, even though the total number of cells goes up, the gains come at a decreasing rate. 
• Your starter is 5 gallons of wort = 18.9 liters
  • Even if we assumed that 18.9 liters of starter gave you double what 8 liters would give, you're still only at 800 billion cells-far off from what your needs are

Here's where things go somewhat beyond my knowledge. You're stirring and aerating the starter and that will definitely lead to more cells. The question I can't answer is "how many more cells?" One paper I found says "almost two times higher" but I'm curious what @Jasper Akerboom's thoughts are.

So if we assume that you would have had 800 billion cells without constant aeration (which is likely too high) and that constant aeration will give you 2x the cells, you're going to end up with about 1.6 trillion cells with constant aeration. 1.6 trillion cells is close to the goal, but still somewhat low and relies on a generous estimate of what you would have had without aeration.

One other point: so far we're assuming that the yeast in the homebrew pack is not only in good health but also that there is a low % of dead cells. Ultimately, it's unlikely the homebrew pack is in perfect health and has 0% dead cells, and so that estimate of 1.6 trillion is likely high.

Even so, if you do indeed have 1.6 trillion then you're close, but still on the low end of the spectrum which might be close enough but also might be low. Close enough that you should probably be fine, but low enough that it could lead to problems (I want to emphasize, tho, that I don't know that for certain). I tend to err on the side of over-pitching, but that's just me. (Having said that, if we change the formula above to be "500,000 cells/ml" instead of "750,000 cells/ml", the cells needed becomes 1.5 trillion, meaning you would be right on the money.

Either way, I want to emphasize once more that this estimate is itself based on an overly generous extrapolation and on an assumption that the homebrew pack is at peak vitality and viability. If either of those is off in a meaningful way, it could lead to an estimated cell count that is well below what you need.

It's also worth highlighting that these estimates are strain dependent: some weizen strains can be severely under-pitched and still perform well and fully attenuate a beer. And so, once again, you might actually be fine with the number of cells you have.

With all of that in mind, the other aspect that jumps out to me is the prop being re-pitched just 24 hours later. It's my understanding that cell growth is typically done after ~24 hours, but I can't help but wonder if cell growth is taking longer in your starters and that waiting an additional 24 hours might help. In that same paper I mentioned above, the starters that received 1 L per hr and 3 L per hr of O2 didn't see meaningful yeast growth until after the 24 hour mark. If I were prepping a starter, I would give it 36-48 hours but, again, that's just me. If possible, grabbing an FG on the starter after 24 hours would give you an idea of how fermentation has come along and give you an idea of whether or not it needs more time. 

One follow up question: are you using any yeast nutrient in your starter? Are you using any yeast nutrient in your beer?

Thanks Nassim! so here is what I do:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• I generally pitch 1 for Ales into 12L of DME, and  2 into 18L of DME
• What is the gravity of your starter?
• OG of the DME is 1.045.  I boil the appropriate amount of water then add DME to hit this target. Based on my research between 10 to 12 P is where I want my started to be at, so 1.045 hits that range (sorry about switching up units of measure)
• What is the final gravity of your starter after fermentation?
• I actually have not tested FG
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• No, as I am only pitching into 2 bbls, I am able to get enough cells to pitch just from the carboy.
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• I have been pitching the between 24 to 30 hours after starting the pitching the Homebrew pack into the starter slurry.
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• I have not been waiting, do not crash and do not decant, just pitch the entire content, beer and cells, into the wort.
• What is a typical starting gravity of the wort that the yeast is pitched into?
• It depends but it is generally 1.045 to 1.058

Hi Steven, this sounds frustrating! Can you tell us a little more about your propping regime? I have a handful of questions that might help us determine what's going on:

• How many home-brew packs do you start with and into how many mL (or liters) of wort do you pitch them into? Considering that you're using a carboy, I'm assuming 5 gal/19 liters or less.
• What is the gravity of your starter?
• What is the final gravity of your starter after fermentation?
• Do you step the starter up after the fermentation in the carboy? If so, how many mL (or liters) of wort are you pitching those cells into? 
• How soon after pitching the yeast into your starter wort do you then either pitch the yeast into the next starter wort or into the production wort?
• Do you crash your starter after fermentation is complete? If not, do you wait for all the yeast to settle out before decanting off the beer? Alternatively, if you don't crash your starter, do you pitch the entirety of the contents (i.e., all the yeast + all the beer from the starter)?
• What is a typical starting gravity of the wort that the yeast is pitched into?

With that info, it might be easier to figure out what's going on!

Nassim

I have a small system, generally only pitching 2 to 4 bbls at a  time.  I have just started to propagate yeast from HomeBrew packs using a carboy, DME, stir plate, force aeration, etc.  While I get good cell growth and the yeast seems healthy i.e. no sensory issues, we are struggling with poor fluctuation during crashing from my propped yeast vrs. when I get a full pitch from my favorite yeast lab.  Thoughts?