Yeast slurry

[MyQul]

. If I have the space and time, and the yeast strain is highly flocculant, I'll use about 150mL of unwashed slurry to pitch another brew..

I understand unwashed slurry to be 1.2BL cells per ML as 40%-60% of slurry is break material/trub. So a ball park figure of around about 100ml needs to be pitched- you pitch 150ml.

Do you seperate out your break material/trub from your wort prior to pitching. I usually just dump all the break material/trub in my FV, so this figure of 1.2ml wouldn't be correct for me and I would need to seperate out the break material/trub from the wort for it to be correct?

 

[McMullan]

I understand unwashed slurry to be 1.2BL cells per ML as 40%-60% of slurry is break material/trub. So a ball park figure of around about 100ml needs to be pitched- you pitch 150ml.

Do you seperate out your break material/trub from your wort prior to pitching. I usually just dump all the break material/trub in my FV, so this figure of 1.2ml wouldn't be correct for me and I would need to seperate out the break material/trub from the wort for it to be correct?

Yes, I let most of the break material settle before transferring the wort. 150ml is the approximate volume of my stainless ladle. To be honest, I don't fill it to the rim, as things get messy. I'd guesstimate that I am pitching about 120-130ml of unwashed slurry.

 

[MyQul]

Yes, I let most of the break material settle before transferring the wort. 150ml is the approximate volume of my stainless ladle. To be honest, I don't fill it to the rim, as things get messy. I'd guesstimate that I am pitching about 120-130ml of unwashed slurry.

Thanks. I was pretty sure that the 1.2bl/ml thick slurry that I've read/been advised was based on most of the trub being removed, although I am aware there are plenty of brewers that don't bother - like me

 

[saccharomyces]

I never pitch at high krausen. I allow the yeast to finish, floc and build up their glycogen and trehalose reserves.

However, allowing fermentation to proceed to quiescence pretty much ensures that the cells have depleted their ergosterol and unsaturated fatty acid (UFA) reserves and have undergone morphological changes. The storing of glycogen is followed by thickening of the cell wall, both of which are survival mechanisms. Cell wall thickening has to be reversed, and the ergosterol and UFA reserves that were depleted after high krausen was reached have to be replenished (all reproduction after the end of the log phase is for replacement only, and mother cells share 50% of their ergosterol and UFA reserves with each daughter). These processes increase dissolved oxygen (O2) requirements and lag time upon pitching. Pitching at high krausen ensures that one is pitching cells that at the peak of health with ergosterol and UFA reserves that merely need to be topped off. Lower initial O2 requirements means that more dissolved O2 is available for the cells that are created during the log phase.

Yeast cells do not need glycogen reserves to reproduce or convert glucose (C6H12O6) to ethanol (CH3CH3OH), carbon dioxide (CO2), and other metabolites. They need pliable plasma membranes. A pliable plasma membrane allows nutrients to enter and waste product to exit the cell. That's where ergosterol and UFAs enter the picture. Ergosterol and UFAs make a yeast cell's plasma membrane more pliable. Ergosterol and UFAs are synthesized by shunting oxygen and a small amount of carbon (sugar is carbon bound to water; hence, the name carbohydrate) to the respirative metabolic pathway. All reproduction in batch propagation and fermentation is fermentative due to the glucose level of the solution being above the Crabtree threshold of 0.3%. To put things into context, pale extract contains approximately 14% glucose. In order to remain below the Crabtree threshold, we would have to hold the wort gravity to around 1.008, which is a 2% weight by volume (w/v) solution due to the fact that 1ml of water equals 1g.

0.02 x 14 = 0.28% glucose w/v

A glucose level of 0.28% prevents the Crabtree effect from kicking in, allowing the Pasteur effect to take over. Reproduction becomes respirative, resulting pyruvate being converted mainly to energy, water (H20), and CO2 via the Krebs cycle. Respirative reproduction is at least 16 times more efficient than fermentative reproduction. That's why the large dry yeast manufacturers propagate aerobically in a bioreactor.

To put thing into layman's terms, one should never allow a starter to ferment out because doing so places the culture in the yeast equivalent of hibernation. The storing of glycogen is the yeast equivalent of a bear putting on fat for the winter. Yeast cells store glycogen because they do not know how long it will be before a carbon source (e.g., sugar) becomes available. The glycogen that is stored at the end of fermentation is slowly consumed while the yeast cells are in storage. The cells die after they consume all of their glycogen reserves, resulting in autolysis. The word "autolysis” is composed of the Latin "auto," which means self (e.g., automobile means self-mobile) and the Latin "lysis," which means to break apart. When put together, autolysis translates to "self-break apart" or "self-destruct." The reason why we refrigerate crops is to slow metabolism; thus, lengthen the amount of time that it takes for the cells to deplete their glycogen stores. The thickening of the cell wall is in part to prevent premature autolysis.

If one has ever watched a brewery top crop, one has noticed that they skim the first head (known as the brown head) and crop the head that appears after the first head is removed. The first head is removed because it contains organic matter that was scrubbed from the wort as it came to high krausen (it also contains cells that exhibit early flocculation). The second head is taken at roughly 50% attenuation, which is still high krausen. We want to pitch a starter at high krausen for the same reason why brewers skim at high krausen; namely, the cells are in the peak of health. Healthy cells have lower O2 needs upon pitching, and they do not need to reverse the morphological changes that occur at the end of fermentation; hence, lag time is reduced and more dissolved O2 is available for the yeast cells that are created during the lag phase, resulting in healthier fermentations and resulting crops.

 

[saccharomyces]

Thanks. I was pretty sure that the 1.2bl/ml thick slurry that I've read/been advised was based on most of the trub being removed, although I am aware there are plenty of brewers that don't bother - like me

From https://www.wyeastlab.com/com-yeast-harvest.cfm:

"Estimates of cell counts can be made using percent yeast solids of the slurry. Percentage of yeast solids per volume of slurry can be estimated by allowing a sample to sediment under refrigeration and estimating the percent solids. Generally 40-60% yeast solids will correlate to 1.2 billion cells per ml. This will vary with the yeast strain. By using this method with every brew, a brewer can achieve consistent pitch rates batch to batch resulting in a more consistent product. The following picture relates sedimentation to cell count."

 

[McMullan]

However, allowing fermentation to proceed to quiescence pretty much ensures that the cells have depleted their ergosterol and unsaturated fatty acid (UFA) reserves and have undergone morphological changes. The storing of glycogen is followed by thickening of the cell wall, both of which are survival mechanisms. Cell wall thickening has to be reversed, and the ergosterol and UFA reserves that were depleted after high krausen was reached have to be replenished (all reproduction after the end of the log phase is for replacement only, and mother cells share 50% of their ergosterol and UFA reserves with each daughter). These processes increase dissolved oxygen (O2) requirements and lag time upon pitching. Pitching at high krausen ensures that one is pitching cells that at the peak of health with ergosterol and UFA reserves that merely need to be topped off. Lower initial O2 requirements means that more dissolved O2 is available for the cells that are created during the log phase.

Yeast cells do not need glycogen reserves to reproduce or convert glucose (C6H12O6) to ethanol (CH3CH3OH), carbon dioxide (CO2), and other metabolites. They need pliable plasma membranes. A pliable plasma membrane allows nutrients to enter and waste product to exit the cell. That's where ergosterol and UFAs enter the picture. Ergosterol and UFAs make a yeast cell's plasma membrane more pliable. Ergosterol and UFAs are synthesized by shunting oxygen and a small amount of carbon (sugar is carbon bound to water; hence, the name carbohydrate) to the respirative metabolic pathway. All reproduction in batch propagation and fermentation is fermentative due to the glucose level of the solution being above the Crabtree threshold of 0.3%. To put things into context, pale extract contains approximately 14% glucose. In order to remain below the Crabtree threshold, we would have to hold the wort gravity to around 1.008, which is a 2% weight by volume (w/v) solution due to the fact that 1ml of water equals 1g.

0.02 x 14 = 0.28% glucose w/v

A glucose level of 0.28% prevents the Crabtree effect from kicking in, allowing the Pasteur effect to take over. Reproduction becomes respirative, resulting pyruvate being converted mainly to energy, water (H20), and CO2 via the Krebs cycle. Respirative reproduction is at least 16 times more efficient than fermentative reproduction. That's why the large dry yeast manufacturers propagate aerobically in a bioreactor.

To put thing into layman's terms, one should never allow a starter to ferment out because doing so places the culture in the yeast equivalent of hibernation. The storing of glycogen is the yeast equivalent of a bear putting on fat for the winter. Yeast cells store glycogen because they do not know how long it will be before a carbon source (e.g., sugar) becomes available. The glycogen that is stored at the end of fermentation is slowly consumed while the yeast cells are in storage. The cells die after they consume all of their glycogen reserves, resulting autolysis. The word "autolysis” is composed of the Latin "auto," which means self (e.g., automobile means self-mobile) and the Latin "lysis," which means to break apart. When put together, autolysis translates to "self-break apart" or "self-destruct." The reason why we refrigerate crops is to slow metabolism; thus, lengthen the amount of time that it takes for the cells to deplete their glycogen stores. The thickening of the cell wall is in part to prevent premature autolysis.

If one has ever watched a brewery top crop, one has noticed that they skim the first head (known as the brown head) and crop the head that appears after the first head is removed. This first head is removed because it contains organic matter that was scrubbed from the wort as it came to high krausen (it also contains cells that exhibit early flocculation). The second head is taken at roughly 50% attenuation, which is still high krausen. We want to pitch a starter at high krausen for the same reason why brewers skim at high krausen; namely, the cells are in the peak of health. Healthy cells have lower O2 needs upon pitching, and they do not need to reverse the morphological changes that occur at the end of fermentation; hence, lag time is reduced and more dissolved O2 is available for the yeast cells that are created during the lag phase, resulting in healthier fermentations and resulting crops.

My methodology produces predictable fermentations that always reach expected attenuation. And the beer tastes fantastic. That kind of disproves much of what you imply, at least at the scale of the home brewer :hmm:

 

[saccharomyces]

My methodology produces predictable fermentations that always reach expected attenuation. And the beer tastes fantastic. That kind of disproves much of what you imply, at least at the scale of the home brewer :hmm:

One can also achieve consistent results from pitching non-rehydrated dry yeast just as one can achieve consistent results and full attenuation by pitching relatively fresh White Labs vials directly into wort. However, neither practice is optimal if long term culture maintenance is desired.

Many brewers are looking for ways to stretch their brewing dollars. One way to achieve this goal is to repitch. Repitching requires one to take steps to maintain yeast health. Pitching, cropping, and stepping at high krausen are time proven methods to maximize yeast health (it's a big part of the reason why Harveys has been able to repitch the same top-cropped yeast culture for over 50 years). I did not make this stuff up. Yeast propagation is well researched just as quiescence and the survival mechanisms that yeast employ at the end of fermentation are well researched.

The number one reason why stir plate users wait until quiescence to pitch is because the media smells and/or tastes foul. Foul smells and tastes are signs that the culture is stressed. That stress is the result of the stir bar causing cell shear stress.

 

[YeastFace]

This is a great conversation, Gents.

 

[MyQul]

From https://www.wyeastlab.com/com-yeast-harvest.cfm:

"Estimates of cell counts can be made using percent yeast solids of the slurry. Percentage of yeast solids per volume of slurry can be estimated by allowing a sample to sediment under refrigeration and estimating the percent solids. Generally 40-60% yeast solids will correlate to 1.2 billion cells per ml. This will vary with the yeast strain. By using this method with every brew, a brewer can achieve consistent pitch rates batch to batch resulting in a more consistent product. The following picture relates sedimentation to cell count."

Yes, this is one of the sources I have read. As I say I understand the 40-60% yeast solids is based on having seperated out most of the trub from the wort. So to achieve 1.2bl/ml I need to seperate my trub out from my wort which I currently dont do.

Given that on the shaken not stirred thread on jims forum you state "My pitching rates for normal ale strains are 3 to 5 billion cells per liter for normal gravity British-style ales and 5 to 8 billion cells per liter for normal gravity American-style ales." You also state that most online yeast calulators are wrong. So how do I work how many cells to put in a 1L starter to build up to the British-style 5-8BL/pL pitching rate?

 

[Twostage]

Right, I'm now officially one of the slurry men (blatant reference to the Beatles). I used the slurry from an extract based ESB 2 litre test brew in a 5 litre AG ESB this lunchtime. The FV now looks like a lava lamp on speed.

I know there's a lot of science around this but I just gave the slurry a good shake and poured it in.

I also used all of the wort in the FV, hot and cold break and all (did strain out the hops though). This was after reading this :-
http://www.morebeer.com/articles/oxygen_in_fermentation

which basically make the case that yeast can use the break material in the early stages of fermentation.

The yeast in question is Danstar Nottingham by the way. If I can get myself organised I'm going to use the 5 litre slurry in a 21 ESB litre brew.

 

[ManseMasher]

I started this thread, and to be honest, I wish I hadn't! All I wanted to know was how to re-use what I had from the bottom of my fv. Didn't expect an MSc in yeastology! Appreciate all responses, but for an average homebrewer, you have a)lost my interest and b)confused the s**t out of me. Sorry.

 

[Twostage]

I started this thread, and to be honest, I wish I hadn't! All I wanted to know was how to re-use what I had from the bottom of my fv. Didn't expect an MSc in yeastology! Appreciate all responses, but for an average homebrewer, you have a)lost my interest and b)confused the s**t out of me. Sorry.

Going back to your original post and based on my experience today - just put some or all of the slurry from one brew into the next. Mine was from a cold crashed beer that I just left out in the kitchen to warm up whilst I did the next brew.

The Yorkshireman in me agrees with your 'cheapskate' comment - if I can brew a total of 28 litres of beer from an original pitch of 3 grams I'll be well pleased :smile:

 

[saccharomyces]

Given that on the shaken not stirred thread on jims forum you state "My pitching rates for normal ale strains are 3 to 5 billion cells per liter for normal gravity British-style ales and 5 to 8 billion cells per liter for normal gravity American-style ales." You also state that most online yeast calulators are wrong. So how do I work how many cells to put in a 1L starter to build up to the British-style 5-8BL/pL pitching rate?

I adjust my starter volume size (I grow all of my starters from slant). For example, my large batch size is roughly 21 liters (my standard batch size is approximately 13.25L). If I want to pitch 3 billion cells per liter, I need to grow approximately 63 billion cells. At a maximum cell density of 200 billion cells per liter, that's a 300ml starter. Pitching that low can be a challenge when starting with a full White Labs vial because they ship from White Labs with 100 billion cells. Hence, one would have to split a relatively fresh White Labs vial into halves or thirds because one wants some new cell growth in the starter. I do not know the average age of a White Labs vial in the UK, but most vials sell before they reach two months of age at my local home brew supply store. At two months, one can assume that a White Labs vial contains approximately 50 billion cells.

As far as to yeast calculators, they are overly simplistic models of what is a complex biological process. No two yeast strains behave exactly the same way when pitched into wort (a strain will often behave differently when used in two different breweries). Hence, my stance on the only true way to know how a yeast culture is going to perform in one's brewery it is to use it, observe its performance, and document what one sees. If the culture does not perform as one expected, pitch more (less yeast derived flavors) or less (more yeast derived aromas and flavors) yeast next time. Commercial breweries know how much to pitch because they know how a culture is going to behave in their brewery. There's no one perfect pitching rate.

 

[saccharomyces]

I started this thread, and to be honest, I wish I hadn't! All I wanted to know was how to re-use what I had from the bottom of my fv. Didn't expect an MSc in yeastology! Appreciate all responses, but for an average homebrewer, you have a)lost my interest and b)confused the s**t out of me. Sorry.

If one can measure, one can repitch slurry. It's that simple. Everything else that I posted was about maximizing yeast health. A simple rule of thumb is to pitch 150 to 200ml of thick slurry (i.e. sediment) for every 23 liters of wort for beers up to around 1.065. Only crop from off-flavor-free fermentations that were below 6% alcohol by volume. One can expect a clean fermentation if one follows these simple rules and does not allow the internal temperature of the FV to rise above 20C at the peak of fermentation (some strains can go higher without throwing a lot of trash).

 

[MyQul]

If one can measure, one can repitch slurry. It's that simple. Everything else that I posted was about maximizing yeast health. A simple rule of thumb is to pitch 150 to 200ml of thick slurry (i.e. sediment) for every 23 liters of wort for beers up to around 1.065.

As you say above 150-200ml is a broad rule of thumb to successfully ferment 23L of <1.065 wort. But If I want to follow your guidlines of 3bl/L-5bl/L pitching rate for a British style Ale. So lets say I'm aiming for 5bl/L, based on 1.2bl per ml cels for thick slurry, I need to pitch approx 96ml of thick yeast slurry for a 23L batch? 5blx23L= 115bl divided by 1.2bl/ml= 95.8ml (rounded up to 96ml)

I adjust my starter volume size (I grow all of my starters from slant). For example, my large batch size is roughly 21 liters (my standard batch size is approximately 13.25L). If I want to pitch 3 billion cells per liter, I need to grow approximately 63 billion cells. At a maximum cell density of 200 billion cells per liter, that's a 300ml starter. Pitching that low can be a challenge when starting with a full White Labs vial because they ship from White Labs with 100 billion cells. Hence, one would have to split a relatively fresh White Labs vial into halves or thirds because one wants some new cell growth in the starter. I do not know the average age of a White Labs vial in the UK, but most vials sell before they reach two months of age at my local home brew supply store. At two months, one can assume that a White Labs vial contains approximately 50 billion cells.

I don't buy liquid yeast (well not at the moment but I may do in the future) as it's so expensive here in the UK, about £10/$16 including shipping. So I normally either use dried yeast and harvest slurry or bottle culture and harvest slurry.

Base on what you have told me, being, the maximum cell count in a 1L starter is 200bl cells. I thought this might work, to work out innoculation rates of starters:
If I had some slurry in the fridge for a few weeks and was unsure of the exact viability I could innoculate a 1L starter to ensure a maximum cell density - I thought 70bl-100bl innoculation rate, is this to high/low? Then knowing there is approx 200bl cells in the starter divide the starter based on required pitching rate. So for e.g if I required 100bl cells I would just pour half the starter into the wort. What do you think?

Sorry if it seems I'm bombarding you with questions. There is so much misinformation the internet, particularly about yeast. So I would like to pick your brains while I have the chance.

Cheers in advance :hat:

 

[McMullan]

I started this thread, and to be honest, I wish I hadn't! All I wanted to know was how to re-use what I had from the bottom of my fv. Didn't expect an MSc in yeastology! Appreciate all responses, but for an average homebrewer, you have a)lost my interest and b)confused the s**t out of me. Sorry.

Yeah, academic types will masterbate over the most trivial things, without any regard for real world practicalities. It's a very straightforward procedure, ManseMasher: when you're ready to pitch into your fresh, oxygenated wort, remove as much of the beer from the yeast cake as possible, because you want the slurry at the bottom. Tilt the FV so the slurry gathers to one side. Then scoop out a good (150ish ml) ladle's worth of slurry and stir it into your fresh, oxygenated wort. Job done. I use a stainless ladle and sterilise it in the oven (150 degrees for about 15min). When it has cooled it goes in a bucket of starsan, until needed. Before scooping out the slurry, mist spray the air above the FVs with starsan. Spray your arm that's going in the FV as well.

 

[McMullan]

One can also achieve consistent results from pitching non-rehydrated dry yeast just as one can achieve consistent results and full attenuation by pitching relatively fresh White Labs vials directly into wort. However, neither practice is optimal if long term culture maintenance is desired.

Many brewers are looking for ways to stretch their brewing dollars. One way to achieve this goal is to repitch. Repitching requires one to take steps to maintain yeast health. Pitching, cropping, and stepping at high krausen are time proven methods to maximize yeast health (it's a big part of the reason why Harveys has been able to repitch the same top-cropped yeast culture for over 50 years). I did not make this stuff up. Yeast propagation is well researched just as quiescence and the survival mechanisms that yeast employ at the end of fermentation are well researched.

The number one reason why stir plate users wait until quiescence to pitch is because the media smells and/or tastes foul. Foul smells and tastes are signs that the culture is stressed. That stress is the result of the stir bar causing cell shear stress.

Consistent results are achieved by consistent methodology. We shouldn't underestimate the ability of yeast to adapt very quickly to our own ways of doing things. The reason I take my yeast to the finish line is that they'll be stored until needed. That might be up to a week, sometimes longer, after prepping them. It guarantees I have yeast fit for purpose on brew day. They thrive in wort containing at least a little trub, which provides, e.g., sufficient unsaturated fatty acids and precursors for ergosterol. The truth is there are no ultimate prescriptions for brewing good beer. Just opinions, ranges to target and some basic guidelines to follow. We all brew in our own way, but somehow we all manage to make great beer. In terms of yeast slurry, actually, yeast generally, my advice is use healthy yeast and avoid the risk of under-pitching.

My starter wort usually smells quite pleasant, but I do use my stirrer gently to create a little beneficial mixing. Do you have a credible reference for stir bars causing 'shear stress' to yeast membranes? I was under the assumption that foul starter 'beer' was caused by oxidation?

 

[saccharomyces]

Do you have a credible reference for stir bars causing 'shear stress' to yeast membranes? I was under the assumption that foul starter 'beer' was caused by oxidation?

If you perform a Google search on the terms "magnetic stirrer" and "shear stress," you will get many hits related to patents that attempt to overcome the phenomenon in stirred cultures as well as publications about the phenomenon, including rotational speeds that limit shear stress. I am not pulling this information out of thin air. I started to study this phenomenon after switching to a magnetic stirrer from hand shaken starters.

 

[saccharomyces]

If I had some slurry in the fridge for a few weeks and was unsure of the exact viability I could innoculate a 1L starter to ensure a maximum cell density - I thought 70bl-100bl innoculation rate, is this to high/low? Then knowing there is approx 200bl cells in the starter divide the starter based on required pitching rate. So for e.g if I required 100bl cells I would just pour half the starter into the wort. What do you think?

Yes, pitching half of the starter should work. However, one should always document the performance of a fermentation. If you do not keep a brewing log, you should start with your next batch. One has to adopt the mindset that a non-documented event did not occur when studying yeast behavior. One should document the batch volume and wort composition (including starting gravity), the starter volume and medium (wort) composition (including starting gravity), starter age, the amount of time that elapsed between pitching and the start of high krausen, time to reach terminal gravity, and any other notable events coupled with a sensory evaluation of the finished beer.

If one is happy with the fermentation profile from a batch, one should attempt to repeat it. If the results are the same, then one has a metric that one can used when pitching a strain in one's brewery. If one wants a more estery beer, one should try pitching a smaller starter, aerating well, and fermenting with an internal fermentation temperature of 20C. If one wants a less estery beer, one should try pitching more yeast and limiting the fermentation temperature to 16C. If a yeast strain will not ferment at 16C, switch to one that will.

A lot of breweries here in the U.S. use the same yeast strain for American ales that they use for British styles ales (the strain employed is usually a British strain). British styles are pitched at half of the rate of the American ales. There are also breweries that ferment ales and lagers with the same yeast strain. Once again, the difference is pitch rate coupled with temperature.

Sorry if it seems I'm bombarding you with questions. There is so much misinformation the internet, particularly about yeast. So I would like to pick your brains while I have the chance.

While yeast rinsing shows no sign of dying, there is not as much misinformation as there used to be a few years ago. There's a lot of dogma, but dogma is not as bad as it is limiting oversimplification.

 

[MyQul]

@saccharomyces Thanks mate :thumb: Espeically for what I should be writing in a brew log. You always here the advice 'keep notes!' When I first started brewing I used to wonder what notes I should be keeping, what's relvant and whats not. There's so many possible variables in brewing! I'm still only getting my head around this three years on

Unfortunately I don't have room for a brew fridge so can't keep control of temps as rigourously as I'd like to. But my little brewing corner of the kitchen is pretty stable temp wise. I generally pick stains of yeast which will perform well at a given temp at a given time of year/the ambient temp in my brewing corner.