Just say "no" to yeast rinsing (a.k.a. yeast washing in amatuer brewer terms)

[saccharomyces]

I posted this information on the AHA forum over six years ago, but it appears that many brewers have yet to receive the memo with respect to yeast rinsing being a very poor brewing practice. Like secondary fermentation vessels and stir plates, dogma that is contrary to science is very difficult to kill in the amateur brewing community.

A yeast culture "owns" a batch of wort by shutting out competitors. It rapidly consumes dissolved oxygen, which shuts out aerobic microorganisms. A yeast culture also lowers the pH of the medium from around 5.2 to around 4.2, which shuts out pH sensitive anaerobic microflora. The final defense that a yeast culture mounts is the production of ethanol, which is toxic to microorganisms, including the culture itself.

Replacing green beer with boiled water strips the culture of the force field that it built for itself, which means that the water has to be completely free of wild vegetative cells (and spores that can germinate into vegetative cells) because they will feast on dead yeast cells. Bacteria cells multiply three times faster than yeast cells (i.e, an eight-fold increase in bacteria cell count for every two-fold increase in the yeast cell count), which means that a small infection can overtake a larger yeast culture when pitched into fresh wort.

The best way to crop is to "top crop" at high krausen. However, top-cropping requires one to use a true top-cropping strain in order to be most effective. Top-cropping naturally purifies a culture because wild yeast and bacteria do not floc to the top. Top-cropped yeast can be repitched almost indefinitely.

When using a non-top-cropping yeast strain, I usually leave enough liquid behind after racking to be able to swirl the solids back into suspension (my primary volume is 1/3 to 1/2 gallon larger than the volume I expect to rack). Swirling the solids back into solution using green beer, waiting a few minutes for the heaviest fraction to settle, and then decanting the liquid fraction has the same effect as rinsing with boiled water; however, it keeps the low pH, ethanol laden environment intact. If one wants to attempt to rid the culture of mutants, one can decant and discard most of the supernatant (liquid above the solids) as soon as a creamy layer of yeast forms on the bottom of the container.

As stated above, one of the first things that a yeast culture does when pitched into a batch of wort is to lower the pH from around 5.2 to around 4.2. One has heard that pathogens do not grow in beer. One of the reasons why pathogens do not grow in beer is due to its relatively low pH. For example, Clostridium botulin growth is inhibited below pH 4.6.

Contrary to what was written in early amateur brewing books, brewing yeast cultures do not respire in wort due to a phenomenon known as the Crabtree effect. Hence, brewing yeasts do not go through a period of respirative (aerobic) growth before they start to reproduce fermentatively (anaerobic growth). In the presence of glucose levels above the Crabtree threshold, all reproduction is fermentative. As many of you probably noticed while reading Yeast, yeast cells use dissolved oxygen to build ergosterol and unsaturated fatty acid (UFA) reserves (these reserves are shared with with all of the daughter cells). Yeast cells perform this feat by shunting oxygen to the respirative metabolic pathway while simultaneously metabolizing the carbon source via the fermentative metabolic pathway.

What this preference to reproduce fermentatively means to a brewer is that yeast cells pretty much start producing ethanol almost as soon as they are pitched into a batch of wort. While ethanol has a limiting effect on the viability of a yeast culture, it also protects the culture from infection. Boiled water is not truly sterile. Boiled tap water also tends to have a pH of at least 7.0; therefore, it raises the pH of the culture.

With the above said, most experienced amateur brewers eventually reach the conclusion that one can just crop and repitch without doing anything to separate the viable cells from the dead cells and break material, especially if they leave most of the break and hop material in the kettle. Less is definitely more when cropping yeast.

 

[MmmBeer]

That was an interesting, if somewhat dense quotation. I have no first hand experience in yeast rinsing, having never reused yeast, but I have read about the practice in a text that was geared more to the commercial brewing sector, however that mentioned 'acid rinsing'. This would make more sense, as it would maintain conditions that were unfriendly to competitor microbes. I don't know if this is something that goes on in the homebrewing environment?

 

[Clint]

I thought acid rinsing was that frantic dancing at drug fuelled illegal raves...

 

[The Baron]

A interesting read and something I have found out in my many years of re-pitching that there was no benefit from washing yeast. I did not know the reason why until now but some of the boffins will not agree with this me thinks but is it going to stop them from washing and stir plating who knows. At least it looks like real life pitch and re-pitch has some benefits albeit without me knowing the science behind it

 

[chthon]

For me, the advantage of washing yeast is that I can store it in my refrigerator in small pots.

 

[saccharomyces]

One does not need to rinse yeast with water to store it in the refrigerator. The crop shown below was taken from one of my fermentation vessels using the technique outlined above. Yeast does not need to be trub free. It needs to be stored under the beer it created. Rinsing yeast with boiled water is a bad practice that has been kept alive in the amateur community for some odd reason (we are talking about an old bad bad brewing practice that lives on amateur brewing community). It is not supported by science, nor is it used by professional brewers. Yeast washing an entirely different thing. In yeast washing, the pH is dropped to around 2.9 to rid the culture of wild microflora, which tend to be less hardly than domesticated brewers yeast. Ideally, one wants to top-crop with a true top-cropper after the brown head has been skimmed and the second head has formed. The reason being is that wild microflora does not floc to the surface. The practice of top-cropping yeast gave us mixed domesticated brewing cultures over hundreds of years of selective pressure. In less than 100 years, we have taken ale cultures that were once top-cropping and turned them into bottom-harvested yeast via selective pressure with tower and cylindroconical fermentation vessels. I am curious as to how many crop generations it would take to convert a non-true top-cropper into a top cropper. There is yeast in the krausen of a non-true top-cropper, but it is not significant. If crop this yeast and grow it into a culture large enough to ferment a batch of beer and repeat the skimming process/growing/pitch process serially, we should eventually end up with a culture that is true top-cropping.

Here is NCYC 1333 in a stock pot that I was using an open fermentation vessel:

Vial in which I received the culture on slant (a.k.a. slope)

Shot when the brown head was forming

Shot after the second head formed

NCYC 1333 is Yorkshire strain. The head had the consistency of thick pancake batter.

 

[Sadfield]

Washing always struck me as unnecessary, and beer was an adequate medium given that yeast can be recovered from beer bottles decades old.

 

[Thatscold]

Can you elaborate on your comment on stir plates? I don’t have one, but was thinking of purchasing one.

 

[Jim Brewster]

I've reused yeast by pitching onto old yeast, rinsing just seems like potential for introducing infection so I've never felt the need

 

[saccharomyces]

Can you elaborate on your comment on stir plates? I don’t have one, but was thinking of purchasing one.

Contrary to what proponents of stir plates say, a yeast culture does not need to be stirred in order for the cells to remain in suspension. Most brewing strains exhibit what is known as the NewFlo phenotype, which means that the cells will remain in suspension as long as there are sugars that inhibit the flocculin coating (the yeast equivalent of Velcro) on a yeast cell wall from binding to other yeast cells (a.k.a. flocculation). Do you not find it to be curious that the stiring cultures is promoted by amateur brewers, yet, no mention is ever made about stirring wort? That is because it is yet another example of non-science-based amatuer brewing dogma. If you to understand why stir plates are a waste of money, please read my blog entry entitled "Shaken, not Stirred: The Stir Plate Myth Buster" (Shaken, not Stirred: The Stir Plate Myth Buster | Experimental Homebrewing).

 

[Scrattajack]

Yeast does not need to be trub free. It needs to be stored under the beer it created.

So harvesting from your own bottle-conditioned brews is a sound move?

 

[saccharomyces]

Washing always struck me as unnecessary, and beer was an adequate medium given that yeast can be recovered from beer bottles decades old.

The technique for rinsing yeast was originally published in Charlie Papapazian's book "The Complete Joy of Homebrewing." That book was the amateur brewing bible here in the United States until John Palmer's book was released. It was described as a way to re-use yeast. The sad thing is that it lives on as a dated practice when other dated practices from that book such as using a secondary fermentation vessel have gone the way of the do-do bird. One can count on at least one amatuer brewer publishing an article on how to rinse yeast every few months here in the United States. The practice will die one day.

 

[saccharomyces]

So harvesting from your own bottle-conditioned brews is a sound move?

How good is your sanitation? The first yeast I cultured in 1993 was from the sediment in a bottle of Sierra Nevada Pale ale. The thing about harvesting yeast from a bottle of bottle-conditioned beer is that the beer needs to be gently decanted leaving behind about 10ml of fluid and the yeast culture after wiping the lip of the bottle with at least 70% (at least 140 proof) clear neutral spirits to remove and dust that may have been sandwiched between the cap and the top of the bottle. The 10ml of fluid and yeast in the culture is then used to inoculate about 50ml of 5% w/v (1.020 S.G.) boiled and cooled wort (that is 2.5 grams of DME in 50 ml of water). After this small starter reaches high krausen, it be used to inoculate a 10% w/v solution (1.040 S.G.) 1L starter (100 grams of DME boiled in 1L of water). The resulting starter will actually be 1.05L after the 50ml starter is pitched. The 1.05L starter can be pitched directly into 23L of wort after it reaches high krausen. One really needs to pay attention to detail and sanitation when using the dregs from a bottle of bottle-conditioned beer to inoculate 50ml of boiled and cooled 1.020 wort. As most beer infections are pitched with the starter, it is important to limit exposure to native house microflora at this stage. This technique can be used to harvest yeast from any bottle conditioned beer. Remember, the 50ml and 1L starters need to be shaken to aerate the wort, so the containers chosen to have a lid that can be screw down tight and then loosened to allow CO2 to escape after the wort has been inoculate.

 

[Zephyr259]

Contrary to what proponents of stir plates say, a yeast culture does not need to be stirred in order for the cells to remain in suspension. Most brewing strains exhibit what is known as the NewFlo phenotype, which means that the cells will remain in suspension as long as their are sugars that inhibit the flocculin coating (the yeast equivalent of Velcro) on a yeast from binding to other yeast cells (a.k.a. flocculation). Do you know find it to be curious that the stiring cultures is promoted by amateur brewers, yet, no mention is ever made about stirring wort? That is because it is yet another example of non-science-based amatuer brewing dogma. If you to understand why stir plates are a waste of money, please read my blog entry entitled "Shaken, not Stirred: The Stir Plate Myth Buster" (Shaken, not Stirred: The Stir Plate Myth Buster | Experimental Homebrewing).

The SNS starter does sound handy since it's so much quicker than using a stirplate but how do you handle pitch rates? I've been using a calculator for years which works out my starter growth and the model (which I'm pretty sure is based on experimental data) gives a much greater growth rate on stir plate than any other method.

I overbuild my starters and keep back 100 billion cells for the next batch, that's not as easy to do with a SNS starter.

 

[saccharomyces]

The SNS starter does sound handy since it's so much quicker than using a stirplate but how do you handle pitch rates? I've been using a calculator for years which works out my starter growth and the model (which I'm pretty sure is based on experimental data) gives a much greater growth rate on stir plate than any other method.

I overbuild my starters and keep back 100 billion cells for the next batch, that's not as easy to do with a SNS starter.

Most of the stir plate data is the result of amatuer brewer confirmation bias. The experiments are set up that way. The cold hard reality is that stir plates are not used for propagating yeast cells in microbiology. They are used for mixing solutions in a non-contaminating way. The correct device cell culture is known as a shaker table. That is what is used at White Labs to propagate new seed cultures from working slants.

The reality is the only thing that matters in batch yeast propagation is having dissolved O2 available during the lag phase as well as having enough carbon (sugar is carbon bound to water) to support replication through the exponential growth phase (high krausen is the demarcation line between the exponential growth phase and the stationary phase). I can assure you that the stir plate data you are viewing did not compare a stir plate to direct O2 injection. Most of that data was a stir plate versus periodic shaking an Erlenmeyer flask that is not much bigger than the culture. A lot of the stir plate data is BS because a culture cannot exceed maximum cell density for a given volume. What happens is that people are basing their conclusions on yeast sediment volume, not viable cell count. After maximum cell density has been achieved, cell reproduction is for replacement only and a stir plate results in a lot of premature cell death due to shear stress from stir bar (i.e., the stir bar is a source of friction on yeast cell walls).

We are doing is known as step propagation. In step propagation, a culture should be stepped at high krausen, not after it has fermented out. The reason being that for what I mentioned above; namely, all reproduction after maximum cell density has been reached is for replacement only. Since mother cells share the ergosterol and unsaturated fatty acid reserves they built during the lag phase with their daughters and their daughters share their ergosterol and unsaturated fatty acid reserves and so forth, allowing a culture to ferment beyond high krausen being reached results in a waste of these compounds. Allowing a culture to ferment out not only waste ergosterol and unsaturated fatty acid reserves, yeast cells undergo morphological changes in preparation for quiescence. What does this information mean to a brewers, it means that allowing a culture to ferment out increases O2 demand when the yeast culture is pitched as well as results in a longer lag time. Th proof is in the pudding. Every brewer who has tried SNS has either parked or sold his/her stir plate. A stir plate is a "not needed" piece of homebrewing equipment. It is supported by data that is not grounded in science. SNS is little more than a poor man's O2 bottle and diffusion stone coupled with a culturing best practice, which is pitching at high krausen.

 

[Zephyr259]

Most of the stir plate data is the result of amatuer brewer confirmation bias. The experiments are set up that way. The cold hard reality is that stir plates are not used for propagating yeast cells in microbiology. They are used for mixing solutions in a non-contaminating way. The correct device cell culture is known as a shaker table. That is what is used at White Labs to propagate new seed cultures from working slants.

The reality is the only thing that matters in batch yeast propagation is having dissolved O2 available during the lag phase as well as having enough carbon (sugar is carbon bound to water) to support replication through the exponential growth phase (high krausen is the demarcation line between the exponential growth phase and the stationary phase). I can assure you that the stir plate data you are viewing did not compare a stir plate to direct O2 injection. Most of that data was a stir plate versus periodic shaking an Erlenmeyer flask that is not much bigger than the culture. A lot of the stir plate data is BS because a culture cannot exceed maximum cell density for a given volume. What happens is that people are basing their conclusions on yeast sediment volume, not viable cell count. After maximum cell density has been achieved, cell reproduction is for replacement only and a stir plate results in a lot of premature cell death due to shear stress from stir bar (i.e., the stir bar is a source of friction on yeast cell walls).

We are doing is known as step propagation. In step propagation, a culture should be stepped at high krausen, not after it has fermented out. The reason being that for what I mentioned above; namely, all reproduction after maximum cell density has been reached is for replacement only. Since mother cells share the ergosterol and unsaturated fatty acid reserves they built during the lag phase with their daughters and their daughters share their ergosterol and unsaturated fatty acid reserves and so forth, allowing a culture to ferment beyond high krausen being reached results in a waste of these compounds. Allowing a culture to ferment out not only waste ergosterol and unsaturated fatty acid reserves, yeast cells undergo morphological changes in preparation for quiescence. What does this information mean to a brewers, it means that allowing a culture to ferment out increases O2 demand when the yeast culture is pitched as well as results in a longer lag time. Th proof is in the pudding. Every brewer who has tried SNS has either parked or sold his/her stir plate. A stir plate is a "not needed" piece of homebrewing equipment. It is supported by data that is not grounded in science. SNS is little more than a poor man's O2 bottle and diffusion stone coupled with a culturing best practice, which is pitching at high krausen.

Thanks for the detailed response, but you didn't actually answer my question of how you go about hitting a target pitch rate. My recent RIS at 1.103 OG is going to need more yeast than my bitter at 1.040, do you just work with the stated cells on a pack of yeast, pitching more than one pack in high gravity beers, and then do a SNS to get them going?

The calculator that I (and a few other here) use is the brewunited one, which works with experimental data Kai Troester did, I've not dug too deep into his work but it is based on cell counts and not slurry volume as you assume, it also accounts for maximum population density within the starter medium.

End of the day, SNS may be "better" but stir plates work just fine for the majority of homebrewers so there are worse things folks could be doing.

 

[Drunkula]

Is there any cell count data for the shaken not stirred (SNS) methodology compared to stir plates? I read the blog and all theory is nice but I want comparative data.

I see that you've been pushing this idea for at least six years now so there should be some sort of usable data somewhere.

 

[Bill_g]

To Sacharomyces
Very interesting and persuasive arguments. Having read all of your comments and your Shaken not Stirred article what I'd love to see is a step by step 'how to do it' description i.e. take out all the argument, microbiological info etc and just concentrate on the practical details please. Ideally from yeast harvest technique through to final pitching method & rates. Perhaps that information is in your articles but after a single read I feel there's a lack of practical clarity as the method is obfiscated by the microbiological detail. I'd like to give this method a try but would really like to be sure that I follow your method without filling in the gaps with my own assumptions or possibly incorrect interpretation.

 

[BlackRegent]

But White Labs themselves recommend the use of a stir plate for making yeast starters...



I find it hard to believe that they would be sucked into perpetuating a homebrew myth if there were not some evidence to support it

 

[Hanglow]

I did the shaken not stirred method after Sacharomyces (yeast whisperer I think?) first mentioned it on Jims a few years ago and have never felt the need to use a stir plate since. I only use it for the likes of bitters, pale ales etc usually, as it's very easy and works very well - I save about 1l wort from a previous brew which I freeze untill needed, the night before a brewday, then use a typical gallon glass demijohn and rubber bung to shake up and ferment the starter, then pitch the whole lot the next day into the brew.

For bigger brews I reuse yeast from a recently brewed smaller beer like a bitter , or use nottingham which I like for big beers.