The cold hard truth about rinsing yeast with boiled water

[AnOldUR]

Rinsing yeast with boiled water is an unnecessary step that does little more than introduce one or more infection vectors.

Infection vector? That must be like an Arctic Vortex. I swear, people must sit around making this stuff up.

But it is entertaining.

 

[boydster]

I know.. and we used to have Polio and TB ins this country too. I'll take my chances with the gram negative bacteria you provided..

So cervid, you took your chance and didn't get a polio vaccine?

Clearly, one can take the attitude that doing the extra work of boiling and cooling water to store the yeast under is good enough to take the chance, or one could take the approach that there is less work involved and fewer chances to be taken by keeping the yeast under green beer. I guess I don't understand why someone would "take [one's] chance" and add in additional steps, given that the alternative seems less involved. I guess I probably don't care to understand, either, because doing more work to take a greater risk seems foolish to me. What am I missing here? Seems like an easy "necessary risk vs. unnecessary risk" question to me.

 

[mattd2]

Saccharomyces cerevisiae is a yeast species. Megasphaera cerevisiae is a family of gram-negative anaerobic spoilage bacteria.

Not what I was meaning - Where all these discovered by some guy called Cerevis or something?

 

[Bottoms_Up]

There seems to be a lot of hypotheticals. I would like to see the results of further tests, such as the one EAZ suggested.

 

[EarlyAmateurZymurgist]

Exactly! There is one Bacillus species that forms spores and can grow in wort, but it is sensitive to ethanol and hops, so it is not a concern.

Spores are not little magic nuggets of bacteria that can just start growing whenever, like in cold water for instance. You can pitch your yeast stock (however you wash, store, harvest, crop, whatever), and it will have spores in in no matter what you do, but the conditions of your beer prevent the growth.

I agree with your assertions that washing with boiled water is not necessary, although certainly not harmful. Are spores what you should be worried about when preparing your yeast? No.

What about vegetative cell growth while stored under boiled water? I have never had spores germinate in crop that I stored under beer; however, I have had spores germinate while stored under boiled water. Either that, or vegetative cell pickup occurred during the transfer. I am fairly anal about liquid culture transfers. I try to get positive pressure going in the culture and I flame or 95% ethanol sterilize all pouring surfaces.

In the ten year period spanning 1993 through 2003, I tried every way to store yeast that was practical in a home brewery environment. While I have experienced okay results with freezing at -20C, my best long-term results have been with slants. I found that it's just easier to maintain a pure culture using slants and basic aseptic lab technique. Every other technique that I used resulted in lower than desired long-term viability. My wife suggested purchasing a desktop lyophilizer. I think she was kidding, but they are starting to reach the affordable point (affordable is a relative term).

 

[EarlyAmateurZymurgist]

Infection vector? That must be like an Arctic Vortex. I swear, people must sit around making this stuff up.

But it is entertaining.

Actually, it's a real term.

 

[EarlyAmateurZymurgist]

Well.. Not really.. According to EAZ those labs you slant from could be infected to as they are not completely sterile.

I did not claim that all liquid cultures are infected. I claimed that yeast manufacturers have a statistically-controlled acceptable level of contamination, which is a fact. Have you ever plated a commercial yeast culture on selective or differential media?

 

[ColoHox]

What about vegetative cell growth while stored under boiled water? I have never had spores germinate in crop that I stored under beer; however, I have had spores germinate while stored under boiled water. Either that, or vegetative cell pickup occurred during the transfer. I am fairly anal about liquid culture transfers. I try to get positive pressure going in the culture and I flame or 95% ethanol sterilize all pouring surfaces.

In the ten year period spanning 1993 through 2003, I tried every way to store yeast that was practical in a home brewery environment. While I have experienced okay results with freezing at -20C, my best long-term results have been with slants. I found that it's just easier to maintain a pure culture using slants and basic aseptic lab technique. Every other technique that used resulted in lower than desired long-term viability. My wife suggested purchasing a desktop lyophilizer. I think she was kidding, but they are starting to reach the affordable point (affordable is a relative term).

It is very unlikely that storage under water was the reason for contamination, and also unlikely that bacterial spores were the source, for the reasons I have mentioned. However, even with the use of a hood, a biocontainment suit, and practiced sterile technique, contamination with vegetative cells from any number of locations is very likely, in all microbiological situations. Assigning the source of the contamination is notoriously difficult. It is just so easy to setup a lovely experiment testing the two storage conditions, bump the tip of your pipette on whatever, and throw all the results off.

I agree that plating or slanting is the best technique for the maintenance of pure cultures. However, bulk storage is best achieved via freezing. Bulk stocks are produced from your pure cultures on your plate and are, with proper technique, clean. For example, storing 50ml of frozen culture sourced from a plated culture is the proper method. Yes, your slant is pure, but upscaling is time consuming and introduces more chances for contamination. Slanting and freezing are different tools for different jobs.

Fortunately I have access to autoclaves, hoods and a lyophilizer but they would sure be more convenient in my basement.

Cheers to sticking to your guns, but scientists (even amateur ones) recognize the value of an open mind and incorporating new information. Send me some of your Ringwood so I can bulk culture it, would ya.

 

[EarlyAmateurZymurgist]

Not what I was meaning - Where all these discovered by some guy called Cerevis or something?

No, cerevisiae is derived from cerevisia, which is the Latin name for beer. Sacchormyces cerevisiae basically translates to sugar fungus of beer.

 

[mattd2]

No, cerevisiae is derived from cerevisia, which is the Latin name for beer. Sacchormyces cerevisiae basically translates to sugar fungus of beer.

Thanks, thought it would be something like that!

 

[EarlyAmateurZymurgist]

I agree that plating or slanting is the best technique for the maintenance of pure cultures. However, bulk storage is best achieved via freezing. Bulk stocks are produced from your pure cultures on your plate and are, with proper technique, clean. For example, storing 50ml of frozen culture sourced from a plated culture is the proper method. Yes, your slant is pure, but upscaling is time consuming and introduces more chances for contamination. Slanting and freezing are different tools for different jobs.

Are you using a true cryogenic freezer? I did not have great success with cryopreservation at -20C using a home freezer. No matter what I did, I always experienced cell rupture. I believe that problem lies in my inability to control the freeze/thaw rate accurately, especially the freeze rate.

Send me some of your Ringwood so I can bulk culture it, would ya.

Sadly, I no longer have that culture. I left the hobby for decade. I should have deposited it, but I did not feel the need at the time (I was fairly burned out from a decade of intense brewing and playing with yeast cultures). The brewery from which I obtained the culture was an early Pugsley-built brewery. The owners sold the brand name to another local brewery and sold the brew house to an out of state interest.

With that said, there is a early Pugsley-built brewpub in operation in my area that still uses their original yeast culture and brew house. I have attempted to talk the brewmaster into giving me crop, but have had no luck thus far. Getting my old crop was as simple as taking a 4oz sterile baby food with me when I visited the defunct Pugsley-built brewery. I asked the brewer if I could have one of his hydrometer samples, and he said, "Yes." It was dumb luck.

 

[EarlyAmateurZymurgist]

Thanks, thought it would be something like that!

What's weird is that only one Latin-based language has a name for beer that is even close is Spanish.

 

[gwapogorilla]

Water boils at 212F/100C at standard atmospheric pressure (atm). If we raise the pressure under which water is boiled to 15 pounds per square (psi) inch above normal atmospheric pressure, the boiling point increases to 250F/121C. Basically, the water inside of a 15 psi pressure cooker operated at sea level experiences a little more two atms.

Is it the water that raises above 212*...or the steam? Everything I've learned through the years says water gets to 212*, and that's it. Steam on the other hand is hotter than water, "when pressurized". In a pressure cooker, it's the steam due to the increased pressure that raises in temp, not the water itself.

 

[harrke]

The steam and water are in a saturated environment (meaning that there is as much vapor becoming liquid as there is liquid becoming vapor). In this case, the "steam" and "water" are at the same temperature.

 

[mtnagel]

So cervid, you took your chance and didn't get a polio vaccine?

Clearly, one can take the attitude that doing the extra work of boiling and cooling water to store the yeast under is good enough to take the chance, or one could take the approach that there is less work involved and fewer chances to be taken by keeping the yeast under green beer. I guess I don't understand why someone would "take [one's] chance" and add in additional steps, given that the alternative seems less involved. I guess I probably don't care to understand, either, because doing more work to take a greater risk seems foolish to me. What am I missing here? Seems like an easy "necessary risk vs. unnecessary risk" question to me.

But what I haven't seen answered is how to store harvested slurry for several months without agar slants and freezing? Many people have used rinsed yeast successfully up to a year later. But everything I've read says to not use the harvested yeast slurry after 2-4 weeks. I don't brew enough to do that. How can I make my slurry last longer without agar slants and freezing (which I may look at in the future)?

 

[cervid]

If i didn't ask, i don't know, 5 times for am answer from you that would be one thing. If you didn't directly respond to me twice after i asked the question and still be unable to answer said question, well that's a different matter. Just say you don't know.

I got all my vaccines, you can't go to college if you don't have them. I don't think I got MMR though, if I did, I didn't pass my titer test 6 years ago to get operating room access privileges. I've risked my life many times, as I'm sure everyone else has. I'm not so uptight that I'm afraid to risk a little 5 gallon batch of beer. Our a pint of yeast.

But, if you're the expert on thus, why haven't you performed said experiment yet? I think the onus I'd on you to do that. Maybe you should've done that before debating in such a know it all manner, speaking as if you have facts and are dealing with certainties.

Oh and, I don't think anyone is attacking you, it's a debate. You brought it on yourself. If you're going to argue against the way people have been doing something for so long, the burden of proof is on you.

Note: on phone working, sorry if spellcheck got me.

 

[masonsjax]

But what I haven't seen answered is how to store harvested slurry for several months without agar slants and freezing? Many people have used rinsed yeast successfully up to a year later. But everything I've read says to not use the harvested yeast slurry after 2-4 weeks. I don't brew enough to do that. How can I make my slurry last longer without agar slants and freezing (which I may look at in the future)?

It means you shouldn't use only the slurry after four weeks but should instead make a starter from that slurry. You can safely store it much longer than a month but you should make a starter before using it.

 

[AnOldUR]

Infection vector? That must be like an Arctic Vortex. I swear, people must sit around making this stuff up.

Actually, it's a real term.

But obscure enough that when Googled I only get reference to computer viruses. You're definitely a bright guy, but have this flaw of latching on to stuff like "boiled water isn't sterile" and become obsessed with it. You revel in spitting out your interpretation of science in the faces of people knowing that they don't have the education to contradict you. Like I said, taking it in with an open mind this is entertaining, but can also be educational. But what you say has to be taken with a grain of salt. Is it useful, practical information to us as homebrewers or is it someone’s attempt to boost their ego? I think a little of both.

Please don't take this as a personal attack. It's my honest observation. I'll take my blue collar opinions into lurk mode and only observe from here on out.

 

[masonsjax]

Infection vector, as in another site for infection to take hold. Makes sense to me. *shrug*

 

[rpkincaid]

Does anyone know what goes into white labs tube or wyeast packs with the yeast? Is it fermented wort/media or rinse water? Anyone know the pH of the liquid in those packages?

 

[ColoHox]

It's not obscure, although perhaps not the perfect term for this situation:

http://en.m.wikipedia.org/wiki/Vector_(epidemiology)

A fomite is likely the source of the "infection": http://en.m.wikipedia.org/wiki/Fomite

 

[EarlyAmateurZymurgist]

But what I haven't seen answered is how to store harvested slurry for several months without agar slants and freezing? Many people have used rinsed yeast successfully up to a year later. But everything I've read says to not use the harvested yeast slurry after 2-4 weeks. I don't brew enough to do that. How can I make my slurry last longer without agar slants and freezing (which I may look at in the future)?

Two to four weeks is the pitching without feeding period. You can keep a culture under beer for a long time. Even cultures that have been keep under unrefrigerated high gravity beer can often be restarted after six months to a year. Look at how many people have had success propagating Belgian strains. Is this storage method feasible? Sure, but it is not optimal, and neither is storage under boiled tap water.

 

[mtnagel]

It means you shouldn't use only the slurry after four weeks but should instead make a starter from that slurry. You can safely store it much longer than a month but you should make a starter before using it.

Thank you for replying. I always assumed I'd have to make a starter.

But, how much longer is, "much longer?"

And what do I use for my viability %? Mrmalty says the viability drops to 10% after 53 days and stays at 10% until 365 days when it drops to 1% until infinity apparently. I'm betting that isn't quite what happens in reality

 

[mtnagel]

Two to four weeks is the pitching without feeding period. You can keep a culture under beer for a long time. Even cultures that have been keep under unrefrigerated high gravity beer can often be restarted after six months to a year. Look at how many people have had success propagating Belgian strains. Is this storage method feasible? Sure, but it is not optimal, and neither is storage under boiled tap water.

Thank you very much!

Any thoughts on MrMalty's viability calculation that I mentioned above:

And what do I use for my viability %? Mrmalty says the viability drops to 10% after 53 days and stays at 10% until 365 days when it drops to 1% until infinity apparently. I'm betting that isn't quite what happens in reality

 

[EarlyAmateurZymurgist]

The steam and water are in a saturated environment (meaning that there is as much vapor becoming liquid as there is liquid becoming vapor). In this case, the "steam" and "water" are at the same temperature.

Your profile states that you work in reactor operations. Are you a former Navy "Nuke?"

 

[masonsjax]

Thank you for replying. I always assumed I'd have to make a starter.

But, how much longer is, "much longer?"

And what do I use for my viability %? Mrmalty says the viability drops to 10% after 53 days and stays at 10% until 365 days when it drops to 1% until infinity apparently. I'm betting that isn't quite what happens in reality

To me viability percentage isn't important. As long as there is some living yeast, starters can be made and stepped up until desired pitch rate is achieved. I've successfully done it with slurry that was in my fridge for close to two years. I generally only use a handful of strains lately and they don't sit for more than 6 months, which is no problem.

 

[mtnagel]

To me viability percentage isn't important. As long as there is some living yeast, starters can be made and stepped up until desired pitch rate is achieved. I've successfully done it with slurry that was in my fridge for close to two years. I generally only use a handful of strains lately and they don't sit for more than 6 months, which is no problem.

Yeah, it's probably me just being anal, but I like to calculate and see the number of cells I created to match the number of cells needed for a given batch. Of course those numbers are approximations on approximations (without counting with a microscope), so I shouldn't worry so much, but I still do

 

[EarlyAmateurZymurgist]

If i didn't ask, i don't know, 5 times for am answer from you that would be one thing. If you didn't directly respond to me twice after i asked the question and still be unable to answer said question, well that's a different matter. Just say you don't know.

I answered a lot questions out of turn.

I got all my vaccines, you can't go to college if you don't have them. I don't think I got MMR though, if I did, I didn't pass my titer test 6 years ago to get operating room access privileges. I've risked my life many times, as I'm sure everyone else has. I'm not so uptight that I'm afraid to risk a little 5 gallon batch of beer. Our a pint of yeast.

While I did not ask you if you bothered to get vaccines, my "uptightness" is more about off-flavors than the fear of illness. I like super clean fermentations. The only way to achieve that result is to be super anal about biological quality control. Bacteria is not the only threat to beer, so is mold and wild yeast contamination.

Oh and, I don't think anyone is attacking you, it's a debate. You brought it on yourself. If you're going to argue against the way people have been doing something for so long, the burden of proof is on you.

Challenge is probably a better word than attack, but the tone of your posts sound like attacks. You have not presented one shred of evidence to support the claim that rinsing yeast with boiled water and storing it under boiled water is better than leaving it under green beer. I have presented several reasons why not doing it is beneficial to the culture. Even ColoHox agrees that it is biologically safer to store a culture under green beer.

By the way, rinsing yeast with boiled water is not a time honored practice. Rinsing yeast with boiled water and storing yeast under boiled water did not become a large-scale practice in the amateur brewing community until last few years, mainly because it is practiced like a religion on this site (the yeast rinsing threads on this site are referenced on other sites, which is how I found HBT). The first thing that forum members do when a forum member asks how to reuse yeast is to direct him/her to a yeast rinsing thread. Yeast rinsing is unnecessary step that can be harmful to the culture. That's a fact.

 

[Orthobrewsky]

Since you are a doubting Thomas, I challenge you to a store a culture rinsed with boiled water under under boiled water and an unrinsed sample from the same culture under beer. In two months, I want to you send the culture to a reputable lab for analysis. If there is no difference in the bacteria or mold counts between the cultures, I will acquiesce and never discuss this topic again.

Have you done this? If so, I'd be very interested in the results. Until you do this or reference the report of someone who has, you are just making conjectures.

 

[VT-NAV]

But obscure enough that when Googled I only get reference to computer viruses. You're definitely a bright guy...

I'm not sure which Google you're using, but when I go to google.com and type in "infection vector" I get this top result - which is how epidemiologists use the phrase.

Farther down, there are also some results relating to malware and computer viruses such as you described.

"Vector" is commonly used to term to describe the agent or method of transmission of a disease or infection. For instance, European black rats carried fleas that were the Bubonic Plague vector.

In the context of beer, his use of the term "infection vector" is entirely appropriate.

You're accusing someone else of being arrogant, but are in the process of making an argument that can be summed up as "I've never heard of this phrase before therefore it must be bullcrap," - an argument which happens to be classic academic arrogance.

 

[ColoHox]

Have you done this? If so, I'd be very interested in the results. Until you do this or reference the report of someone who has, you are just making conjectures.

Yes, the onus of proof is on the claim-maker. Some solid evidence would be great!

You have attacked EAZ's claims in this whole thread without posting once about your approach? Does that mean you have never attempted preserving yeast and are just irritated with EAZ's claims?

Why not post your personal experience in yeast preservation so we can compare and contrast the different approaches?

 

[Orthobrewsky]

If you're going to argue against the way people have been doing something for so long, the burden of proof is on you.

And there's a good point. Also, we have heard an argument from silence repeatedly, such as:

"Chris White never mentions this practice when speaking before professional brewers"

"not one scientific paper exists that supports the practice of rinsing yeast with boiled tap water and/or storing it under boiled tap water."

Even assuming that EAZ really knows everything Chris White has said and has read every scientific paper in existence, I don't think the argument is very good.

I have specifically asked for studies or quotes from authorities stipulating that such a practice is significantly harmful. I have not received any.

Arguing from silence just isn't good enough in this case. However, any of us who disagree with EAZ might make a good argument from science. Why? This is such a well known and widespread practice, even being recommended in very popular books by Chris White/Jamil, John Palmer, Gordon Strong, etc. If a clear condemnation of the practice from a brewing scientist cannot easily be found, then, as they say, the silence is deafening and, as they also say, silence is assent.

For the record, EAZ, I have no reason to think that Chris White would give the distinct impression, in writing, that the book Yeast is primarily his work unless it was. It would be entirely against any scientific ethics to not at least approve of what is in the book. I also think it is clear that Jamil has talents other than self-promotion.

 

[boydster]

While I did not ask you if you bothered to get vaccines...

I am probably the person he directed that comment towards because I asked him if he decided not to get vaccinated against polio. He seemed to equate the irrelevance of worrying about contracting polio in the US with the irrelevance of worrying about contamination of a yeast culture stored under boiled tap water in this post:

I know.. and we used to have Polio and TB ins this country too. I'll take my chances with the gram negative bacteria you provided..

But hey, thanks for stepping up to the challenge I proposed to EAZ..

I'm still not understanding something though. Help me. EAZ, your argument seems to be that one can keep a culture more effectively than the current common practice allows for, and with fewer steps. If true, there is something to gain: time, simplicity, and culture stability. cervid, your argument seems to be that there is no appreciable difference between keeping the culture under green beer or boiled tap water, and so one should continue using the boiled tap water technique. I see nothing to gain, because if there truly is no appreciable difference then why would anyone want to go through the trouble of including additional steps that offer no benefit? Doesn't that make the argument kind of pointless?

Am I wrong about either of your stances? If so, I apologize for my ignorance and please correct me.

 

[Orthobrewsky]

Yes, the onus of proof is on the claim-maker. Some solid evidence would be great!

You have attacked EAZ's claims in this whole thread without posting once about your approach? Does that mean you have never attempted preserving yeast and are just irritated with EAZ's claims?

Why not post your personal experience in yeast preservation so we can compare and contrast the different approaches?

Do you mean something like this? https://www.homebrewtalk.com/f163/c...t-boiled-water-451925/index3.html#post5806534

I admit it's not much, but the best I can do with the equipment I have. So far as his claims go, I stated early on that his approach certainly had merits, but I think his confidence level about certain things is not justified. He seems to be saying more than just that he thinks his recommended process is best, but that what is commonly done is harmful, and at some points he seems to be saying it is actually likely to result in infection.

Actually, I think his recommended process may indeed be best.

 

[EarlyAmateurZymurgist]

Have you done this? If so, I'd be very interested in the results. Until you do this or reference the report of someone who has, you are just making conjectures.

The closest thing that I have encountered to a published formal study is part of an article that Chris White wrote for BrewPub magazine.

http://www.probrewer.com/resources/library/bp-healthyyeast.php

"Storing yeast under water, as opposed to under beer, is becoming more popular. Sterile distilled water storage puts yeast in a resting state, and some reports suggest yeast can be stored in this manner for years, with no refrigeration. Storage under water is generally done with small quantities of yeast, which are then propagated in a lab. But it is possible that this can be applied to storage of yeast slurries. Some brewers are now trying this. The key is to use sterile distilled water and wash the yeast slurry several times in the sterile distilled water to remove any traces of beer. This is best done with a centrifuge, but that is impractical for most craft brewers. White Labs has had mixed success with sterile water storage, so time will tell if this procedure will work for craft breweries."

Notice that Chris states that he used "sterile distilled water," not boiled tap water. He also used centrifuged cultures. Storing cultures completely nutrient and organic matter free under sterile distilled water is something that the American Type Culture Collection (ATCC) was promoting two decades ago. However, they were promoting the technique as a way to maintain laboratory cultures, not brewery crops.

 

[afr0byte]

The closest thing that I have encountered to a published formal study is part of an article that Chris White wrote for BrewPub magazine.

http://www.probrewer.com/resources/library/bp-healthyyeast.php

"Storing yeast under water, as opposed to under beer, is becoming more popular. Sterile distilled water storage puts yeast in a resting state, and some reports suggest yeast can be stored in this manner for years, with no refrigeration. Storage under water is generally done with small quantities of yeast, which are then propagated in a lab. But it is possible that this can be applied to storage of yeast slurries. Some brewers are now trying this. The key is to use sterile distilled water and wash the yeast slurry several times in the sterile distilled water to remove any traces of beer. This is best done with a centrifuge, but that is impractical for most craft brewers. White Labs has had mixed success with sterile water storage, so time will tell if this procedure will work for craft breweries."

Notice that Chris states that he used "sterile distilled water," not boiled tap water. He also used centrifuged cultures. Storing cultures completely nutrient and organic matter free under sterile distilled water is something that the American Type Culture Collection (ATCC) was promoting two decades ago. However, they were promoting the technique as a way to maintain laboratory cultures, not brewery crops.

Got it. If you're going to rinse, use pressure cooked water.

 

[Seven]

By the way, rinsing yeast with boiled water is not a time honored practice. Rinsing yeast with boiled water and storing yeast under boiled water did not become a large-scale practice in the amateur brewing community until last few years, mainly because it is practiced like a religion on this site (the yeast rinsing threads on this site are and referenced on other sites, which is how I found HBT). The first thing that forum members do when a forum member asks how to reuse yeast is to direct him/her to a yeast rinsing thread. Yeast rinsing is unnecessary step that can be harmful to the culture. That's a fact.

Not with me it isn't! I employ the simple method of capturing slurry from the fermenter once fermentation is complete and re-use it within a week or two. Mainly because I'm lazy but also because I didn't see the point in washing it with water that is probably laden with various chemicals or other impurities. I always felt the entire "yeast washing" process was yet another way to contaminate my sample. I hadn't considered the pH difference between water/beer until now. Thanks for that info!

 

[Orthobrewsky]

The closest thing that I have encountered to a published formal study is part of an article that Chris White wrote for BrewPub magazine.

http://www.probrewer.com/resources/library/bp-healthyyeast.php

"Storing yeast under water, as opposed to under beer, is becoming more popular. Sterile distilled water storage puts yeast in a resting state, and some reports suggest yeast can be stored in this manner for years, with no refrigeration. Storage under water is generally done with small quantities of yeast, which are then propagated in a lab. But it is possible that this can be applied to storage of yeast slurries. Some brewers are now trying this. The key is to use sterile distilled water and wash the yeast slurry several times in the sterile distilled water to remove any traces of beer. This is best done with a centrifuge, but that is impractical for most craft brewers. White Labs has had mixed success with sterile water storage, so time will tell if this procedure will work for craft breweries."

Notice that Chris states that he used "sterile distilled water," not boiled tap water. He also used centrifuged cultures. Storing cultures completely nutrient and organic matter free under sterile distilled water is something that the American Type Culture Collection (ATCC) was promoting two decades ago. However, they were promoting the technique as a way to maintain laboratory cultures, not brewery crops.

Well, you said it was the closest you could find. For those who don't know, what I was asking for was a study in which a typical, homebrewer rinsed sample was compared for the presence of unauthorized microorganisms with an otherwise identical sample harvested and stored in the way you recommend.

However, this was an interesting response. I was aware of the technique referenced in your post. To the extent that you are fighting the misconception in the minds of some typical rinsers that they are doing what White spoke of, I support you fully. There's no chance of achieving this special kind of suspended animation without a very thorough rinse with sterile distilled water. In this case, the sterility if the water is very significant, because the water you use will account for nearly all of the liquid involved.

 

[EarlyAmateurZymurgist]

Got it. If you're going to rinse, use pressure cooked water.

Also, if one is planning to store yeast under sterile distilled water, it needs to be centrifuged yeast; otherwise, there is no advantage to storing yeast under sterile distilled water.

Chris even admits that it is generally accepted by the brewing community that yeast is best stored under beer in the same article.

"Yeast is a living organism and is most happy and healthy when feeding on wort sugars. When fermentation is complete, yeast cells flocculate to the bottom of the fermenter. They then go into a resting state. Yeast under beer is fairly stable, and most brewers agree that the best place to store yeast is under beer."

His advice for using yeast that has been sitting under beer a while is also a generally accepted practice.

"The best thing to do for yeast after it has been stored for two weeks, if it tests clean, is to add some fresh wort before using it. This helps to restore yeast strength and ensures a successful fermentation. Simply pour off beer that has separated from flocculated yeast, add fresh wort at 9° to 12° Plato, and let it sit at room temperature for 10 to 20 hours. Assuming yeast activity was evident in this 'starter' or 'activator,' pitch into fresh wort as usual. This is also useful for slurries that are 55 percent to 90 percent viable; this method can "nurse" the slurry back to health."

Storage time

"How long can yeast be stored? It's best to use the yeast in one to three days. Again, this is often not possible, especially if multiple strains are being used in the brewery. The magic number seems to be two weeks. If you reuse your yeast in less than two weeks, you usually will have no problem. At two or three weeks you may or may not have problems. After four weeks, the viability of yeast slurry is usually 50 percent or lower."

If bacteria growth while in storage was not a concern, Chris would not have included this paragraph:

"As yeast cells sit in storage, they consume their glycogen reserves. Glycogen deprivation weakens their cell walls and makes them more susceptible to rupture. Cold temperatures retard this process, but you should avoid freezing yeast, as ice crystals also will rupture cells. The ideal storage temperature is 33° to 38° F. When yeast cells rupture, they release their contents into the liquid phase. Bacteria can feed off the nitrogen released in this process and multiply rapidly. So the yeast slurry needs to be as free of contamination as possible when stored. Cold temperatures also will help retard bacterial growth. "

 

[ColoHox]

If bacteria growth while in storage was not a concern, Chris would not have included this paragraph:

"As yeast cells sit in storage, they consume their glycogen reserves. Glycogen deprivation weakens their cell walls and makes them more susceptible to rupture. Cold temperatures retard this process, but you should avoid freezing yeast, as ice crystals also will rupture cells. The ideal storage temperature is 33° to 38° F. When yeast cells rupture, they release their contents into the liquid phase. Bacteria can feed off the nitrogen released in this process and multiply rapidly. So the yeast slurry needs to be as free of contamination as possible when stored. Cold temperatures also will help retard bacterial growth. "

This highlights the importance of adding a cryoprotectant to frozen stocks. Deep freezing also suspends metabolic activity of the yeast and any contaminating organisms. In those conditions, bacteria are not growing while the yeast are dormant, the cold affects the entire sample.