The cold hard truth about rinsing yeast with boiled water

[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.

 

[EarlyAmateurZymurgist]

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.

There is definite merit in freezing, but I am not convinced that freezing in an consumer-level deep freezer provides any significant long-term advantage over slants. Now, if we are talking about about a freezer that is capable of -80C or lower temperatures, then freezing is the only way to go.

You mentioned the benefit of using 50ml stocks. Are your frozen stocks mostly composed of yeast cells? Or are they 50ml liquid cultures?

 

[Orthobrewsky]

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.

About that post I referenced--I didn't get any comments from EAZ, but I'd be interested in his thoughts. I did what is so often described by homebrewers, specifically a single rinse. I add around a quart of water to about a quart of yeast cake/beer. I like to drink as much of my beer as I can, so I tilted and left very little above the cake when i siphoned. The beer was diluted to around 50% concentration, making it like a very low gravity beer. Based on western civilization being made possible through most everyone drinking very weak beer in lieu of contaminated water, I think the alcohol level should still be toxic or at least inhibitory to most bacteria.

The pH rose a bit, but wasn't so bad and my water is pretty middle of the road on alkalinity, so I think my results are probably pretty average for folks doing a single rinse. Thus, I think most people are keeping the "force field" mostly intact. I wonder if my results cause EAZ to be any less worried about the typical yeast rinser.

It would not be difficult or expensive for folks to rinse with low alkaline water, so that the pH would change little. Otherwise, a drop or two of acid might be a nice precaution. However, I think that if people follow the typical recommendation of trying to reuse yeast within a few days and not go longer than two weeks, there would probably be very little difference in outcomes between these methods.

 

[Bottoms_Up]

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)?

I generally only brew 10 gallons every 3 or 4 months. During that time, I keep the yeast slurry in the fridge, but do a "yeast starter" on it every 6 weeks or so with DME and yeast nutrient to help keep its viability (I use a stir plate and a 2 liter Erlenmeyer flask). Since some have kept yeast alive without doing a starter for many months, I figure that repeating a yeast starter no more than about 6 weeks is more than adequate to keep it quite viable. Also, I calculated the yeast viability, and using 6 weeks seems to be a good compromise, since I do another yeast starter a few days before brewing in any case. Thus I assume that you could keep yeast quite viable for well over a year if you repeat a yeast starter no longer than about every 6 weeks during that time.

I have been using the same lager yeast in this way for well over a year with no noticeable detrimental effects so far. I have been rinsing with some boiled and cooled water, but based on the discussion in this thread, I will change to storing the yeast under beer. In addition, I think it wise to take extra effort to remove as much trub as possible before transferring to the fermenter. Personally, I get very little trub when recovering the yeast. In this way, there's little worry about saving almost all the yeast slurry (I only discard a very small amount from the bottom of the slurry, where the heavier trub, etc. has fallen). Also, I usually pour the slurry into Mason jars after the slurry has settled for no more than about 1 or 2 minutes. This is because I save lager yeast, which settles very rapidly (based on my experience, and the experience of a few others, most ale yeasts seem to stay in suspension for at least 20 or 30 minutes, while lager yeasts generally settle within minutes, and usually before the trub settles - thus, in terms of layers, the white milky layer is at the bottom, the trub layer is above that, and the beer layer is above that).

 

[tagz]

About that post I referenced--I didn't get any comments from EAZ, but I'd be interested in his thoughts. I did what is so often described by homebrewers, specifically a single rinse. I add around a quart of water to about a quart of yeast cake/beer. I like to drink as much of my beer as I can, so I tilted and left very little above the cake when i siphoned. The beer was diluted to around 50% concentration, making it like a very low gravity beer. Based on western civilization being made possible through most everyone drinking very weak beer in lieu of contaminated water, I think the alcohol level should still be toxic or at least inhibitory to most bacteria.

The pH rose a bit, but wasn't so bad and my water is pretty middle of the road on alkalinity, so I think my results are probably pretty average for folks doing a single rinse. Thus, I think most people are keeping the "force field" mostly intact. I wonder if my results cause EAZ to be any less worried about the typical yeast rinser.

It would not be difficult or expensive for folks to rinse with low alkaline water, so that the pH would change little. Otherwise, a drop or two of acid might be a nice precaution. However, I think that if people follow the typical recommendation of trying to reuse yeast within a few days and not go longer than two weeks, there would probably be very little difference in outcomes between these methods.

The procedure you referenced seems like a solid way to go. You are reducing the alcohol to more desirable levels and keeping the pH on the lower end of the spectrum. If you were using boiled RO water, all the better. I'm no scientist but that seems to meet the criteria for safe storage on the homebrew scale. It's what I typically do.

 

[mtnagel]

I generally only brew 10 gallons every 3 or 4 months. During that time, I keep the yeast slurry in the fridge, but do a "yeast starter" on it every 6 weeks or so with DME and yeast nutrient to help keep its viability (I use a stir plate and a 2 liter Erlenmeyer flask). Since some have kept yeast alive without doing a starter for many months, I figure that repeating a yeast starter no more than about 6 weeks is more than adequate to keep it quite viable. Also, I calculated the yeast viability, and using 6 weeks seems to be a good compromise, since I do another yeast starter a few days before brewing in any case. Thus I assume that you could keep yeast quite viable for well over a year if you repeat a yeast starter no longer than about every 6 weeks during that time.

I have been using the same lager yeast in this way for well over a year with no noticeable detrimental effects so far. I have been rinsing with some boiled and cooled water, but based on the discussion in this thread, I will change to storing the yeast under beer. In addition, I think it wise to take extra effort to remove as much trub as possible before transferring to the fermenter. Personally, I get very little trub when recovering the yeast. In this way, there's little worry about saving almost all the yeast slurry (I only discard a very small amount from the bottom of the slurry, where the heavier trub, etc. has fallen). Also, I usually pour the slurry into Mason jars after the slurry has settled for no more than about 1 or 2 minutes. This is because I save lager yeast, which settles very rapidly (based on my experience, and the experience of a few others, most ale yeasts seem to stay in suspension for at least 20 or 30 minutes, while lager yeasts generally settle within minutes, and usually before the trub settles - thus, in terms of layers, the white milky layer is at the bottom, the trub layer is above that, and the beer layer is above that).

Yeah, that's what I was thinking too, but EAZ said it wasn't that great either:

I am sorry for not answering your question. I planned to get to it, but thread kept scrolling.

Keeping a liquid culture alive without periodically repitching it is not a viable long-term storage strategy. You can periodically feed the culture by decanting the green beer and adding fresh bitter wort, but that's like putting a band-aid on a sucking chest wound. It may work for a while, but you will eventually have to replace the culture.

But maybe it's good enough.

 

[dlester]

Nice write-up about yeast and washing. I agree that boiling doesn't get it all, but never put together that washing the yeast may actually be inserting wild yeast. Hmm, thanks for that. I have heard that washing yeast can kill them, and therefore avoided it. Not sure I care whether that statement is true or not, but I typically avoided washing yeast by removing all trub after the boil and using a conical fermenter to collect yeast.

I first whirl pool the wort at flameout in the boiler. After 20-30 minutes of settling, I push the wort to my liquor tank and do a second whirlpool using my pumps. The first whirl pool in the boiler is good, but is not wide enough to push all the trub to the middle of the boiler. It sounds like over-kill, I know. However, it really isn't that much more work and my wort transfers to the fermenter perfectly clear. Since I use a conical fermenter, I let out and throw away a small amount of what first comes out followed by storing the rest that follows.

Thanks again for the article,
Cheers

 

[tagz]

Nice write-up about yeast and washing. I agree that boiling doesn't get it all, but never put together that washing the yeast may actually be inserting wild yeast.

Boiled water shouldn't introduce wild yeast, as yeast can't survive 212F. He's saying there are some spores that can survive, but it questionable if those same spores can survive once hops and alcohol are introduced.

The larger point is keeping the slurry at a lower pH and under a layer of low ABV liquid to stop bacteria from growing.

 

[Warthaug]

I am late to the game, but as someone who is both a microbiology prof and whom maintains yeast for both research and brewing purposes, I have a bit I would like to add to the discussion.

1. Firstly, in response to the OP's point about spores, he is partially correct - some (not all) spores can survive boiling. However, their impact on washed yeast is going to be minimal. Spores are not metabolically active, and if washed properly, the resulting environment will be nutrient depleted. This means the spores will not germinate - and if they do they will be unable to grow to any significant degree. Of course, lysed yeast make great food, but if that is occurring at a level that supports germination of bacterial spores you have much more serious issues than a small number of spores in your washing water.
   
2. I'd also like to address the OP's point about sterilized water. While we do use autoclaved water in the lab, it is considered sterile only until you open the bottle (air is chalk-full of bacteria & molds). Meaning, when we work with cultures in the lab (which is not done in biocontainment hoods unless the organism is a biohazard level 2+ or higher organism, or there is a need for absolute cleanliness) we are working with (at least in theoretical terms) contaminated water. And we don't generate fresh water ever time - bottles will sit, and be repeatedly used, over periods of several weeks. And yes, if you try you will be able to pull culturable organisms out of bottles of autoclaved, but opened water. So the comparison is not one of sterile vs non-sterile water; rather he comparison is one of water with differing (but in both cases, very minute) degrees of contamination.
   
3. Thirdly, I'd like to address the repeat discussion of centrifuged yeast. In practical terms there is no great difference between centrifuged yeasts and yeast which has settled. In theory you can get a better separation of yeast from material that is more or less dense in a centrifuge, but in reality to achieve any meaningful stratification of yeast versus other suspended particles requires solutions of much higher density than provided by water or wort. For water/wort suspended organisms/trub, all centrifugation does is condense the settling time from hours/days to a few minutes. The ability to the separate the yeast & other settled materials from the supernatant is effectively equal in both systems (unless you add stuff to greatly increase the density of the media - something we do in the lab, but something not normally done in breweries).
   
4. Fourthly I'd like to comment on much of what has been written about the costs/benefits of storing under fermented wort vs. water. While fermented wort does provide modest acidity and alcohol to act as a preservative, it also provide a medium which can be consumed by many organisms. Ethanol, dextrins, hop compounds, etc, all represent metabolizable substrates that many organisms can consume. As anyone whose done some sour brewing using organisms in the secondary knows, there are a lot of beasties out there who love to live in pre-fermented wort. In other words, fermented wort provides some protection from some organisms, while simultaneously providing a nutrient-rich environment for others. Adding ethanol or acid to water produces a similar effect. And don't forget, that acid and alcohol is stressful to the yeast,even in low-alcohol beers. Alcohol especially, and to a lesser extent acids, are waste products; their presence negatively impacts metabolic pathways, even in relatively low concentrations. Just because they are not at acutely toxic doses does not mean that they are not negatively impacting the yeasts.
   
   In contrast, water doesn't provide the acidity (although this could easily be added by the addition of a buffer) or alcohol, so it is less preservative against ethanol/acid susceptible organisms. But it is also devoid of nutrients, meaning it will not support the growth of organisms. In other words, with water vs. fermented wort you're dealing with 6 of one and a half dozen of the other - wort protects against some infections while supporting the growth of others; water provides no protection, but also doesn't support growth. IMO water has a slight edge in that you also rid the culture of metabolic end-products (ethanol, esters, etc) that can stress yeast. But that advantage comes with a bit of risk - any time you open your stored yeast you risk contamination from organisms in the air and in/on any equipment and materials you are using.
   
5. One last thing and then I'll stop whining. Contrary to what many have written here, water is extensively used in microbiology as a washing and storage medium. Any time we want to strip away metabolic products, remove selective media components, cleanly swap organisms between different type of growth medium, etc, our default method is washing - e.g. we pellet (centrifuge) the organism, decant the old media, resuspend the organism in water, re-pellet, and lastly resuspend in new media (sometimes we repeat the water-wash 3 or more times if high cleanliness is required). Likewise, short-term storage is also often in water. Because water does not support the growth of organisms, and is not harmful to (most of) the organisms we are studying, its a great way to temporarily store a culture in a metabolically inactive state.

When you get down to it, this discussion of yeast washing is somewhat off target. As I mentioned above, both storage under beer and storage under water have their advantages and disadvantages. If you can keep things clean, washing can reduce your risk of contamination through depleting the storage medium (e.g. fermented wort) of nutrients which can be consumed by contaminants, and can reduce stress on the yeast by ridding the medium of metabolic waste products like ethanol. However, if you are not clean you risk contamination from environmental sources - and boiled water is not the concern; there will be far more viable organisms floating around in the dust in the air, or on the surface of a poorly cleaned funner/container, then viable spores will be remaining in some boiled tap water.


Bryan

 

[harrke]

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

Yes. Submarine Officer in Groton and Ballston Spa.

 

[tagz]

Thank you Wathaug. That post makes the thread worth it.