How many times do you wash your yeast when harvesting?

[saccharomyces]

I have stored mine in my fridge for 6 months and still had 80% attenuation for fermentation

But that's not the only test of good yeast. If many cells have died then you would be under pitching with potential for off flavours etc.

+1

Ideally, cropped yeast should be used within a month. Agar slants and cryogenic storage are better ways to store yeasts for longer periods. I maintained several cultures for ten years on agar slants.

 

[evanvine]

Zero! Yeast rinsing is an unnecessary step that has the potential to do more harm than good. I have covered the reasons why rinsing yeast with boiled water is a bad idea in other threads. However, put succinctly, yeast rinsing is a practice that is not support by science. Trub is actually beneficial to the health of the yeast culture while in refrigerated storage, and green beer is a much better storage medium than boiled water. The best time to separate the yeast from the trub and green beer is immediately before one pitches. All one needs to do is to decant he liquid fraction of the crop and replace it with fresh cool wort from one's batch before swirling the yeast into suspension. The trub and dead yeast cells will rapidly settle leaving the viable yeast cells in suspension. One then pitches the liquid fraction into one's FV.

This post is totally at variance with Chris White's book "Yeast" p168! :wha:

 

[rpt]

Zero! Yeast rinsing is an unnecessary step that has the potential to do more harm than good. I have covered the reasons why rinsing yeast with boiled water is a bad idea in other threads. However, put succinctly, yeast rinsing is a practice that is not support by science. Trub is actually beneficial to the health of the yeast culture while in refrigerated storage, and green beer is a much better storage medium than boiled water. The best time to separate the yeast from the trub and green beer is immediately before one pitches. All one needs to do is to decant he liquid fraction of the crop and replace it with fresh cool wort from one's batch before swirling the yeast into suspension. The trub and dead yeast cells will rapidly settle leaving the viable yeast cells in suspension. One then pitches the liquid fraction into one's FV.

This post is totally at variance with Chris White's book "Yeast" p168! :wha:

But you need to use sterilised water, not just boiled. You can do this in a pressure cooker.

 

[saccharomyces]

This post is totally at variance with Chris White's book "Yeast" p168! :wha:

I own a copy of Mr. White's book. Nowhere in that text does he claim that storing cropped yeast under boiled water is better than leaving it under green beer. On page 168, Mr. White merely answer's the question of how does one select the best yeast from the entire contents of a FV. He mentions in passing that it "may" be beneficial for commercial breweries to use the technique to separate yeast from green beer when harvesting yeast from high gravity beers. However, anyone who has studied brewing science knows that repitching yeast that was cropped from a high gravity wort is not a good practice.

Once again, separating the viable yeast from the trub can be accomplished by decanting the liquid fraction of a crop before pitching, replacing it with fresh cool wort, and swirling the contents back into suspension. The viable yeast will remain in suspension while the dead yeast cells and organic matter will rapidly settle to the bottom of the container in which the crop was stored. The liquid fraction is then pitched into one's FV.

As I have mentioned before, yeast takes control of a batch of wort by consuming all of the dissolved oxygen, lowering the pH, and producing ethanol. While ethanol does in fact reduce the length of time that a yeast culture remains viable, it also keeps wild microflora at bay (the reason why alcohol is part of any first aid kit). Additionally, by storing yeast under boiled water, we also raise the pH of the culture and potentially expose it to spores (boiling does not kill spores), which can now germinate because we have removed the culture's force field.

 

[johnnyboy1965]

Will everyone stop saying "dissolve O2 into a liquid", you cannot do this...sorry yes you can

 

[evanvine]

The heading is RINSING!!
It also says to separate the yeast from alcohol!!
I think I'll take Mr Whites informed advice rather than yours.

 

[phettebs]

Sacch,
Do you have any links to peer-reviewed studies on the subject? I'd be interested in learning more.

Baz

 

[rpt]

The section on rinsing yeast starting on p168 does not talk about storing yeast after rinsing. It only describes the method as a way of separating the yeast from the trub. It says that yeast do not store well in a high alcohol environment but doesn't make any recommendation on storing. The caption to figure 5.14 shows the layers after rinsing a harvested slurry and says "Decant the top layer and pitch the middle layer into your wort". So I think the section is about how to extract yeast from a harvested slurry and then pitch this into a new brew. The implication is this is happening straight away and not after any storage.

Interestingly p198 does talk about storing yeast under water as "sterile distilled water puts yeast in a resting state, and some reports suggest yeast can be stored in this manner for years without refrigeration." To do this you wash the yeast several times in sterile distilled water (i.e. rinse it) to remove any traces of beer. The procedure involves sterilising 2 to 3ml of distilled water in an autoclave and then transferring a colony from a plate to the water.

 

[saccharomyces]

The heading is RINSING!!
It also says to separate the yeast from alcohol!!
I think I'll take Mr Whites informed advice rather than yours.

Nowhere in the text does Dr. White state that separating yeast from normal beer ethanol levels is beneficial to the health of the culture. Ethanol is a natural environment for yeast whereas nutrient-free water is not. In fact, yeast can metabolize ethanol in the presence of oxygen via a phenomenon known as diauxic shift. Trub is actually beneficial to the culture because it serves as a source of lipids while the yeast is in storage.

 

[evanvine]

As phettebs asked, do you have some backup for your claims?

 

[saccharomyces]

Sacch,
Do you have any links to peer-reviewed studies on the subject? I'd be interested in learning more.

Baz

I have not found a single peer-reviewed paper that supports yeast rinsing. Lord knows that I have tried to find one that supports it, so that I can put a fork in the issue.

A book that I consider to be the bible on brewer's yeast is "Brewing Yeast and Fermentation" by Boulton and Quain (http://www.amazon.com/Brewing-Yeast-Fer ... 1405152680). The authors do a great job of making a complex subject approachable while maintaining the rigor of a textbook.

With that said, saccharomyces cerevisiae is probably the most studied microorganism on the planet. There are publications related to just about every aspect of the species. As I have been trying to get a handle on petite mutation lately, I been focusing my attention on papers related to something known as reactive oxygen species (ROS). Here's a link to a paper that deals with replicative ageing and senescence in Saccharomyces cerevisiae that I found while searching on ROS that you may find of interest: http://mic.sgmjournals.org/content/146/5/1023.full.pdf.

 

[saccharomyces]

As phettebs asked, do you have some backup for your claims?

The better question is where are the peer-reviewed scientific publications that support the practice of rinsing yeast with boiled tap water and storing it under boiled tap water? I guarantee that you will not find one published scientific paper that supports the practice. Heck, I have yet to find a professional brewing textbook that supports the practice, which is not surprising because it goes against everything that we know about how a yeast culture goes about "owning" a batch of wort.

Fact #1 - No wort is 100% wild microflora free
Fact #2 - Yeast shutdown aerobic microflora growth by consuming all of the dissolved oxygen in solution
Fact #3 - Yeast shutdown pH sensitive microflora growth by lowering the pH of the solution
Fact #4 - Yeast kill off (or at least keep at bay) all but the most hardy remaining microorganisms by producing ethanol, which is toxic to most microflora

Adding oxygen to green beer does not allow aerobic microflora to start because

A.) They will usually be stopped in their tracks by the low pH and/or ethanol
B.) Yeast will go into aerobic growth mode using ethanol as its carbon source via a phenomenon known as diauxic shift (which is one of the reasons why we do not want to aerate unfiltered beer)

Storing cropped yeast is about making compromises. Storing rinsed cropped yeast under boiled tap water may extend the life of the culture, but it does so by increasing the likelihood of contamination. It also removes a source of lipids; namely, the trub. Storing cropped yeast under green beer may reduce the length of time a culture remains viable. However, it keeps the culture's protective force field intact. It is easier to propagate a less viable culture than it is to clean up an infected culture.

In closing, I have helped many amateur brewers identify the sources of recurrent infections in their brew houses over the last twenty-one years. Nine times out of ten, the infection was pitched with the yeast culture. A small bacterial infection in a pitched yeast culture can overtake the culture because bacteria cells divide every thirty minutes on average whereas yeast cells divide every ninety minutes on average. As we dealing with exponential growth patterns, it doesn't take long for a small infection to dominate the fermentation.

Let's put the problem into cell counts (the symbol "^" denotes raised to the power of)


Yeast Cell count after 90 minutes of growth

initial_yeast_cell_count * 2^(90 / 90) = 2 x initial_yeast_cell_count

Bacteria Cell count after 90 minutes of growth

initial_bacteria_cell_count * 2^(90 / 30) = 8 x initial_bacteria_cell_count



Yeast Cell count after 6 hours (360 minutes) of growth

initial_yeast_cell_count * 2^(360 / 90) = 16 x initial_yeast_cell_count

Bacteria Cell count after 6 hours (360 minutes) of growth

initial_bacteria_cell_count * 2^(360 / 30) = 4,906 x initial_bacteria_cell_count



Yeast Cell count after 12 hours (720 minutes) of growth

initial_yeast_cell_count * 2^(720 / 90) = 256 x initial_yeast_cell_count

Bacteria Cell count after 12 hours (720 minutes) of growth

initial_bacteria_cell_count * 2^(720 / 30) = 16,777,216 x initial_bacteria_cell_count


Yeast Cell count after 24 hours (1,440 minutes) of growth

initial_yeast_cell_count * 2^(1440 / 90) = 65,536 x initial_yeast_cell_count

Bacteria Cell count after 24 hours (1,440 minutes) of growth

initial_bacteria_cell_count * 2^(1440 / 30) = 281,474,976,710,656 x initial_bacteria_cell_count

 

[evanvine]

You ignore the question asked!
You answer a convenient one of your own.
You still have not provided one shred of supporting evidence.....

 

[clibit]

I'm still in the early stages of my brewing career proper, started taking brewing more seriosuly about a year ago, so I don't know much about this and I'm not a scientist. But I can see the logic of what sacc is saying. I have re-pitched yeast from trub a few times and I'm reluctant to mix it with anything new, probably because I don't trust my ability to ensure everything is sterile. So I was doing no rinsing/washing, just collecting trub in boiled jars and then swirling and pitching the liquid portion into the FV (always within a week of capturing the yeast). It worked. I can see the sense in pouring off the old beer from the jar of trub and adding the fresh wort and mixing together, then pouring the new liquid section into the FV. I'm going to do it, cos I like the logic. It also saves the hassle of washing, as well as the encumbent risk, without adding some of the old wort to a new batch. I'm wondering how long after capturing the yeast it would be safe to pitch into a new batch, and whether anyone thinks I'm barmy.

 

[saccharomyces]

You ignore the question asked!
You answer a convenient one of your own.
You still have not provided one shred of supporting evidence.....

Since you have coveniently based your entire thesis on your interpretation of what was written in "Yeast," here's something that Chris wrote for probrewer.com: http://www.probrewer.com/resources/libr ... yyeast.php

"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. But two crucial factors are temperature and time."

While Chris mentions storing small quantities of centrifuged yeast (i.e., reference cultures) under sterile distilled water in the article, nowhere in the article does Mr. White say anything about storing yeast under boiled tap water. Boiled tap water is a far cry from sterile (a.k.a. autoclaved) distilled water.

"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."


Q.E.D.

 

[evanvine]

Since you have coveniently based your entire thesis on your interpretation of what was written in "Yeast

Fair comment

nowhere in the article does Mr. White say anything about storing yeast under boiled tap water.

Again fair comment!
Filtered and boiled rain water works well for me.

Boiled tap water is a far cry from sterile (a.k.a. autoclaved) distilled water.

Agreed!

One of my local breweries (Shipstones) now sadly long taken over by the big boys, used to claim that they kept the same yeast culture going for over 100 years.
I get the impression that autoclave (pressure cooker) and sterile didn't much come into things in those days.

You still don't mention any publication that backs your claims up.
I wonder what your pedigree is?

 

[wezil]

Hi, a hell of a lot of brewing (should I say 'craft', 'folklore' or 'science', choose your favourite) doesn't stand a critical eye either! I've given up trying to debunk them! (some people believe in yeti's, others in pumping O2 through the wort etc.)!!!!

 

[wezil]

Heading off the expected flak, big brewers use O2 to aerate wort BECAUSE it is sterile!!! fresh air will do just as well but the filters needed to ensure sterility would be prohibitively expensive to use. (that's that sorted) :whistle:

 

[Good Ed]

Hi, a hell of a lot of brewing (should I say 'craft', 'folklore' or 'science', choose your favourite) doesn't stand a critical eye either! I've given up trying to debunk them! (some people believe in yeti's, others in pumping O2 through the wort etc.)!!!!

I agree, it's all a bit of a black art craft really; plastic buckets, cool boxes, kettle elements, yeast in plastic bottles in the fridge etc. It's good to know about all the science and how things should be done, but we shouldn't get too hung up on it, just observe good practice and whatever works for you to produce good beer. That said you learn plenty of new things on this forum each day :thumb:

 

[zgoda]

Heading off the expected flak, big brewers use O2 to aerate wort BECAUSE it is sterile!!! fresh air will do just as well but the filters needed to ensure sterility would be prohibitively expensive to use. (that's that sorted) :whistle:

Medical filters aren't that expensive, I know of at least one very small brewery that uses it. Such filters are used generally by medical labs and the price is not prohibitive enough that even smallest lab has one. Still, the oxygen is cheaper but its use requires very expensive equipment and there are some serious safety considerations.