why can't i just keep repitching?

[brewshki]

Hi Everyone,

I have been researching a few topics about yeast and I cannot find an answer anywhere. I am really sorry if I am just dumb and cannot find the correct thread, but I really need some help haha.

I learned about yeast washing and ended up using a batch of yeast from a hefeweizen in a second batch of the same recipe. My questions is not about this process, but why I cannot just keep doing this forever?

Why can't I just keep washing each batch of yeast and reusing it?

If I cannot, how can the yeast companies keep churning out the same kind of yeast with the same characteristics?

I think it would be pretty cool to keep using a strain of yeast, but not if there is some sort of issue.

Please let me know if I am just being stupid!

Thanks!

 

[jack181]

heres something i found its a bit of a read. i will link the source i got it from so you can read the stuff i have missed...


source: ( https://www.wyeastlab.com/com-yeast-harvest.cfm )
Yeast Harvesting / Re-Pitching

Harvesting and re-pitching yeast is a common practice in most breweries. Brewers should be able to re-use yeast for at least 7 generations and often as many as 10 generations if good harvesting and storage practices are followed. Harvesting and re-pitching yeast is a great way to spread the cost of the culture over many brews. The particular method of harvest will depend upon the yeast strain used and brewery configuration, however the principles will remain consistent.

Consistency
The most important concept in harvesting is consistency. Consistent harvesting and re-pitching practices will promote consistent fermentations and yeast performance. Variations in the timing or temperature of the yeast harvest will result in inconsistent cell densities and will affect the subsequent pitch rates. Other variables such as wort composition, dissolved oxygen at run-in, and the fermentation temperature will also affect the quality of the harvested yeast. Yeast harvests will never be identical from brew to brew but variables can be controlled and inconsistencies minimized.

Selective Mutation
The profile of a yeast culture can change over time if harvesting practices are not consistent. Not all yeast cells in a culture are genetically identical. There are genetic variations within any population and these variations cause some yeast cells to exhibit different characteristics. Cells that flocculate early tend to be less attenuative and will settle to the bottom of the tank with trub. Cells that stay in suspension and flocculate later tend to be more attenuative and will end up at the top of the yeast bed. Repeated selection of either of these extremes will change the profile of the culture and alter fermentation characteristics. Yeast to be harvested should be selected from the middle portion of the yeast bed when harvesting from the bottom of a tank, or from the middle skim when harvesting from the top of a tank.

What Yeast Should Be Harvested
Not all yeast in the brew house can be successfully re-pitched. When choosing a tank to harvest from and what culture to re-use, the following guidelines should be adhered to:

Yeast Generation: Always select the youngest generation of yeast available for harvest. Using fewer generations will minimize opportunities for mutation or contamination.
Previous Fermentation: Always harvest from a low gravity and low hopped beer. High gravity and/or highly hopped beers can stress the yeast and have detrimental affects on future fermentations. Do not harvest yeast from beers with alcohol contents greater than 6.5% ABV.
Yeast Evaluation: Only harvest yeast from fermentations that have exhibited normal fermentation characteristics. Always evaluate the yeast slurry as it is harvested. The slurry should appear thick and creamy with very little trub and no “off” flavors and aromas. Strong sulfur or phenolic aromas indicate possible problems with either sanitation or stress. Yeast should be tested for purity if possible and checked for viability and cell density. If there are any concerns over the health or purity of a culture, DO NOT USE IT!

 

[brewshki]

heres something i found its a bit of a read. i will link the source i got it from so you can read the stuff i have missed...


source: ( https://www.wyeastlab.com/com-yeast-harvest.cfm )
Yeast Harvesting / Re-Pitching

Harvesting and re-pitching yeast is a common practice in most breweries. Brewers should be able to re-use yeast for at least 7 generations and often as many as 10 generations if good harvesting and storage practices are followed. Harvesting and re-pitching yeast is a great way to spread the cost of the culture over many brews. The particular method of harvest will depend upon the yeast strain used and brewery configuration, however the principles will remain consistent.

Consistency
The most important concept in harvesting is consistency. Consistent harvesting and re-pitching practices will promote consistent fermentations and yeast performance. Variations in the timing or temperature of the yeast harvest will result in inconsistent cell densities and will affect the subsequent pitch rates. Other variables such as wort composition, dissolved oxygen at run-in, and the fermentation temperature will also affect the quality of the harvested yeast. Yeast harvests will never be identical from brew to brew but variables can be controlled and inconsistencies minimized.

Selective Mutation
The profile of a yeast culture can change over time if harvesting practices are not consistent. Not all yeast cells in a culture are genetically identical. There are genetic variations within any population and these variations cause some yeast cells to exhibit different characteristics. Cells that flocculate early tend to be less attenuative and will settle to the bottom of the tank with trub. Cells that stay in suspension and flocculate later tend to be more attenuative and will end up at the top of the yeast bed. Repeated selection of either of these extremes will change the profile of the culture and alter fermentation characteristics. Yeast to be harvested should be selected from the middle portion of the yeast bed when harvesting from the bottom of a tank, or from the middle skim when harvesting from the top of a tank.

What Yeast Should Be Harvested
Not all yeast in the brew house can be successfully re-pitched. When choosing a tank to harvest from and what culture to re-use, the following guidelines should be adhered to:

Yeast Generation: Always select the youngest generation of yeast available for harvest. Using fewer generations will minimize opportunities for mutation or contamination.
Previous Fermentation: Always harvest from a low gravity and low hopped beer. High gravity and/or highly hopped beers can stress the yeast and have detrimental affects on future fermentations. Do not harvest yeast from beers with alcohol contents greater than 6.5% ABV.
Yeast Evaluation: Only harvest yeast from fermentations that have exhibited normal fermentation characteristics. Always evaluate the yeast slurry as it is harvested. The slurry should appear thick and creamy with very little trub and no “off” flavors and aromas. Strong sulfur or phenolic aromas indicate possible problems with either sanitation or stress. Yeast should be tested for purity if possible and checked for viability and cell density. If there are any concerns over the health or purity of a culture, DO NOT USE IT!

Very interesting. I will follow the link and read more soon.

 

[CA_Mouse]

The Yeast Labs are dealing with pure cultures of the strains. When you wash your cake, you have a slightly mutated strain due to your processes, this is normal. When you pitch onto that yeast, because you tray to have the same processes as the time before, your yeast will mutate once again. I believe that by the 4th or 5th usage in this manner, the yeast cells have mutated to your "house" strain. If you were to take a sample and send it to a lab, they can tell you what strain it was and how it has mutated. There are commercial breweries and bakeries that have done this for years. San Francisco Bread comes from a bakery that has been using a sourdough starter that is over 140 years old that came to the US from France. The brewery that produces Hobgoblin, Wychwood, have been using the same house strain for nearly 20 years.

To clarify your process, you said you are washing the yeast, I think you may mean rinsing. Washing yeast requires the use of acids and a centrifuge or autoclave. Using boiled and cooled water to rinse your yeast and then store it in a fridge isn't quite the same thing. Repitching onto a yeast cake is even easier still, since you are decanting the finished beer and adding fresh wort to the existing yeast without cleaning trub or hop material from it.

 

[AK7007]

a centrifuge or autoclave

What lab are you from that can use centrifuges and autoclaves interchangeably?

But on the topic that the OP was interested in - yes, you can repitch forever if you are ok with the strain changing over time. You can pay a lab to maintain a generally stable strain, rebuying from time to time, or you can do what we do in research labs, more or less:
http://byo.com/hops/item/1662-yeast-ranching-advanced-homebrewing

The main tip I would give for this kind of thing that is different from the article would be to never thaw your frozen cultures - just scrape the frozen sample with a sterile loop and streak on a plate.

 

[MindenMan]

A couple of years ago, I re pitched WAY too many times, and my beer went south: over attenuated, odd flavors, etc.
What I do now is I start with as pure strain, build up its volume and pitch most of it into the batch of beer I am brewing while putting the "leftover" into the fridge. I do not re-pitch more than once onto the yeast cake anymore, I just dump it. Three days before I brew again, I build up a large starter and pitch the biggest part into my fermenter, and put the small part into the fridge. I have re-used my "pure" starter strain for over a year with no ill effects. Just my $0.02

 

[zoomzilla]

All of these examples from yeast taking on undesirable characteristics are based on rinsing yeast that has already fermented a beer and contain highly stressed yeast and hop trub. My method of yeast harvesting doesn't have these problems so shouldn't I be able to get more generations from my method? When I buy a vial from white labs I make a starter with 1.040 gravity using DME and pure o2 diffusion. I then decant the beer and transfer the yeast into 5 sanitized vials then place those vials in the fridge. I use each vial as a starter until I get to the fifth vial which I make a starter from and repeat the whole process. The yeast I use for starters never comes from "real" beer. Shouldn't this method result in more healthy generations?

 

[CA_Mouse]

A couple of years ago, I re pitched WAY too many times, and my beer went south: over attenuated, odd flavors, etc.
What I do now is I start with as pure strain, build up its volume and pitch most of it into the batch of beer I am brewing while putting the "leftover" into the fridge. I do not re-pitch more than once onto the yeast cake anymore, I just dump it. Three days before I brew again, I build up a large starter and pitch the biggest part into my fermenter, and put the small part into the fridge. I have re-used my "pure" starter strain for over a year with no ill effects. Just my $0.02

I do nearly the same with my CalAle yeast. I make a starter with 500ml more than I need. I will decant that portion just before pitching and refrigerate for my next brew, building another starter again with 500ml more than required.

 

[CA_Mouse]

What lab are you from that can use centrifuges and autoclaves interchangeably?

I have never said that I work in a lab. I only pointed out that one of those was required for washing yeast.

 

[CA_Mouse]

All of these examples from yeast taking on undesirable characteristics are based on rinsing yeast that has already fermented a beer and contain highly stressed yeast and hop trub. My method of yeast harvesting doesn't have these problems so shouldn't I be able to get more generations from my method? When I buy a vial from white labs I make a starter with 1.040 gravity using DME and pure o2 diffusion. I then decant the beer and transfer the yeast into 5 sanitized vials then place those vials in the fridge. I use each vial as a starter until I get to the fifth vial which I make a starter from and repeat the whole process. The yeast I use for starters never comes from "real" beer. Shouldn't this method result in more healthy generations?

I like this process, but haven't tried anything quite this detailed. If I was brewing every 3 or so days, I think this would be ideal. For me, brewing every other week, this would be over kill.

Great process though! :rockin:

 

[zoomzilla]

I like this process, but haven't tried anything quite this detailed. If I was brewing every 3 or so days, I think this would be ideal. For me, brewing every other week, this would be over kill.

Great process though! :rockin:

I figure if I can get 4 batches from each generation it will take much longer to get to that tenth generation. It keeps me brewing more too because I don't want that last vial to sit very long

 

[HarborTownBrewing]

When I toured Cigar City in Tampa, they said (if I remember correctly) that they use the yeast 5 times, then they dump it and begin with a new one. They noted that you can use a yeast 7 times but they have found slight mutation at 7 times, and they didn't want their beer not to be consistent.

They seem to take it pretty seriously as well: they have 2 scientists on staff to test samples of the beer and yeast they are producing.

 

[m00ps]

Similar to above, I harvest my yeast from starters rather than wash the already used yeast. This way, I get fresher, less stressed yeast that has not been exposed to hop oils and gone through fermenting a whole beer. It makes for much more consistent and healthy yeast to use for next time. I've got yeast in my fridge that I bought over a year ago and their on their 8th or 9th generation. Havent noticed any noticeable difference in performance other than some actually seemed to get stronger with successive generations

TLDR: just harvest from the starter, works better, less work

 

[AK7007]

The yeast I use for starters never comes from "real" beer. Shouldn't this method result in more healthy generations?

Yes. But there will still be drift over time. When yeast are stressed, they intentionally increase their mutation rate. The theory is that organisms that do this are hoping to stumble on some mutation that makes them better adapted to whatever stress it is that you are putting them under. (kinda, yeast don't think, they just do) "Real" beer has way more cell divisions than a starter. Mutations become more or less prominent in a population when there are dividing cells. Add all that up, and a starter will have less drift, not no drift. You will eventually be different from Wyeast/White Labs. Freezing is likely the only way to keep one exact strain stable over time.

 

[brewshki]

Wow. This is a ton of awesome information. Thank you