Re-Using Yeast (what's the science)?

[Verio]

Reposting this as a new thread, so I don't hijack the Yeast Cake thread.

I have pitched directly on a yeast cake several times on consecutive batches with no problems. I have also poured the entire cake in a large mason jar and kept it in the fridge for almost a week before washing the yeast out. My harvested yeast have been reused as long as 5 months later in the fridge with no problems at all.

Can someone explain the science to me on this? Why is a Yeast Cake viable after a beer has been sitting on it for potentially months, unrefrigerated, but as soon as the beer is mostly racked off of it, it's only viable for a few weeks, and must be refrigerated during that time?

 

[cheezydemon3]

That science is horsesh!t in my book.

Seeing is believing for me.

Yeast hasn't been around for millenia bacause it is so fragile and sickly.

 

[MalFet]

I suspect the logic has more to do with sanitation and less to do with actual yeast population.

Yeast is pretty good at going dormant when food sources disappear, but it is still vulnerable to infection. I'm not so sure I'd assume that a yeast cake _months_ old would be a great source of healthy yeast, but whatever is there is likely going to be clean because it is sealed off from the environment by a layer of fermented beer. Yeast in a mason jar is more vulnerable to bacteria either left on the jar or introduced during transfer.

 

[Verio]

That science is horsesh!t in my book.

Seeing is believing for me.

Well, some people are touting around here like they're experts on yeast, so I'm quite intrigued on the matter.

How can an organism that requires refrigeration and supposedly an "ice pack" when shipped to my house, be viable after sitting for 2 months in my closet at 75 degrees unrefrigerated?

Does a magical transformation happen when I rack my beer off, that makes the yeast now need refrigeration to survive? If that's the case, why not leave an inch or two of beer on top, and then have my yeast viable for much longer unrefrigerated?

 

[Revvy]

Reposting this as a new thread, so I don't hijack the Yeast Cake thread.



Can someone explain the science to me on this? Why is a Yeast Cake viable after a beer has been sitting on it for potentially months, unrefrigerated, but as soon as the beer is mostly racked off of it, it's only viable for a few weeks, and must be refrigerated during that time?

The beer protects the yeast from spoilage since it's an anerobic enviroment. Once it is exposed to air with pontential nasties it's gonna get contaminated. You put it into a sealed jar with more liquid over it (whether you clean it or not as long as you fill the airspce) or you slant it, cool it to dormancy temps, so it's not active and hopefully not mutating.

What's so hard to grasp about this? What am I missing here? What's the beef about that?

 

[Verio]

I suspect the logic has more to do with sanitation and less to do with actual yeast population.

Yeast is pretty good at going dormant when food sources disappear, but it is still vulnerable to infection. I'm not so sure I'd assume that a yeast cake _months_ old would be a great source of healthy yeast, but whatever is there is likely going to be clean because it is sealed off from the environment by a layer of fermented beer. Yeast in a mason jar is more vulnerable to bacteria either left on the jar or introduced during transfer.

The going advice for the month on here is to let your beer sit for 2 months before bottling or kegging. That's the information being pasted into almost every newbie post by Revvy and others.

If yeast is protected from infection and stable after being dormant, what's the timetable on how long its viable? Does yeast decay over a certain amount of time, and if so, what's the timetable? Does refrigeration delay decay?

 

[Verio]

The beer protects the yeast from spoilage since it's an anerobic enviroment. Once it is exposed to air with pontential nasties it's gonna get contaminated. You put it into a sealed jar with more liquid over it (whether you clean it or not as long as you fill the airspce) or you slant it, cool it to dormancy temps, so it's not active and hopefully not mutating.

What's so hard to grasp about this? What am I missing here? What's the beef about that?

My beef is that spending the extra time of scooping the yeast, washing it, and then having it potentially only viable for a few weeks in the fridge seems like a bad piece of advice.

Based upon your information here, I could just rack 95% of my beer off, leave my yeast cake to sit for however long I wanted in dormancy in the fermentor and then when I'm good and ready to make a new batch of beer, scoop the yeast, wash it, and then make good beer.

Dormancy of yeast would have nothing to do with an infection. Bacteria will grow whether or not the yeast is alive. That's why food still rots in a fridge.

 

[Revvy]

My beef is that spending the extra time of scooping the yeast, washing it, and then having it potentially o

Who the helll says it's only viable for a few weeks??????

If you made a starter, then the age of a yeast isn't really an issue.

Bobby M did a test on year old stored yeast here; https://www.homebrewtalk.com/f13/testing-limits-yeast-viability-126707/

And my LHBS cells outdated tubes and packs of yeast dirt cheap 2-3 dollars each and I usually grab a couple tubes of belgian or other interesting yeast when I am there and shove it in my fridge. and I have never had a problem with one of those tubes.

I usually make a starter but I once pitched a year old tube of Belgian High Gravity yeast directly into a 2.5 gallon batch of a Belgian Dark Strong, and after about 4 days it took off beautifully.

With any stored, old yeast you just need first to apply the "sniff test" if it smell bad, especially if it smells like week old gorilla poop in a diaper left on the side of the road in the heat of summer.

Then make a starter, and if it takes off you are fine. The purpose of a starter is to reproduce any viable cells in a batch of yeast....that;s how we can grow a starter form the dregs in a bottle of beer incrementally...and that beer may be months old.

Even if you have a few still living cells, you can grow them....That's how we can harvest a huge starter (incrementally) from the dregs in a bottle of some commercial beers. You take those few living cells and grow them into more.

If yeast can be grown from a tiny amount that has been encased in amber for 45 million years, 45 million year old yeast ferments amber ale we really don't need to sweat too much about how old a yeast is, if it's properly stored.

Really even with "old yeast" if there is a few cells, they will reproduce. In your case it may just take awhile.

I know other folks on here who have gone a couple years with harvested yeast.

 

[Revvy]

Based upon your information here, I could just rack 95% of my beer off, leave my yeast cake to sit for however long I wanted in dormancy in the fermentor and then when I'm good and ready to make a new batch of beer, scoop the yeast, wash it, and then make good beer..

I dunno, if you managed to protect that 5% of beer once you racked off the rest of it from getting infected (like racking it to a gallon jug to reduce headspace, you probably would be fine.

Give it a try and report back.

Another thing that occured to me about yeast and yeast viability,.

I don't know if you know the story of Charlie Papazian's yeast (White Labs "Cry Havoc") or not. He talked about it on basic brewing. The recipes in both Papazian's books, The Complete Joy of Homebrewing and The Homebrewers Companion, were originally developed and brewed with this yeast. Papazian had "Cry Havoc" in his yeast stable since 1983.

He has used it nearly continuously since 83, sometimes pitching multiple batches on top of a cake, sometimes washing or not washing, etc. In a basic brewing podcast iirc last year he talked about how a batch of the yeast after a lot of uses picked up a wild mutation, and he noticed an off flavor in a couple batches.

Now most of us would prolly dump that yeast. Instead he washed it, slanted or jarred it (I can't recall which,)marked it, and cold stored it, and pretty much forgot about it for 10-15 years. He had plenty other slants of the yeast strain, so he left it alone.

Well evidently he came across that container of yeast, and for sh!ts and giggles made a beer with it. Evidently after all those years in storage, the wild or mutated yeast died out leaving behind a few viable cells of the "pure" culture, which he grew back into a pretty hardy strain...which iirc is the culture that White Labs actually used for their cry havoc...because of it's tenacity and survivability.

He's been using his yeast constantly for decades, in various strains.....

It really to me, just goes to show once again how really hard it is to f up this beermaking, and that to give the yeast the props they deserve.

But my biggest question is why the heck is your tone so hostile? You seem really really pissed about something?

 

[MalFet]

The going advice for the month on here is to let your beer sit for 2 months before bottling or kegging. That's the information being pasted into almost every newbie post by Revvy and others.

I dig it, daddy-o. I've made very similar statements myself, even in the last day. I would say the standard advice is more in the league of one month, but of course that depends on many factors and a gravity reading is the only real guide. I've left big beers on yeast for several months with no ill effects to the beer, but that's a different question than the viability of the yeast underneath.

If yeast is protected from infection and stable after being dormant, what's the timetable on how long its viable? Does yeast decay over a certain amount of time, and if so, what's the timetable? Does refrigeration delay decay?

Yes to all your questions that can be answered with a yes, and it's complicated to the ones that can't. From my understanding, under ideal circumstances, yeast can stay dormant indefinitely (practically). There are stories of yeast under oil slants that are 60-70 years old and still alive. That said, there are many factors that make this unrealistic under most circumstances: heat, UV light, temperature changes, other hostile critters, hydrostatic pressure, oxidation, osmotic imbalances, etc.

Main thing is sanitation. If you look at the messages about yeast ranching, they all emphasize the need for sterilization (rather than just the sanitization that is sufficient for most homebrew purposes). If you are trying to keep a population of dormant yeast, even a small initial bacterial population can wipe you out. The fridge doesn't fix this problem, but it slows metabolic rates to a crawl and thus keeps the bacteria from taking over.

Low population itself is not a problem. Good plating techniques involve building a starter from as few as a single cell. It's a technical process, though, and there are many reasons that you want to make sure that you pitch a proper amount of yeast.

 

[Revvy]

main thing is sanitation. If you look at the messages about yeast ranching, they all emphasize the need for sterilization (rather than just the sanitization that is sufficient for most homebrew purposes). If you are trying to keep a population of dormant yeast, even a small initial bacterial population can wipe you out. The fridge doesn't fix this problem, but it slows metabolic rates to a crawl and thus keeps the bacteria from taking over.

Low population itself is not a problem. Good plating techniques involve building a starter from as few as a single cell. It's a technical process, though, and there are many reasons that you want to make sure that you pitch a proper amount of yeast.

+1!!!

 

[Verio]

Snip.
But my biggest question is why the heck is your tone so hostile? You seem really really pissed about something?

I'm not trying to be hostile at all. I first started the thread by asking about why refrigeration is required for storage after harvesting the previous yeast, but not required if it's kept in it's current form. I asked for the "science" behind why it works, because I'm a very technical person, not the type who works on gut feelings or zodiac symbols.

Instead I get a very hostile response from you. I'm not sure why you interpreted that as a hostile question.

I guess what ultimately gets under my skin is trying to understand why a LHBS or a online distributor would need to refrigerate the yeast and also try to up-sell a cold shipment item to get to your house. It can't be because of bacteria, because bacteria still grows in refrigerated environments.

I guess what I'm trying to nail down is, is how long yeast can survive, and if the temperature has any affect on the half-life. For me, it's more of a question of cost savings and not a lot of room to spare. If I can store a yeast cake in the garage for 3 months with some beer left on top of it, and an airlock and it still be as viable as a 1 gallon jar in the fridge... I'd rather just leave it in the garage and not hear it from the wife.

I hope that makes a bit more sense on where I'm trying to come from.

 

[cheezydemon3]

When I rack beer off I always seal up the fermenter until I brew again.

I open it up and, as Revvy suggests, sniff.

If all is well, I put sanitary water (spelled TAP for lucky me) maybe a gallon, into the fermenter and dump off most of the yeast, approximately 3/4 usually.

Pitch cooled wort on the leftovers and watch the beauty.

My longest storage was just over 4 months. THE CAKE WAS CRACKED AND DRY but smelled fine. I left it all in, worrying over viability. It nearly blew the airlock.

Fantastic beer.

 

[Verio]

I dig it, daddy-o. I've made very similar statements myself, even in the last day. I would say the standard advice is more in the league of one month, but of course that depends on many factors and a gravity reading is the only real guide. I've left big beers on yeast for several months with no ill effects to the beer, but that's a different question than the viability of the yeast underneath.



Yes to all your questions that can be answered with a yes, and it's complicated to the ones that can't. From my understanding, under ideal circumstances, yeast can stay dormant indefinitely (practically). There are stories of yeast under oil slants that are 60-70 years old and still alive. That said, there are many factors that make this unrealistic under most circumstances: heat, UV light, temperature changes, other hostile critters, hydrostatic pressure, oxidation, osmotic imbalances, etc.

Main thing is sanitation. If you look at the messages about yeast ranching, they all emphasize the need for sterilization (rather than just the sanitization that is sufficient for most homebrew purposes). If you are trying to keep a population of dormant yeast, even a small initial bacterial population can wipe you out. The fridge doesn't fix this problem, but it slows metabolic rates to a crawl and thus keeps the bacteria from taking over.

Low population itself is not a problem. Good plating techniques involve building a starter from as few as a single cell. It's a technical process, though, and there are many reasons that you want to make sure that you pitch a proper amount of yeast.

THANK YOU!!!

This makes a lot of sense. Sterlization vice sanitization. I know the difference there. Refrigeration doesn't stop bacteria, it just slows it, if it's there.

 

[Revvy]

type who works on gut feelings or zodiac symbols.

Instead I get a very hostile response from you. I'm not sure why you interpreted that as a hostile question.

I wasn't being hostile at all, asking "what's you beef?" is being hostile? Like I said, it seemed like the tone of your initial post is that you came in over from some other thread drama all angry and the way you demanded the science behind the answers meant you had a chip on your shoulder. I just was giving you my idea and asking what was so all fired anger inspiring to have you come in all hell bent for leather to whoever dared post. That's all.

 

[dcott]

Maybe I'm wrong, but I'm pretty sure that refrigerating the yeast has nothing to do with protecting the yeast. It makes the yeast go dormant to prevent reproduction.

As yeast cells reproduce, each successive generation is subject to mutation (just like any species). If a yeast generation mutates and reproduces, successive generations will use that genetic data. If it is a different yeast than the pure strain that you were planning on making beer from, it wont make the same beer, might make bad beer, or might not even make beer.

Since yeast need oxygen to reproduce, after they use all the oxygen in your wort, and eat all the food they can (fermentable sugar) they flocculate (go dormant, just like in the fridge). Once you rack the beer off, they are once again exposed to oxygen and can begin reproducing.

Keeping them in the fridge at this stage simply preserves their integrity for beer making, it doesn't preserve them.

Yeast are perfectly capable of surviving all around us. Just think about how brewing/bread baking/wine making came about. It was an accident because someone left grain lying around and the floating yeast started fermenting. We simply have a lot more control now over isolated strains which allows us repeatable success.

Also, bacteria are most aerobic organisms, which means that once you expose your yeast cake to air, they can occupy the same place as the yeast, and take over. Refrigerating helps prevent this as well.

 

[dcott]

Also, as a further example, this is why sourdough bread is sour. It uses random floating yeast. Good for bread/bad for beer.

Mmmmm.... Bread.....

 

[MalFet]

I'm not trying to be hostile at all. I first started the thread by asking about why refrigeration is required for storage after harvesting the previous yeast, but not required if it's kept in it's current form. I asked for the "science" behind why it works, because I'm a very technical person, not the type who works on gut feelings or zodiac symbols.

Instead I get a very hostile response from you. I'm not sure why you interpreted that as a hostile question.

I guess what ultimately gets under my skin is trying to understand why a LHBS or a online distributor would need to refrigerate the yeast and also try to up-sell a cold shipment item to get to your house. It can't be because of bacteria, because bacteria still grows in refrigerated environments.

I guess what I'm trying to nail down is, is how long yeast can survive, and if the temperature has any affect on the half-life. For me, it's more of a question of cost savings and not a lot of room to spare. If I can store a yeast cake in the garage for 3 months with some beer left on top of it, and an airlock and it still be as viable as a 1 gallon jar in the fridge... I'd rather just leave it in the garage and not hear it from the wife.

I hope that makes a bit more sense on where I'm trying to come from.

I get what you are saying, but you are conflating a couple of different factors.

The first is temperature control on smackpacks. That isn't a concern about infection, but about yeast population and viability. White Labs and Wyeast spend a ton of money to ensure that they have incredibly pure cultures going into those containers, so there is no risk of a bacterial infection taking over (barring a major quality control fubar). That said, if you leave those 100 billion cells in the sun, their population might cut in half, and that remaining half might be low on glycogen reserves. You could certainly build back up from those 50 billion cells to have a great yeast pitch, but it undermines the convenience of just being able to dump in the packet. Again, this is just a question of yeast pitching rates. Brewers for millennia have used amounts of yeast that we would today consider to be radically underpitching, but the consensus today is that a good yeast pitch rate (say, 1mil cells / mL / plato) will give a faster ferment and a cleaner flavor profile.

The concerns for yeast under beer are similar. You can certainly harvest, but after several months you need to make sure your population dynamics are where you want them to be. You could certainly build this population back up from however low it is, but the lower it is to begin the more technical and time consuming it will be. That's not to say it's insurmountable, but it is easier to bring 100 billion cells to 200 billion cells than it is to bring 1 million cells to 200 billion.

The harvested yeast in jars also faces an infection risk in addition to population concerns. The refrigeration helps to mitigate both the rate of yeast population drop and the growth of an unwanted infection by slowing metabolic rate. Fridges do this effectively, and it is why they were invented to help limit food spoilage. It doesn't stop the bacteria from growing completely, but it buys you time until you can to pitch.

 

[MalFet]

Maybe I'm wrong, but I'm pretty sure that refrigerating the yeast has nothing to do with protecting the yeast. It makes the yeast go dormant to prevent reproduction.

As yeast cells reproduce, each successive generation is subject to mutation (just like any species). If a yeast generation mutates and reproduces, successive generations will use that genetic data. If it is a different yeast than the pure strain that you were planning on making beer from, it wont make the same beer, might make bad beer, or might not even make beer.

Since yeast need oxygen to reproduce, after they use all the oxygen in your wort, and eat all the food they can (fermentable sugar) they flocculate (go dormant, just like in the fridge). Once you rack the beer off, they are once again exposed to oxygen and can begin reproducing.

Keeping them in the fridge at this stage simply preserves their integrity for beer making, it doesn't preserve them.

Yeast are perfectly capable of surviving all around us. Just think about how brewing/bread baking/wine making came about. It was an accident because someone left grain lying around and the floating yeast started fermenting. We simply have a lot more control now over isolated strains which allows us repeatable success.

Also, bacteria are most aerobic organisms, which means that once you expose your yeast cake to air, they can occupy the same place as the yeast, and take over. Refrigerating helps prevent this as well.

From my understanding, that's not actually true. The refrigeration keeps the yeast healthy because it essentially puts them (and everything around them) into metabolic slow motion.

Also, I've been told by people far more knowledgeable than I that the mutation thing is a myth. I bought a yeast geneticist friend a few beers a few weeks ago so I could pick his brain about this. He suggested that yeast mutation is of practically zero concern to homebrewers, because the vast, vast majority of random mutations that could occur lead to decreased reproductive fitness and thus would not come to dominate the slurry population.

The chance that you would have meaningful mutation in time-frames scaled to homebrewing are infinitesimal. The Charlie Papazian story that Revvy cites is an interesting example of that rare occurance, but it's also the exception that seems to prove the rule. The mutated strain got out competed and died out.

There is another question of selective pressure. When harvesting yeast from a cake, for example, you don't want to only pick the top or the bottom because you'll end up with only low or high flocculation, respectively. This isn't mutation, but rather a systematic way of emphasizing already existing genetic variants. It's kind of like if you only allowed redheads to have children. You'd end up with more redheads, but not because of mutation.

The punchline to all this, though, (which I can back up with my own anecdotal experience) is that the fridge definitely preserves yeast.

 

[Revvy]

When harvesting yeast from a cake, for example, you don't want to only pick the top or the bottom because you'll end up with only low or high flocculation, respectively. .

This is really interesting, and never occurred to me. It reminds me of why we usually don't recommend harvesting yeast from secondary. But that also begs the question about the traditional means we use to wash the yeast and jar it (as shown in the yeast washing illustrated sticky) wouldn't then dumping the waters onto the yeast cake and moving it to a gallon glass jar then tend to mix up the various flocculant yeasts?

 

[dcott]

From my understanding, that's not actually true. The refrigeration keeps the yeast healthy because it essentially puts them (and everything around them) into metabolic slow motion.

Also, I've been told by people far more knowledgeable than I that the mutation thing is a myth. I bought a yeast geneticist friend a few beers a few weeks ago so I could pick his brain about this. He suggested that yeast mutation is of practically zero concern to homebrewers, because the vast, vast majority of random mutations that could occur lead to decreased reproductive fitness and thus would not come to dominate the slurry population.

The chance that you would have meaningful mutation in time-frames scaled to homebrewing are infinitesimal. The Charlie Papazian story that Revvy cites is an interesting example of that rare occurance, but it's also the exception that seems to prove the rule. The mutated strain got out competed and died out.

There is another question of selective pressure. When harvesting yeast from a cake, for example, you don't want to only pick the top or the bottom because you'll end up with only low or high flocculation, respectively. This isn't mutation, but rather a systematic way of emphasizing already existing genetic variants. It's kind of like if you only allowed redheads to have children. You'd end up with more redheads, but not because of mutation.

The punchline to all this, though, (which I can back up with my own anecdotal experience) is that the fridge definitely preserves yeast.

Cool stuff! I fridge all my yeast anyway (better to be safe than sorry).

That's interesting about the slim chance of mutation over generations. The worry of pure strain preservation has been keeping me from washing/culturing. Definitely good to know. I still make my starters from pure strains (generally Wyeast), since SWMBO probably wouldn't be too happy having a bunch of bell-jars of yeast in our fridge, but I may get a cheap mini-fridge off craigslist for yeast washing/culturing.

I'll just tell her I'm indulging my lifelong fantasies of being a mad scientist

 

[Verio]

I get what you are saying, but you are conflating a couple of different factors.

The first is temperature control on smackpacks. That isn't a concern about infection, but about yeast population and viability. White Labs and Wyeast spend a ton of money to ensure that they have incredibly pure cultures going into those containers, so there is no risk of a bacterial infection taking over (barring a major quality control fubar). That said, if you leave those 100 billion cells in the sun, their population might cut in half, and that remaining half might be low on glycogen reserves. You could certainly build back up from those 50 billion cells to have a great yeast pitch, but it undermines the convenience of just being able to dump in the packet. Again, this is just a question of yeast pitching rates. Brewers for millennia have used amounts of yeast that we would today consider to be radically underpitching, but the consensus today is that a good yeast pitch rate (say, 1mil cells / mL / plato) will give a faster ferment and a cleaner flavor profile.

The concerns for yeast under beer are similar. You can certainly harvest, but after several months you need to make sure your population dynamics are where you want them to be. You could certainly build this population back up from however low it is, but the lower it is to begin the more technical and time consuming it will be. That's not to say it's insurmountable, but it is easier to bring 100 billion cells to 200 billion cells than it is to bring 1 million cells to 200 billion.

The harvested yeast in jars also faces an infection risk in addition to population concerns. The refrigeration helps to mitigate both the rate of yeast population drop and the growth of an unwanted infection by slowing metabolic rate. Fridges do this effectively, and it is why they were invented to help limit food spoilage. It doesn't stop the bacteria from growing completely, but it buys you time until you can to pitch.

This is great information. From knowledge and theory to application - I've also read on here, that the vials and packs you get from mainstream yeast producers are actually underpitching the required amount. This may not be a big deal for medium gravity beers... but does preserving yeast and washing it actually gain you anything, other than 6 bucks a brew... if you're doing a low-medium gravity beer, or is it always important to make a starter, even if you're doing a beer at around 1.050?

Also, this may be side-tracking, but related to yeast cakes and yeast strands... how can a yeast cake be terribly useful unless you're brewing a very similar type of beer again, if the yeast has an important part in the flavor profile of a beer? For example... I just brewed a Fat Tire clone using California V yeast.... which I presume I wouldn't want to use for my next brew, which is either going to be a Hefeweizen or a Belgian Wit, right?

 

[Verio]

I still make my starters from pure strains (generally Wyeast), since SWMBO probably wouldn't be too happy having a bunch of bell-jars of yeast in our fridge, but I may get a cheap mini-fridge off craigslist for yeast washing/culturing.

I'll just tell her I'm indulging my lifelong fantasies of being a mad scientist

My wife thinks I've lost it with this beer stuff. It's allowed me to unplug from the computer (which I do IT Security for a living) and get outside and use my hands. Since I started brewing in November of last year, I haven't been on my computer much, except to do research, etc. I love it.

 

[boostsr20]

Based upon your information here, I could just rack 95% of my beer off, leave my yeast cake to sit for however long I wanted in dormancy in the fermentor and then when I'm good and ready to make a new batch of beer, scoop the yeast, wash it, and then make good beer.

You also lost the co2 blanket that was protecting your beer so no, that isn't good practice. If your looking for "expert" scientific advice then look somewhere else. If you want advice from your brewing peers on what works, what doesn't, and what is good practice to keep your beer safe, then stick around.

 

[MalFet]

This is really interesting, and never occurred to me. It reminds me of why we usually don't recommend harvesting yeast from secondary. But that also begs the question about the traditional means we use to wash the yeast and jar it (as shown in the yeast washing illustrated sticky) wouldn't then dumping the waters onto the yeast cake and moving it to a gallon glass jar then tend to mix up the various flocculant yeasts?

The TL;DR summary of everything this guy told me was "don't worry at all about mutation, but worry a lot about unintended selective pressures." I don't wash yeast, but I would suspect that it could lead to different levels of floccing in relatively short generation cycles. I'm still trying to figure out how this applies to my yeast freezing, though, as there's no immediately obvious connection between "yeast that freezes better" and "yeast that tastes better".

I don't want to completely dismiss mutation, though. If you are constantly rebuilding yeast populations from very small starting colonies (like Papazian), I suspect mutation will be more likely just because there is less of a yeast "herd" to keep errant genetics in check.

I'll just tell her I'm indulging my lifelong fantasies of being a mad scientist

Mad science FTW!

 

[MalFet]

This is great information. From knowledge and theory to application - I've also read on here, that the vials and packs you get from mainstream yeast producers are actually underpitching the required amount. This may not be a big deal for medium gravity beers... but does preserving yeast and washing it actually gain you anything, other than 6 bucks a brew... if you're doing a low-medium gravity beer, or is it always important to make a starter, even if you're doing a beer at around 1.050?

Also, this may be side-tracking, but related to yeast cakes and yeast strands... how can a yeast cake be terribly useful unless you're brewing a very similar type of beer again, if the yeast has an important part in the flavor profile of a beer? For example... I just brewed a Fat Tire clone using California V yeast.... which I presume I wouldn't want to use for my next brew, which is either going to be a Hefeweizen or a Belgian Wit, right?

There's a lot of information out there about pitching rates, including a fair bit of controversy. Any summary I can offer will reveal my own biases, but a commonly used rule of thumb is 1 million cells per mL per degree plato. Usually people append "25% more for lagers and 25% less for ales" to that rule. So a 20L batch of 1.040 ale would need 750,000 cells * 20,000 mL * 10 plato, or about 150 billion cells.

For the record, that's more than a smackpack. Both Chris White and the Wyeast people say that 100 billion cells is sufficient for anything up to 1.060. I like pitching more than that on most of my beers, because I think it gives me a cleaner profile. On a beer where I want a bit of funk (like a Belgian), sometimes I will intentionally underpitch. Lately I've been experimenting with saisons with proper pitch rates but significant under oxygenation...it's another factor to play around with, but there aren't really right answers.

 

[brewingkitty]

What's so hard to grasp about this? What am I missing here? What's the beef about that?

this cracked me up, man!

by the way, i checked 10 slants from over a YEAR ago in my fridge and they are all still healthy cream colored!!

 

[statseeker]

This is really interesting, and never occurred to me. It reminds me of why we usually don't recommend harvesting yeast from secondary. But that also begs the question about the traditional means we use to wash the yeast and jar it (as shown in the yeast washing illustrated sticky) wouldn't then dumping the waters onto the yeast cake and moving it to a gallon glass jar then tend to mix up the various flocculant yeasts?

If the highly flocculant yeast settles on the bottom together in clumps, and the lowly flocculant yeast settles either on top of it or in the beer itself, the lowly flocculant yeast would be fewer in numbers in the primary after the beer is racked off the yeast cake and even fewer still after the first and second washings, although the first may not be a very accurate separation. Maybe a third washing should be added to the mix, this one collecting and separating the low flocculation ("loner") yeast from the high flocculation ("popular") yeast. There must be a way to time the settling of the high and low flocculation yeasts (i.e. yeast type A reaches the bottom of the carboy faster than yeast type B, yeast B remains in suspension longer than yeast A). Maybe I'm out in left field here. But during my washing I've seen some yeast stay in suspension in the water days after washing, could those be the lowly flocculating yeast? And the ones already settled 18-24hrs later be the more highly flocculating variety?

 

[RukusDM]

What I've been trying when washing yeast is to go through a couple of additions of boiled and sanitized water. I let it set in the fridge after each wash till everything settles.

This is really a test and not a practice. What I'm attempting to do is really wash the solids (dead and live yeast, trub) and remove the beer (for lack of a better term) and add water again until I don't get "Beer" on top.

My hope is I'm just cleaning bad stuff out of the sample and give a better environment to store the yeast for a later starter.

Again this is just a test to see what happens.

Any thoughts on this?

 

[MalFet]

What I've been trying when washing yeast is to go through a couple of additions of boiled and sanitized water. I let it set in the fridge after each wash till everything settles.

This is really a test and not a practice. What I'm attempting to do is really wash the solids (dead and live yeast, trub) and remove the beer (for lack of a better term) and add water again until I don't get "Beer" on top.

My hope is I'm just cleaning bad stuff out of the sample and give a better environment to store the yeast for a later starter.

Again this is just a test to see what happens.

Any thoughts on this?

Interesting questions. Anything I say is just speculative, as I have never washed yeast. (It seems like a perfectly viable thing to do -- I'm just never organized enough to plan two consecutive brews using the same yeast).

In theory, you want a good diversity of floc'ers in your yeast. The ones that drop out quickly help keep your beer clear, and the ones that drop out late get you those last couple points of attenuation. What you want to avoid is selectively harvesting only early or late flocculating yeast. If you had only the early guys, you'd end up under attenuated; if you had only the late, you'd end up with murky beer. Diversity is good.

So the question is whether your method is selectively dumping too much of your relatively unflocculant yeast. I've wondered about this when I crash and decant starters. My gut instincts (though nothing more) tell me that it is not a problem. While you are certainly dumping out some yeast when you decant, I suspect that a good, hard and cold crash causes even relatively unflocculant yeast to drop out of suspension.

The experiment here, which I may try some day, would be to do a forced attenuation test comparing a standard yeast sample and a sample that has been washed and crashed a few dozen times. I would be curious to see the results.

Before then, though, theory-crafting makes me think that you can do a few things to keep your yeast diverse. First, keep your fridge visits relatively long and cold. You want your yeast to have enough time to fully settle out. Second, when you are dumping, err on the side of leaving more liquid rather than less. You'll get slightly less cleaning per round, but I suspect that the last bit of liquid in a decanting pour would end up containing more yeast than you'd want. Third, when you harvest, make sure you get a nice cross-section. Don't pull only from the top or the bottom.

Bigger picture, I suspect that all of this is only an issue if you are reusing yeast over and over and over again. For three or four pitches, I don't think it would make as much of a difference.

 

[RukusDM]

Well I've read that picking top and bottom as you referenced is bad. What I've done more specificly is to scrape out yeast sludge mix from the bottom and put it in a sanitized container then add the distilled sanitized water and do the successive washes from that not targeting just yeast.

Its a slightly different take on the yeast wash where you just add several quarts of water and slosh around and wait to settle and then decant yeasts.

I'm sure the current methods work well, I just wanted to produce a cleaner environment for yeast storage. The less total sugars suspended in liquid would seem to be a better thing as those are what contribute to spoilage and bacteria cultures to grow.

I don't have any real science that pushed me to try this other than trying to remove as much sugar from the storage medium as possible before long term storage.

I would assume if there are no sugars for food then bacteria would have a hard time taking over even if you had some in the stored yeast. I would assume they would also become dormant or die.

Again, not based on any real science, but more on feel and very basic understanding of bacteria.

 

[pkeeler]

If you wanted to use a clean yeast for every brew, you could get some WY 1056 or WY 1272 and, like Papazain, use it over and over. I've made starters from the dregs of previous batch bottles.

Slants, sterilization, etc. are just factors of safety. Each one adds additional insurance against yeast changes (mutations, genetic drift) and bacterial infection. However, each comes with a cost (in time and/or money). Same with buying a new smack pack with every brew, it adds up. However, if you want a different yeast, you are going to have to buy it. The only way Wyeast can stay in business is to offer all these different yeasts because you have an entire store of free yeast in your basement or refrigerator. Are they really all that different though? That is for another thread LOL

Personally, I like to spend about $.75-1 per brew on yeast. So, that means I buy a smack pack, make a beer, wash the primary cake into 6 ball jars (7 oz), refrigerate them until I use them. Now, I'm not that meticulous about sanitizing and I can't guarantee the genetic purity of the strain (no slant system or microscope). But it works for me, probably because I'm putting so much slurry into each ball jar. I could have made 12 jars with less slurry, but I would think the lower amounts of yeast in each jar increases my risk of something going wrong (but I have no idea what those percentages are really). Now, I could probably take each of those 6 and make another generation and get my beer cost for yeast to $0.15. But I would have to worry more about sanitation and genetic drift of the original batch. Plus, I'd have to get another fridge to hold all these ball jars ;-) Oh, and I like trying new yeast, and would never make 36 in a row with the same yeast!

Now, as to washing vs. leaving the cake. If the cake is under beer and the fermenter is filled with CO2, you could probably leave it. Probably how beer was made for millenia (beer racked off, new beer racked on). However, personally, I'd hate to have my next beer dissolve that crap off the sides of the fermenter. It is hard to wash the fermenter and leave behind the yeast cake.

As for leaving beer in the primary for 4-6 weeks. Seems like people get away with it. However, yeast washing seems to me to be one of those times where moving the beer to a secondary makes sense. I like to harvest yeast fresh, maybe 1 week from pitching. But I don't know if it makes any difference; and I don't care to get involved in the "Primary Only" religious crusade that is happening around here.

 

[COLObrewer]

A ton of good information here, I'm glad to see so many people with so many questions, that's how we learn.

A couple of things I thought about while reading through this thread:

1. Regarding collection of yeast to re-use; I believe the conical fermentors (at least the large commercial ones) have a valve allowing them to extract yeast from the middle of the cake in order to select the best cross section of yeast for maintenance and propagation. I'm not sure how well this works since "all trubs does not an ideal sample make". It's just an observation, I probably read it somewhere.

I'm curious about those commercial breweries with flat bottom fermentors, do they have a valve that collects from a certain height in the vessel? Do they all do this? I imagine they could pump it from the level they want with an adjustable pipe coming from the top also?

2. I have been curious for some time regarding all the talk of infection, it seems to be a growing concern, maybe it's just tracking with a growing number of new brewers. I have gotten infections but they have been only in beers that I have had "open" for extended periods of time in my cellar. So far these have been good infections, (Knock on brett infected wood).

I am convinced now that most infections come from the practice of brewing where we eat, clean, prepare food. As studies have shown the place where the greatest number of bacterium reside in the home is the kitchen, (I wouldn't brew in the bathroom though). This is because of the great need for sanitation in this hobby, we want to be close to the source of water, cleaning supplies etc. Or maybe it is WHY we need sanitation so much?

Personally I mostly brew outside, or in the shop, it makes things cumbersome because of all the carrying, hoses, etc. I was contemplating installing a wash tub in the shop for this reason but now I'm not so sure that this is the main reason We've not had a problem with infection. I'm not the most sanitary person brewing to be sure and lately I seem to be flirting with unsanitary procedures wondering each time if this is the practice that will get me an infection.

I'm wondering what the ratio of infection is for someone that brews outside or away from the kitchen, compared to someone that always brews in the kitchen?

Sorry for my rambling, brew on my friends

 

[MalFet]

Personally I mostly brew outside, or in the shop, it makes things cumbersome because of all the carrying, hoses, etc. I was contemplating installing a wash tub in the shop for this reason but now I'm not so sure that this is the main reason We've not had a problem with infection. I'm not the most sanitary person brewing to be sure and lately I seem to be flirting with unsanitary procedures wondering each time if this is the practice that will get me an infection.

I'm wondering what the ratio of infection is for someone that brews outside or away from the kitchen is, compared to someone that always brews in the kitchen?

Based on other (mostly-unrelated) work I do, I suspect it's a bit of a trade-off. Kitchens are chock full of lacto, pedio, and aceto, but the outside is full of mold and wild yeast. My bigger concern with shifting everything outside would be air movement. If you are in a well protected area (like your shop, perhaps) it might be a moot point, but rapid air movement transports dust, and dust is like the spaceship that gets infections all up in your junk.

Don't get me wrong, I don't think that brewing outside -> infections. Your wort is hot enough to manage that, and a nice big yeast pitch stacks the deck in favor of the good guys. I think sanitation for brewing is relatively straightforward -- not that we haven't all had bad luck once or twice -- and that it is perfectly possible to brew inside our out infection free.

I certainly wouldn't plate yeast outside, though. A lot of the protective measures involved in yeast culturing involve manipulating air currents to keep dust away from your samples. Outside, that wouldn't be possible to control.