Reused US05 for three generations. Last generation had bizarre ester profile...why?

[tyrub42]

Hi everyone,

I just wrote to Fermentis about this, but I'd love to get your opinions as well. I have seen a few threads about US05 giving off esters, but this is a unique case, as I harvested and re-pitched the same yeast twice (three batches total, including the first batch with the fresh packet). I'm just going to paste my letter to Fermentis here, and see what you all think.

I'm preparing to start using/harvesting/reusing liquid yeast, so I have reused US05 three times in the last 6 weeks to get a feel for it. The last beer, which I bottled yesterday, shocked me a bit with the yeast profile. It has lots of banana and clove esters in it, to the point that the single-malt pale ale drinks more like a hybrid saison or a Belgian Pale Ale. This was extremely surprising for two reasons:

1. I was of course not expecting it from US05
2. There are no signs of infection, no undesirable off flavors (no diacetyl, acetaldehyde, etc), my FG was exactly on target, and the beer tastes delicious. Heck, even the NZ Orbit hops seem to really compliment the taste of the yeast.

I am excited to taste it after bottle conditioning, but more to the point, while I do enjoy this happy accident, this is the first unexpected situation I've run into in my homebrewing tenure and I would like to get your input about why it happened. I'd like to outline the way I reused the yeast, and my suspected reasons for this, and get your input on it.

The first time, I took a pint of 'slurry' (yeast cake mixed with the beer that is left after transferring, making a thick yeasty goo), and a pint of sterile water, combined them in a sterile jar, and refrigerated for 2 days until I had brewed again. The particulate settled to the bottom, and the murky water at the top. I let it adjust to room temperature, and pitched the liquid, while leaving most of the particulate behind. I fermented that batch (27-liter, 1.076og) at 16c/60f before warming to 21c/70f for the last week in primary.

The second time, I just filled a sterile 300ml jar with 'slurry', refrigerated it for 3 days, and repitched into wort on brew day. Of the 300ml, I would estimate that 150ml was beer and hop particulate, while 150 was yeast cake. I fermented this beer (26 liter, og 1.053) at 21c/70f for the whole fermentation before cold crashing and bottling.

Both times I repitched slurry, signs of fermentation were present at 10-12 hours pot pitching. Both fermented at roughly the same pace as fresh 05, finishing the bulk of active fermentation in 2-3 days, and bubbles stopped within 5 days.

It would seem that the yeast were stressed somehow, although the lack of diacetyl etc. would suggest that it wasn't too severe, right?

The three factors I can think of here that could have stressed the yeast to produce these flavors (as contamination doesn't seem to be a factor) are:

-The three generations had different fermentation temps: 18c/64f, 16c/60f, and 21c/70f respectively. Would this be a factor in stressing the yeast enough to produce these esters? The second batch did have a slight presence of peachy esters, but it was very subtle and non-invasive, and that is apparently normal for 60f-and-under fermentations with 05

-The last time I repitched, I did not let the slurry warm up to room temperature. I did take it out of the refrigerator, but it was between 41f/5c and 50f/10c going into wort that was 68f/20c. Could this have shocked the yeast enough to produce this effect?

-If there was slight contamination in the original yeast packet from another strain, could that strain have taken over the flavor over three generations?

If you can think of anything else, or have any questions, please let me know. I'd like to get to the bottom of this, in order to both reproduce this effect in the future (this beer is seriously good, and prefect for summer), and more importantly, avoid it when I don't want it. I'm glad this was a happy accident, but accidents in general are not what I want in brewing of course.

To clarify how the beer tastes, it is almost like a mix of 05 and t58, but the esters are really all banana and clove without any peppery quality. My friend who helped bottle said it was her favorite beer she's ever had, and I actually poured her an uncarbonated glass to drink, so it is a palatable beer, and thank god the yeast was healthy enough to consume any diacetyl etc, so it's actually remarkably clean, but it is a shock, and most of my homebrewing friends and professional brewer friends have basically had the same opinion as I do: something obviously happened, but not sure what it was that did it.

What do you all think?

Best,
Tyler

 

[TheMadKing]

That's pretty interesting. There's so many variables that it's really impossible to tell what happened without a complete laboratory analysis, and even then it will be difficult. Yeast can evolve and mutate very quickly, so it's possible that over 3 batches you've done something that favors higher ester producing yeasts.

 

[mongoose33]

You don't say what your fermentation temperature was. Same as earlier batches? Are you controlling it in any fashion? Might the temperature have been higher?

 

[tyrub42]

You don't say what your fermentation temperature was. Same as earlier batches? Are you controlling it in any fashion? Might the temperature have been higher?

I did mention it, but it was easy to miss in my overly verbose post haha. They were quite varied as well:

The three generations had different fermentation temps: 18c/64f, 16c/60f, and 21c/70f respectively.

These are my initial fermentation temps. All were raised to 21f/70c after active fermentation had stopped (for better 'cleanup' as well as dry hopping)

 

[RedlegEd]

...
The first time, I took a pint of 'slurry' (yeast cake mixed with the beer that is left after transferring, making a thick yeasty goo), and a pint of sterile water, combined them in a sterile jar, and refrigerated for 2 days until I had brewed again. The particulate settled to the bottom, and the murky water at the top. I let it adjust to room temperature, and pitched the liquid, while leaving most of the particulate behind. [my emphasis added] I fermented that batch (27-liter, 1.076og) at 16c/60f before warming to 21c/70f for the last week in primary.
...
What do you all think? Best,
Tyler

Tyler,
Reading this literally means you pitched the beer/water that was on top of the yeast cake in the jar, right? If that's the case, then I think you really underpitched the second batch. The "normal" process is to decant most of the top layer of beer/water in the jar, leaving just enough to swirl and get the yeast cake back into a pourable slurry, then pitch that. It looks like you followed that process with your subsequent batch, but at that point, you may have really stressed the yeast from the previous batch. Ed

 

[mongoose33]

I did mention it, but it was easy to miss in my overly verbose post haha. They were quite varied as well:

The three generations had different fermentation temps: 18c/64f, 16c/60f, and 21c/70f respectively.

Sorry I missed it.

Are you controlling temps at all or just fermenting at ambient? Are the temps above the actual wort temp or ambient temp?

I think 70f is generally too high, and if it's ambient you're measuring and not wort temp, then it's higher than 70f.

I think that's your difference right there--temps. It's well known that fermenting too warm will create flavors (off-flavors, perhaps, depending on what you're going for) that aren't generally intended. Banana and clove are two of those.

Since you like this taste--and I'd wait until after carbonation and conditioning before I concluded that--reproducing it would require the same temperature regime.

 

[tyrub42]

Sorry I missed it.

Are you controlling temps at all or just fermenting at ambient? Are the temps above the actual wort temp or ambient temp?

I think 70f is generally too high, and if it's ambient you're measuring and not wort temp, then it's higher than 70f.

I think that's your difference right there--temps. It's well known that fermenting too warm will create flavors (off-flavors, perhaps, depending on what you're going for) that aren't generally intended. Banana and clove are two of those.

Since you like this taste--and I'd wait until after carbonation and conditioning before I concluded that--reproducing it would require the same temperature regime.

It was basically wort temp, in that my temp control is taped to the fermenter at its warmest point (near the top, farthest from the cooling element in the fridge). 70 is good for 05; I'm actually more worried that 60 was too low (and of course that range of temps between batches). Don't get me wrong, most of these variable are because I am trying to experiment and was doing batches very quickly one after another; I never expected this result though.

Thanks!

 

[tyrub42]

Tyler,
Reading this literally means you pitched the beer/water that was on top of the yeast cake in the jar, right? If that's the case, then I think you really underpitched the second batch. The "normal" process is to decant most of the top layer of beer/water in the jar, leaving just enough to swirl and get the yeast cake back into a pourable slurry, then pitch that. It looks like you followed that process with your subsequent batch, but at that point, you may have really stressed the yeast from the previous batch. Ed

Thanks for the reply, Ed! I ended up pitching the water/beer, the top layer that settled on the water/beer, and a bit of the sludge that floated up to the top of the jar. from a 1-liter jar that was half-filled with sediment and half filled with liquid, I had about 300ml left after pitching the rest (the 300ml was mostly particulate and very little liquid, though, so I likely pitched 150-200ml of the particulate into the beer). From the fermentation activity (lag time, insanely vigorous fermentation, clean finish), and lack of any off flavors, I had actually suspected that if anything I over-pitched, so this is super valuable information for me for the future; much appreciated. The second repitch was the more-basic 'slurry' method that I read about here, and will be my go-to in the future. It was also in a much lower-og beer. Fermentation was far less vigorous in it, but I guess that was just due to the lower og (1.053 vs 1.073)

Anyway, from this more in-depth description, do you still think underpitching the second batch was a big factor in this? That would be nice and easy to correct (or utilize) in the future.

 

[SlitheryDee]

I suppose I would expect some changes as you get into later generations. I've got some Nottingham I harvested that is on it's third generation. I'm tempted to keep going with it over and over until it does something I don't like or it gets infected. There are enough warnings out there about repitching harvested yeast over and over again to make me sure that something will happen, but if it keeps making beer I find it hard to say I'll be dissatisfied with the results.

 

[mattdee1]

I've had the exact same Saison-esque results from S-05 pitched straight from the original packet. When I researched it a bit, I saw several others saying the same thing. My fermentation temperatures went a little awry on that batch, so that is the explanation I've settled upon for why it happened... but who knows.

If you really want tight control over such things, maybe it's worth spending the $3-$4 for new dry yeast packs rather than rolling the dice with re-pitching.

 

[isomerization]

The clove notes descriptor is throwing me off. US-05 is supposed to be POF-negative (phenol off flavor). So that suggests to me, you either had a contamination with wild yeast, a previously used POF+ yeast or a water issue (e.g. chloramines).

I am also confused as to how you are harvesting/re-pitching. I think a much better strategy would be to 1) make a starter with excess volume than needed, 2) decant off the excess (after its 'done') into a sanitized mason jar and 3) use this for your next starter. This eliminates the need to "wash" the yeast and genetic mutations are going to occur at a much, much lower rate than taking yeast from a fermented batch.

 

[tyrub42]

The clove notes descriptor is throwing me off. US-05 is supposed to be POF-negative (phenol off flavor). So that suggests to me, you either had a contamination with wild yeast, a previously used POF+ yeast or a water issue (e.g. chloramines).

I am also confused as to how you are harvesting/re-pitching. I think a much better strategy would be to 1) make a starter with excess volume than needed, 2) decant off the excess (after its 'done') into a sanitized mason jar and 3) use this for your next starter. This eliminates the need to "wash" the yeast and genetic mutations are going to occur at a much, much lower rate than taking yeast from a fermented batch.

Thanks so much for the reply!

I doubt chloramine would be the problem. This is all filtered water with an extremely good filtration system (pilfered from a school). Contamination is a possibility, but due to the fact that it didn't affect FG, and there's no sourness/off flavors aside from the esters, it seems odd. Also, I'm in Taiwan, and our wild yeasts are groooosssss haha.

I was harvesting/repitching that way to practice for when I start using Conan. Apparently it changes quite a bit over 3-5 generations, so I wanted to try to reuse it in this way. I'm a bit nervous about that now though, so I may just do what you suggest and re-culture from a gen-1 starter. I have some friends with a beer company here, so the Conan will, if all goes well, be banked and ready to reuse pretty much indefinitely, so I'm trying to get practice harvesting and repitching with that slurry method to see generational development in the yeast.

I'll start testing some bottles as they condition a bit, so I'll update more about the esters, but there was definitely some clove and substantial banana in the nose and flavor...I was extremely surprised as well.

 

[RedlegEd]

Anyway, from this more in-depth description, do you still think underpitching the second batch was a big factor in this? That would be nice and easy to correct (or utilize) in the future.

Tyler,
Sorry for the late reply, I've been on the road. If you did pitch 150-200ml of the slurry along with the beer/water mix on top, then you more than likely got a good pitch, so I'm not sure what caused the esters. I know that a lot of folks will purposely stress their yeast when making hefeweizen, just to promote those banana esters and clove phenols. US-05 is also known to throw different flavors (peach/stone fruit comes to mind) depending on the fermentation temperature. I've always had consistently clean results using that yeast, and I try to keep my ferm temps in the 62° - 68°F range, with a bump up to 70°-72°F for a day or two at the end to finish it off. I think your subsequent plan to bank some 1st gen Conan, as well as re-use multiple generations will provide you some really interesting comparative examples. Please let us know how things come out. Ed

 

[tyrub42]

Tyler,
Sorry for the late reply, I've been on the road. If you did pitch 150-200ml of the slurry along with the beer/water mix on top, then you more than likely got a good pitch, so I'm not sure what caused the esters. I know that a lot of folks will purposely stress their yeast when making hefeweizen, just to promote those banana esters and clove phenols. US-05 is also known to throw different flavors (peach/stone fruit comes to mind) depending on the fermentation temperature. I've always had consistently clean results using that yeast, and I try to keep my ferm temps in the 62° - 68°F range, with a bump up to 70°-72°F for a day or two at the end to finish it off. I think your subsequent plan to bank some 1st gen Conan, as well as re-use multiple generations will provide you some really interesting comparative examples. Please let us know how things come out. Ed

Thanks for the reply! I'm starting to think that the last repitch was under-pitched, now that I reread the Guide to making and repitching slurry. I repitched 300ml of slurry into the batch, which should have given me more than enough cells for the 26 liters of 1.053 wort, BUT there are several factors that I did not consider enough beforehand:

-most importantly, I don't filter out my whirlpool hops before fermenting (I know it sounds weird, but I tried it both ways and found that there are no negative flavor contributions and a slight increase in hop character when I do this), and half of my dry hops are unbagged, pitched directly into the fermenter. That means that there were 6oz of hop matter sitting in with the yeast cake, which I would estimate was probably responsible for half of the particulate in there, so even though I pitched 300ml, I would guess that I may have only had 150-225 billion cells (no way to tell for sure, but if we estimate 1-1.5 billion per ml, I would have to cut that in half to account for the hop matter).

-some may have died off in their 2-day refrigeration, and then the shock of pitching cold slurry (out of the fridge for about 10-15 minutes only) into 68-degree wort very possibly killed lots of cells or at least stressed them, and there is a real chance that I under-pitched and stressed the last batch and that's what caused the esters.

If this is the case, I am extremely lucky, because I just tried a bottle after only 2 days of bottle conditioning, and it is honestly a beautiful beer. I detected no Diacetyl or any other yeast-related off flavors, even though I usually pick up significant amounts on premature bottles (they carbonate pretty fast, but even in the TW heat they need a full week before the yeast cleans everything up). The ester expression is exactly how I described it out of the fermenter: almost like I pitched 05 and a saison yeast together. More banana than clove, and no presence of stone fruit, which I did get slightly when I fermented it very cold in another batch (60f/16c). Finishes more on the 05 side with a crisp, clean, dry finish and the Orbit hops did a great job, although they were honestly much subtler than I was hoping they'd be, given how great my fridge smelled as it was fermenting. So far all four people who have tried it have loved it. I'll always hold a grudge against the beer, myself, though, since this was a total accident, which makes me feel like a lot less of a superbrewer than the batches that come out exactly the way I plan, haha. I'm excited to see it after conditioning is finished and have some of my refined-palated give me their impressions.

Thanks again for the help!

 

[tyrub42]

This has been a really helpful thread for me, and I know now that next time I want to repitch slurry, I better at least take my hop matter into account a bit better and let the yeast get to pitching temp properly. Thanks so much, everyone!

 

[Ashevillain]

Hey based on the OP these quotes from a book I've read may or may not offer some insight. I would say the quick temp swing as well as even pitching at 68 instead of ~62 could have caused some issues. It doesn't sound like contamination at all but, figured this info couldn't hurt and it immediately came to mind as I read your post.

"I wouldn't risk trying to repitch dry yeast. Rehydrate a fresh pack for every beer. There's always a tiny amount of contamination in dry yeast that you won't notice in one generation, but after multiple uses, it may start to show up. It's not worth the couple of bucks you'll pay for a fresh pack."

"If the beer starts fermenting too warm, it doesn't help to cool it down later-- the damage has already been done."

-Karnowski

These quotes were selected in a narrow context, but I feel they apply correctly here though there is no explicit statement that dry yeast will actually show signs of contamination after multiple generations.

 

[tyrub42]

Hey based on the OP these quotes from a book I've read may or may not offer some insight. I would say the quick temp swing as well as even pitching at 68 instead of ~62 could have caused some issues. It doesn't sound like contamination at all but, figured this info couldn't hurt and it immediately came to mind as I read your post.

"I wouldn't risk trying to repitch dry yeast. Rehydrate a fresh pack for every beer. There's always a tiny amount of contamination in dry yeast that you won't notice in one generation, but after multiple uses, it may start to show up. It's not worth the couple of bucks you'll pay for a fresh pack."

"If the beer starts fermenting too warm, it doesn't help to cool it down later-- the damage has already been done."

-Karnowski

These quotes were selected in a narrow context, but I feel they apply correctly here though there is no explicit statement that dry yeast will actually show signs of contamination after multiple generations.

Both of those statements are true, but I am thinking the esters are more likely to be related to stressing the yeast than contamination with an estery strain (which I would expect to be a more gradual presence in the beer through generations).

I'm not repitching for cost savings (I am saving quite a bit since I'd need 2 packs for most of my beers, but if I'm putting in 8 hours of work, 6 bucks isn't super important haha); it was just for practice and experimentation. I'm really happy that this happened in a batch that works so well with the estery yeast, because this would have sucked in my oldschool DIPA that I did last generation.

I always pitch at my target fermentation temp or around it, except for the 16c/60f fermentation, which was pitched at 19-20, but was cooled to 16 within a couple of hours, well before yeast started to show signs of fermentation. Warming a beer up after primary fermentation stops is generally a good thing though, as it helps extract hop oils if dry hopping, and helps yeast clean up the beer a bit. For these reasons, all of my beers are at 69-70 for at least a few days before cold crashing (if I cold crash) and bottling.

Thanks!

 

[Ashevillain]

Yep I deff agree on driving fermentation. Pretty much guarantees you've cleaned everything up after a solid ferm. Another point that you just brought out is that the previous batch was a DIPA. While I'm sure it wasn't much over 8% if that, higher abv beers can leave the yeast worn out and they may be stressed when tackling further batches. And of course the hop matter will pad your actual population as you said.

You can even drive ferm sooner (day 3-5)and it can promote healthy population/shave a day or 2 off total ferm, the added warmth helps keep them happy as stuff to eat becomes less readily available. I have noticed minute differences in driving towards the end vs starting earlier, never unpleasant and worth playing around with.

 

[RedlegEd]

...
I always pitch at my target fermentation temp or around it, except for the 16c/60f fermentation, which was pitched at 19-20, but was cooled to 16 within a couple of hours, well before yeast started to show signs of fermentation. Warming a beer up after primary fermentation stops is generally a good thing though, as it helps extract hop oils if dry hopping, and helps yeast clean up the beer a bit. For these reasons, all of my beers are at 69-70 for at least a few days before cold crashing (if I cold crash) and bottling.

Tyler, I really don't think the pitch temperature has anything to do with your situation. Brülosophy did an Exbeeriment where they altered the pitch temp and the bottom line is it had no effect. When you pitch your yeast, they go through lag and exponential growth phases before they start fermentation. As long as you sufficiently aerate / oxygenate your wort, pitching warm then cooling to fermentation temperature during these phases should not create off flavors. Once you're into the fermentation phase, then higher than "normal" temperatures (for that strain of yeast) may have an effect on off-flavors (especially Diacetyl.) Even that is subject to speculation as multiple Brülosophy Exbeeriments have shown where you can't always make that blanket statement. My process now for both ales and lagers is to cool my wort to <72°F, aerate/oxygenate, then pitch and continue to cool to fermentation temperatures in my ferm chamber. Using this method, I've found I don't need to build as big a starter with lagers, and with ales the yeast seem to take off faster and stronger. This is all anecdotal, of course, but my observations seem to be consistent and my beer is good. Ed

 

[Ashevillain]

Ed this makes sense to me and I've read those xBMTs as well except for the variable temp one thats nuts! Perhaps the variable to be considered is how long it takes the volume of wort that's too warm for ferm to cool to ferm temps after being pitched. I'd imagine if the volume can get into an ideal range before any fermentation begins you are actually giving your yeast a comfy head start, but if it doesn't drop to temp quickly enough, they get too much of a head start and unwanted ester production occurs.

 

[tyrub42]

Tyler, I really don't think the pitch temperature has anything to do with your situation. Brülosophy did an Exbeeriment where they altered the pitch temp and the bottom line is it had no effect. When you pitch your yeast, they go through lag and exponential growth phases before they start fermentation. As long as you sufficiently aerate / oxygenate your wort, pitching warm then cooling to fermentation temperature during these phases should not create off flavors. Once you're into the fermentation phase, then higher than "normal" temperatures (for that strain of yeast) may have an effect on off-flavors (especially Diacetyl.) Even that is subject to speculation as multiple Brülosophy Exbeeriments have shown where you can't always make that blanket statement. My process now for both ales and lagers is to cool my wort to <72°F, aerate/oxygenate, then pitch and continue to cool to fermentation temperatures in my ferm chamber. Using this method, I've found I don't need to build as big a starter with lagers, and with ales the yeast seem to take off faster and stronger. This is all anecdotal, of course, but my observations seem to be consistent and my beer is good. Ed

Great to know, thanks! My ground water is like 84 degrees here, so I need to use sterilized frozen water bottles to get it down from about 90. Knowing that a few degrees won't affect flavor as long as it's right in the chamber and cooled before fermentation starts is awesome!

Just cracked another bottle and OMG did I luck out with this batch. Tastes fantastic already even though it still has several days of bottle conditioning left to go. The esters are a bit fruitier with less clove and more banana than I perceived at bottling, and it goes super well with the citrusy Orbit hop blend. If only I'd done this on purpose...

 

[RedlegEd]

Just cracked another bottle and OMG did I luck out with this batch. Tastes fantastic already even though it still has several days of bottle conditioning left to go. The esters are a bit fruitier with less clove and more banana than I perceived at bottling, and it goes super well with the citrusy Orbit hop blend. If only I'd done this on purpose...

Even though you have the recipe, it sounds like you'll be chasing this happy accident again. I wish you the best of luck and if you figure out the "secret," please let us know. Ed

 

[flars]

Did you use the same Orbit hop blend in all three beers? If so were the hops from the same lot.

 

[tyrub42]

Did you use the same Orbit hop blend in all three beers? If so were the hops from the same lot.

No, this was the first time using them. Farmhouse had em at like 2.80 per 4oz and they seemed like they'd shine in a lighter beer, which I usually don't make. Another lucky move as the citus they throw out goes really well. Not as NZish as I was expecting, although I guess that's what happens when a region's biggest superstar is Nelson lol.

 

[tyrub42]

Even though you have the recipe, it sounds like you'll be chasing this happy accident again. I wish you the best of luck and if you figure out the "secret," please let us know. Ed

With all of your help, I'm a lot closer than I thought I'd be at figuring it out (not sure if I'd do it again on purpose, but that is some tasty stuff ). Thanks again!

 

[flars]

No, this was the first time using them. Farmhouse had em at like 2.80 per 4oz and they seemed like they'd shine in a lighter beer, which I usually don't make. Another lucky move as the citus they throw out goes really well. Not as NZish as I was expecting, although I guess that's what happens when a region's biggest superstar is Nelson lol.

I asked because it is possible the taste you are perceiving could in part be from the hops and only partly the yeast. Orbit is a blend of hops. Each year the flavors from the hop blend will be different.

 

[tyrub42]

I asked because it is possible the taste you are perceiving could in part be from the hops and only partly the yeast. Orbit is a blend of hops. Each year the flavors from the hop blend will be different.

Yup, the blend changes yearly. This was 2015. Good stuff, but definitely subtler than I was hoping for. Not the freshest, but they were vac sealed in a freezer so I believe they were still in good shape.