Removing Excess Banana Ester with Heat?

[Azura]

I haven't seen any scientific data or anecdotal homebrew posts that confirm or deny the following hypothesis:

I believe based on cumulative anecdotal homebrew experience that excess esters (banana specifically) may be significantly reduced by increasing the FV heat to 74-78F on day 4-5.

This method appears to work very well with WY1469 which makes fairly heavy banana and moderate stone fruit without late heat intervention. Hitting it with late heat puts the banana comfortably below the stone fruit reliably. Then the stone fruit shines.

Can anyone confirm or deny this with science or an anecdote with a decent sample size?

 

[leonardoreges]

I think it’s the complete opposite.
If you increase temp it’ll give you more esters.

 

[xico]

Yup, increased temp will bump the ester production up. Esters are chemically volatile it is true. And if you go down on this page to boiling points of isoamyl acetate you will see however that this ester is very stable with a 288F vaporization. As plausible as your observations may be, the evidence seems to show that something else is going on to get the stone fruit to shine.

Pfriem warm their bottled beer to 82F when conditioning to ramp ester character without risk of fusel creation. There are other methods to reducing ester character in hefeweizen yeast. I love hefeweizens and sadly have yet to make something as delicious as what is served in Bavaria. It is a good entry-level yeast to make a drinkable beer but one of the hardest to make exceptionally well.

When you under-pitch your yeast they need to divide one or two more times than they would otherwise. This means fewer yeast get more access to O2 in the wort to make fatty acids which are the precursors for esters. Over-pitching and the yeast treat your wort like a starter only they are without O2 and need to shift metabolic pathways on a dime and skip appropriate reproduction. This will stress the yeast out that some claim induce ester production but I've found no scientific evidence to back up that claim.

Another way to control this is to avoid introducing any more oxygen that what you can pick up in the cooling and transferring process. Less O2, fewer esters. So I definitely would not use bottled oxygen or do any excessive shaking and aim to pitch higher than pitch lower. Remember, the weizens are made under the purity law so no squirts of pure O2 is being done to make the best examples of hefes.

Finding the sweet spot for a hefe yeast in terms of pitch rate is experimentally determined unfortunately. I readily handle 9 hefe strains in the brew program I help run and they are the only group of commercial strains that no one (in our program) has put enough time into to develop parameters for ester profile.

As another idea, fermenting under pressure will suppress ester production as well. There are threads on here for making spunding valves that can attach to a corny or a manifold connected to several cornies. I have had a lot of success reducing the isoamyl acetate production which in excess smells like bazooka joe gum to me and not something I want to put in my face.

 

[Smellyglove]

Yup, increased temp will bump the ester production up. Esters are chemically volatile it is true. And if you go down on this page to boiling points of isoamyl acetate you will see however that this ester is very stable with a 288F vaporization. As plausible as your observations may be, the evidence seems to show that something else is going on to get the stone fruit to shine.

Pfriem warm their bottled beer to 82F when conditioning to ramp ester character without risk of fusel creation. There are other methods to reducing ester character in hefeweizen yeast. I love hefeweizens and sadly have yet to make something as delicious as what is served in Bavaria. It is a good entry-level yeast to make a drinkable beer but one of the hardest to make exceptionally well.

When you under-pitch your yeast they need to divide one or two more times than they would otherwise. This means fewer yeast get more access to O2 in the wort to make fatty acids which are the precursors for esters. Over-pitching and the yeast treat your wort like a starter only they are without O2 and need to shift metabolic pathways on a dime and skip appropriate reproduction. This will stress the yeast out that some claim induce ester production but I've found no scientific evidence to back up that claim.

Another way to control this is to avoid introducing any more oxygen that what you can pick up in the cooling and transferring process. Less O2, fewer esters. So I definitely would not use bottled oxygen or do any excessive shaking and aim to pitch higher than pitch lower. Remember, the weizens are made under the purity law so no squirts of pure O2 is being done to make the best examples of hefes.

Finding the sweet spot for a hefe yeast in terms of pitch rate is experimentally determined unfortunately. I readily handle 9 hefe strains in the brew program I help run and they are the only group of commercial strains that no one (in our program) has put enough time into to develop parameters for ester profile.

As another idea, fermenting under pressure will suppress ester production as well. There are threads on here for making spunding valves that can attach to a corny or a manifold connected to several cornies. I have had a lot of success reducing the isoamyl acetate production which in excess smells like bazooka joe gum to me and not something I want to put in my face.

Are you sure about the statement with less o2 produces less esters? My experience is the opposite, also lots of sources claim the same.

 

[xico]

This is an excerpt from here. There are a lot of variables at play in the brewing process so it's hard to identify how or procedures tweak outcomes. Do you repitch your yeast, buy fresh every time, or start cultures up from colonies? The culture may have stored enough glycogen from two starter steps that it doesn't need an O2 added. How many step ups and with what nutrients and vitamins will drastically alter the yeast's performance. I may be wrong but my understanding of fermentation compared to respiration for yeast lines up with the above link.

It is more a continuum where you want to find middle-ground between the two extremes. I think some strains benefit from a shot of pure oxygen and others don't.

"Wort composition plays a large role in the formation of esters. This makes sense because if the yeast live in the wort then they probably pull most of their nutrients from the wort. The most influential substance in the wort is oxygen. If there is too much oxygen the yeast will use it to make unsaturated fatty acids and sterols for generating cell walls. This process uses up a lot of acyl CoASH meaning the yeast can’t use the acyl CoASH to make esters. Low oxygen concentrations help keep levels of acyl CoASH high resulting in more ester production. However, if oxygen levels are too low,the yeast will not be able to grow and divide. This can result in slow or incomplete fermentations and even massive cell death called autolysis."

 

[Northern_Brewer]

I think it’s the complete opposite.
If you increase temp it’ll give you more esters.

More esters in general - but the OP is talking about changing the mix of esters that ends up in the final beer. I was reading something recently about a temperature profile that specifically reduced ethyl acetate and isoamyl acetate (??I think??) with a high-temperature "soak" of some kind - can't remember where it was though. I guess it's something to do with yeast either eating certain esters and not others, or converting them to other forms.

 

[xico]

Of my limited time in Bavaria I have had the opportunity to speak with hefeweizen brewers and quite a few of them still do decoction mashes. I am willing to suspect there is something happening in this process that affects the outcome of flavor. @Northern Brewer, if you come across any information regarding your post I would be very interested in reading it.

It makes sense that certain chemical compounds might be favored as products of metabolism with temperature as a variable. Metabolic pathways even for simple organisms like brewing yeast is still not well understood regarding esterification. Any information that can shed light on the dark would be most welcomed.

 

[Azura]

I think it’s the complete opposite.
If you increase temp it’ll give you more esters.

You are correctly thinking about the principles of early fermentation temperature. I am referring to what happens when I increase the temperature to 75F after 4 days of steady 65F fermentation with a banana producing yeast. Even though there is no science or even homebrew talk that I can find to support my observations, I will continue to do it because remaining in the low 60s to finish produces more banana than I want.

 

[Azura]

Are you sure about the statement with less o2 produces less esters? My experience is the opposite, also lots of sources claim the same.

Same here. Less o2 in the wort = more esters with the same pitch rates +/- 30% of the Mr Malty pitch rate. When I use wy1469, the only o2 in the wort is present because it was dumped into a bucket. Maybe 3ppm? Infusing pure o2 to 8-10ppm doesn't produce adequate esters with 1469.

The results of my zero pure o2 process were too much banana and some stone fruit until I increased the late primary temperature to 75F. Then the stone fruit was forward and the banana was a background note. I am happy with this result.

Not sure why this happens, but I don't think it has anything to do with the boiling temperature of the banana ester.

 

[Azura]

More esters in general - but the OP is talking about changing the mix of esters that ends up in the final beer. I was reading something recently about a temperature profile that specifically reduced ethyl acetate and isoamyl acetate (??I think??) with a high-temperature "soak" of some kind - can't remember where it was though. I guess it's something to do with yeast either eating certain esters and not others, or converting them to other forms.

My homebrew observations in this context are wy1469 @ 65F for 4 days then 75F for 3 days then 60F for 3 days before cold crashing reduces banana and pushes the stone fruit forward compared to a steady 65F for 10 days. Not sure why it happens. However, it does reliably happen according to my notes, so I continue to do it.

A lot of yeasts produce banana. I prefer banana to be 3/10 intensity. wy1469 can produce 7/10 intensity with low o2 and 15% less than Mr Malty pitch rates. The method I have described puts the banana in the 2-4/10 range and the stone fruit becomes the prominent ester.

 

[leonardoreges]

So you’re stating this fermentation profile worked for this single yeast?
To me increasing temp yields more esters in general, so the ester profile will depend on the yeast profile. And most of the Hefeweizen yeasts produce primary banana esters. Maybe what you’re saying works for this yeast, not in general.

 

[ESBrewer]

I cannot confirm that isoamyl acetate would break down under those conditions, but it is certainly possible that ester character may change during fermentation and also during conditioning. Esters do not remain intact once they are produced but they exist in equilibrium and may be converted to other esters depending on strain specific enzymes, conditions (including temperature, pH and substrates present). I've read that especially Brettanomyces esterases tend to break banana flavor (isoamyl acetate) and thus favor other esters. The change in temperature could also affect esterase activity and thus may change esters but I think the effect is going to be yeast strain specific and may be affected by other conditions, too. Anyway, it is an interesting observation and if you see it consistently with this strain, it is certainly true. It could also be that banana flavor is still present but masked by the stone fruit when it is formed.

 

[Azura]

So you’re stating this fermentation profile worked for this single yeast?
To me increasing temp yields more esters in general, so the ester profile will depend on the yeast profile. And most of the Hefeweizen yeasts produce primary banana esters. Maybe what you’re saying works for this yeast, not in general.

I'm increasing temperature when 80-90% of the wort has fermented. Not much ester production will occur that late in the game.

This method has worked for more than one yeast to specifically reduce banana. Another example is wy3726. It's the Blaugies saison strain. Most people ferment it hot at 80F including Blaugies. I like to ferment it cool at 65F with no added o2 and moderately underpitched. It produces big banana, clove, anise and earth at a steady 65F. Hitting it with late heat reduces the banana a lot. The phenols remain the same.

 

[Azura]

I cannot confirm that isoamyl acetate would break down under those conditions, but it is certainly possible that ester character may change during fermentation and also during conditioning. Esters do not remain intact once they are produced but they exist in equilibrium and may be converted to other esters depending on strain specific enzymes, conditions (including temperature, pH and substrates present). I've read that especially Brettanomyces esterases tend to break banana flavor (isoamyl acetate) and thus favor other esters. The change in temperature could also affect esterase activity and thus may change esters but I think the effect is going to be yeast strain specific and may be affected by other conditions, too. Anyway, it is an interesting observation and if you see it consistently with this strain, it is certainly true. It could also be that banana flavor is still present but masked by the stone fruit when it is formed.

Good post. Even when I don't ramp up the temperature late, I have noticed that banana is a volatile ester that subjectively decreases after a few weeks of cold keg conditioning. I always wonder what happened to it. Did a banana ester thief invade my beer?

My observations are the late fermentation heat bump decreases banana in the sample at packaging, then cold conditioning decreases it more by drinking time.