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Sourcing bacterial strains for rum fermentations

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For those that are using bacteria to increase acid production in their rums, where are you sourcing your bacteria from?

  • House strains from aged dunder?
  • From a lab?

I've been looking into C. saccharobutyricum, but there doesn't seem to be a reliable source selling any samples.

Thanks!

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Miyarisan C. Butyricum from Japan.

It’s a well studied strain from a biological perspective, used as a probiotic there - so you have no worries about botulinum toxin.   Readily available, you can buy it on eBay or Amazon, ferments glucose, produces enough butyric acid to hate yourself.  Most of the lab culture suppliers have numerous strains available, but you will need to propagate from slants.

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Does the butyric acid not come through in the distillation? That stuff is seriously disgusting.

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In obvious quantities, it's a major fault.  The game is to create and capture the esters, but not the acids.  You've got 3 opportunities to create esters from the acids, fermentation, distillation, and maturation.  Even still, it'll be there.  Spend some time with some really funky Jamaicans and you can pick it out amongst the funk.  Some of the “buttery” flavor of old rums is butyric in very low concs.  Butyric distills primarily in the late tails, but starts to pick up as ethanol concentration starts dropping quickly near the end of the run.

 

 

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13 hours ago, Silk City Distillers said:

produces enough butyric acid to hate yourself

😂😂😂 

I'm guessing that there's some technique on when you decide to introduce your bacteria into the fermentation, so it gets killed off by alcohol % before things get out of control?

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I’ve spent 3 years working on mixed culture rum.  Getting your hands on cultures is the easy part.

Don’t believe everything in the old rum papers.  Some theories are outright wrong, some are right but for the wrong reasons, some are right but the non-standard terminology make it difficult to understand what they mean (eg. what’s “low wines” and “high wines” mean in high-ester rum distillation), and just about everything not from a direct source is a misunderstanding, misinterpretation, or just complete nonsense.

Half the fun of old rum is trying to decipher the mystery.

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I've been working with a brilliant micro biologist recently. He has isolated Arroyo's specific butyric acid producing bacteria and it may be available soon on a slant. Harnessing it productively, as @Silk City Distillers said, is another story. You may need to invest in more analysis than most small operations are currently using. The birectifier is likely useful and we're about to start using it on some model ferments. The delta acidity concept is likely also very useful, but you may need to invest in a nice automatic titrator.

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Do you really think there is some sort of strain-specific phenomenon?  At the time most of these bacteria were in the very broad 'bacillus' category.  Clostridium is a fairly common soil bacterium, it's arguable that in the history of muck pits, there were likely multiple strains involved.  Propionibacteria are every bit as interesting as Clostridium in mixed culture fermentation.  I might try to argue that the propionic acid esters are more "rummy" than butyric, which are largely just "pineapple" - yawn, boring.  It's fairly easy for me to create pineapple-bomb like rums with clostridium.

Arguable that to some extent, many of these bacterium are producing their own unique ratio of our favorite carboxylics, the specific selection of bacteria directly influencing ester ratios in ways the old guys could never imagine.  Combine this with the Rochte/Berglund approach to catalytic distillation, and can control the process in ways never before imagined.

 

 

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21 hours ago, Silk City Distillers said:

Do you really think there is some sort of strain-specific phenomenon?  At the time most of these bacteria were in the very broad 'bacillus' category.  Clostridium is a fairly common soil bacterium, it's arguable that in the history of muck pits, there were likely multiple strains involved.  Propionibacteria are every bit as interesting as Clostridium in mixed culture fermentation.  I might try to argue that the propionic acid esters are more "rummy" than butyric, which are largely just "pineapple" - yawn, boring.  It's fairly easy for me to create pineapple-bomb like rums with clostridium.

Arguable that to some extent, many of these bacterium are producing their own unique ratio of our favorite carboxylics, the specific selection of bacteria directly influencing ester ratios in ways the old guys could never imagine.  Combine this with the Rochte/Berglund approach to catalytic distillation, and can control the process in ways never before imagined.

 

 

Not a lot is known about the difference in the strains in a rum context. Kervegant differentiates a few. We kind of just focused on Arroyo's strain because it was uniquely historical and doable. It may differ because it produces more butyric acid and less acetic acid as well as less higher alcohols. The next step is playing with it to see how practical it is to use and what tools it may take to wield without costly runaway trains. My colleague is also looking at propionibacteria.

I've been reading up on catalytic distillation, but my money is on targeting Damascenone and the other rum oil components. I suspect that if you target rum oil, all the esters you want will come along for the ride. I just got a paper from the 1980's that may give practical ideas on hunting for Damascenone all along the production process.

Some of these projects need to move from my kitchen to Silk City on a Saturday afternoon.

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When you're looking at natural biological activity in yeast/bacteria there's a ton of secondary process that can effect the outcome based on conditions. I think there's a lot of people that believe they can laser focus on achieving an outcome, over production of a specific by product like fatty acids, without understanding the conditions that it requires. How you ferment, what you ferment, the conditions of the ferment (open/closed, tall/short vessel, etc) will effect each strain of yeast/bacteria differently. So what works in an open short wooden fermenter in the summer in Jamaica might not work the same as in Chicago in winter in a closed SS tall tank.  I agree it's a good starting point to use what they use as a starting point - but to SCD's point - it's probably best to experiment to see what work for you. You can also manipulate yeast to produce acetic, lactic, propionic, and other acids, but in lower quantities. 

It's fully good to use the try it and see method to get started, but it doesn't help with repeatability. You really need to account for as many factors as you can to understand which conditions are best for the outcome you want. Timing of the additions, temps, pH, ferment size, ambient temp/time of year, anything. The Birectifier is something that can help with this to check for non-quantitative olfactory effects. 

I think mixed culture fermentations is some of the best stuff going on today in the industry. It's taking something that happened in the old days and recreating it after we took it out of the process for sanitary/efficiency reasons. I'm happy to see people working on it! 

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1 hour ago, Foreshot said:

When you're looking at natural biological activity in yeast/bacteria there's a ton of secondary process that can effect the outcome based on conditions. I think there's a lot of people that believe they can laser focus on achieving an outcome, over production of a specific by product like fatty acids, without understanding the conditions that it requires. How you ferment, what you ferment, the conditions of the ferment (open/closed, tall/short vessel, etc) will effect each strain of yeast/bacteria differently. So what works in an open short wooden fermenter in the summer in Jamaica might not work the same as in Chicago in winter in a closed SS tall tank.  I agree it's a good starting point to use what they use as a starting point - but to SCD's point - it's probably best to experiment to see what work for you. You can also manipulate yeast to produce acetic, lactic, propionic, and other acids, but in lower quantities. 

It's fully good to use the try it and see method to get started, but it doesn't help with repeatability. You really need to account for as many factors as you can to understand which conditions are best for the outcome you want. Timing of the additions, temps, pH, ferment size, ambient temp/time of year, anything. The Birectifier is something that can help with this to check for non-quantitative olfactory effects

 I think mixed culture fermentations is some of the best stuff going on today in the industry. It's taking something that happened in the old days and recreating it after we took it out of the process for sanitary/efficiency reasons. I'm happy to see people working on it! 

Great points here. It is such exciting territory that hopefully will excite consumers. There are so many fermentation complications that can be explored which creates a lot of room in the market. Analysis is likely the key. We will need to figure out where you start (likely the birectifier) and where you go second (likely automatic titration for acidity).

A big hole is understanding the role of noble volatile acids (non-acetic) in spirits. The last fractions of so many great role model spirits are quite tart. It gives them structure, preventing them from being flabby. This possibly makes them more enjoyable to consume neat and while young. There is a fixation on esters, but it may be fruitful to give attention to desirable volatile acidity. It may be key to designing batch distilled spirits that can be brought to market faster. Lactic acid bacteria may seem not too glamorous, but it may be key.

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4 hours ago, Foreshot said:

When you're looking at natural biological activity in yeast/bacteria there's a ton of secondary process that can effect the outcome based on conditions. I think there's a lot of people that believe they can laser focus on achieving an outcome, over production of a specific by product like fatty acids, without understanding the conditions that it requires. How you ferment, what you ferment, the conditions of the ferment (open/closed, tall/short vessel, etc) will effect each strain of yeast/bacteria differently. So what works in an open short wooden fermenter in the summer in Jamaica might not work the same as in Chicago in winter in a closed SS tall tank.  I agree it's a good starting point to use what they use as a starting point - but to SCD's point - it's probably best to experiment to see what work for you. You can also manipulate yeast to produce acetic, lactic, propionic, and other acids, but in lower quantities. 

 It's fully good to use the try it and see method to get started, but it doesn't help with repeatability. You really need to account for as many factors as you can to understand which conditions are best for the outcome you want. Timing of the additions, temps, pH, ferment size, ambient temp/time of year, anything. The Birectifier is something that can help with this to check for non-quantitative olfactory effects. 

 I think mixed culture fermentations is some of the best stuff going on today in the industry. It's taking something that happened in the old days and recreating it after we took it out of the process for sanitary/efficiency reasons. I'm happy to see people working on it! 

I dig this.

I've had a lot of luck producing extremely impactful and flavorful ferments that distill into complex spirits by utilizing spontaneous or hybrid-spontaneous ferments. The problem is that there's low consistency from batch-to-batch, and it's nigh impossible to capture whatever went into the ferment when 99% of the microbes probably die off early on. The challenge I'm working through right now is trying to understand how I might replicate a wild-like ferment using a multi-strain fermentation.

One avenue - looking at a lot of this research, and following @bostonapothecary's work - assuming that many of these microbes come from the Jamaican terroir that you may get from a spontaneous ferment, and trying to construct something that way.

The second is maybe sending off some sugar cane juice to a yeast lab, and having them identify fermentation friendly strains within the juice, and trying to run a ferment with those, similar to how Jester King brewery got started up.

Regardless, I'm learning a lot from being attached to this conversatio  SO KEEP TALKING PLEASE.

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I have an astoundingly lengthy correspondence chain with the microbiologist I've been working with. I don't know his specific academic background as far as lab or field work, but I suspect he is above average in cleverness. What is blowing my mind is the very significant amount of paper research he is doing to back up positively identifying the organisms and creating successful selection/isolation protocols. It has required quite a lot of books. Whoever he consults for will have a big short cut to success.

One interesting thing to throw out there from the collected research on Pombe yeasts is that Africa and Caribbean strains diverged at some point. When the literature describes off aroma and character not fitting for beverage, that may only apply to African strains.

One thing I'd like to see is more of the development of a lower skill folk method for working in this territory, sort of like the pied de cuvee procedure. You can create a small scale sterilized must, walk it over to a vine, take your clippers and drop a single grape or fruit right in to capture their yeast/bacteria. Sometimes it is left to ferment right in the field. There are lots of accessible ways to vary selection with this; pH, brix, specific added acids, or even antiseptic botanicals. The very first starter material for sour mash ferments had hops. As this scaled up to the next size footing, the hops were left behind. Certain very specific botanicals have also been known to harbor certain aroma-beneficial micro organisms. They have evolved together. The crude low tech pied de cuvee method could likely help select for them. However, it is probably wise to expect a ton of failures. I wish some universities could be enlisted to back this stuff up.

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Distilling is far more forgiving than brewing with regards to negative bacterial contribution and need for sanitization or sterilization.  This is evidenced by the lack of a tradition of boiling wort or wash to sterilize, antibacterials (hops), and distilling's longer tradition of open fermentation.  What brewers are only today beginning to embrace about wild yeast, bacterial contribution, open fermentation - these have been standard procedures in distilling, whether the distillers knew the benefits or not ... or even knew why.  Keep in mind, though something like an acetobacter infection is a disaster in beer or wine, it's a nuisance in distilling that results in a larger heads cut (lower yield).  What might be applicable to brewing or wine, might not be to distilling, and vice-versa (brettanomyces comes to mind, which I think is a disaster for distillers).

The exact same procedures for wild yeast capture for brewing directly apply to distilling, spend some time with brewing communities like Milk the Funk (Facebook Group).  While it's easy to isolate the yeast strains out of these, it's very difficult to match the bacterial strains.  There are some brilliant, brilliant, backyard biologists involved there (and plenty of PhDs too).  Like Lloyd says above, and he's right, replication becomes very very difficult.  During fermentation, bacteria will die out, certain yeast strains will dominate, others will die.  

We've fermented with lots of yeast that you would never find in the traditional distilling world.  Torulaspora, Metschnikowia, Hanseniaspora, and others.  We have a few test batches that were co-pitches of the above plus traditional yeasts alongside some interesting bacteria that I absolutely love.

Two things I've learned that are a bit of a disappointment.  Distilling is a rather coarse process, it's very easy to lose some of the subtle flavors created during fermentation.  Esters tend to bunch together, meaning if you take a heavy heads cut, you lose everything you worked to create.  I concur about acetic acid and ethyl acetate being a major problem.  It's very easy for high ethyl acetate to "crowd out" the other esters during distillation.  You are forced to take a wider cut, and by doing it, you cut away too much of many other esters.  I too tend to review the literature on specific bacterial strains to understand which tend to be the lowest acetic producers, this is really really important.

The other is that aging is a double-edged sword, and probably the most disappointing - subtle flavors tend not to survive aging.  Almost three years back I did some incredible higher-ester whiskies using English ale strains.  Fruity, floral, very interesting.  By the two year mark, it became very difficult to distinguish between traditional whiskey strain batches.  Based on the glide path, by year 4 it might be completely indistinguishable.  They may evaporate off, they may form other more complex compounds or longer chain esters, but they don't stick around.  I've considered doing test batches with miniscule heads cuts, in order to create aged blending stock that hopefully retains some of these flavors after maturation.  Again, too many projects, too little time.

That said, blending is key key key here.  Especially talking high ester and heavy rums, back to the original topic.  Keep in mind the goal of these processes IS NOT TO MAKE FINISHED RUM IN ONE SHOT.  It is to make blending stock, to be blended with other, lighter, cleaner, other rums, to produce a finished product.  Hell, even if high hogo funk town is your goal, you are still blending.  Nobody is drinking Hampton DOK and enjoying it.  The other factor that favors blending, it's very difficult to establish tight consistency with some of these bacteria.  Certain strains of clostridium are strict anaerobes - good luck managing strict anerobic starters, purging with nitrogen to eliminate all dissolved oxygen is a requirement).  Consistent starting cell counts would be very difficult outside a lab.  The end result is going to be a fairly wide range of ester concentrations.  Creating a wide range of mono-culture (bacterial) aging stock is probably the safest approach - eg. Lactic acid ester based blenders, propionic blenders, butyric blenders.  Same could be done with heavier alcohols in the tails (isoamyl alcohol makes beautiful esters).   Want a rum that tastes like buttery, nutty, banana bread?  Lactic esters are your friend, as are the isoamyl alcohol esters. - Go ahead and build it from the ground up.  Again, no lack of projects, complete lack of time.

 

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22 minutes ago, Silk City Distillers said:

Distilling is far more forgiving than brewing with regards to negative bacterial contribution and need for sanitization or sterilization

Seriously - my sanitation protocol is non-existent anymore. I can't remember the last time I really used starsan. I would say bacterial contributions are mostly beneficial to flavors though negative for yield. 

 

Milk the Funk has an AMAZING wiki. Properly annotated, written by PhDs, tons of research and explanation. 

http://www.milkthefunk.com/wiki/Table_of_Contents

http://www.milkthefunk.com/wiki/Alternative_Bacteria_Sources 

 

30 minutes ago, Silk City Distillers said:

Esters tend to bunch together

To his point see this chart - scroll down to esters: http://masterclass.boxwhisky.se/en/the-middle-cut 

 

32 minutes ago, Silk City Distillers said:

subtle flavors tend not to survive aging.

This is the part that sucks. What I get right off the still are the absolute best flavors. Even after a few days the flavor changes and settles down. 

 

41 minutes ago, Silk City Distillers said:

They may evaporate off, they may form other more complex compounds or longer chain esters, but they don't stick around.

That's another thing that people don't necessarily understand - time in a barrel or bottle isn't static for esters or other chemical compounds.Barreling isn't just for oaking. There's a lot of things that happen in a barrel that we don't talk about. Chemical reactions still happen, only slower. Water can easily reverse esterifacation. And now people are experimenting with lower ABV barrel entry so it's a recipe for removing esters. I don't disagree with the lower entry ABV, but understand why you're doing it what will happen due to it matters. 

 

36 minutes ago, Silk City Distillers said:

That said, blending is key key key here.

I think this is the hardest part for new craft people. No blending stocks. Cash is king and everything gets bottled and sold. The model of DOK and blending stocks requires time and planning which not a lot of craft people can do. It is the right model, just not super practical. People need to laydown some breather barrels for blending and that's not something they may be able to afford. 

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12 hours ago, bostonapothecary said:

One thing I'd like to see is more of the development of a lower skill folk method for working in this territory, sort of like the pied de cuvee procedure. You can create a small scale sterilized must, walk it over to a vine, take your clippers and drop a single grape or fruit right in to capture their yeast/bacteria. Sometimes it is left to ferment right in the field. There are lots of accessible ways to vary selection with this; pH, brix, specific added acids, or even antiseptic botanicals. The very first starter material for sour mash ferments had hops. As this scaled up to the next size footing, the hops were left behind. Certain very specific botanicals have also been known to harbor certain aroma-beneficial micro organisms. They have evolved together. The crude low tech pied de cuvee method could likely help select for them. However, it is probably wise to expect a ton of failures. I wish some universities could be enlisted to back this stuff up.

As a huge fan of mezcals, I'd love to see more distillers use this approach. It seems like it's been embraced whole-heartedly in the beer and wine worlds, but most distillers (folks on this thread excluded) have seem more focused on sourcing local to produce something mass-market than they are on trying to ferment local to produce something unique.

In case anyone is wondering or hesitant to experiment, I will buy your weird, one-off spirit.

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5 hours ago, Silk City Distillers said:

Keep in mind the goal of these processes IS NOT TO MAKE FINISHED RUM IN ONE SHOT.  It is to make blending stock, to be blended with other, lighter, cleaner, other rums, to produce a finished product.  Hell, even if high hogo funk town is your goal, you are still blending.  Nobody is drinking Hampton DOK and enjoying it.  The other factor that favors blending, it's very difficult to establish tight consistency with some of these bacteria.  Certain strains of clostridium are strict anaerobes - good luck managing strict anerobic starters, purging with nitrogen to eliminate all dissolved oxygen is a requirement).  Consistent starting cell counts would be very difficult outside a lab.  The end result is going to be a fairly wide range of ester concentrations.  Creating a wide range of mono-culture (bacterial) aging stock is probably the safest approach - eg. Lactic acid ester based blenders, propionic blenders, butyric blenders.  Same could be done with heavier alcohols in the tails (isoamyl alcohol makes beautiful esters).   Want a rum that tastes like buttery, nutty, banana bread?  Lactic esters are your friend, as are the isoamyl alcohol esters. - Go ahead and build it from the ground up.  Again, no lack of projects, complete lack of time.

 

This absolutely seems to be true in practice, but I feel that the 21rst century has accumulated enough science that we can make stand alone "suave" spirits that ring all the bells. I think the question is, if it takes a lot of large fixed costs for analysis and experimentation, how small scale can you do it? Its also very multi disciplinary and larger than one mind, so how small would the team be that was needed to bring it together? Just kind of a thought exercise.

I think its too risky to experiment with yeasts blindly. There should be articulate targets like reduced ethyl acetate, reduced fusel oil, or an attempt at unlocking rum oil related congeners. Seeing role models dissected really clarifies the focus.

Omg, the lack of time is wild. I do so much paper research and i don't feel I'm wasting my time. I feel like it won't be worth performing certain fermentation experiments until I finish another year's worth of work on paper. I'm bent on bringing the delta acidity concept into the process of managing contribution from bacteria.

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5 hours ago, Foreshot said:

This is the part that sucks. What I get right off the still are the absolute best flavors. Even after a few days the flavor changes and settles down. 

 

That's another thing that people don't necessarily understand - time in a barrel or bottle isn't static for esters or other chemical compounds.Barreling isn't just for oaking. There's a lot of things that happen in a barrel that we don't talk about. Chemical reactions still happen, only slower. Water can easily reverse esterifacation. And now people are experimenting with lower ABV barrel entry so it's a recipe for removing esters. I don't disagree with the lower entry ABV, but understand why you're doing it what will happen due to it matters. 

 

I think this is the hardest part for new craft people. No blending stocks. Cash is king and everything gets bottled and sold. The model of DOK and blending stocks requires time and planning which not a lot of craft people can do. It is the right model, just not super practical. People need to laydown some breather barrels for blending and that's not something they may be able to afford. 

One hunch I have about the subtle flavors isn't that they aren't always from single aroma compounds. Some esters are kind of muted unless they are perceived with an ideal amount of ethyl acetate to pump them up. The EA blows off in the angel's share and that amount must be accounted for. If the congener profile becomes uneven, things can go flat.

Are they distilling to a lower ABV and building the water in, or diluting to a lower ABV for entry? Supposedly there is a big difference, due to the water shock of the later scenario, but many esters can reform in as short a time as six months. I think the barrel entry proof is going to make the biggest differences for spirits in newer barrels because more water dissolves more tannin. There is lots of great data points in American Whiskey By The Numbers and approachable mid century research papers from Seagram/Hiram Walker.

If I was distilling, I'd be buying Caribbean blending stocks. I'd market it as "hosting" and claim my "access" to the fine examples. I would also be reverse engineering the hell out of those blending stocks.

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18 hours ago, bostonapothecary said:

esters can reform

So from the reading I've done there are my thoughts on this: They can and do, but the equilibrium of the mixture is based on the volume and polarity of alcohols and carboxylic acids involved. The more polar molecules will reform esters more often. So what esters go in aren't necessarily the ones that come out. They are constantly being destroyed and reformed. The long term relative equilibrium would favor esters that form from the more polar molecules with fewer of the ones that are less polar. You can see this in action by noticing the drift in aroma and flavors in spirits even though they are in a not reactive environment like glass or stainless steel. It's also relative to the ABV of the spirit. Lower ABVs are going to destroy more esters with less reforming. Higher ABVs destroy fewer esters (less water for hydrolysis) and favors more ester formation. And the thing you mention a lot is the acidity of the mixture, and the more Fisher catalyzed esterification will happen. 

A little odd video of this is here - pay attention to 6:50 and 9:40, it applies to us: https://www.youtube.com/watch?v=PVL24HAesnc 

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On 1/18/2019 at 8:19 AM, Foreshot said:

So from the reading I've done there are my thoughts on this: They can and do, but the equilibrium of the mixture is based on the volume and polarity of alcohols and carboxylic acids involved. The more polar molecules will reform esters more often. So what esters go in aren't necessarily the ones that come out. They are constantly being destroyed and reformed. The long term relative equilibrium would favor esters that form from the more polar molecules with fewer of the ones that are less polar. You can see this in action by noticing the drift in aroma and flavors in spirits even though they are in a not reactive environment like glass or stainless steel. It's also relative to the ABV of the spirit. Lower ABVs are going to destroy more esters with less reforming. Higher ABVs destroy fewer esters (less water for hydrolysis) and favors more ester formation. And the thing you mention a lot is the acidity of the mixture, and the more Fisher catalyzed esterification will happen. 

A little odd video of this is here - pay attention to 6:50 and 9:40, it applies to us: https://www.youtube.com/watch?v=PVL24HAesnc 

I wish there was more data on this. The best questions were asked before the GCMS era. We can look at things so easily now which would yield some awesome dissertations.

Supposedly, built in water destroys the least esters, but watering high ABV destroys the most. I think it is the final act of getting it to drinking proof that needs to be considered the most. As we all know, challenging economics surrounding building in all that water rather than adding it at the last minute. Isn't ethanol very polor? So what may happen is that higher alcohol esters may break and ethyl esters reform. This would be bad because you're limiting diversity and freeing fusel oil. I don't really understand the higher alcohol esters. Some literature claims they are the weakness of continuous column of stills. Basically higher alcohols get trapped in a zone and increase the chance of ester formation. Problem is that these esters are often plebeian and ordinary, overly diffusive in the top notes, and can make a California brandy or Old Granddad smell cheap like a banana. This problem may assume we are talking about basic ferments that don't have diverse quantities of fatty acids.

What do you think of this: many esters formed during distillation are temporary place holders. We hope for ethyl esters to increase the volatility of noble fatty acids even though they will break and not reform. These temporary place holder esters just get them across the cut and in to the hearts defying their typical fate. This may be fine because noble volatile acidity may contribute to quality. However, if a higher alcohol ester breaks this may be very bad. Amyl alcohol is less polar than ethanol so that favors reformation with ethanol and the free amyl alcohol increases fusel oil content. Amyl alcohol is also perceived as the most dissonant of the higher alcohols. But how significant is that number of freed up amyl? Who knows.

What I wish we knew more about is,  exactly how volatile are all of the higher alcohol esters? The birectifier fractions hint that they are less volatile than fusel oil, but a few are famously more volatile (isoamyl acetate). In many cases, these esters may only function as a temporary place holder for fusel oil, reducing its volatility which is a win and allows you to distill further into the run collecting more of other high value congeners. It is best to reduce fusel oil at fermentation, but to some degree (not well understood), it may be reduced by reactive distillation (mentioned up thread by @Silk City Distillers). Maybe we can't assume all esters are straight forwardly useful?

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7 hours ago, bostonapothecary said:

What do you think of this: many esters formed during distillation are temporary place holders

Yes-ish. You talk about getting the right ones in abundance. I agree with this. If you have an abundance of good ones it helps the equilibrium go the way you want. In distilling we set the conditions for outcome we want. We can't dictate the outcome. Your ideas align with that philosophy.

7 hours ago, bostonapothecary said:

we are talking about basic ferments that don't have diverse quantities of fatty acids.

Yes. All ferments have a wide variety of fusel oils and fusel alcohols, it's just a matter of how much. Most commercial distillers I know hit ~1.000 and run it. It makes a clean taste not much by way of character. I find the ferments that I abuse more have more fusels and end up being more interesting - mostly good but sometimes bad.

7 hours ago, bostonapothecary said:

exactly how volatile are all of the higher alcohol esters?

This is something we need to research more. I believe, though I don't have evidence, that the removal of the water molecule reduces the boiling point. I think that's why most esters come over in the early heads to early hearts.

 

Side note, some interesting things I found while researching this post:

https://www.solubilityofthings.com/water/alcohols <- simpler alcohols are miscible, but higher alcohols are less so to the point they aren't really at all. This could help explain what happens when you phase separate low wines. It's not just fusel oils, but fusel alcohols too.

https://sites.duke.edu/apep/module-1-gender-matters/content/content-what-is-alcohol/ <- chart showing # per 100g of Butanol and higher alcohols, including Amyl (pentanol). Anything above this will float and be able to be removed by phase separation. 

https://socratic.org/questions/how-do-covalent-bonds-dissolve-in-water <- Alcohol floats on water until given time to diffuse.

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Chart of relative polarity: https://www.aceorganicchem.com/Elite/organic-chem-15-organic-solvents-likes-dissolve-likes/

Water > Carboxylic > Ethanol.

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14 hours ago, Foreshot said:

This is something we need to research more. I believe, though I don't have evidence, that the removal of the water molecule reduces the boiling point. I think that's why most esters come over in the early heads to early hearts.

The birectifier contradicts this somewhat. Ordinary ethyl-acetate appears in the first two fractions, and though quite concentrated, stays perfectly clear. Most extraordinary longer chain, higher molecular weight esters appear in the fifth fraction (while 75% of fusel oil is in the 4th). The turbid cloudiness turns out to be high value esters shocked out of solution. I've experienced aromas I assume to be be iso amyl acetate (banana) in the second fraction. Other esters may lurk in the first fraction but be overshadowed by the cloying noxiousness of the ethyl-acetate.

What I just described is highly sorted fractioning by birectifier. On a normal less fractioned run everything would be spread out with significant overlapping. A lot more of what is in fraction 5 (high value) stretches way out into the tails, which you can't capture without risking too much fusel oil.

It would be awesome to add titratable acidity. Then we could look at how esters either break and reform or how they stay broken but maybe continue contributing as noble-volatile acidity. This would cost $4000 for the titrator and be pretty low skilled.

To bring it around for those reading along, understanding much of this may be key if you plan on adding secondary bacterial ferments.

img_0724.jpg

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Just reviewing some of the literature on β‐Damascenone formation.

Clearly not something unique to rum, it would be considered the most significant constituent of Bourbon as well (by FD/OAV), as well as in Shochu.  However, it's OAV is so stratospheric, it merely has to exist at all for it to top the chart.  So you have it existing across three very different fermentation feedstock: grain, cane, and potato.  Not to mention three products produced in very different ways, especially the koji fermented sweet potato.  Found in both wine and beer as well.

The Shochu paper seems to be incredibly insightful, since β‐Damascenone  exists as a component of sweet potato, but does not even remotely account for the total β‐Damascenone  in the distillate.  It appears that β‐Damascenone is not at all formed during fermentation, and is actually negatively impacted by fermentation.  However, it's not the β‐Damascenone in the feedstock, or the production process, but the necessary (Carotenoid?) precursors to be available during distillation to form it by acid hydrolysis.

The Formation of β‐Damascenone in Sweet Potato Shochu - Yoshizaki - 2011 - Journal of the Institute of Brewing - Wiley Online Library

https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.2011.tb00464.x

The researchers found that:

"most of the β‐Damascenone  in Shochu is formed by acid hydrolysis during distillation."

"As the distillation period lengthened, β‐Damascenone  levels increased moderately, suggesting that lengthening the distillation period is one method that may be used to increase B-damascenone"

"Furthermore, whether the β‐Damascenone  level in shochu was affected by the pH of the second mash during distillation was investigated.  The β‐Damascenone  level in second mash at pH 3.5 was greater than in the second mash at pH 4.0 and 7.0."

 

1127610204_ScreenShot2019-01-21at6_41_27PM.png.165c5dfd4b740b4418e0d76077426197.png

 

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On the degradation of β‐Damascenone during fermentation:

Investigation of the β-Damascenone Level in Fresh and Aged Commercial Beers
https://pubs.acs.org/doi/pdf/10.1021/jf020085i

Quote

This study investigated the increase of β-damascenone content during aging in a variety of commercial Belgian beers. Quantities detected in fresh beers were generally low (from 6 ng/g to 25 ng/g). After 5 days at 40 °C, the level increased (to as much as 210 ng/g) in most of the beers studied, according to the type of beer. Further experiments showed that wort initially contains large quantities of β-damascenone (450 ng/g), but that degradation of the compound during fermentation accounts for the low concentrations observed in fresh beers. Production during beer aging can be partially explained by acid hydrolysis of glycosides. 

 

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