Introduction

Fermentation has long been frowned upon, among craft distillers. Most believed that fermentation was simply the place where your base alcohol was made. The followers of the iStill Blog know that I have made it my personal crusade to inform the industry that fermentation is not just about alcohol production, but also about flavor production. The better you control your fermentation, the better flavors you can distill into your spirits.

Today we take another step down the fermentation rabbit hole. Let’s see how deep it really is. Let’s dive in deeper and establish another level of fermentation knowledge, for even more control and even better flavors! Because that’s where you need to shine, dear craft distiller: at the production of better tasting spirits, in the understanding that better taste molecules are mostly formed during fermentation.

Fermentation science

When yeast is introduced to a mash, a liquid with fermentable sugars present, the yeast will first – as long as there’s oxygen – grow and reproduce. As oxygen levels in the mash drop, the yeast cells stop propagating and turn on their secondary metabolism: the one that turns those fermentable sugars into alcohol and where CO2 is produced as a by-product.

When fermenting in a (relatively) sealed vessel, at atmospheric conditions, like – well – in an ordinary fermenter with water-lock, CO2 is produced and partially released. This CO2 that gets released from the fermentation quickly replaces any headspace and any remaining air or oxygen above the ferment. Why? Because part of the CO2 that’s released bubbles out of the fermenting liquids. And because CO2 is heavier than air. There you have it: part of the CO2 bubbles up and is released, while another part of CO2 remains trapped inside the fermenting liquids.

The concentration levels of dissolved CO2 within the fermenting liquid are based on sugar levels, alcohol percentage, and temperature. In general, the amount of CO2 will range from ∼1.4 to 2 g/L, when brewing between 12 °C and 25 °C. Higher temperature fermentations are often the result of faster fermentations, and as fermentation is an exothermic chemical process, that creates a lot of heat, faster ferments associate with (and cause!) more CO2 production and warmer temperatures.

Chen and Gutmanis (1976) reported significant inhibition of yeast growth above ∼0.65 g/L CO2 dissolved in the media. Given the above, this makes perfect sense. As oxygen is depleted, yeast switches to its secondary metabolism, that does no longer support yeast cell growth and propagation. Instead, in this secondary survival mode, sugars are turned into alcohols, and CO2 is produced as the aforementioned by-product.

Furthermore, these researchers reported a 20% reduction in fermentation activity when CO2 concentration dissolved in the fermenting liquids reached ∼1.1 g/L. High concentrations of CO2, dissolved in the fermenting liquids, were shown to affect yeast viability and induce a general stress response. Concentrations of dissolved CO2 in the ferment were shown to impact yeast viability.

Summary

A summary? As yeast is added to the mash, it consumes oxygen and reproduces. As oxygen levels deplete, yeast switches its metabolism, where it stops reproducing, and starts producing alcohol and CO2. The level of about 0.65 g/L of dissolved CO2 seems to be the threshold where propagation stops and where alcohol production starts. All is good so far, but … as dissolved CO2 levels rise, they start to harm the yeast’s viability to produce alcohol (ethanol) as well as flavors (ester molecules). Too much CO2 harms the alcohol and flavor production of your fermentation! A level of 0.65 g/L is good, a level of 1.1 g/L is bad already to the extent that it deteriorates the yeast performance, both in terms of alcohol and flavor production, by 20%. Higher levels of dissolved CO2 will further impact yeast performance negatively.

More scientific proof of CO2-induced yeast stress

Landaud et al. (2001) studied the effect of different CO2 concentrations on the free amino nitrogen (FAN) consumption rate of yeast during fermentation. These researchers found that the FAN consumption rate of yeast was 300% faster when the CO2 concentration was reduced from 3.65 to 1.78 g/L. In laymen’s terms? Higher CO2 levels hamper the yeast’s ability to consume “food” and get access to the energy they need to get the job (of alcohol and ester production) done.

Knatchull and Slaughter (1987) reported a reduction in the absorption of branched-chain amino acids by yeast cells, resulting in a reduction of higher alcohols and esters when fermenting under high CO2 concentrations. What this means in plain English? That they found out, via scientific research, that higher levels of dissolved CO2 result in less tasty fermentations.

Problem definition

High levels of dissolved CO2 stress-out the yeast. As a result, the yeast produces lower amounts of both alcohols and esters. The consequence is that you, as a craft distiller, have a less efficient and a less effective fermentation cycle, resulting in lower and slower yield, and in less flavorsome spirits.

That is a problem. That is a BIG problem. It is a big problem, because the craft distiller’s business case depends on flavor and yield. No, the craft distiller is never going to out-produce Big Alcohol on costs per liter or production efficiency. And as this automatically results in higher production costs for craft distillers, two existential questions emerge from that conclusion:

1. How can the craft distiller produce as efficiently as possible, to obtain the lowest possible production costs?
2. Can craft distillers create better tasting spirits that warrant the higher price per bottle, relative to Big Alcohol?

An efficient fermentation that generates the best flavors possible is KEY to your operation. It is essential to the long term viability of the craft distilling industry. It is what gives us, craft distillers, our place in the market.

High levels of dissolved CO2 hamper the craft distiller’s alcohol production efficiency and flavor production effectivity, and are – therefore – a direct and ominous threat to your value proposition specifically, and the long-term success of the craft distilling industry in general.

Solution

iStill has invented a way for you to control the levels of dissolved CO2 during fermentation. We call it the iStill Burst Protocol. It is a piece of control, a new software patch basically, that we added to our fermenters and the iStills (that can also be used as fermenters), some time ago.

What the iStill Burst Protocol does, is that it allows you to choose short bursts of agitation at specific intervals. What the burst agitation protocol does, is that it pushes big amounts of dissolved CO2 out of solution. If you set a specific interval, this means that you release dissolved CO2 on a regular basis, constantly making sure that the yeast, your yeast, operates within its best performance window.

An example

Imagine that you want to ferment a molasse batch into a rum wine. Molasses ferments quickly, so you’ll see a lot of CO2 build-up and a warm if not hot ferment. Molasses are high in ashes and in unfermentable sugars, conditions that already induce yeast stress. High temperatures and high levels of dissolved CO2 add more stress to the yeast, potentially deteriorating your results, leading to lower yield and off-flavors in your rum wine and – later – in your rum.

Here’s an example how the iStill Burst Protocol helps:

1. Choose a 36 hours fermentation time;
2. Add the yeast and do not disturb the fermentation for the first 8 hours;
3. So that yeast growth and propagation are not hampered;
4. After 8 hours, when oxygen levels are depleted and CO2 is on the rise …
5. Do 4 minutes iStill Burst Agitation periods every 45 minutes from then onwards;
6. Now, during the alcohol and ester production phase …
7. The levels of dissolved CO2 are reduced every 45 minutes …
8. Which leads to healthier and les stressed-out yeast …
9. Resulting in higher yield and better flavors, via a faster production of alcohols and esters!

iStill’s Burst Agitation Protocol: an amazing USP!

Our research shows that iStill’s Burst Agitation Protocol helps produce 20% more alcohols and flavors in only 60 to 80% of your normal throughput time! How’s that for lowering your production costs and improving the amount of flavor you sell per bottle?

Do you want to learn more about this amazing new innovation? Please reach out to Veronika@iStillmail.com and register for the hands-on Master Distillers Course. We still have a few spots available in April.

Do you want to order an iStill distillery or an iStill fermenter? Email me directly at Odin@iStillmail.com, so that we can plan a video call for us to discuss your plans and our amazing distilling solutions.

Choose the iStill Burst Protocol …

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Introduction

The big boys do it, so the small ones should follow suite? No freaking way. Continuous distillation is an industrial process, optimized for the cost-efficient production of low to medium quality spirits. It is not a technology that is suited for craft distillers, as it won’t grant them access to the same cost-efficiency gains, but it will deliver on sub-standard quality of output. Let’s dive in deeper!

Continuous distillation: the technique

The word “continuous” says it all. Continuous distillation is a technique that constantly distills. Twenty-four hours per day, seven days per week. The fermenters, where a 7 to 8% whisky beer is made over the course of about three days, directly fead the continuous distillation column and the continuous distillation column processes all the wash that fermenter has to offer. Is the fermenter empty? Then another fermenter comes online, to ensure a continuous feed to the continuous still. The now empty first fermenter is refilled with fresh mash. Yeast is added to the grain/water-mixture, so that a new batch of whisky beer can be produced.

In general, the continuous still gets fed with beer in the middle and are heated from the bottom. Alcohol purification is achieved via bubble cap or perforated plates inside the column. Grains, water, and high boiling point alcohols (tails) move down. Ethanol and low boiling point alcohols (heads) move up. Usually, multiple take-off points are fitted on the column, so that specific compositions of hearts, heads, and tails can be collected.

Continuous distillation: the problems it solves

Continuous distillation is an industrial approach to alcohol production. It is a very efficient way to produce huge amounts of middle-of-the-road quality alcohol. What’s great about it is that it knows no downtime. Contrary to pot or batch distillation, there is not refill, heat-up, clean-up, and discharge time.

Also, in a specific continuous distilling application that is called the Coffey Still, the beer is used as coolant, saving both on cooling water and pre-heating the wash prior to distillation. This double efficiency gain makes the continuous still, relative to traditional copper potstills, a very effective distillation device, that is hard to beat on production costs per liter of alcohol produced.

Continuous distillation: the problems it causes

In a pot or batch distillation technique, a boiler, that feeds the column, is filled with whisky beer. That batch of beer is processed completely. When all the alcohol is collected and strengthened by the column, the run is finished. The stillage, mostly water and spend grains and some tailsy alcohols, is cleaned out from the boiler. Fresh wash is added to the boiler. The boiler is brought to a boil again, and the cycle starts all over again.

Contrary to continuous distillation, batch distillation has a beginning, a middle, and an end. Contrary to continuous distillation, the output of batch distillation first produces heads, then hearts, then tails. As such, batch distillation is much better at separating out heads and tails than continuous distillation is. In vodka production, batch distillation creates a better, cleaner product, because the heads and tails smearing can be completely taken out, where – in continuous distillation – there’s always going to be some heads and tails present in the end product, as the column is always fed with the same beer, that simply always happens to have some heads and tails present.

But there is more. Continuous distillation, as it works from one and the same substrate all the time, gives very limited control over smearing. The above paragraph mentions that vodka made on a continuous still is less pure than batch distilled vodka. But an inherent amount of smearing is always the case in continuous distillation, and it mostly depends on the beer that’s fed into the system. In other words: when making taste rich spirits, like brandy, rum, of whisky, where the right amount of heads and tails smearing matters, continuous stills under-deliver. They have an amount of smearing that is a given, and that is very difficult to manage upwards or downwards. For that a laboratory is needed, where heads and tails can be extracted and re-assembled to create certain flavor profiles (e.g. via hydroseparation protocols in between two continuous runs). Yes, more plates can produce different outcomes, in terms of smearing, but a plate is a crude device for separation. Many, four or five at least, are needed to get to any differentiation as far as smearing is concerned. At the cost of creating a very high ABV spirit that is pretty tasteless.

Summary? Given the continuous feed of always the same product, continuous stills do not offer much control over heads and tails smearing, contrary to what batch distillation offers. Continuous distillation produces mediocre vodka and mediocre brandy, rum, and whisky efficiently.

Why continuous distillation sucks for craft distillers

Here’s why continuous distillation sucks for craft distillers:

• Craft distillers can never outcompete Big Alcohol on cost price per liter;
• Instead, they must compete by bringing higher-quality spirits to the market place;
• A higher quality that makes up for the higher production costs;
• A higher quality that can only be achieved via batch distillation, and not via continuous distillation;
• Ah, and if you buy an iStill, you get even more control over flavor profiles;
• While saving 75% on energy costs, relative to other, more traditional batch stills;
• Yes, you read that correctly: iStills offer the quality of perfected batch distillation;
• At production costs lower than even the best continuous stills offer!

If you want to make the best spirits in the world, in the most repeatable and efficient manner possible, purchase an iStill.

https://istill.com/halloffame

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Introduction

For an introduction on vapor speed, and its importance to distilling top-shelf taste-rich products, please read this first: https://istillblog.com/2024/02/07/distilling-top-shelf-whisky-is-all-about-vapor-speed/

A summary on vapor speed

Higher vapor speeds result in more heads and tails smearing. Lower vapor speeds result in less heads and tails contamination of your hearts cut. Higher vapor speed distillation result in more three-dimensional spirits, where lower vapor speed distillation runs result in less contamination and a cleaner less tasty product. In double distillation approach, potstill-style, managing vapor speed is king.

The relation between rum varieties and vapor speed

Rums can be classified in high-ester rums, medium-ester rums, and light rums. Light rums have less taste molecules. What is highlighted in a light rum is the molasse or sugar cane flavor, that sits in the middle of the run, in your hearts cut. Light rums taste of the substrate the rum is made from and not much else. The production of light rum benefits from low vapor speeds, as these allow for a good separation of heads, hearts, and tails. The lack of heads and tails contamination results in a clear sugar cane or molasses flavor. Yes, quite one-dimensional, but that’s why it is a lighter style rum.

Medium flavor rums have more flavor than light rums. There are some fruity flavors at the beginning and some rooty, nutty flavors at the back. A perfectly made medium-ester rum has as much fruity esters and rooty, nutty esters as it has substrate-related hearts flavors. Medium vapor speeds allow for more smearing of fruity flavors, and of rooty and nutty tails-associated flavors into hearts. Medium vapor speeds make great medium flavor rums.

A high-ester or heavy rum has an overdose on both fruity and rooty, nutty, and even earthy flavors. The way to get there, in a double distillation, potstill distillation protocol – as far as vapor speeds are concerned – is that you distill faster. Faster runs result in higher vapor speeds and higher vapor speeds result in more smearing of heads and tails into hearts. Yes, the product will take more time to age and to mellow out, but it will become a more interesting, three-dimensional product in the end!

On flavor intensity and vapor speed

As a generic rule about 30% of the esters – of flavor molecules – are heads associated. Only 20% of the esters in any drink are hearts associated. The remaining 50% of flavor can be found in the tails that smear into hearts.

The above knowledge creates a nice model that helps understand how much the difference in flavor intensity and length can be, when we compare the various rum categories:

• Light rum can have up to 20 ppm of flavor molecules – that’s 20 esters per one million molecules;
• Medium rum can have up to 60 ppm of esters – 20 heads, 20 hearts, and 20 tails associated;
• High-ester rum has at least 100 esters per million molecules – 30 heads, 20 hearts, and 50 from tails.

Look at those numbers again, and realize that medium rum has two to three times more flavor than light rum. High-ester rum has 5 to 6 times more flavor than light rum. And all you need to make those three very distinct products from one and the same ferment … is an understanding of cut points and vapor speeds.

How to get there? How to create the rum of your choice? Well, a finishing run on a power setting of 30% allows you to cut a great light rum. Are you into medium-taste rums, then put the power between 40 and 50%. For a high-ester rum, push your iStill to 50-60% power. As an alternative method, you can also go for a wider hearts cut, as it also allows for more heads and tails smearing.

Please understand that 100 ppm rum is the minimum threshold for what I consider to be high-ester rum. Wanna go higher in taste, as far up as 300 to 600 ppm? Backset-cycling and the Maillard Reaction will get you there. Do you want to learn how these work? Purchase an iStill. It comes with our online educational facility included. We don’t just sell you the still, we also educate you to become the best craft distiller you can be.

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Introduction

Distilling top-shelf whisky in potstill mode is all about vapor speed. Better said: distilling top-shelf whisky, brandy, gin, rum and any other taste-rich spirit is all about vapor speed. To be even more precise: distilling top-shelf taste-rich spirits depends on cuts for heads, hearts, and tails, on and vapor speed. This iStill Blog post dives into vapor speed; the variable less well-known than cut points.

Today, I want to teach you on how vapor speeds influence flavor composition and on how certain pot distilled drink-categories benefit from higher, medium, or lower vapor speeds. Finally, I want you to learn more about vapor speed control. I mean, a better understanding of the importance of vapor speed is one thing, but how does one apply that knowledge into the production of higher-quality whisky, gin, rum, or brandy? Via control over vapor speeds. Let’s dive in deeper via an example!

An example

We are going to talk pot distilled whisky here, but please know that the framework presented here is just as applicable to other taste-rich, pot distilled spirit. I’ll focus on whisky to save on words.

So, here’s the example. Imagine you do a finishing run on a single malt whisky. Your cut points for heads, hearts, and tails are 81 degrees Centigrade, 94 degrees Centigrade, and 97 degrees Centigrade. You collect the heads faction until the temperature in the column is 81C. You then collect hearts until 94C. You collect tails until 97C and then stop the run.

A definition of vapor speed

In essence, a distillation device consists of three parts. A boiler, where an alcohol-rich fluid is brought to a boil. A boil that produces gasses. The riser or column that transports these gasses away from the boiler. Towards the cooler. And then, finally, the third component: the cooler. The cooler collapses the gasses back to liquid phase. Important, as we are producing alcoholic beverages, not alcoholic gasses. 🙂

So there you have it: liquids turn to gasses that turn into liquid. And as most alcohol molecules are “lighter” and have lower boiling points than water, the gasses produced by the boiler have a higher alcohol content. Thus we make alcoholic spirits. Now what about that definition of vapor speed, Odin? Almost there …

Before we get there, I want you to take in one more thing: the phase-change from liquids (in the boiler) to gasses (in the column) and back to liquid (in the cooler) is not a one-on-one change. Volume-wise amazing things happen during those phase-shifts. Gasses, when formed, hugely expand in volume. Liquids, when formed, hugely contract in volume. By no less than a factor of 100! Imagine that you distill – let’s say in a minute – a cup of liquid. That cup translates into a volume of 100 cups of vapor. As columns or risers are smaller, both in volume and diameter, than boilers, it is now easy to see that the liquid to gas phase-change results in those gasses speeding up and moving through the riser or column at relatively high speed.

The definition of vapor speed? The gas speed inside your column or riser, while you are preforming a distillation run. Now, let’s dive into the influence of vapor speed on flavor.

The influence of vapor speed on distilling

Vapor speed influences many things related to the creation of taste-rich spirits. Here is a summary:

1. Heads smearing;
2. Tails smearing;
3. Water smearing.

Heads smearing and vapor speed

The heads faction consists of low boiling point alcohols and associated fruity esters. Given the statically defined cut points mentioned above (81c for heads, 93c for hearts, and 97c for tails), what happens if you distill with higher vapor speeds? The higher speeds will concentrate more of the hearts-associated ethanol in your heads cut. Do to the higher vapor speeds, hearts will bleed into heads, both contaminating the heads cut with good alcohol, and leaving more headsy alcohols and flavors behind, to be blended into your hearts cut.

Higher vapor speeds result in more headsy alcohols and fruity flavors being smeared into your hearts cut. The result? A more flavorful hearts cut, because that faction is now contaminated not just with the grain flavors that associate with hearts, but also with the fruitiness of the additional heads smearing.

Just as higher vapor speeds result in more heads smearing into hearts, lower vapor speeds result in less heads smearing into hearts. Lower vapor speeds result in a better separation of heads, where headsy alcohols and their associated fruity taste molecules stay in the heads cut and do not blend over into hearts.

As a general rule, we can conclude that faster vapor speeds result in more heads smearing into hearts. Lower vapor speeds result in less heads smearing into hearts.

Tails smearing and vapor speed

Higher vapor speeds result in the earlier selection of “heavier” or higher boiling-point alcohols coming over. High boiling-point alcohols associate with earthy, rooty, nutty flavors. High vapor speed distillation therefore results in earlier tails smearing. As a result, the hearts faction, at those higher vapor speeds, gets contaminated with more tailsy alcohols and earthy, rooty, and nutty flavors earlier.

Lower vapor speeds have the opposite effect. They allow for a better separation between the hearts and the tails faction. Less smearing and a cleaner hearts cut, where the substrate flavors of hearts are not overpowered by the rooty, nutty, and earthy flavors.

As a generic rule, we can now conclude that faster vapor speeds result in more tails smearing into hearts. Lower vapor speeds result in less and later tails smearing into hearts.

Water smearing and vapor speed

Finally, as water is a “heavier”, higher boiling-point molecule than ethanol, the alcohol most present in your hearts cut, it is important to understand that vapor speeds in your riser or column also influence the amount of water that gets smeared into your run in general, and into your hearts cut specifically.

Contrary to heads and tails smearing, water has no flavor. But higher or lower vapor speeds still have an influence. In potstill runs, higher vapor speeds result in more water coming over. Lower vapor speeds result in less water smearing. In plain English? Higher vapor speeds result in lower ABV output.

What vapor speeds are ideal for whisky?

I define whisky as a three-dimensional drink, where the substrate that it is made from can be identified. This means that all three flavor boxes need to be ticked off. Whisky needs to have a fruity beginning, a middle where one tastes the grain, and a long finish with earthy, rooty, and nutty flavors. In order to get the right amount of smearing, higher vapor speeds are needed to produce interesting whiskies.

Vapor speed control

In general, whisky is distilled on a potstill with a relatively slender riser or column. The small diameter results in higher vapor speeds. The higher vapor speeds enable the smearing of heads and tails into hearts.

Given your set-up is what it is, another approach to improved whisky distillation is that you distill faster. Push the power that goes into the boil upwards, so that you create more gasses that need to travel through the same column or riser … resulting in higher vapor speeds and more smearing.

Or simply purchase an iStill, as it is the only still with a fully optimized design for vapor speed control. Yeah, that’s the tool you need if you want to produce top-shelf flavor-rich spirits. The iStill Hybrid even allows you to make whisky in one single go in column mode … for even more taste! More on that in a later post.

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