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[All of this information has existed on the blog, but I am slowly putting it in one place. I will pre publish this then complete it as quickly as I can. Any questions or suggestions would be greatly appreciated.]
Welcome to the birectifier community!
The birectifier is a laboratory tool for distillers whose history goes back more than a century. It was initially used by chemists inventing the field of laboratory distillation before it first appeared in the writings of the spirit scientist Karl Micko. From there, it was passed on to Professor Luckow and Professor Wustenfeld who elaborated many of the organoleptic tests. Rafael Arroyo got it from Luckow and immortalized it in Studies on Rum. There is a description of it popping up in Trinidad and with a few government scientists in Europe.
In the late 1940’s, the birectifier went obsolete when chromatography was invented as well as the spinning band design for laboratory micro distillation. It becomes relevant again because of its dramatic affordability relative to any competing option and emphasis on organoleptic analysis which centers the experience of the distiller and builds their intuition. Today, the birectifier forms a minimum of analysis any distillery should be capable of in house.
What we need to cover:
- Learn how it works
- Setup the birectifier
- Load the sample & clean the column
- Develop a heating routine
- Collecting the fractions
- Troubleshoot scenarios
- Setting up an organoleptic tasting panel (tools & methods)
- Stacking on quantitative analysis
- Setting up companion organoleptic tests
- Interpreting the results
- Exploring gin
- Exploring single botanicals
- Special tests
- Glassblowing design evolution—Arroyo to today
How does the birectifier work and what can it evaluate?
The birectifier is simply a distillation column that is wound like a trumpet so it is not too tall and its proportions are scaled to give certain results when inputting 100 ml of absolute alcohol (250 ml @ 40% ABV). The design allows the output to be paced at 25 ml per 15 minutes with a single variable: energy input to the heating mantle. Other designs only achieve the same reflux with a two variable system that is too challenging to control at the micro level or delegate to junior staff. The birectifier design is about pragmatism.
Vapor travels up the outer column, traverses an extended arm, condenses in an air cooled dephlegmator, descends to the base of the inner rectifier as liquid, then is reboiled and emerges as output to the condenser. Two different vapor traps connect the rectifying sections and equalizes slight amounts of pressure that build up.
Initial output is just under the azeotrope of 96% ABV and remains near that concentration until the beginning of the 4th fraction. High value aroma, defining the personality of a spirit, exists in a narrow band of volatility and is squeezed just past the transition of the 4th to the 5th fraction. Congeners line up into predictable locations and historic quantitative data tells us what is where. We can put a face to the name of common congeners and assess their intensity organoleptically. Sometimes we can also spot congeners that basic forms of GCMS miss like high value rose ketones. We can also perform quantitative analysis on individual fractions, but it is remarkable how quickly an experienced operator may, for example, assess the fusel oil collected in fraction 4 versus the effort and expense of creating a quantitative result. If the chief decision maker is assessing the result, the birectifier can be relied upon to create actionable information saving significant time and expense.
We do not necessarily have to generate the quantitative data tables that Arroyo published in Studies on Rum. They do, however, provide a foundation of basic science that supports our abbreviated organoleptic assessment and that is how distillers will typically use the birectifier.
The birectifier thus becomes a scalpel meets stethoscope meets magnifying glass for distillers. And it operates the way they do; it distills! as opposed to other fractioning methods based on absorption (chromatography). Time spent operating a birectifier will turbo charge the intuition of a distiller and create extreme familiarity with congeners. Distillers can also perform role model case studies and get incredible first hand experience with spirits they do not even produce. How do your own spirits compare to market leaders and what actions can bring them closer together?
The biggest value proposition for the birectifier may actually be gin. Once you learn birectifier operation for fermented distilled spirits, the same processes can be applied to botanical distillates. The aroma of gin spreads out across all the fractions and it rapidly becomes clear how a given sample compares to role models and how it can be sculpted to better achieve its sensory goals. Single botanical assessment rapidly identifies outliers that may need adjustment for a botanical charge.
How do you setup the birectifier?
The birectifier may be many operators first wet chemistry device. Certain fittings were chosen to make setup and break down easier and reduce the risk of breakage. Two laboratory stands are required with two clamps. One stand will hold the 500 ml heating mantle and boiling flask. The column will be inserted in the boiling flask then supported by clamping with minimal pressure at the center of the straight section of the column. The boiling flask is always loaded with 3-4 pieces of small pumice stones to prevent bumping from super heated hot spots.
Thermometers (1/4″) are inserted in the proper fittings and a vapor seal ensured with o-rings. Thermometer height is adjusted so that the bulb is measuring from the two transition points. The first transition point is from the dephlegmator arm to the side seal at the top of the coil. The second transition point is at the side seal where vapor exists the column to the Liebig condenser.
The condenser is attached to the column with a ball socket fitting and requires a no. 18 pinch clamp. The second laboratory stand and clamp supports the condenser. The condenser angle is roughly positioned at 55° and it is important that both the ball/socket fittings’ internal bore are aligned so that no accidental reflux is generated from misalignment and consequent reduction in aperture.
Stacked objects or a classic laboratory jack are used to elevate collection flasks underneath the condenser take off.
The heating mantle is plugged into a voltage regulator featuring a digital readout of volts, amps, and watts. Notes on energy usage are always physically attached to the voltage regulator so that a repeatable heating schedule can be conducted by any delegated operator.
Condenser tubing of adequate length is attached and run out the back of the setup around the heating mantle. Hose barbs may either be 1/4″ or 5/16″ and appropriate diameter tubing must be used. If near a sink, water pressure from a faucet can be used to supply coolant. If setup mobility is desired, a peristaltic pump can be used. The birectifier typically only needs 1.5 gallons of water per operation.
Loading the sample & cleaning the column
After fractioning a spirit, there can be substantial aroma clinging to the inside of the column. Much of these congeners are also poorly soluble in water so you cannot easily flush them with steam. The best way to clean the birectifier and prepare it for the next sample is running a charge of 50 ml of 40% ABV neutral spirit. It is often satisfactory to heat this small charge at the energy level used for collecting the last fractions of typical birectifier operator. Only 20 ml of output need to be collected and is enough to flush the column and condenser, rinsing all residual aroma back into the boiler.
It is valuable to standardize a cleaning routine so that it can be executed in a predictable time frame and timers can be set so that it never runs too long.
To generate traditional fractions, the birectifier requires a charge of 100 ml of absolute alcohol diluted to 250 ml (40% ABV). This charge size is proportional to the column’s reflux and designed to align congeners in desired fractions for evaluation.
It is best to measure the ABV of sample, input the required volume for 100 ml of absolute alcohol then top with dilution water in a volumetric flask to 250 ml. The quick formula for the charge is 10,000 / the ABV (as a whole number and not a percentage); i.e. 10,000 / 40 = 250 ml; 10,000 / 57.14 = 175 ml. Notice the formula simply has the numerator and denominator multiplied by 100 to avoid decimals. A 250 ml volumetric flask is used to standardize the charge size before loading into the boiling flask. 5.0 ml of water can be used to rinse the volumetric flask so as to capture the maximum of absolute alcohol.
The 100 ml of absolute alcohol is fairly sensitive so the initial ABV must be assessed with temperature correction. If the charge is not large enough, high value aroma will emerge too early and taint the isolation of higher alcohols in the 4th fraction. Adequate ethanol proportional to flux and a 25 ml / 15 minute out pushes high value aroma into the 5th fraction.
If you had to err, lean on too much absolute alcohol by a few ml. This scenario is sometimes preferred when there is not enough time for accurate temperature correction. The very first birectifiers used a charge of 96 ml of absolute alcohol which was no doubt proportional to the device having relatively lower reflux. It would not be out of line to evolve your own process to 102 ml of absolute alcohol due to any unique particularities empirically observed.
If an err is made with too little absolute alcohol, which can happen by taking as a given someone else’s measure of ABV, it can become appropriate to stop the 4th fraction early and transition to the 5th fraction. Aroma, temperature queues, and visual queues within the column can guide this decision.
Developing a heating routine
The system requires very precise management of energy input so that fractions are faithfully collected at 25 ml / 15 minute increments. The more faithfully collected, the better we are able to make meaningful comparisons across distilling runs. To maintain a constant rate of flow, the energy required is dynamic and ramps upwards because of how alcohol is exhausted over the course of the run.
As an example of a theoretical heating ramp, the first three fractions are collected at roughly the same energy level because the ABV for those fractions is near the azeotrope. The most significant ramping is in the 4th fraction where ethanol is rapidly being depleted. The 5th-8th fractions are nearly aqueous and collected at roughly the same energy level. Typically when I collect the 4th fraction I use three different ramps and we’ll get to that.
To back up a bit, I advocate using a 500 ml Glas-Col brand mantle (model 100B TM106) over a Chinese version. Do not use a Glas-col heating controller because you’ll need something far more precise with a digital read out.
For heating controllers, I have systematically tried everything, but now I wholeheartedly endorse Auber controllers and have a custom specified version for the birectifier I can direct anyone to (roughly $400). Auber sells what are basically affordable Chinese clones of American Watlow controllers. Auber’s customer service is awesome and true Watlow is unaffordable.
The affordable heating controller option is a Variac variable voltage controller (rated for adequate amps) and there is an infinite supply on the used market. Some have integrated digital read outs for voltage which is ideal, but if yours does not you can install an affordable “kill-a-watt” meter inline to give a digital voltage reading as well as amps and watts.
[When you go from a modern digital voltage regulator to a Variac, you may notice I’ve made some oversimplifications. I typically count my energy input in volts or a percentage of line current, roughly 40-70. I do this because the numbers are simple to remember and it is highly repeatable. A Variac can also operate this way, but when we compare different Variacs and different mantles and different incoming line currents, we may want to talk in watts. Watts = volts * amps. Instead of “70” as an upward bound for collecting the aqueous fractions, I have needed about 250 watts. On my particular Variac, that was 113 volts and 2.2 amps. Framing the lower bound for the first fractions is near 125 watts. If you’re trying to understand the numbers on the kill-a-watt, amps will change proportionally to volts. On my particular mantle, the watts are 270 when the volts are 115 implying the amps would be 2.35. Lowering voltage below 115 correspondingly lowers amps and thus has a two fold impact on changing watts.
Some other mantles are 250 watts at 110 volts and thus 2.27 amps. This change would impact the values needed for a heating routine.
My incoming line current is 123 volts. 70% of 123 is 86.1 volts. That means my digital voltage regulator needs 86 volts to do the same work that my Variac does at 113. Because we are evaporating water, we are likely talking the same wattage. The difference then is the devices drawing different amps, but I cannot say why.
This is just something to consider when developing your own heating schedule for your own proprietary heating controller & mantle. You will get repeatable results but your numbers may differ from mine.
Something else to note is that I can install a kill-a-watt easily on my Variac to see volts, amps, and watts, but I cannot put the same device on my digital controller.]
The Glas-col 100B TM106 heating mantle outputs 270 watts which puts the Amp draw well below 10 and gives a lot of options for high end second hand Variacs (watts = volts * amps).
It is safe to call the birectifier initial heat up frustrating (because you want to go fast!). You cannot apply a lot of energy to heat quickly then turn it down. The heating mantle simply has too much inertia. If your first fraction is optimally collected at 39-41% power then that is how much energy initial heating should require and it simply takes as long as it takes. Botching the first fraction cannot be recovered from. Some times initial heat up for a 250 ml sample takes 20 minutes. I can reliably set my initial energy for heat up and collecting the first fraction then set a timer and walk away. Most often I can return with only 60 seconds of extra time needed before the first fraction starts being collected.
For fractions 1-8 my current heating profile looks like this:
Fraction 1: 39% <–Near azeotrope
Fraction 2: 39% <–Near azeotrope
Fraction 3: 40% <–Near azeotrope
Fraction 4: 42-55-70% <–Near azeotrope but alcohol exhausting
Fraction 5: 70% <–Alcohol exhausted in the beginning
Fraction 6: 70% <–Aqueous
Fraction 7: 70% <–Aqueous
Fraction 8: 70% <–Aqueous
These numbers will differ slightly if you are referencing volts directly or reading a percentage of your incoming line current which can deviate slightly from 115V and even vary by time of day.
The first three fractions are very similar in energy required and so are the last three. The fraction that changes dramatically is fraction 4 because near all alcohol is exhausted in that fraction. On your very first running, you have multiple tries to arrive at the correct number for the first three fractions and then again for the last four. On your next running, because you’ve established your beginning energy needs and ending, the focus will be about perfectly executing fraction 4 which may need the voltage changed multiple times. I often change it at the very beginning as the vapor temperature starts to rise. Changing it again after the first 1/3 of volume and then again at 2/3. To get good results, it is definitely not necessary to sit there and increase the energy by one point every minute.
Energy numbers for collecting fractions have stayed fairly consistent in my lab as spring weather rolled into summer and humidity increased. After a while, I have been able to look at the drips almost like a metronome to know things are proceeding correctly. As a rule of thumb, it is better to be too slow than too fast. As another rule of thumb, for the first four alcoholic fractions, you should be able to count off nearly one drip per second so you can set your stop watch and count out thirty drops in roughly thirty seconds. For the last four fractions, where alcohol is exhausted, the drips change in size and even become less consistent in interval due to surface tension changes.
A change of a single percentage point of energy input can add or subtract an entire minute off collecting a fraction. Heating is that sensitive!
For every fraction I collect as I create my heating schedule, I note the time and update my ramped voltage charts. The more systematic you become, the less time you’ll burn creating your routine. Being very patient with the very first start up will save you a lot of time down the road. It may also be useful to collect your very first run in a 25 ml graduated cylinder. That way, at 5 minute intervals, you will know if you are on track (roughly 8ml / five minutes). You can even take a sharpy to your volumetric flasks and divide them into thirds. It is useful to write your energy levels directly on your heating controller so anyone the task is delegated to can start accurately without having to reinvent the wheel.
Initial heating can take almost 15 minutes before a rapid boil even begins. In the next approx 5 minutes before output is collected you can watch vapor slowly start to creep up the walls of the column like a lurchy phantom (it is very cool). The slow pace of this process may also help congeners line up in sequence.
If it looks like I am coming up slow, two or three minutes before a fraction is due, I increase the energy by a point. Fifteen minutes is an ideal, but do not panic if you are collecting a few fractions at 16 or 17 minutes.
With experience, and no specific background in wet chemistry, I have been able to run the birectifier accurately and minimize active time with the unit so that I can multi task during the process. Frequently, once a fraction starts, I set a timer for 14 minutes and only come back to observe the last 60 seconds.
Collecting the fractions
Collecting birectifier fractions should feel natural to any distiller. A 25 ml volumetric flask or graduated cylinder is allocated to every fraction and they are simply collected at 25 ml / 15 minutes so that faithful comparisons can be made from sample to sample. The main decision to make is how many fractions to collect? Historically this has ranged from 6-8. Arroyo collected all 8 in Studies on Rum and reported that flaws may appear in the last fractions. Collecting all 8 fractions would require 2.5 hours which assumes roughly 20+ minutes for heat up. Actionable information can be gotten much faster than other analysis methods. However, the process can be truncated to save time.
I have heard of a user collecting only the first two fractions because they were only concerned with the ethyl acetate in a sample related to its maturation and they were not setup for a quantitative ester determination. They were able to compare their fractions to those of the original white dog and other maturing samples. This seems an imperfect substitute for an ester determination but it required no extra setup or new skills and they knew how to make the results actionable within their production.
A basic quantitative result can be derived from organoleptic assessment. Fraction 1 or possibly the combination of fraction 1 & 2 would be systematically diluted to an “exhaustion point”. The old German blenders called this the exhaustive test and Kervegant called it quantitative tasting. Dilution is performed in a series of 100 ml volumetric flasks with a volumetric pipette. When resources are limited, this method can be incredibly useful. The numerical result would only be useful inhouse.
A classic quantitative ester determination could be pursued with NaOH and standardized sulfuric acid as a back titrant. The same heating mantle, heating controller, and 500 ml boiling flask used for the birectifier could be employed. The only additional piece of equipment needed would be a 24″ air condenser.
Another user told me at times they have only collected the first four fractions. Their aim was only to assess higher alcohols and saving time was important to them. Their organoleptic tasting panel included nothing but the 4th fraction and role model comparison. This was a 90 minute time commitment with very little active time spent adjusting the process.
Arroyo’s data tables show us that nearly 75% of higher alcohols are expected to be collected in the 4th fraction so that fraction alone becomes an accurate snap shot at higher alcohols. Organoleptic comparison to role models can easily teach what is permissible and what requires attention or investment.
Titration for higher alcohols is more exotic than acid titrations or ester determinations. It requires exotic reagents, standardized references for comparison, and as best I can tell, completely obsolete relative to GCMS options. Organoleptic analysis with the birectifier is the only practical alternative to GCMS for fusel oil investigations.
If time allows the fifth fraction of a spirit is always worth collecting and typically defines the majority of the personality for a spirit.
The 6th, 7th & 8th fractions of a fermented distilled spirit can often be redundant. With routine work and experience where the information in latter fractions is predictable and not needed, it is perfectly acceptable to skip collecting them to save time. These later fractions are where many flaws are thought to reside. They should be collected if any flawed character is suspected.
For gin analysis, experience has shown that it is only ever necessary to collect 6 fractions which would require 2 hours.
For liqueurs where there is appreciable sugar, collecting 6 fractions may provide all the information needed and avoid allowing the stillage to get too concentrated in the boiling flask.
Troubleshooting scenarios
Very few scenarios come up that require troubleshooting.
- Pumice stones must always be used to prevent bumping which is caused by super heated hot spots which round flasks and mantles are prone to. After a year of using the same stones, I did replace them when I should have observed a rapid boil, but did not see one. Jostling the heating mantle when the liquid is super heating can cause an eruption of boiling. The solution is simply to always use boiling stones and be aware they may eventually need replaced.
- Undue reflux can be caused by misalignment of the ball connector joining the column to the condenser. The ball fitting is only to alleviate any stress when setting up or breaking down the unit. The two side of the joint must be aligned to maximize the inner diameter of the bore.
- If too little absolute alcohol is inputted there may not be a sufficient volume to complete the 4th fraction while isolating high value aroma in the 5th fraction. The solution is to change to the 5th fraction early. The decision should be made using aroma, temperature, and visual queues of vapor change within the column to aid the decision. The 4th fraction being off by a few ml taints the results but does not void the results. Often enough information can still be gotten from the fractions. Being 2 ml short in volume may only represent 1.0 ml in absolute alcohol and thus a 1% err in concentration. A short 4th fraction should be topped to 25 ml before organoleptic analysis.
- If one fraction goes over 25.0 ml due to lack of attention the solution is often to transfer the overage with a pipette to the fraction currently being collected. If the overage may be a single ml, it may be appropriate to visually estimate and collect the current fraction short by a corresponding amount. These errors only taint the results, but do not void them. Recovering fraction alignment can keep a sample on track to get usable information from time invested.
- If a spirit is abnormally high in long carbon chain congeners surface tension may cause the condensed liquid to exit the condenser is globs that do not easily enter a narrow volumetric flask. This may only afflict certain heavy rum blending stocks or certain heavy rye whiskies. The solution is to switch sample collection from a narrow 25 ml volumetric flask to a wider 25 ml volumetric cylinder. Globby output or visual queues of globular condensate on the inner walls of the column may imply the chemical nature of poorly volatile congeners. Congeners exhibiting this phenomena are fairly uncommon and may become a liability in a finished spirit. They may also indicate the still they came from is going to require more attention to cleaning and flushing its condenser.
Setting up an organoleptic tasting panel (tools & methods)
Different operators have historically setup their organoleptic tasting panels in different ways. Professor Luckow did it one way and Arroyo did it another. There is even room for more variation. The key to any process is consistency so that experience and memory can be built.
Arroyo simply diluted every 25 ml fraction to 100 ml with water.
Professor Luckow diluted the first 4 fractions with 2 parts water to 1 part sample. The last four fractions were diluted with 1 part water to 1 part fraction. I have preferred Professor Luckow’s process. With Luckow’s method, the first four fractions, which are collected near the azeotrope, end up at roughly 30% ABV which is a unique threshold for sensory appraisal. It may also minimize any potential ester breakage. The last fractions are very low in ABV and do not benefit from excessive dilution. The concentration of the last fractions at 1:1 dilution give any free volatile a unique feel for appraisal.
Arroyo’s process, favoring extra dilution, may have been used to allow extra volume for titrations, whereas, Luckow’s may have been optimized for organoleptic appraisal.
Frequently, my own process only uses 10 ml of a 25 ml fraction so that extra volume is left over to store as reference or setup other investigations such as increased dilution.
I enjoy observing the 1rst and 2nd fractions apart because the second fraction, as a less concentrated version of the 1rst, can provide a unique vantage point and help spot anything unique. However, experience and experimentation may evolve a process where the 1rst and 2nd fractions are combined. A lot of experience with a routine production may lead a user to avoid setting up the 3rd fraction which is extremely neutral. Fractions 6,7 & 8 may benefit trading organoleptic analysis for a simple titratable acid determination. Outliers in volatile acidity may quickly direct attention to cleanliness or adherence to distillation parameters.
The tools to setup a tasting panel are simple but can be optimized to make the process quicker. There are different ways to skin the cat depending on precision required. All things start with uniform tasting glasses and covers. “Watch glass” covers can be readily purchased, but Luckow & Arroyo each had a preference for lids made by a glassblower. If the entire 25 ml sample is used, it is simply dumped in the tasting glass and topped with the required volume of acceptable water via the volumetric flask or a volumetric cylinder.
If a partial quantity is setup, such as 5.0 or 10.0 ml. a 0-5000μl (0-5.0 ml) pipette can be used. The volumetric flask is transferred to a volumetric cylinder which is wide enough for the pipette. What is required is drawn and the rest is transferred for storage. A cost effective alternative to a automatic style pipette is simply a graduated syringe with a luer lock “blunt needle” which is a metal straw tip. These can be incredibly practical for dispensing samples across many distillery tasks. They lack the accuracy of a true pipette but are capable of drawing directly from a volumetric flask due to the narrowness of the tip.
Not all fractions are worth entering long term storage, but all can be stored for an intermediate term. The last aqueous fractions may become susceptible to growth of microorganisms which metabolize the volatile acids. If these fractions need to be stored as unique educational reference for a distillation phenomenon it would be advisable to stabilize them with ethanol such as from the third fraction with a round number dilution factor.
A lot of the language I have used for making case studies may seem unique to spirits evaluation. Often what is experienced is highly abstracted from the typical sensory matrix or incredibly concentrated. What I often try to remark is whether something is inline with expectation or an outlier, ordinary or extraordinary, can be related to the presence of a specific chemical or congener class, etc. What we are looking for is encircling an experience with a sense of scale. Sometimes I remark on whether something is culinary or non-culinary which often implies concentration. Culinary aromas are often associated with fruit, but generically, and non-culinary aromas are perceived as gluey or acetone-like.
Fraction 1: My remarks here typically relate to the concentration and then whether there are any extra details. In some rums where you try to generate butyric acid, often you end up with ethyl formate and it appears here. Iso-amyl-acetate can also appear here and present a distinctive easy to call out banana aroma. It can be hard to parse ethyl acetate from acetaldehyde and it would be helpful to experience distinctive case studies where acetaldehyde was a positive for being excessive. Arroyo called them both acetic radicals and they may both have the ability to feel acetone-like and therefore hard to parse.
When examining gins or single botanicals, excessive generic terpenes can accumulate here and louche upon dilution then separate over night. This can be a cause for concern and if significant separation is observed a gin might turn milky in a cocktail. Some role model gins exhibit slight clouding in this fraction. Role models can clearly teach what is normal and acceptable. Juniper aroma may appear here but almost like an incomplete slice of its aroma.
Fraction 2: Fraction 2 is often a diminutive version of fraction 1. Every now and then, because everything is less concentrated extra aroma can become clearer and more positive to identify such as ethyl formate or iso-amyl-acetate.
In a gin, a different tonally weightier slice of juniper aroma may be observed.
Fraction 3: Here, I’m typically remarking on its expected neutrality. Frequently there can be slight hints of higher alcohols against a clear backdrop. Rarely does a spirit have distinctive aroma here, but it has been observed with tequila and some of the most opulent rums where it seems to carry distinctive character also observed in fraction 2. I have wondered if it could be an acetal.
In a gin, juniper aroma transitions to coriander and we see that their relationship in a gin as dominant botanicals may have something to do with their unique bands of volatility.
Fraction 4: 75% of a spirit’s fusel oil is thought to be collected in the 4th fraction so the information can be extremely valuable to a distiller. Language here tries to describe the magnitude typically in terms of ordinary, expected & acceptable or an outlier that needs attention. You can even notice qualitative differences here and sometimes I use the wraith metaphor; you breath it in and it wants to reach in a little further. Often this denotes the sensation of high levels of fusel oil and dominance of amyl alcohol. Amyl alcohols are thought to be perceived as sharper than rounder butyl alcohols. Different yeasts under different conditions may influence a fusel oil tamber where the expression can be perceived as having a shape. Schizosaccharomyces pombe ferments may exhibit very obvious below average fusel oil quantities. Their tamber is also much rounder and more palatable. The literature notes that they produce much more butyl alcohols. It can also be remarked if high value aroma appears early at the end of the 4th fraction (as opposed to the beginning of the 5th). This remark has more weight when there is confidence that exactly 100 ml of absolute alcohol has been inputted and all fractions have been executed faithfully.
In a gin, this fraction becomes a wild card and some penetrating botanicals like cardamom may show up here. It may also exhibit a continuation of coriander aroma. Exploration may reveal that some auxiliary botanicals in a gin appear here versus fraction 5 and it would be useful to categorize that propensity. Sometimes language will differentiate aromas that are penetrating versus persistent.
Typically I taste 1-4, then backwards 8-5 to avoid the fatigue of fraction 5 which is the most concentrated.
Fraction 7,8: Fractions 7 & 8 can be grouped. Often you are trying to differentiate them or note similarities. Often you are also noting the presence of gustatory acidity. Sometimes in a heavy pot distilled spirit they can feel as tart as lemonade while not having objectionable character. It can be surprising how tart a sample may seem relative to the presence of sweaty inharmonious free volatile acids. Objectionable free volatile acidity like butyric may clearly stand out here as well. Other flaws like Arroyo’s tufo from scorched yeast may end up here. In some cases where damascenone is present at significant levels, it may easily be detectable in all of fractions 5,6,7,&8. In very heavy spirits, these fractions may exhibition insoluble droplets, just like fractions 5 & 6, but also insoluble crystalized precipitates that float on the surface. It is important to note what is harmonious and inharmonious here and role model case studies illustrate what is permissible and what may represent a distillation fault.
In gins & liqueurs, these fractions are not collected. They may also not be collected for extremely routine work where it is predictable what will be fore here.
Fraction 6: In various spirits this fraction may exhibition a continuation of high value character observed in fraction 5 or it may seem remarkably similar to fractions 7 & 8, differing only in degree of intensity. The consideration to note is resemblance to those of 7 & 8, but any obvious continuation of high value character reveals how extraordinary a sample is. If a fraction 5 has radiance from rose ketones, often that character spills over here. If carotene derived aroma like TDN or TNN is present, it may be experienced here as a menthe-like note. Few samples have observable high value aroma in this fraction and often when you see it, you already knew the sample was extraordinary.
In a gin, this fraction can either be extremely light in aroma and clean or exhibit a slight staleness. Single botanicals may demonstrate cooked or stewed character and a staleness that may be a liability during co-distillation.
Fraction 5: The vast majority of congeners that define the personality of a spirit reside in the 5th fraction. It can be surprising how generic the other fractions are comparatively. The 5th fraction in a fine spirit can be incredibly powerful and awe inspiring. It can also be hard to remark on. Often we note its power and that is all we need to know we are dealing with something fine. Frequently, there are visual queues. There can be an oil slick of droplets on the top or the fraction can be a milky emulsion that settles to the top like cream after 24 hours. No specific basic science foundation backs up what the droplets or emulsion are, but no doubt esters are the majority and possibly from specific types. When tasted, some fraction 5’s are especially sharp and acrid while others are surprisingly palatable. Fruit, as a metaphor, we often associate with esters is not always obvious because of the concentration. Some feel like they completely come from the world of perfume. Experiencing a strong positive for ethyl butrate was more like Niagara ice win than pineapple. Some times rose ketones are present like damascenone and the experience can have a radiant glow with an animalic note. A 5th fraction can change in character over the course of days under a watch glass as esters blow off and become brooding. It is not clear if obscured rose ketones are revealed or esters break and sweaty free volatile acid is experienced alongside esters. True animalic notes are easy to confuse with sweaty VA and experience with positives will reinforce the distinction. Rose ketones are typically evident right away and their radiance often spills into the 6th fraction.
For extremely powerful fraction 5’s, it is not wrong to dilute even further than Professor Luckow’s 1:1. The fraction is both isolated and at 10x concentration. It may be beneficial to add back neutral ethanol and then further stretch the sample until the esters refract. Fraction 5 is also ripe for GCMS because noisy ordinary congeners and excessive ethanol have been carved away.
The fifth fraction of a gin represents the majority of auxiliary botanicals. Character here may be more persistent than fraction 4’s penetrating character. Fixative aromas important to premium gins may also reside here. Chamomile has been observed in fraction 5. Concentration may be palatable. Sometimes a unique viscosity is observed.
The birectifier has been used for extensive case studies across spirits types but organoleptic mysteries still remain that hopefully will be resolved by developing a community of users. Arroyo provided data tables in Studies on Rum to guide an understanding of the congener range that can be observed in each fraction. We would be wise to conduct similar work with GCMS to build a bridge between advanced analysis and pragmatic organoleptic work.
In some cases the birectifier actually solves GCMS mysteries because it is able to high value aroma like rose ketones. Compounds like damascenone are a blind spot for forms of GCMS typically used by distilleries. In this case, there is reasonable certainty what is observed with the birectifier but boundary pushing university level forms of GCMS would have to be used to truly demystify observations and that work would be incredibly valuable to the industry.
Other mysteries that need resolved are better understanding of the first fractions and learning to differentiate ethyl acetate from acetaldehyde. This may simply require observing artificial mixtures. There would also be benefits in understanding at what quantitative levels culinary expressions of ethyl acetate cross over to non-culinary expressions. If we smell glue & acetone did we cross the 200 ester mark? And then if we wanted to pursue basic quantitative tasting in the form of the exhaustive test, could we correlate various dilutions to ethyl acetate quantities? A foundation of solid data would turbo charge the usefulness of organoleptic analysis.
Similar mysteries exist in the 5th fractions. How big are the droplets observed and what exactly are they? How easy is it to differentiate esters? Can basic sensations or dilution tests be correlated with quantitative data? When we cannot quantify things, what we often rely on is role model comparison; what is normal or abnormal? what is exemplary or category leading? We can often be led to exactly the same decision making we would arrive at if we had quantitative results, but in less time with lower learning curve for interpretation. However, a quantitative foundation is always helpful.
Gin and botanical mysteries are similar. It is far easier to put a name to face with congeners like esters, aldehydes, and higher alcohols. Terpenes and various components of essential oils are not so easy and it is even hard to say how quantitative data would help. Luckily, because we know where the aroma is observed, we know where to shift our focus during distillation. We can also reverse engineer role models attaching our own names to congeners. This kind of analysis feels like: “I don’t remember names, I remember face.” When we work this way, it is extremely beneficial to invest in studying commercial role models before analyzing your own spirits.
People that don’t read music are often the most exciting musicians. Quantitative results are foundational but not requisite for spirits analysis.
Stacking on quantitative analysis
The original users of the birectifier added quantitative analysis to their organoleptic assessments. Some forms are easy but some forms get complicated, prone to err, and are expensive. Arroyo noted many things in his data tables for each fraction:
- Temperature range in degrees C.
- Appearance (organoleptic observations like “clear” or “cloudy”.
- ABV
- Mgs. volatile acidity
- Mgs. esters
- Mgs. aldehydes
- Mgs. Fusel oil
- Remarks (organoleptic observations like “turbid on dilution” or “oil droplets”.
Recording temperature range and ABV for each fraction may not be requisite to understanding a spirit so much as helpful understanding whether a charge was loaded correctly, fractioning was performed accurately if delegated, and that your hand blown birectifier column may be comparable to someone else’s executed by another glassblower. I have found using two thermometers to be extremely useful in recovering from any errors and confirming during operation that the charge had the correct amount of ethanol.
Titratable acidity is the easiest form of quantitative analysis to add and can be practiced at varying degrees of sophistication. Scientists like Arroyo converted results to Mgs. per 100 ml of absolute alcohol while commercial distillers often used inhouse notation where it was only noted the volume of titrant used for a standard sample size. Short hand notations were only concerned with what was normal or abnormal and worthy of more attention. At its most basic, it can be determined with a burette and standardized NaOH.
Ester determinations are an extension of titratable acidity and you actually start with a TA determination. They require one additional piece of labware, an air condenser, and one additional reagent, standardized sulfuric acid.
Aldehydes titration is exotic and has been abandoned for GCMS solutions.
Fusel oil determinations are no longer performed by titration because of both complexity and relative inaccuracy. The current quantitative solution is GCMS but it is surprising how successfully decisions can be made on organoleptic analysis.
The only titrations practical in the modern day distillery are acids, esters, and the formol number which assays free nitrogen in a ferment.
Setting up companion organoleptic tests
The old turn of the century spirit buyers and government scientists used a few companion organoleptic tests to evaluation spirits.
- Exhaustive test
- Evaporation test
- 30% ABV white bubble test
- Sulfuric acid test
- Surface tension test
The most powerful test eventually became called the exhaustive test of systematic dilution. Samples are systematically diluted into water with volumetric flasks until a vanishing point is determined. Kervegant called this quantitative tasting because a number is arrived at from organoleptic assessment. A panel of tasters can give consensus. This test is very surprising and may even be how monks standardized products like Chartreuse as botanical intensity fluctuated. Many basic spirits only stretch 1:100 while many premium spirits can be in a range of 1:150-1:250. Grand Arôme rums can stretch from 1:400 to nearly 1:2000. When this test is used on individual birectifier fractions, there is a lot of concentration and the dilution factor can be extremely high.
The evaporation test entails putting 1.0 ml of sample into a nosing glass capped with a watch glass cover. The sample slowly evaporates underneath and is nosed. Finally, the residue is felt for any oiliness. Experience with this test can make determination of spirit quality that may lead to deeper inquiries and it is useful in scenarios where a spirit sample is extremely precious and nothing but a single milliliter can be spared.
The 30% ABV white bubble test entails using a spirit bubble to precisely dilute samples as small as 20.0 ml to 30% ABV. This low ABV is thought to be a unique sensory vantage point where ethanol is not longer a sensory distraction and other aromas are unwound. Often the depth of esters can be observed as well as any flaws. This test is rapid to setup, requires very little sample size and can help categorize samples for blending purposes. The 1:2 dilution of the first four birectifier fractions aims at a dilution near 30%.
The sulfuric acid test relies on the idea of the strong acid destroying many types of congeners while a few others such as rose ketones like damascenone survive to be easily nosed. It is cheap, fairly easy to dispose of, and sometimes helpful. Unfortunately a brimstone aroma sometimes develop with no clear pattern why. Arroyo used 10 ml of a sample with 3.0 to 5.0 ml of 90% concentrated sulfuric acid. He attributed the brimstone aroma to the possibility of sulfur compounds in molasses, but that may not be accurate. This test may help identify rose ketones aroma if used only in the 5th fraction. An alternative that may also help understand aroma in 5-8th birectifer fractions is saponification with concentrated NaOH, similar to an ester determination. This may help differentiate the sweatiness of free volatile acids with the animalic quality of damascenone. If left to sit, esters may break in the 5th fraction dramatically changing the character. NaOh may be the best strategy to subtract that broken aroma to observe what remains.
The surface tension is based on the idea that as carbon chain length increases, so does surface tension. This is derived from Traube’s Rule that describes a relationship between hydrocarbon chain length and surfactant activity. It states that for every extra CH2 group in a surfactant molecule, the surface activity approximately triples. Arroyo explored this, but did not put a lot of weight on it. This idea is nearly obsolete, but may hold value for attaching a semi-quantitative value to a birectifier fraction. There are many ways to precisely measure surface tension, but for practical purposes the distiller would simply use a capillary tube and a ruler to determine how much of a sample was drawn up the tube. This is rapid and may only generate inhouse numbers that help identify outliers and would simply back up organoleptic assessment. This data may gain value when only one evaluator is available for organoleptic assessment as opposed to a team.
Unique surface tension may be observed in the last fractions of birectifier analysis and the condensate may become extremely globby. Sometimes condensate may become so erratic leaving the condenser that it does not enter a narrow mouthed volumetric flask and a wider graduated cylinder must be used. There is no hard evidence, but spirits with an abnormal surface tension may even encounter an abnormal angel’s share due to evaporation being impacted.
Interpreting the results
The birectifier can assist yeast selection, fermentation optimization, distillation optimization, flaw monitoring, and maturation monitoring. Guiding these processes depends on interpreting the results. A lot of the interpretation relies on confidence and that comparisons across fractioning runs are sound. That is why the column has very specific proportions that are correlated to fractioning 100 ml of absolute alcohol and why fractions must be collected as faithfully at 25 ml / 15 minute as possible.
When you are confident in what you observe you can be actionable and this often is either a corrective action or a path forwards scaling up.
Many common correlations were explored by Arroyo. His concern with yeast selection mainly revolved around fusel oil production and high value aroma for given best bet substrate parameters. The fate of much high value aroma is bound to fusel oil because it is less volatile which is illustrated by the order of the fractions.
Fermentation optimization can take many forms, often increasing risk or decreasing risk, speeding up the process or slowing it down. What are the trade offs? If a ferment is slowed down and risk is increased is there an aroma payoff? What is compromised? How does changing a nutrient change what is observed in the fractions? How does changing pH? How about potential alcohol? Often increasing potential alcohol can hold back aroma beneficial activity by bacteria at the end of fermentation. Was an economy increase worth sacrificing product quality or is the product still within established house character? Much house character will be observed in the 5th fraction which largely defines the personality of a spirit.
Distillation optimization often takes the form of identifying assets and liability. It is typically learned there is less liabilities in the heads from sound ferments than typically believed. A heads cut can often be restricted to a demisting test which rinses the condenser from the last distillation run. Interpreting the last fractions can direct a lot of optimization. Could a lower distillation proof be justified by the lack of free volatile acids or objectionable character? Could a cut be pushed to a percentage point lower ABV based on a prediction of assets and liabilities? Or should it go in the opposite direction? Does a decadent amount of high value aroma justify a longer slower heating? If a ferment is trying to push boundaries harnessing free VA was it successfully limited in the distillate? A fermenter is in the nth iteration since a deep cleaning and liabilities are observed to be increasing, what rules of thumb for distillation can be adopted as activity by bacteria increases?
Flaws can be revealed in the fractions that are hard to detect within the sensory matrix, and corrective action needs to be taken. Most flaws are thought to be observed in fractions 6,7 and 8. Arroyo’s biggest flaw to remove was tufo from scorching yeast during distillation and his corrective action was the large investment in a centrifuge to separate yeast pre-distillation. Other flaws may be the character of substandard grain. Attempts at heavy rum often risk polluting a spirit with free volatile acidity that never becomes ester. Another flaw for a spirit intended for a long maturation in oak is excessive starting ethyl acetate because this will sufficiently accumulate over its time in wood. The opposite may be true of a spirit looking for maximum vitality while being unaged.
Since we are not always quantifying results, we are often observing what is normal, abnormal, or extraordinary. Often that is enough to make decisions. The most helpful thing to understand are the correlations between production parameters and congener formation. Have no fear is you do not know all the background. The birectifier can help a distiller ask more pointed questions of colleagues, consultants, and specialists. Fraction samples can also be shipped to support more pointed questions.
The ability to share experiencing the fractions and confront the character face to face can help build decision making buy in across team mates with varying degrees of experience. Putting a face to the name is a powerful opportunity in distillery science. Influencing many large distilleries is like turning a battleship and buy in becomes key. The teams at many large distilleries have shown interest in doing more organoleptic analysis because it is widely recognized there are blind spots to GCMS. There is no more effective way to build buy in than sharing the experience of birectifier fractions.
Exploring gin
Gin analysis may be the great value proposition for the birectifier. It clearly slices up the aroma of a gin into distinctive fractions that are easy to compare and project production correlations upon. Role models can be studies and product variations observed. Congener categories within aromatized products can be more harder to understand than fermented distilled spirits giving GCMS analysis a steep learning curve. Organoleptic analysis allows you to greet every congener face to face and clearly see where they are in the distilling run. Gin distillers take to these experience like a duck to water.
Fraction 1: When examining gins or single botanicals, excessive generic terpenes can accumulate here and louche upon dilution then separate over night. This can be a cause for concern and if significant separation is observed a gin might turn milky in a cocktail. Some role model gins exhibit slight clouding in this fraction. Role models can clearly teach what is normal and acceptable. Juniper aroma may appear here but almost like an incomplete slice of its aroma.
Fraction 2: A different tonally weightier slice of juniper aroma may be observed.
Fraction 3: Juniper aroma transitions to coriander and we see that their relationship in a gin as dominant botanicals may have something to do with their unique bands of volatility.
Fraction 4: This fraction becomes a wild card and some penetrating botanicals like cardamom may show up here. It may also exhibit a continuation of coriander aroma. Exploration may reveal that some auxiliary botanicals in a gin appear here versus fraction 5 and it would be useful to categorize that propensity. Sometimes, language will differentiate aromas that are penetrating versus persistent.
Fraction 5: The fifth fraction of a gin represents the majority of auxiliary botanicals. Character here may be more persistent than fraction 4’s penetrating character. Fixative aromas important to premium gins may also reside here. Chamomile has been observed in fraction 5. Concentration may be palatable. Sometimes a unique viscosity is observed.
Fraction 6: This fraction can either be extremely light in aroma and clean or exhibit a slight staleness. Single botanicals may demonstrate cooked or stewed character and a staleness that may be a liability during co-distillation.
Fractions 7 & 8 are not collected.
Gin and botanical mysteries are similar. It is far easier to put a name to face with congeners like esters, aldehydes, and higher alcohols. Terpenes and various components of essential oils are not so easy and it is even hard to say how quantitative data would help. Luckily, because we know where the aroma is observed, we know where to shift our focus during distillation. We can also reverse engineer role models attaching our own names to congeners. This kind of analysis feels like: “I don’t remember names, I remember face.” When we work this way, it is extremely beneficial to invest in studying commercial role models before analyzing your own spirits.
Exploring single botanicals
A structed look at single botanicals via birectifier fractions can be extremely beneficial. This can help with sourcing comparisons and understand what is volatile where so that formulations can be elaborated. The birectifier cannot quantify essential oil like a Clevenger apparatus, but to a strong & useful degree it can help reveal differences in the quantity of essential oil. Quantitative tasting with the exhaustive test can be a useful proxy for essential oil yield.
The birectifier quickly reveals qualitative differences among botanicals that competes with the most advanced, elaborate, and expensive analysis. Qualitative work can also reveal the overlap in characteristics among botanicals that may drive a deeper understanding of synergies and possible contrast enhancement strategies. Patterns that run through the fractions may even guide a distiller away from all in the pot co-distillation towards the blending of specialty optimized distillates to form a final product.
A lot can be said and you are near a frontier!