Birectifier Analysis Of A Full Bodied Rum Tails Fraction

This was a very exciting case study and illustrates quite a bit. The birectifier was used to examine the tails fraction of a full bodied rum distillate. The results support a lot of distillation concepts that are not too well understood by the new American industry. It would be great to see the art of making cuts go from being mystified to a little more structured and paint by numbers. Gentle forms of analysis like the birectifier are the way.

If you are fairly new to understanding cuts, it may help to read my primer: Advanced Cutting Basics. A big value proposition for the birectifier is helping you follow role models (look through my case studies) and nail your cuts so you are distilling at the peak potential of your fermentation. The sad truth is that many distillers are loading up warehouses full of pricey barrels of sloppily cut spirits. The birectifier method can turn that around pretty quick.


The big lesson and poorly understood concept is that the highest value congeners are less volatile than fusel oil. This means that distillation can only do so much and that quality is ultimately dictated by fermentation. If we reduce fusel oil in a ferment, we can distill at lower proofs, further into the run, and capture more high value congeners.

For the analysis, a charge was scaled to 100 ml of absolute alcohol. It was a little more than the 250 ml we usually load into the birectifier because the ABV was less than 40%, but everything went fine.

The first three fractions are incredibly neutral as we’d expect. This is the tails after all, so there is very little chance of low boiling point, low molecular weight congeners like ethyl acetate and acetaldehyde.

Very important to notice is that the 4th fraction of the tails has far less fusel oil than the hearts. This merely represents surplus fusel oil. The distiller maxed out what could be put in the final spirit and this was surplus. I actually also analyzed the hearts fraction and I think the cut was nailed pretty well regarding fusel oil content (I did however think too much heads were cut away). This fourth fraction will continue to accumulate each time the tails are recycled (I think this was the first iteration after a tails stripping run). It should be monitored (until intuition develops) and eventually processed to deal with the surplus (I give multiple ideas for that).

The fifth fraction here is absolutely wild. These fermentations are producing tons of gorgeous high value congeners and quite a bit is making it into the spirit, but quite a bit isn’t. If more of this could be pushed into the hearts, the value of the spirit would increase markedly. Fusel oil is the limiter.

But how do you do it? How can fusel oil be reduced? Nutrients can be optimized, also fermentation temp, yeast selection, and yeast pitching rate. Quite a lot can be done, but it may also require adding a few analysis skills to keep it all accurate. Distillation is paint by numbers, especially when you have a birectifier to follow role models. What you may need a consultant for is more challenging fermentation issues, like maintaining your high value congeners while reducing your fusel oil. You’ll get far more out of your consultant when you can point them to very specific issues and feel much better about the money spent.

One thing to note is that this tails fraction 5 contained a lot of soapy stuff not found in the fraction 5 of the hearts. They actually precipitated to form a ring around the tasting glass. It is not exactly fair to say all congeners are merely surplus, there likely are absolutely some things you may not want. Some of these soapy poorly soluble congeners may be normal in a new make and dealt with by filtration later.

The last three fractions show no fermentation faults or scorching problems during distillation that may produce off aromas. There was less noble volatile acidity than I would have thought for such an estery spirit, but there is still a lot I do not understand about the volatile acid congener category.

This new American distillery has quite a lot going for them, but after seeing their hearts and tails fraction via birectifier, we now very clearly know what to work on and how to give the spirit a more even congener profile.

This was all done with very little hard science. We simple sorted congeners, precisely cut the spirit up, and then evaluated the fractions. Each one tells a simple to understand actionable story.

Do you know what is in your tails? Are you maximizing the potential of your ferment by articulate distillation? The birectifier method is the most economical way to help.


Fraction 1: Very neutral, faint indescript character.

Fraction 2: Very neutral.

Fraction 3: Very neutral, faint fusel oil on palate.

Fraction 4: Detectable fusel oil, but nothing offensive. Less than what is in a complete beverage, but the recycling scheme is unknown.

Fraction 5: Very aromatic, a little confusing. A lot of persistence. Acrid, but not overwhelming on the palate. Acrid milkiness. Persistence. Noble aromas.

(A lot of that acridness is normal. It may come from trying to perceive longer chain esters without their shorter chain companions helping to support them. If you have long chain esters, but botched your heads cut and are too light on ethyl acetate, your spirit may be a little muted and flat.)

Fraction 6: Faint funk. Possible butyric acid character also found in hearts.

Fraction 7: Tailsy character, but not overwhelming. Detectable gustatory acidity.

Fraction 8: Tailsy character, but not overwhelming. Detectable gustatory acidity.

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