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Two exciting experimental rums from Callum Upfold in New Zealand crossed me desk so I decided to evaluate them head to head with the birectifier. Both are unaged, pure culture, S. Pombe, fission yeast rums derived from molasses. The first saw a 7 day ferment which maintained a fermentation pH above 5.0. This was distilled to 67% and we could also say it is in the style of Arroyo.
The second saw a longer 10 day molasses ferment and it also saw some muck. This was distilled to 68% ABV. I’m not sure it featured dunder, but I suspect that is the case. This best resembles high acid Jamaica style ferments.
These are both very heavy spirits you would clearly consider estery, but each in their own unique way. Because of their power, my favorite way to enjoy them was blending them down with other lighter rums.
Something these rums bring up is a notion of body in spirits. Many new tasters are finding that fission yeast rums can have superior aroma, but be noticeably different in a sense of body. What some tasters may be observing is that fission yeast rums are below average fusel oil producers and even though fusel oils are ordinary congeners, often existing in surplus (and cut out of the hearts), they do have a sensory impact. The concept of body is also multi factorial and maturation will also fill it out as cask extractives make their mark and ethyl acetate increases. Arroyo described his spirits as having a suavity and that may have been a template for beauty with a different sense of body in a new make spirit; light on its feet. Arroyo intentionally engineered his rum to be low in ethyl acetate and fusel oil. When they went into the cask, his experiments described maturation happening faster. Arroyo also had more radiance from damascenone. There is still a ton to learn about how heavier spirits of various structures mature as well as other impacts like blending fission yeast rums with budding yeasts to get all the fusel oil one could desire.
The high acid Jamaica style rum was very clearly much higher in ethyl acetate than the high pH rum. The question would become whether those generic esters were backed up by higher value esters in the later fractions. Despite very different fermentation styles, both rums had below average fusel oil which is a hallmark of fission yeasts. Both spirits had particularly powerful 5th fractions but no obvious rum oil from damascenone. All the character seemed to be driven by esters. The high acid spirit did however, have a character that created radiance in the fifth fraction, but it wasn’t so obvious, just something you could feel in comparison. This hint of radiance, however, carried over into unique character in the 6th fraction where there was a Bundaberg-menthe character which is quite possibly TDN (think petrol in reisling). The rums differed markedly in the last three fractions with the high pH spirit seeing very little volatile acidity while the high acid spirit had easily detectable volatile acidity. The high acid spirit did feature muck, but there was no obvious free butyric acid.
If we were lucky, we’d be filling barrels with as much of these two spirits as we could get. I encountered incredible notes when organoleptically evaluating these that I wanted to lift right out and put directly into a blend!
High pH Fraction 1: Not overly concentrated. Slightly generically fruity, no non-culinary aromas.
High Acid Fraction 1: Fairly concentrated to the point of non-culinary gluey aroma. No obvious fruitiness. No obvious formate.
High pH Fraction 2: Very clean. Not much aroma carried over from fraction 1. Fairly neutral.
High Acid Fraction 2: Slight fruitiness from ethyl acetate. Not as concentrated as I expected.
High pH Fraction 3: Very neutral as expected.
High Acid Fraction 3: Very neutral.
High pH Fraction 4: Below average fusel oil associated with a fission yeast. Slight bleed through of radiant fraction 5 aroma.
High Acid Fraction 4: Below average fusel oil associated with a fission yeast. Slight bleed through of estery fraction 5 aroma.
High pH Fraction 5: Beautiful estery aroma with no obvious rum oil character. Visually louched and aromatically powerful. Not as acrid as I expected on the palate. No obvious gustatory acidity.
High Acid Fraction 5: Beautifully estery. No obvious rum oil character but somehow a radiance that seems to lift the aroma relative to the high pH fraction 5. No obvious Bundaberg-menthe. Visually louched and aromatically powerful. Not as acrid on the palate as I expected but a point more than the high pH sample.
High pH Fraction 6: No significant gustatory acidity, but with a lingering ester character and slight persistence.
High Acid Fraction 6: Notable gustatory acidity, Bundaberg-menthe like character associated with a form of rum oil.
High pH Fraction 7: No significant gustatory acidity, but with a lingering ester character and slight persistence.
High Acid Fraction 7: Notable gustatory acidity. Slight estery aroma and animalic rum oil aroma.
High pH Fraction 8: No significant gustatory acidity, but with a lingering ester character and slight persistence.
High Acid Fraction 8: Notable gustatory acidity. Slight estery aroma and animalic rum oil aroma.