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I don’t know if it is safe to call this a control experiment because the purpose was a little different. It became a control for a high acid ferment with fission yeast but no major bacterial presence. I started by asking the question: what does the pH look like of a ferment that has a TA of 15 g/L with 1/3 of that being volatile? 15 g/L is generally thought to be the beginning of grand arôme territory which has been reported to stretch all the way to 30 g/L. The answer was much different than expected. I really thought the pH may be in the 3’s, but instead it was still in the very low 4’s. Hampden conducts ferments in the 3’s so they must have TA’s well beyond 15 g/L.
As a comparison, a winery ferment can have 1/3 the TA of our ferment but have a pH in the 3’s because the acids are stronger. If budding yeasts can easily ferment in the 3’s, pH is not a concept that will help ensure fission yeast dominance. We need to look at TA as well as the ratio of fixed to volatile acids. Good thing I’ve been exploring titration!
The next question was will it even ferment? This ferment featured light dunder from a budding yeast ferment and very significant amounts of added lactic acid to get the TA to climb to 10 g/L. From there, vinegar was added to bring the TA from 10 to 15 g/L. The ferment was then pitched with a fission yeast starter. It certainly fermented and the duration was nearly a month.
The fractions are interesting. Something to note right away is the below average fusel oil in fraction 4 followed by droplets on the surface of the fifth fraction. Droplets are thought to be bauer oil which is composed of esters who acids come from the cells of dead yeasts. This ferment was centrifuged after fermentation was complete so could these droplets be attributed to something else or was a month long enough for the ferment to absorb acids from long dead yeast? I did not predict I would be observing any droplets.
A big curiosity is where did all that vinegar go? It cannot all become the ethyl acetate observed in the first two fractions. Shouldn’t there be easily discernible free acetic acid in the last fractions? One theory is that high acid ferments which typically also featured mixed bacteria under go chain elongation where short chain acids are elongated into longer (better smelling) forms. Bacteria is best known for this and lactic acid may be transformed into propionic or butyric acid, possibly even longer forms. This ferment likely saw no chain elongation by bacteria. However, fission yeast are also thought to be capable of chain elongation. This ferment may reveal what fission yeasts can do, and it may be with acetic acid in particular which explains all the vinegar used by distilleries like Hampden. As a speculative theory, the droplets observed and the general high ester content of fraction five may primarily be the product of yeast facilitated chain elongation by a fission yeast. Acetic acid goes in and something much higher value comes out.
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Fraction 1: Concentrated to the point of non-culinary aromas. No discernible fruitiness.
Fraction 2: Fairly neutral for a fraction 2 with a concentrated fraction 1, but I have observed this before.
Fraction 3: Very neutral
Fraction 4: Noticeable fusel oil, but I think its safe to call it a below average amount.
Fraction 5: Crystal clear despite a definite ester presence. Droplets on the surface. Possibly the faintest rum oil character. Nothing acrid on the palate.
Fraction 6: Slight gustatory acidity. Otherwise, fairly neutral.
Fraction 7: Slight gustatory acidity. Otherwise, fairly neutral.
Fraction 8: Slight gustatory acidity. Otherwise, fairly neutral.