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High acid dirty ferment #3 was not too remarkable, but raises a lot of questions and helps frame the process. It definitely had esters, but no so much rum oil. It also had a significant amount of free butyric acid and its hard to say if that would ever become ester through maturation.
One of the main concepts with this ferment was its low formol number which is a measure of nitrogen. At 168, it is considered near the minimum required to complete a ferment, but that rule of thumb is also for wines where the ABV can easily exceed 12%. However, in stressful conditions, it is advised to increase nitrogen further than normal. An open question is whether yeast-bacteria symbiosis is affected by nitrogen level. We may be looking for formol numbers as high as 300, but at levels higher than that we risk forming ethyl carbamate.
This ferment definitely gained in TA which is primarily attributed to activity by bacteria, but it is hard to say if any of that was volatile and therefore significant to the aroma. Soon, we are going to start adding volatile acid analysis (via the RD80 cash still) so hopefully we can get more insights on volatile acidity. This ferment had very little acetic acid added and that can easily be noticed in fraction 1.
Something else we need to learn more about is stimulating chain elongation. Fission yeast very likely can elongate butyric acid into a higher value acid of increased chain length. Chain elongation may prevent a ferment completing with excessive free butyric acid.
This ferment completed in roughly 17 days.
I got zero sense of quality during birectifier operation whereas others you can smell a fraction 5 developing from across the room.
Ferment #3
6/26 pH 4.31 TA 9.64 F#156 SG 1.086
6/27 Added 100 ml muck (to boost nitrogen) / 100 ml 4.5% vinegar
7/7 pH 4.18 TA 12.28 F#150 SG 1.030
7/13 pH 4.156 TA 13.36 F#168 SG 1.025 [TILT] SG 1.022 [liter volumetric flask] Surface is totally at rest
Fraction 1: Not overwhelming. A little bit of fruitiness and slight non culinary aromas. Not too powerful. This likely did not have a lot of acetic acid.
Fraction 2: Fairly light.
Fraction 3: Very neutral.
Fraction 4: Definite aroma of fusel oil, but fairly light. Some fraction 5 aroma can be detected.
Fraction 5: Full of estery aroma. Louched with small droplets on the surface, but it did not form an emulsion that settled to the surface. No strong or distinct rum oil aroma. Not acrid on the palate like other more concentrated fraction 5’s.
Fraction 6: Droplets on the surface. Free butyric acid. More like fraction 7,8 than like 5.
Fraction 7: Free butyric acid detected. Slight gustatory acidity and cheetos character. No off aroma besides butyric.
Fraction 8: Free butyric acid detected. Slight gustatory acidity and cheetos character.