I would like to thank friend of the blog, Haresfur, for donating this sample!
Bundaberg is quite the fascinating rum. I really don’t know how I feel about it, but it is distinct in the rum world. My first experience a few years ago was drinking a nip from the 1970’s acquired as part of a collection. After that, I discovered the research of D.A. Allen who isolated rum oil from the fusel oil fraction of Bundaberg’s continuous still and identified the carotene derived compound TDN which is also responsible for the petrol aroma of reisling wines.
TDN (trimethyldihydronaphthalenes) and/or its cousin, TTN (trimethyltetrahydronaphthalenes), is not the ionone, damascone or damascenone of the rum oil we’ve been pursueing, but the French did group them together in 1975.
My research partner recently sent me a rum fermented with brettanomyces under careful conditions that had the aroma of Bundaberg on steroids. I described its fraction 5 as such:
Fraction 5: Abundant rum oil with little droplets all over the surface. Very penetrating aroma. Not exactly estery, no acrid taste on palate. Almost a very focused peanuty oiliness on the palate, something I have never experienced before. Now there is almost a distinct camphorous menthe on the palate. I almost feel like I encountered vix vapor rub. Detectable gustatory acidity. Possibly a very unique surface tension that is creating legs all over the glass. How intense this is makes it hard to taste anything else and it should probably be evaluated last.
I have not done adequate reading on brettanomyces, but Cory describes it as very important to the future of rum and being intensely studied by the Brazilians for both fuel ethanol production and cachaça. We think of brett as a spoilage organism in wine and a curiosity in beer, but it may have features of its metabolism that can be targeted to generate both incredible efficiency for ethanol production as well as high value aroma.
I am hesitant to call rum oil related aromas like TDN and TNN high value. There is something that draws you in for a time, but that allure is fleeting, and in appreciable concentrations, almost fatiguing. They no doubt have a role as blending stocks. Another rum that may feature these aromas is Tanduay from the Philippines.
Victoria Green’s 2015 thesis, The microbial ecology of a rum production process, takes a very in depth look at Bundaberg and there is nothing to suggest these aromas comes from brettanoymces. We are merely noticing aromas that are possible and likely derived from carotene.
Total acidity: 40.093 mg/100 ml absolute alcohol.
Fixed acidity: 2.665 mg/100 ml absolute alcohol.
Volatile acidity: 37.428 mg/100 ml absolute alcohol.
Esters via titration: (coming soon!)
Fraction 1: Concentrated and non-culinary but not in the typical way. Not exactly fruity. Kind of light.
Fraction 2: Very light and close to neutral for a fraction 2.
Fraction 3: Very neutral as expected.
Fraction 4: Definite presence of fusel oil, but nothing out of the ordinary.
Fraction 5: Fascinating character. Estery aroma and something like rum oil. Flickers of menthiness. Not overwhelmingly concentrated. Similar character to what I experienced in a 1970’s sample. Could this be the TDN or TNN found by D.A. Allen?
Fraction 6: Faint character similar to fraction 5. No obvious gustatory acidity.
Fraction 7: Fairly neutral. No obvious gustatory acidity.
Fraction 8: Fairly neutral. No obvious gustatory acidity.
Stillage: Titratable acidity (I may have erred measuring this because I intended to find very little acidity. It appears to have very little volatile acidity as seen in fraction’s 7,8, but a significant fixed acidity. Fixed acidity comes from time in barrel and either barrel extractives or from other liquids that may have rested in the barrel. Barrels can only contribute so much and beyond that there can be either elegance or an odd set of breast implants on a scrawny rum. Historically, fruit juices were even added to rum to contribute fixed acids. These acids can be delicious and even put pressure on the volatile acid / ester equilibrium. I’m all for acid games, but for the most part this is the realm of commodity rum and not fine rum. I’m not accusing Bundaberg of anything but merely introducing the topic as we collect more data and learn more.