Rum is produced by the fermentation of sugar cane juice, syrup or molasses, followed by distillation and then aging in oak barrels. Rum is a highly diverse distilled spirit because it has a somewhat simple standard of identity, with the only requirement being that it must be produced from sugar cane or its byproducts. The lack of regulation allows for manufacturers to pick and choose from a variety of manufacturing practices when they are creating their rum. Rum cannot only be made from different types of starting materials but variation exists in type of yeast and bacteria used for fermentation, length of fermentation, distillation apparatus used, barrel type and length of maturation. In today’s drink and bar culture, rum is experiencing a resurgence. High quality rums, typically those aged at least five years and regarded as best of their class, are being compared with fine spirits, such as Bourbon, Brandy, Cognac and Scotch. Therefore, the goal of the study was to better understand the complex flavor chemistry of rum, including its aroma composition and the effect of ethanol on flavor perception, with a main focus on premium aged rums. Nine rums were evaluated consisting of two mixing rums (Bacardi Superior [BW], Bacardi Gold [BG]) and seven premium rums (Appleton Estate V/X [AE], Appleton Estate Extra [AE12], Ron Abuelo: Añejo 7 years [RA7], Diplomatica Reserva Exclusiva [DR12], El Dorado 12 year old [ED12], Ron Zacapa (Centenario) XO: Solera Gran Reserva Especial [RZ], Dictador XO Insolent [DX]). Identification of the odor-active compounds in the nine rums by gas chromatography-olfactometry (GCO) and GC-mass spectrometry (GC-MS) analysis yielded 59 odor-active regions containing 64 odor-active compounds. Aroma extract dilution analysis (AEDA) provided a ranking of the potency of odorants. The most potent rum ordorants, although not necessasarily present in every rum, were found to be acetal (melon), 2-/3-methyl-1-butanol (chocolate), β-damascenone (applesauce), 2-phenethyl alcohol (roses), cis-whiskey lactone/4-methylguaiacol (sweet, coconut-like), eugenol (spicy, clove), sotolon (curry, maple-like), syringol (smoky, spicy), (E)-isoeugenol (floral, clove), vanillin (vanilla, sweet-like), ethyl vanillate (vanilla, sweet-like), and syringaldehyde (vanilla). Thirty-four of the compounds identified by GCO and AEDA were quantitated by stable isotope dilution analysis. Differences among the samples included the absence of 4-ethylguaiacol and eugenol in BW and the presence of ethyl vanillin in only DR12 and DX. The mixing rums and DX were found to have the lowest concentrations of all compounds quantitated in the rums. The quantitation results were converted to odor activity values (OAVs) to gain a better understanding of the importance of the compounds to the overall aroma of the rum. Twenty-six compounds were found to have OAVs >1 in at least one rum. Fifteen compounds had OAVs >1 in all nine samples including 2-methylpropanal, acetal, 3-methylbutanal, 2-methylbutanal, ethyl 2-methylpropanoate, ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, 3-methyl-1-butanol, 2-methyl-1-butanol, ethyl hexanoate, β-damascenone, guaiacol, cis-whiskey lactone and vanillin. In order to characterize the sensory differences among rum products a rum flavor lexicon was created through the use of web-based material. This is the first lexicon to be created for rum as well as the first to use web-based materials for the lexicon development. The final lexicon consisted of 147 terms sorted into 22 categories. Descriptive sensory analysis was then conducted to verify the rum flavor lexicon and to quantitate the sensory differences among nine rums previously evaluated by analytical measures. Thirty-three of the 38 terms used to evaluate the rums were found on the flavor wheel, validating that the lexicon contained terms relevant to the sensory evaluation of rums. Twenty-three sensory attributes were found to be significantly different among rums. Two rums, DX and DR12, were characterized by having higher intensity ratings for brown sugar, caramel, vanilla and chocolate aroma, caramel, maple and vanilla aroma-by-mouth, and caramel aftertaste compared to the other seven rums. Sensory profiles of the other seven rums were similar to oneanother. Descriptive analysis was also conducted to gain insight into the effect of ethanol on flavor perception. Two rums, RA7 and DR12, were evaluated at three different dilution levels: straight rum, 1:2 dilution with water, and a 1:2 dilution with 40%ABV. Dilutions of rum with water, while hypothesized to alter the flavor profile of rum, yielded similar profiles to straight rum, except with slightly lower attribute intensity ratings. However, dilution with 40% ethanol did significantly change the profile of rum and also had the lowest intensity rating in the dilution series for most attributes. Finally, chemometric analysis was conducted to correlate the sensory and analytical data using principal component analysis consisting of quantitation, OAV and flavor dilution factor data. Correlations between sensory evaluations with either quantitation or OAV data explained the most variation among rums, accounting for 68.6% or 65.5%, respectively. Results indicate the changes in vanilla, caramel, maple and chocolate aromas are driven by vanillin and ethyl vanillin. Additionally, roasted aroma is defined by an absence of compounds rather than increases in concertation of any specific aroma compounds. Overall, the main differences between mixing and premium rums is the concentrations of compounds, with mixing rums having lower concentrations of all compounds. Differences in concentration and ratios of compounds relative to each other seem to be the driving forces behind the difference in flavor perception among rums. These findings help to better characterize rum as a category and articulate the differences that exist among rum categories. Sensory evaluation of rum provides insight into how rums are perceived by the human senses and the developed flavor lexicon will aid in communication between all levels of rum production and consumers.
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Understanding the complex aroma chemistry of premium aged rums
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