Resumen de Distillation strategies: a key factor to obtain spirits with specific organoleptic characteristics
The design of distillation strategies to obtain spirits with specific aroma profiles remains a challenge for producers who use traditional methods (batch distillation). In the case of industrial distillation (continuous distillation), progress has been achieve in terms of separation and purification of volatile compounds, products which can later be diluted or mixed again. However, the legislation of most spirits tends to demand the use of traditional methods. Therefore, spirit industry requires the updating of traditional processes with more advanced technologies.
The main objective of this thesis has been to describe and optimize the distillation and evolution of the volatile compounds of young spirits during and after the process to obtain products with specific aromatic characteristics. This main objective has been divided into four partial objectives: i) to describe the effect of the controlled variation of the internal reflux of a batch column with a partial internal condenser (BCPC) on the distillation of the congeners; ii) develop and test a regression model for a BCPC system, to predict and optimize the process; iii) explore aroma interactions between volatile compounds of wine spirits to correlate their chemical concentration with sensory analysis; and iv) study the evolution of a bottled spirit during a year, to understand the effect of temperature, light and pH.
To carry out the subsequent studies, three types of distillation systems were used: a 50 L stainless steel BCPC with copper packed bed, a 20 L copper Alembic Charentais style, and a 2 L glass BCPC with copper packed bed. For the analysis of the composition of fermented beverages and their spirits, gas chromatography with a flame ionization detector (GC-FID) has been used. Sensory analyzes were carried out in a tasting room, both assessors training sessions and studies evaluations. Analysis of variance (ANOVA), response surface methodology (RSM), multi-objective optimization by desirability functions, principal component analysis (PCA) and artificial neural networks (ANN) were the methodologies used for data analysis.
The main conclusion of this thesis is that BCPC systems show a great capacity to produce clearly differentiated spirits from the same raw material, with marked chemical and organoleptic characteristics. This goal is achieved by establishing optimal distillation strategies. With regard to the operating conditions of the distillation process, a drastic reduction of the internal rectification after a high rectification during head fractions increases the levels of terpenic compounds, alcohols and esters (pleasant aromas) and decreases the levels of head compounds (unpleasant aromas) in heart fractions. On the other hand, low pH favors the decomposition of linalool and acetaldehyde to form α-terpineol and acetal, respectively, and favors the formation of ethyl esters by esterification. In addition, larger volumes of head fractions reduce head compounds at the expense of reducing C4-C10 ethyl esters and linalool, and increasing tail compounds. With regard to aroma interaction effects, ethyl hexanoate (fruity aroma) shows a sensory masking effect on linalool (flowery aroma) and ethyl acetate (glue-like aroma); acetaldehyde and ethyl acetate increase fruity perception at low levels of ethyl hexanoate; and high levels of ethyl acetate show a masking effect on the fruity descriptor at high levels of ethyl hexanoate. With regard to the storage conditions after distillation, low pH reduces the relevant compounds associated with fruity and terpenic aromas (ethyl esters and linalool) and pungent (acetaldehyde) for seven months; however, this effect is barely significant after one year. Furthermore, storing fruit spirits at high temperatures considerably reduces the concentration of most compounds.
Finally, the methodologies used in this doctoral thesis allow the evaluation and optimization of the production process of spirits in a systematic, simple and economical way. Hence, results can be useful and applicable to spirits industry.
