The influence of base wine composition and wood maturation on the quality of South African brandy

[摘要] ENGLISH ABSTRACT:Brandy production is a multi-step process that involves grape harvesting, base winefermentation, distillation, wood maturation and blending. Within each of these productionprocess steps there are a number of factors that can influence the composition andresultant quality of the base wine, unaged and wood matured distillates. These factorsinclude geographic and climatic features of the origin of grapes used, viticultural practices,grape maturity, grape variety, vintage variation, vinification techniques, storage of the basewine prior to distillation, distillation technique, age and origin of oak wood used formaturation and barrel toasting levels.The composition of flavour is extremely complex in wine and distilled beverages suchas brandy. A multitude of compounds can take part in the formation of flavour, and it israre that a particular compound, that is solely responsible for nuances of a specific flavour,is identified. Thus, taking brandy production factors and the nature of aroma and flavourinto account, it is clear that thorough understanding of the complexities affecting theperception of quality in brandy is difficult.In commercial brandy production, standard operating procedures do not allow for theseparate distillation of brandy base wines from different producers and mixing of basewines from different regions and producers thus occurs. This makes it difficult to determinewhether the quality determination of the base wine is in fact an indication of the quality ofthe resultant distillate after the required period of wood maturation. Therefore, the aim ofthis study is to determine whether there is any merit in storing and distilling brandy basewines from different producers and regions separately. This was done by firstlydetermining the demographic and production factors that influence brandy base winecomposition. Secondly, the influence of brandy base wine composition on the quality of therespective unaged potstill distillates as well as the ultimate style and quality of the threeyearold wood matured potstill distillates was determined.For this purpose, four potstills with a capacity of 2000 L each were isolated and usedfor commercial scale distillations of 33 and 25 brandy base wines in 1999 and 2000,respectively, at the DisteIl distillery in Worcester. The experimental outlay used in thestudy closely emulated Distell's standard operating procedures for commercial brandyproduction.Chenin blanc and Colombar are the two most popular grape varietals used in themaking of brandy base wine in South Africa. Due to the complexity of the brandyproduction process, the first part of the study only focussed on South African youngChenin blanc wines, with a predominantly fermentation derived aroma. The concentrationof iso-amyl acetate, hexyl acetate, ethyl caprylate, ethyl caprate, 2-phenethyl acetate andoctanoic acid was significantly higher in wines awarded gold and silver medals anddecreased significantly with subsequent decreases in quality categories. Ethyl lactateexhibited the opposite pattern. A quality predictor model based on the behaviour of 21volatile compounds quantified in these wines had a resonable prediction accuracy whenhaving to predict the quality of wines made in the same vintages as it had been trained on.It was significantly poorer when tested on a completely different vintage of wines to theones it had been trained on. The number of vintages, number of wines per vintage and thenumber of compounds quantified for the model influence its prediction accuracy.Twenty-seven volatile compounds were quantified in 33 and 25 brandy base wines,their unaged and three year old distillates from 1999 and 2000, respectively. ANOVA andCART analysis showed that vintage, region, harvest time, choice of cultivar and yeaststrain can have a significant influence on the volatile compound composition of brandybase wines, their unaged and three year old distillates. These factors as well as thevolatile compound composition were also found to influence the sensory quality of theseproducts. Base wines, unaged and three year old distillates originating from the De Doomsregion, which predominantly cultivates table grapes, were of significantly lower quality thanthose from the remaining regions. Products made from grapes harvested early in theseason were of significantly higher quality. The volatile aroma compound composition wasfound to differ significantly between the 1999 and 2000 base wines and distillates,irrespective of the exclusion of those samples that had undergone partial or completemalolactic fermentation. Consequently, quality indicating compounds may vary fromvintage to vintage. The relationship between the quality of brandy base wines and theconcentration of n-butanol, iso-amyl acetate, ethyl lactate, ethyl caprylate, octanoic- anddecanoic acid was the same as that reported in young Chen in blanc wines in this study. Inunaged distillates, increased levels of ethyl lactate also exert a negative influence ondistillate quality. Iso-amyl acetate, hexyl acetate, ethyl caproate, ethyl caprylate, n-butanol,octanoic acid, ethyl caprate and decanoic acid showed some positive correlation, whilstiso-butanol, ethyl lactate, acetic acid, acetaldehyde and ethyl acetate showed a significantnegative correlation to three-year old distillate quality.Sensory descriptive analysis on selected good, average and poor quality distillatesusing the South African brandy aroma wheel showed that there are small differences inprofile between the good and average distillates, there were however significantdifferences between the good and poor quality distillate profiles throughout maturation.After three years of wood maturation, the aroma profile of poor quality distillates can becharacterised by prominent herbaceous and woody aromas, which are more intense thanthe fruity aromas. Good quality distillates contained characteristically intense fruity aromas.Volatile compound concentration differences were noted during the course of and afterthree years of wood maturation and in barrels of varying ages. Distillates matured in newblock barrels exhibited significant differences in volatile and wood compound compositionafter three years when compared to remaining barrels used. The style classification of thethree-year old potstill distillate was influenced by demographic and production factors andvolatile compound composition, but not by the sensory quality of the distillates.In summary, vintage, region, cultivar, harvest time and choice of yeast strain have asignificant influence on the volatile composition of brandy base wines, their unaged andthree year old potstill distillates, which in turn affects the sensory quality of these products.These effects cannot be viewed in isolation as they jointly exert an influence on thecomposition and quality of these products. From a commercial perspective, this study hasprovided a valuable indication as to which production and demographic factors caninfluence the quality and style of potstill brandy. Thus, future brandy base wine intakeshould, as far as possible, take place in such a manner to allow base wines originatingfrom the same cultivar or region or harvest time or combination thereof (and to a lesserextent yeast strain) to be received simultaneously at the distillery for distillation.

[发布机构] Stellenbosch University