Five 1999 varietal Douro table wines (Touriga Nacional, Touriga Francesa, Tinta Roriz, Tinto Cão, Tinta Amarela/Tinta Barroca mixed), one aguardente and five model Ports (aguardente fortified table wines) were quantified for 15 compounds by GC-MS using selected characteristic ions. Although aguardente constitutes around one fifth of the volume of Port, it was found to be the major contributor of numerous compounds including: ethyl hexanoate (81 to 90%); ethyl octanoate (94 to 98%); ethyl decanoate (98 to 99%); benzaldehyde (87 to 94%); a-terpineol (76 to 91%); linalool (58 to 91%); ethyl hydrocinnamate (100%). Aguardente volatiles make an essential contribution to young Port aroma, adding fruity, balsamic and spicy aroma complexity.
2,6,6-Trimethylcyclohex-2-ene-1,4-dione (TMCHD), a norisoprenoid with a sweet honey aroma descriptor, is reported for the first time as a minor constituent of single-varietal table and fortified wines from the demarcated Douro region. Olfactory gas chromatography (GC-O) of a volatile wine extract, previously isolated by preparative gas chromatography, indicated the presence of a zone containing an intense honey descriptor. The targeted odor compound was identified by GC-MS, GC-O, and Kovats index. Quantitative analysis using a selected characteristic ion (m/z 96) indicated that young Douro fortified wines from the 1997 vintage contained up to 4 microg/L TMCHD. The sweet honey sensory threshold limit for TMCHD in a model Port wine solution was found to be 25 microg/L. TMCHD is therefore only likely to contribute as a collective element to Port wine aroma. The wine volatile diacetyl was identified as a strong contributor to the sweet caramel aroma descriptor often associated with Port.
In winemaking, non-Saccharomyces yeast species contribute important organoleptic complexity. Current interest focuses on abundant and dominant strains characteristically present in the early phase of spontaneous alcoholic fermentations. Non-Saccharomyces species are particularly relevant in Port wine production such that the fermentation is prematurely stopped, after the metabolism of only one half of the available sugar, through fortification with aguardente. This work aimed to isolate, identify and characterize non-Saccharomyces species present in spontaneously fermenting Port. To accomplish these goals, yeasts were isolated from a selection of frozen must samples (2012–2016 harvests), using a pre-screening process choosing only the best candidates based on the organoleptic quality of the corresponding fortified wine. From five hundred non-Saccharomyces isolates, twelve species were identified. The three most abundant species, Hanseniaspora uvarum, Lachancea thermotolerans, and Metschnikowia pulcherrima, representing 89% of the isolates, exhibited particularly high diversity with high growth performance variability when exposed to typical stress conditions associated with common enological parameters. Less abundant species included Issatchenkia orientalis, Torulaspora delbrueckii, Hanseniaspora vineae, Hanseniaspora osmophila, Candida zemplinina, Rhodotorula mucilaginosa, Hanseniaspora guilliermondii, Issatchenkia occidentalis, and Zygosaccharomyces bisporus. This is the first study providing insights into the identification and characterization of non-Saccharomyces species responsible for spontaneous Port wine production.
1,3-Dimethoxybenzene was identified by GC-O, GC-MS and Kovats indices (polar Supelcowax, 1709; non-polar Rtx-5MS, 1158) as a new volatile component of port wine. Sensory evaluation described this compound as having a sweet medicinal odour with hazelnut, resinous and woody notes. Respective threshold limits in model wine and port wine were 21 and 47 mg l À1 . Quantitative analysis by GC-MS, using a selected characteristic ion (m/z 138), indicated that young port wines from the 1998 vintage contained up to 3 mg l À1 whereas ports from the 1999 vintage contained up to 20 mg l À1 .
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