GRAPE SPIRITS FOR PORT WINE PRODUCTION: SCREENING THEIR AROMA PROFILE

Abstract

Port is a fortified wine, produced from grapes grown in the demarcated Douro region. The fortification process consists in the addition of a grape spirit (77% v/v) to the fermenting juice for fermentation interruption, resulting in remaining residual sugars in the wine and increased alcohol content (19-22%). The approval of grape spirits follows the Appellation (D.O. Port wine) rules1 and it is currently carried out based on analytical control and on sensory evaluation done by the public Institute that upholds the control of the quality of Douro Appellation wines. However, the producers of Port wines would like to have more information about quality markers of grape spirits. Thus, this work intends to characterize the aroma profile of several samples (23) of grape spirits for Port wine production. That characterization was done by using aroma descriptive analysis with a sensory panel and by using olfactometry (GC-O) in order to screen, with a sniffers panel, the most potent odorant compounds across the several volatile compounds of the samples. It was also determined the sensory thresholds of some of the identified compounds in order to determine the odorant activity value of each compound.

The aroma profile results revealed different grape spirits aroma profiles. The PCA applied to the average results (from a sensory panel) of aroma attributes intensities allows the separation of the samples across the two principal components, which explain more than 50% of the variability. The overall quality appears to be linked to the positive side of component 1 more associated with the fruity, floral and sweet odor notes. The samples with low quality are placed in the opposite side of this component, and linked to higher intensity of odour notes such as tails, herbaceous and oily.

The chromatographic analysis (GC-O and GC-MS) of several grape spirit samples pointed out as potent odorants several compounds that belong to different chemical families, namely esters, alcohols, terpenic compounds, acids and ketones. Based on the sensory thresholds, determined by the sensory panel in hydroalcoholic solutions (20% v/v), the odorant activity values were calculated for the different odorant compounds. The obtained results showed, that the compounds, which presented the higher odorant activity values were esters and terpenic group compounds.