Differentiation and characterization of Spanish fortified wines with protected designation of origin based on volatiles using multivariate approaches

Mint aromas in wine, which manifest as “cool” or “fresh” character, can originate from different chemical classes, one of which is the terpenoids. A broadly diverse, naturally occurring class of chemical compounds, terpenes possess wide applications across multiple industries due to their pharmaceutical, antiseptic, medical, and aromatic properties. Monoterpenes, a subclass of terpenoids, likewise play a major role in wine sensory perception. Within the monoterpenes, those possessing “mint” odor qualities have often been studied in the context of “vegetal” or “herbal” wine faults; however, their role in positive aromatic evolution is less understood. Yet an extensive 2015 study of older premium Bordeaux red wines identified mint as a contributing factor in quality bouquet development. From that point, it was necessary to investigate the origins of those monoterpenes as well as the chemical conditions required for their development during ageing. Those two key points could finally facilitate predicting the apparition of minty character in older wines based on their composition while young.
A principal contributor is the cyclic monoterpene limonene, which was isolated relatively early in grapes and wine. Not only does limonene itself possess a cool, fresh odor, it is also a precursor for, and possible derivative of, additional mint monoterpenes. Among the most commonly found monoterpenes, limonene and its derivatives can constitute the majority of the essential oils of citrus fruits, mint and herb plants, and coniferous trees. Many of these mint monoterpenes also occur in grapes and wine. With aromas ranging from woody and earthy to citrus to mint and herbaceous, their contribution to wine is potentially diverse and multi-faceted. While sometimes, found at concentrations below the sensory threshold, synergistic effects between these molecules could render them perceivable.
This review looks at limonene and its transformation as studied in different matrices, and potential parallels or analogues in wine. Moreover, within the complex kinetics of wine aging, the relative concentrations of mint monoterpenes appears to continue to evolve and change, with additional evidence from model wine solutions suggesting they may even revert to their originating precursors. Continued study of mint monoterpenes and their role in wine aromatics will contribute to a deeper understanding of the development of aging bouquet and the longevity of premium wines.

Volatile sulfur compounds (VSCs), mainly hydrogen sulfide and methanethiol (H2S and MeSH), are the responsible for reductive off-odor in wine.

Barrel ageing is a transformative process that alters a wine’s organoleptic properties and consequently its price. Even though it is considered beneficial mostly for red wines, ageing can also be used for white wines but for shorter time periods. Due to barrel costs, space requirements and the markets’ demands for fast release of each new vintage, new products such as oak chips or shavings have been developed to help minimize the time needed for the extraction of essential wood compounds.

The objective of the present work is to assess yeast effects on the development of wine varietal aroma throughout aging and on wine longevity.

Three independent experiments were carried out; two fermenting semi-synthetic musts fortified with polyphenols and aroma precursors extracted from Tempranillo (1) or Albariño (2) grapes and with synthetic precursors of polyfunctional mercaptans (PFMs), and a third in which a must, mixture of 6 different grape varieties was used. In all cases, fermentations were carried out by different Saccharomyces cerevisiae strains and one S. kudriavzevii, and the obtained wines were further submitted to anoxic accelerated aging to reproduce bottle aging. The volatile profile of the wines was analyzed using several chromatographic procedures, in order to provide a comprehensive evaluation of wine aroma. Aroma compounds analyzed included fermentation volatile metabolites, grape-derived aroma compounds including PFMs, and Strecker aldehydes (SA).

Results revealed that the effects of yeast on wine aroma throughout its self-life extend along three main axes:

1. A direct or indirect action on primary varietal aroma and on its evolution during wine
aging.

2. The direct production of SA during fermentation and/or their delayed formation by producing the required reagents (amino acids + dicarbonyls) for Strecker degradation
during anoxic aging.

3. Producing acids (leucidic, branched acids) precursors to fruity esters. More specifically, and leaving aside the infrequent de novo formation, the action of the different strains of yeast on primary varietal aroma takes four different forms:

1.- Speeding the hydrolysis of aroma precursors, which leads to early aroma formation without changing the amount of aroma formed. In the case of labile molecules, such as linalool, the enhancement of young wine aroma implies a short-living wine. 2.- Metabolizing the aroma precursor, reducing the amounts of aroma formed, which can be of advantage for negative aroma compounds, such as TDN or guaiacol; 3.- Transforming grape components into aroma precursors, increasing the amounts of aroma formed, as for ethyl cinnamate, leucidic acid or vinylphenols; 4.- Forming reactive species such as vinylphenols able to destroy varietal polyfunctional mercaptans.

Overall, it can be concluded that the yeast carrying alcoholic fermentation not only influences fermentative wine aroma but also affects to the wine varietal aroma, to its evolution during aging and to the development of oxidative off-odors

Aroma diversity is one of the most important features in the expression of the varietal and geographic identity and sensory uniqueness of a wine. Italy has one of the largest ampelographic heritages of the world, with more than five hundred different varieties. Among them, many are used for the production of dry still white wines, many classified as Protected Designation of Origins and therefore produced in specific geographical areas with well-defined grape varieties. Chemical and sensory characteristics of the aroma of these wines have never been systematically studied, and the relative diversity has never been described and classified.