Jordi Ballester

Yeast–yeast interactions revealed by aromatic profile analysis of Sauvignon Blanc wine fermented by single or co-culture of non-Saccharomyces and Saccharomyces yeasts

There has been increasing interest in the use of selected non-Saccharomyces yeasts in co-culture with Saccharomyces cerevisiae. The main reason is that the multistarter fermentation process is thought to simulate indigenous fermentation, thus increasing wine aroma complexity while avoiding the risks linked to natural fermentation. However, multistarter fermentation is characterised by complex and largely unknown interactions between yeasts. Consequently the resulting wine quality is rather unpredictable. In order to better understand the interactions that take place between non-Saccharomyces and Saccharomyces yeasts during alcoholic fermentation, we analysed the volatile profiles of several mono-culture and co-cultures. Candida zemplinina, Torulaspora delbrueckii and Metschnikowia pulcherrima were used to conduct fermentations either in mono-culture or in co-culture with S. cerevisiae. Up to 48 volatile compounds belonging to different chemical families were quantified. For the first time, we show that C. zemplinina is a strong producer of terpenes and lactones. We demonstrate by means of multivariate analysis that different interactions exist between the co-cultures studied. We observed a synergistic effect on aromatic compound production when M. pulcherrima was in co-culture with S. cerevisiae. However a negative interaction was observed between C. zemplinina and S. cerevisiae, which resulted in a decrease in terpene and lactone content. These interactions are independent of biomass production. The aromatic profiles of T. delbrueckii and S. cerevisiae in mono-culture and in co-culture are very close, and are biomass-dependent, reflecting a neutral interaction. This study reveals that a whole family of compounds could be altered by such interactions. These results suggest that the entire metabolic pathway is affected by these interactions.

Study of the effect of H2S, MeSH and DMS on the sensory profile of wine model solutions by Rate-All-That-Apply (RATA)

The effect of hydrogen sulfide (H2S), methanethiol (MeSH) and dimethyl sulfide (DMS) on the odor properties of three wine models-WM- (young white, young red and oaked red wines) was studied. Wine models were built by mixing a pool of common wine volatile and non-volatile compounds and further spiked with eight different combinations of the three sulfur compounds present at two levels (level 0: 0μgL-1 and level 1: 40μgL-1 of H2S, 12μgL-1 of MeSH; 55μgL-1 of DMS). For each wine matrix eight WMs were produced and further submitted to sensory description by Rate-All-That-Apply (RATA) method. Hydrogen sulfide and methanethiol were clearly involved in the formation of reductive aromas and shared the ability to act as strong suppressors of fruity and floral attributes. Specifically, hydrogen sulfide generated aromas of rotten eggs, while methanethiol generated significant increases in camembert and decreases in citrus, smoky/roasted and oxidation aromas. The simultaneous presence of hydrogen sulfide and methanethiol enhanced the intensity of the unspecific term reduction, while the specific nuances individually imparted by each of the two compounds could not be further identified. DMS did not exert any outstanding effect on the reductive character of wines and its sensory effect was matrix-dependent. It was involved in the formation of fruity notes such as cooked/candied and red/black fruits in young wines, and vegetal notes (canned vegetables) in oaked red WMs.

Sensory and chemical drivers of wine minerality aroma: An application to Chablis wines

The goal of this work was to evaluate the effect of vineyard position on the minerality of wines and to establish relationships between minerality scores, sensory descriptors and chemical composition. Sensory analyses included minerality rating and free description performed by wine professionals under two conditions: orthonasal olfaction alone and global tasting. Chemical characterization included analysis of major and minor volatile compounds, volatile sulphur compounds, mercaptans, metals, anions and cations. Results showed a significant effect of the river bank on wine minerality scores only in the orthonasal olfaction condition, samples from the left being more mineral than those from the right bank. Methanethiol, involved in shellfish aroma, was significantly higher in wines from the left (more mineral) than from the right bank. Contrary, copper levels, related to lower levels of free MeSH, and norisoprenoids, responsible for white fruit and floral aromas, were higher in wines from the right bank (less mineral).

The perceptual categorisation of blended and single malt Scotch whiskies

BackgroundAlthough most Scotch whisky is blended from different casks, a firm distinction exists in the minds of consumers and in the marketing of Scotch between single malts and blended whiskies. Consumers are offered cultural, geographical and production reasons to treat Scotch whiskies as falling into the categories of blends and single malts. There are differences in the composition, method of distillation and origin of the two kinds of bottled spirits. But does this category distinction correspond to a perceptual difference detectable by whisky drinkers? Do experts and novices show differences in their perceptual sensitivities to the distinction between blends and single malts?To test the sensory basis of this distinction, we conducted a series of blind tasting experiments in three countries with different levels of familiarity with the blends versus single malts distinction (the UK, the USA and France). In each country, expert and novice participants had to perform a free sorting task on nine whiskies (four blends, four single malts, one single grain, plus one repeat) first by olfaction, then by tasting.ResultsOverall, no reliable perceptual distinction was revealed in the tasting condition between blends and single malts by experts or novices when asked to group whiskies according to their similarities and differences. There was nonetheless a clear effect of expertise, with experts showing a more reliable classification of the repeat sample. French experts came closest to a making a distinction between blends and single malts in the olfactory condition, which might be explained by a lack of familiarity with blends. Interestingly, the similarity between the blends and some of their ingredient single malts explained more of participants’ groupings than the dichotomy between blends and single malts.ConclusionsThe firmly established making and marketing distinction between blends and single malts corresponds to no broad perceptually salient difference for whisky tasters, whether experts or novices. The present study indicates that successfully blended whiskies have their own distinctive and recognizable profiles, taking their place in a common similarity space, with groupings that can reflect their component parts.

Impact of glutathione on wines oxidative stability: a combined sensory and metabolomic study

This paper is a comprehensive study regarding the role of glutathione as a natural antioxidant on white wines aging potential. It includes sensory and ultrahigh resolution mass spectrometry (FTICR-MS) metabolomics of aged chardonnay wines from 2008 to 2009 vintages, made after glutathione spiking at alcoholic fermentation or bottling. The closure effect was also considered. The sensory analysis revealed a clear vintage, closure and glutathione effect on wines oxidative character after several years of bottle aging. Spearman rank correlation was applied to link the sensory analysis and the exact mass information from FT-ICR-MS. FTICR–MS along with multivariate statistical analyses put in evidence that glutathione efficiency against wines sensory oxidative stability is related to wines antioxidant metabolome consisting of N- and S- containing compounds like amino acids, aromatic compounds and peptides. The chemical composition and origin of wines antioxidant metabolome suggests that its management since the very beginning of the vinification process is a key factor to estimate wines aging potential.