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Hops stored at room temperature for an extended period are commonly referred to as ‘aged hops’. Degradation of alpha and beta acids occurs during ageing, so the ageing process is accompanied by a significant increase in the concentration of branched-chain fatty acids (BCFAs): isobutyric acid (IBA), isovaleric acid (IVA), and 2-methylbutyric acid (2MBA). These three compounds, having rancid, cheesy, and/or sweaty flavours, are regarded as “off-flavours”. It was previously reported that BCFAs contained at their threshold levels could enhance the flavour intensity of monoterpene alcohols (linalool, geraniol, and β-citronellol; LGC) and change their aroma profiles. In this study, the behaviours of BCFAs during a 12-months ageing process were compared using five Japanese hop varieties. All BCFAs in the hops increased in all varieties during the total ageing period and a drastic increase was especially observed from 9 to 12 months. The content of linalool gradually decreased but plateaued at relatively high levels. In thiol-containing hops, 3-sulfanyl-4-methylpentan-1-ol (3S4MP) decreased drastically from 6 to 12 months, whereas 4-methyl-4-sulfanylpentan-2-one (4MSP) gradually decreased but was plateaued at relatively high levels. Next, to investigate the sensory effect of aged hops on aroma and taste profile of beer, model beers spiked with several combinations of monoterpene alcohols (LGC), 4MSP, and each BCFA were prepared. As a result, BCFAs commonly enhanced the characteristics of fruity, fullness, and maturity in the model beer spiking LGC. BCFAs also more enhanced the characteristics of tropical in coexistence with 4MSP. The sensory effect of BCFAs was expected to enhance hop-derived flavour of beer brewed with both geraniol-rich hops and 4MSP-rich hops. However, the sensory tests also showed an increase in rancid characteristics due to the presence of BCFAs. Therefore, test beers were brewed using fresh and aged 4MSP-rich hops. As a result, although the negative characteristics of rancid gradually increased depending on the dosage of aged hops, the positive characteristics of fruity, tropical, fullness, and maturity increased by mixing only 0.1 g/L of aged hops. [ABSTRACT FROM AUTHOR]

Sauvignon blanc grape samples (n = 21) from across a single Geographical Indication of South Australia were analysed for thiol precursors and amino acids, and fermented in an identical laboratory-scale fermentation trial to investigate the intraregional pattern of varietal thiols in the wines. Precursors and thiols exhibited obvious intraregional diversity, and notably, stronger correlations were observed between a number of amino acids and thiol precursors (especially with glutamic acid, r ≤ −0.73) rather than free thiols. Additionally, pre-fermentation freezing (−20 °C, 1 month) was applied to five selected fresh grape samples and their juices, followed by identical fermentation. In comparison to wines from fresh grapes or frozen juices, significant elevation of varietal thiols (up to 10-fold) occurred in the wines derived from frozen grapes, with parallel increases of precursors (up to 19-fold) in juices from frozen berries. These novel results may lead to new strategies for thiol enhancement during winemaking. [ABSTRACT FROM AUTHOR]

Background: Volatile thiols largely contribute to the organoleptic characteristics and typicity of Sauvignon blanc wines. Among this family of odorous compounds, 3-sulfanylhexan-1-ol (3SH) and 4-methyl-4-sulfanylpentan-2-one (4MSP) have a major impact on wine flavor. These thiols are formed during alcoholic fermentation by the yeast from odorless, non-volatile precursors found in the berries and the must. The present study investigates the effects of vine nitrogen (N) status on 3SH and 4MSP content in Sauvignon blanc wine and on the glutathionylated and cysteinylated precursors of 3SH (Glut-3SH and Cys-3SH) in the berries and the must. This is paralleled by a RNA-seq analysis of gene expression in the berries. The impact of N supply on the expression of the glutathione-S-transferase 3 and 4 (VviGST3 and VviGST4) and the γ-glutamyltranspeptidase (VviGGT), considered as key genes in their biosynthesis, was also evaluated. Results: N supply (N100 treatment) increased the 3SH content in wine while no effect was noticed on 4MSP level. Furthermore, N supply increased Glut-3SH levels in grape berries at late berry ripening stages, and this effect was highly significant in must at harvest. No significant effect of N addition was noticed on Cys-3SH concentration. The transcript abundance of the glutathione-S-transferases VviGST3 and VviGST4 and the γ-glutamyltranspeptidase (VviGGT), were similar between the control and the N100 treatment. New candidate genes which might be implicated in the biosynthetic pathway of 3SH precursors were identified by whole transcriptome shotgun sequencing (RNA-seq). Conclusions: High vine N status has a positive effect on 3SH content in wine through an increase of Glut-3SH levels in grape berries and must. Candidate GSTs and glutathione-S-conjugates type transporters involved in this stimulation were identified by RNA-seq analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive volatile thiol mapping in Italian white wines was presented. • Müller Thurgau wines were rich in volatile thiols, especially 4-MSP. • Sensory analysis confirmed the Müller Thurgau thiolic nuances provided by 4-MSP. • Among 18 white cultivars, Lugana, Müller Thurgau and few other wines were thiolic. • The 3-SH/3-SHA ratio modulated the citrus/grapefruit and tropical odors. Thanks to their low odor detection thresholds, free varietal thiols (VTs) play a key role in the primary aroma of wines, to which they confer an intense scent reminiscent of box tree, grapefruit, citrus fruits, passionfruit and cat urine odor. Excluding wines from a few VT-rich grapevine cultivars, VTs appear to be present in most cultivars at trace levels, although a comprehensive dataset is still missing. The low concentration of VTs combined with their high reactivity and matrix complexity make their determination in wines a challenging task. In this research an optimized liquid chromatography – tandem mass spectrometry (LC-MS/MS) method was validated and used for the quantification of 4-methyl-4-sulfanylpentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH), 3-sulfanylhexyl acetate (3-SHA) and ethyl 3-sulfanylpropionate (E3SP) in 246 samples (vintage 2019) representative of 18 monovarietal Italian white wines. VTs were detected in all cultivars even though higher values of 3-SH were found in Lugana, Müller-Thurgau and Verdicchio cultivars. Müller-Thurgau wines showed the highest level of 4-MSP, that was mainly correlated to the odor descriptors of passionfruit and box tree/cat urine. The VTs composition of Müller-Thurgau was confirmed on a second set of 50 wines from different vintages. From a sensory perspective, the samples of Müller-Thurgau showed the best positive correlations between chemical variables and the odor descriptors thiol note, passion fruit and box tree/cat urine. These notes are significantly related to 4-MSP, suggesting that it could play a relevant olfactory role for the aroma of Müller-Thurgau wines. Sorting analysis allowed to group these wines according to their thiolic characteristics. The chemical variables and the odor descriptors attributable to the thiol notes are important for Müller-Thurgau and Lugana wines, while the contribution of thiol notes was sensorially negligible for the other wines. [ABSTRACT FROM AUTHOR]

A stable isotope dilution assay was developed for quantitation of 4-methyl-4-sulfanylpentan-2-one (4MSP) in hops. The approach included the use of 4-( 13 C)methyl-4-sulfanyl(1,3,5- 13 C 3 )pentan-2-one as internal standard, selective isolation of hop thiols by mercurated agarose, and GC×GC-TOFMS analysis. Application of the method to 53 different hop samples revealed 4MSP concentrations between <1 and 114 μg/kg. Notably high concentrations were associated with United States varieties such as Citra, Eureka, Simcoe, and Apollo, whereas 4MSP was absent from traditional German and English varieties. Further experiments showed that besides the variety, also harvest year and storage vitally influenced 4MSP concentrations, whereas the impact of provenance was less pronounced. Hop processing such as drying and pelletizing had only a minor impact on 4MSP concentrations. Like the majority of other hop volatiles, 4MSP is predominantly located in the lupulin glands.