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Rootstock can significantly alter the concentration of methoxypyrazines (MPs) in the bunch stem (rachis) of Vitis vinifera L. cv. Cabernet Sauvignon and Shiraz, which has implications for winemaking and wine style. The distribution of MPs across the rachis is an important consideration, but such information was not available. This study aimed to address this research question by comparing MP concentrations in different rachis components throughout grape maturation and in the absence of ambient light. Shiraz and Cabernet Sauvignon bunches were sampled throughout development, segmented into four components (peduncle, top rachis, bottom rachis, and pedicel), and 3-isobutyl-2-methoxypyrazine (IBMP) was quantified in each. For both cultivars, IBMP showed a negative correlation with grape maturity, with concentrations in pedicel at harvest being significantly higher than other rachis components. Additionally, light exclusion significantly increased IBMP concentrations in all rachis segments. The concentration of IBMP varied significantly between different rachis components. The greatest concentrations were measured in the pedicel, which also contributed the largest proportion among the components to total rachis by weight. Due to elevated IBMP concentrations in rachis and the difficulties in excluding matter other than grape from a fermentor, the presence of pedicel during fermentation could produce Shiraz and Cabernet Sauvignon wines with higher concentrations of MPs, thereby potentially increasing vegetal sensory characteristics.

Ramsey rootstock has previously been implicated in an approximate 8-fold increase of 3-isobutyl-2-methoxypyrazine (IBMP) levels in the rachis (grape bunch stem) of

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.

Background and Aims The climate‐change driven uncoupling of grape (Vitis vinifera L.) berry ‘sugar‐ripeness’ and ‘flavour‐ripeness’ necessitates an improved understanding of the sugar/flavour nexus. Methods and Results Analysis of grape metabolites and wine volatiles derived from Riesling berries of peduncle‐girdled and Control bunches over the course of 30 days provided time‐dependent insights into changes to grape and wine composition associated with phloem import. Girdling resulted in stable berry mass and concentration of sugar and cytokinin and in reduced concentration of amino acids. Such changes to grape composition correlated with a lasting increase in wine monoterpenoids and a transient reduction in fermentation‐derived wine volatiles. Conclusions Oxidative stress and restricted amino acid import, not sugar accumulation, were identified as possible elicitors for the increased accumulation of varietal wine aroma compounds in Riesling. Significance of the Study The concentration and composition of berry amino acids and cytokinin concentration in grapes during the later stages of rapid sugar accumulation may represent potential targets for vineyard management strategies and grapevine breeding to counter climate‐change driven modifications to the wine volatile profile of aromatic cultivars.

Background and Aims Many variables affect the volatile profile of wine during production, and grape composition is an important source of varietal characters and metabolites for yeast during fermentation. In order to manage wine style through changes in grape composition, the knowledge of when important changes occur in the berries is essential. This study sought to identify stages of berry development that are most critical in defining wine volatile composition. Methods and Results Cabernet Sauvignon and Riesling grapes at several stages throughout development were fermented, after normalising sugar content, and the volatile compounds in the resulting wines were profiled. For both cultivars, the compounds were grouped into six clusters, which best described the changes in concentration of the volatile compounds in the wines. Some varietal compounds showed significant differences in wines made from berries at the various developmental stages; however, many fermentation-derived volatile compounds, especially esters, were also significantly affected by berry developmental stage. Conclusions Dynamic changes occur in the volatile profile of wines made from grapes at several stages of development, but a few common patterns of change are seen for several volatile compounds. Significance of the Study Several distinct phases of berry development associated with either an increasing or decreasing concentration of wine volatile compounds were identified, which will inform the timing of future strategies designed to alter wine composition through interventions in the vineyard.

In an investigation of objective measures that link grape composition to wine quality, this study sought to identify Cabernet Sauvignon grape parameters that predict the sensory properties of the corresponding wines. Eleven chemical measures comprising volatile and non-volatile compounds, enzyme activity plus standard industry harvest measurements were applied to grape samples obtained from different regions throughout South Eastern Australia over three vintages. Grapes underwent controlled vinification and the resulting wines evaluated with sensory descriptive analysis. The entire multi-vintage data sets were combined and modelled using a combination of partial least squares (PLS) and sequential and orthogonalised (SO) -PLS regression techniques. Optimal models were obtained with single sensory attributes rather than global modelling with the entire sensory profile. Five grape chemical measures, which in the main were harvest parameters, were used along with colour, total phenolics and tannin, targeted volatiles, and flavonols, and orthogonalised to model 14 sensory attributes of the Cabernet Sauvignon wines. The seven remaining measures were not used due to their poor ability to model wine sensory attributes, with enzyme activity and tannin by HPLC explaining the least. The study revealed new insights into the relationship between grape chemistry and wine sensory characters, which has implications for developing an objective measurement system for determining grape quality.

Wine is a complex consumer product produced predominately by the action of yeast upon grape juice musts. Model must systems have proven ideal for studies of the effects of fermentation conditions on the production of certain wine volatiles. To identify grape-derived precursors to acetate esters, model fermentation systems were developed by spiking precursors into model must at different concentrations. Solid-phase microextraction-gas chromatgraphy mass spectrometry analysis of the fermented wines showed that a variety of grape-derived aliphatic alcohols and aldehydes are precursors to acetate esters. The C6 compounds hexan-1-ol, hexenal, (E)-2-hexen-1-ol, and (E)-2-hexenal are all precursors to hexyl acetate, and octanol and benzyl alcohol are precursors to octyl acetate and benzyl acetate, respectively. In these cases, the postfermentation concentration of an acetate ester increased proportionally with the prefermentation concentration of the respective precursor in the model must. Determining viticultural or winemaking methods to alter the prefermentation concentration of precursor compounds or change the precursor-to-acetate ester ratio will have implications upon the final flavor and aroma of wines.

Preveraison treatment of Shiraz berries with either 1-naphthaleneacetic acid (NAA) or Ethrel delayed the onset of ripening and harvest. NAA was more effective than Ethrel, delaying harvest by 23 days, compared to 6 days for Ethrel. Sensory analysis of wines from NAA-treated fruit showed significant differences in 10 attributes, including higher "pepper" flavor and aroma compared to those of the control wines. A nontargeted analysis of headspace volatiles revealed modest differences between wines made from control and NAA- or Ethrel-treated berries. However, the concentration of rotundone, the metabolite responsible for the pepper character, was below the level of detection by solid phase microextraction-gas chromatography-mass spectrometry in control wines, low in Ethrel wines (2 ng/L), and much higher in NAA wines (29 ng/L). Thus, NAA, and to a lesser extent Ethrel, treatment of grapes during the preveraison period can delay ripening and enhance rotundone concentrations in Shiraz fruit, thereby enhancing wine "peppery" attributes.