Peduncle-girdling of Shiraz (Vitis viniferaL.) bunches and sugar concentration at the time of girdling affect wine volatile compounds

Abstract

Background and Aims The climate change‐related acceleration of grape (Vitis vinifera L.) berry ‘sugar‐ripeness’ requires an improved understanding of the relationship between berry sugar concentration and wine flavour and aroma. Methods and Results Peduncle‐girdling of Shiraz bunches at three post‐veraison stages identified sugar‐related changes to grape metabolites associated with ripening and to wine volatile compounds. Restricting sugar uptake at 10–14°Brix had severe effects on the accumulation of eight amino acids, cytokinins and, by inference, the cellular redox status. Consequently, wine made from these berries displayed changes to a large number of compounds and compound classes, in particular esters, higher alcohols and C13‐norisoprenoids, which would potentially result in a substantial difference in wine flavour and aroma. When grapes reached 18°Brix, however, peduncle‐girdling caused only minor modification of berry amino acid concentration and wine volatile composition. By comparing wines made from berries of peduncle‐girdled bunches with those made from berries where ripening was delayed by auxin treatments, a small group of volatile compounds was identified that universally responds to treatments delaying sugar accumulation in grapes. Conclusions The findings suggest that once berries have reached a modest sugar concentration, prevention of further sugar uptake even by an invasive treatment, such as girdling, has minimal impact on wine volatile composition. Significance of the Study This study confirms that the manipulation of sugar accumulation can mitigate climate change‐related acceleration of sugar‐ripeness in warm to hot wine regions while maintaining the volatile composition of wine.

Post‐veraison restriction of phloem import into Riesling (Vitis viniferaL.) berries induces transient and stable changes to fermentation‐derived and varietal wine volatiles

“…Unlike the observed arrest in berry growth and sugar accumulation, YAN concentration halved in girdled Riesling berries over the course of the experiment, whereas the YAN decrease in Control berries was comparatively small (Table ). This result was different from girdled Shiraz berries of similar sugar content, where YAN concentration was not affected by girdling, due to severe shrivelling of the girdled Shiraz berries (Böttcher et al ).…”

“…The reduced accumulation of amino acids was an early effect of the girdling treatment, with all but two of the amino acids (glutamic acid and histidine) detected at significantly lower concentration in fruit from girdled bunches compared to Control fruit from 10 dpg onwards. This was a finding different to the girdling response in Shiraz berries, where out of the eight affected amino acids, four had an increased concentration in Girdle berries (Böttcher et al ). As discussed above for overall YAN, the different accumulation patterns of amino acids in girdled Shiraz and Riesling grapes might be explained by the lack of shrivelling in Riesling berries.…”

“…Phloem‐restriction of Shiraz berries at different post‐veraison stages has recently provided new insights into the dependency of wine volatile formation on sugars and other phloem‐transported compounds (Böttcher et al ). In order to better define berry developmental stages associated with wine volatile formation dependent on phloem‐influx, two Riesling berry populations, one with unhindered increase in sugar and other ripening‐related metabolites, the other with stable sugar content and restricted access to phloem compounds, were analysed for selected grape and wine compounds at several time points during the ripening phase.…”

“…Amino acids from powdered berry tissue (200 mg) were quantified as described by Boss et al (). Since proline (Pro) could not be reliably detected by this method at low concentration, this amino acid was measured according to the ninhydrin method of Rienth et al () with modifications as described by Böttcher et al ().…”

“…Restricting sugar import into grapes by peduncle‐girdling is another, more invasive way to uncouple sugar accumulation from the metabolism of compounds with relevance for wine sensory properties. This method was employed by Böttcher et al () on three stages of ripening Shiraz berries. While the girdling of bunches during early stages of ripening greatly altered grape composition and wine volatile profile, peduncle‐girdling at later ripening stages caused only minor modification of berry metabolites and wine volatiles.…”