Author: Constantin HeitkampPublisher:
ISBN: 9781321608861
Category :
Languages : en
Pages :
Book Description
Six different deficit irrigation regimes with four subsamples each were established in a commercial Cabernet Sauvignon vineyard (Dunnigan Hills AVA) in 2011. This study details the second and third vintage of the experiment (2012/13). Three treatments were maintained at constant leaf water potential targets, notably: a well-watered Control (CTL, -10 bars), the grower control (RHP, -13 bars) and a minimal irrigation (ED-, -14.5 bars). Two more "early deficit" treatments were switched at veraison, namely ED (-14.5/-11 bars) and ED+ (-14.5/>-10 bars). A "late" deficit featured stress exclusively post-veraison (-11/-14.5 bars). Differences in canopy development resulting from water availability were especially apparent in 2012, but the planned remote-sensing/canopy modeling by an academic cooperator did not deliver tangible results. Grapes were harvested when treatments reached a 24 Brix target and analyzed by our industry cooperator. Triplicate fermentations of each treatment were performed at the UC Davis Pilot Winery and resulting wines analyzed again as well as submitted to a full descriptive analysis sensory study. Seasonality presented an overriding effect, with 2012 expressing more extreme examples than 2013. Yields were reduced by up to 60% by deficit treatments in relation to their severity, but partially recovered with late season irrigation (ED+). As previously reported, the number of berries per cluster was a main contributing factor. Grape composition was affected primarily in its polyphenolic content, with increases in total tannin and non-tannin phenols of up to 20% with more extreme and more consistent deficits. ED+ effectively recovered overall yield, but did not significantly differ from the well-watered control with regards to composition. Moreover, ED+ exhibited slow late-season sugar accumulation paired with increasing pH-values. Pyrazines were only registered during the 2012 season and followed the well-documented pattern of number of buds/vine and early season canopy light environment, resulting in LD having the highest (49ppt) and ED+ having the absolute lowest values (18ppt). Wine compositions followed the composition observed in grape, with no apparent indications of extractability differences. Wine color presented the most apparent difference, with RHP, LD and ED- exhibiting greater intensity, but only LD showing a noticeably purple hue. Pyrazines were undetectable in wines. Descriptive Analysis training of 15 judges of diverse demographics produced 13 aroma- and 6 taste/mouthfeel attributes. When assessed by year, wines only differed significantly in astringency and "hot" mouthfeel (2012) or astringency and sour taste (2013), all of which clearly followed the concentrations established by the grape and wine analyses. When analyzing both vintages, a total of 9 attributes returned significant differences mostly driven by seasonality, thus insufficiently characterizing treatment effects other than astringency and alcohol. Future work, as currently already partially underway, should examine deficit irrigation effects across different cultivars while recording specific plant metabolomics measurements or whole-canopy modeling. The quantification of individual anthocyanin- and polyphenol-species may prove helpful in determining extraction and color stabilization patterns. Given the recurrently negligible effect of yield and berry size, viticultural decisions should increasingly be driven by economical considerations supplemented by judgmental winemaking decisions to achieve the desired product.