Relationships between berry sensory assessment and wine quality in Vitis vinifera L. Shiraz

Abstract

Berry sensory assessment (BSA) is a technique that can help grapegrowers and winemakers make decisions about harvest date and grape product allocation. BSA as a structured technique has been used by grapegrowers, winemakers and researchers for the last thirteen years. However the number of studies reporting results of the effect of viticultural practices on berry sensory characteristics and wine quality is limited. This thesis examined the BSA technique through four different studies. Study one is a combined review literature review and industry survey paper in which the methodology of Berry Sensory Assessment is presented and the research conducted using BSA is discussed. It also presents the results of a survey channeled to Australian grapegrowers and Australian and New Zealand winemakers about their experience using BSA, their perceptions on its use and their suggestions for improving the methodology. It was evident from the survey that 90% of grapegrowers and winemakers use BSA and they want to understand the link between BSA and wine quality. These results demonstrated the importance of BSA for wine producers and the need for further improvement. The aim of study number two was to determine if berry sensory attributes and berry compositional variables could predict wine sensory attributes, wine compositional variables and wine quality in Shiraz. The analyses of berry and wine sensory attributes, compositional measures and wine quality using partial least squares regression and Pearson’s correlations from two seasons identified several relationships between berry sensory attributes and wine sensory attributes and quality. A significant negative relationship was identified between seed bitterness and wine savoury spice flavour for the two seasons. The berry sensory attribute pulp detachment from the skin was identified as a predictor of various wine sensory attributes (eg. the harder to detach skin from the pulp the higher intensity for wine body colour, rim colour and dark berry aroma) and wine quality scores in the season 2011. The aim of study number three was to determine if berries stored at -20°C for three months could be used instead of fresh berries to conduct BSA. Being able to conduct BSA on frozen berries could help to reduce sensory fatigue in assessors by allowing them to evaluate samples over a longer time period and to schedule BSA away from the busy harvest period. The results of this study determined that sensory profile from Shiraz berries differed in five sensory attributes – pulp sweetness, pulp fresh fig flavour, skin colour extraction, skin bitterness and seed astringency - between fresh and frozen berries at three times of harvest, preventing the evaluation of these five sensory attributes in Shiraz frozen berries. Study number four aimed to determine the effect of three rootstocks on sensory and compositional differences of Shiraz grapes and wines in comparison to a nongrafted control. The trial was conducted over two seasons. Berry and wine sensory and compositional differences were found between the grafted treatments and the nongrafted control. PCA was able to discriminate the wines from the four treatments in three groups of aroma compounds (acetate esters, ethyl esters and higher alcohols) in both seasons. The results of wine quality scores from two seasons showed that the un-grafted treatment had the lowest quality and 110 Richter and Schwarzmann the highest. The findings from this study identified relationships between the sensory and compositional variables in berries and wines that are affecting wine quality. It also showed that that the use of rootstocks has an impact on berry and wine sensory and compositional characteristics.