An investigation of vine water status as a major factor in the quality of Merlot wine produced in terraced and non-terraced vineyards in the Vipava Valley, Slovenia

Terraced vineyards are cultural landscapes with a special value. The increase in costs and the lack of professional workers make viticulture on terraces difficult to be maintained. Thus, in the face of climate change and production challenges, we aimed to study the impact of slope-wise cultivation on wine quality. The quality of Merlot wines from terraced and slightly lower non-terraced vineyards within a small area characterised by similar mesoclimatic features was compared in the seasons 2019 and 2020. The non-terraced and terraced vineyards differed in both soil profile and morphology. The number of buds, number of clusters, and leaf area were standardised, and the stem water potential (SWP) was measured during wine-growing seasons. Upon reaching maturity, grapes were hand-picked on the same day in all vineyards and microvinified. The wines were analysed chemically and sensorially. In both years, the SWP showed higher water stress in the vines from terraces. The yield, berry weight, and leaf area were lower on terraced than on non-terraced vineyards in both years, and the skin- and seed-to-flesh ratios were higher. The darker seed colour pointed to the advanced ripening on terraces, where the wines had a higher alcohol concentration and a higher total dry extract. The wines from terraces had higher concentrations of total polyphenols, anthocyanins, and proanthocyanidins (PAs) than the wines from non-terraced vineyards in both years, and the PAs in the wines from terraces in 2019 had fewer prodelphinidins and were more galloylated. Higher concentrations of higher alcohols and lower concentrations of esters and methoxypyrazines were found in the wines from terraces. The sensory analysis revealed a preference for wines from terraces with better colour intensity, fruitiness, astringency, midpalate, and overall quality. Under experimental conditions (the same harvest date, standardised viticultural variables), the wines from terraces had both better phenolic potential and better sensory quality than the wines from non-terraced vineyards.