How pressing techniques affect must composition and wine quality of Pinot blanc

Abstract

This study investigates how the sensory profile of Pinot Blanc is affected from different maceration and pressing techniques. Grapes were sourced from four vineyards in the village Tramin in South Tyrol. For the experiment 200 kg of grapes from each vineyard site were hand picked the day before harvest for the commercial winery took place. Grapes were stored over night at 4°C, homogenized and processed in the experimental winery at Laimburg research centre the day after harvest. Four different pressing techniques were applied in duplicates of 100kg each. Treatments were composed as follows: (1) “classic”, pre-installed press program with 120 minutes and crumbling after each pressure step, (2) “cremant”, gentle and sequential press program with 180 minutes and fewer crumbling steps (3) “maceration” consisted of a 120 minutes cold soak followed by a very quick press program of 30 minutes and (4) “long pressing” consisted of a two hours maceration during the press program once the free run juice was drained. To track the evolution and extraction kinetics of pH, total acidity, tartaric acid, malic acid, total polyphenols and catechins, juice samples were taken after each cycle and analyzed right away in the laboratory. At approximately 150 kPa pressure the must is divided in fraction one and fraction two what corresponds to the press-wine. Two experimental wines are made out of each batch of grapes: one contains only must from the first fraction, and the other is a combination of fraction one and two in the original proportion. Sensory evaluation took place 6 and 18 months after harvest. Chemical must composition depends on the processing technique in the winery. Total acidity, pH, malic acid and polyphenol content of the must are affected from the chosen press program. Nonetheless the absolute content of the chemical components is different for the different pressing techniques; the trend of the extraction of these must components remains more or less the same during the pressing procedure. An exception was potassium, which showed a different behaviour in the “cremant” press-program. The different pressing techniques had an impact on the sensory profile of the wines. In the aroma profile, wines from the maceration treatment were marked best; whereas for the mouth-feel parameters the control wines achieved slightly better marks. Wines pressed with the “cremant” program were described as less complex, thinner and more acidity driven. Wines from treatment “long pressing” were reductive, less fruity ending up with a low overall quality. Two hours maceration followed by quick pressing showed interesting results. This might be a promising option to save press-capacity and to process more fruit in the short period of harvest. Further, for overall wine quality it was beneficial to use the entire must; wines made without the press-fraction are described as too light, not as complex and not as typical.