Loretta Panero

Influence of Submerged-Cap Vinification on Polyphenolic Composition and Volatile Compounds of Barbera Wines

This study compared floating-cap and submerged-cap vinification techniques for making wine from the Barbera cultivar. The submerged-cap method led to less extraction of phenolics during fermentative maceration than the floating-cap method. After soft pressing (0.5 bars), both the press wine and the marcs had higher total anthocyanin concentrations with submerged cap than with floating cap (+68.6% and +79.8%, respectively). No differences were observed between two submerged-cap trials with different pumping-over cycles during fermentative maceration. Despite the lower extraction of anthocyanins and tannins, at racking off the submerged-cap wines had significantly higher concentrations of total anthocyanins and total flavonoids than the floating-cap wines. The higher losses of total anthocyanins in the floating-cap wines were likely partly due to the greater importance of the enzymatic oxidation reactions in the cap, but especially to the more important precipitations of potassium bitartrate, enhanced by the higher extraction of potassium from the skins during fermentative maceration. The submerged-cap wines were also richer in tannins. The differences between the trials became statistically significant only after the union of the free-run wine with the press wine. For total anthocyanins, tannins, and color, these differences remained significant during the first year of aging.

Comparison of the physicochemical and volatile composition of wine fractions obtained by two different dealcoholization techniques.

Three wines (a Rosé wine, a Pelaverga and a Barbera red wines) were dealcoholized at 5% v/v ethanol with two different techniques: membrane contactor (MC) and distillation under vacuum (D). The influence of the treatments on the physicochemical composition and aromatic profile of the dealcoholized fractions was investigated. The main difference between the two techniques was the concentration grade reached by the dealcoholized fractions, which was 5-6times higher with D than with MC due to the concomitant loss of water. The main fixed compounds (organic acids, cations, polyphenols, anthocyanins) were not lost during the dealcoholization, while the losses of volatile compounds were relevant. Finally, the δ18O isotopic ratio was studied. The δ18O isotope ratio increased with D and decreased with MC. At the same time the δ18O isotope ratio fell within legal limits when the final ethanol content was adjusted to 2% by blending with dealcoholized fractions.

Use of polyaspartate as inhibitor of tartaric precipitations in wines.

All additives used to stabilize wines against the precipitations of potassium bitartrate have some limits: metatartaric acid (MTA) is effective but very unstable, carboxymethylcellulose is stable and effective in white wines but affects color stability in red wines, mannoproteins have a variable effectiveness depending on wine composition. This work was aimed at testing the effect of new stabilizing products on tartaric precipitations, focusing on the use of Na and K polyaspartate salts (PASPs). The effectiveness of 4 different PASPs and 1 MTA added to red and white wines was compared using the mini-contact test and cold test. The dose effect and the stability of the products over time were also studied. The PASPs showed a similar stabilizing effect and a longer stability over time compared to MTA. PASPs can be considered interesting as additives for wine tartaric stabilization. Further work is in progress to better characterize their enological properties.

Influence of early seeds removal on the physicochemical, polyphenolic, aromatic and sensory characteristics of red wines from Gaglioppo cv .

The technique of seeds removal during the fermentative maceration was conceived to limit the extraction of polyphenols from the seeds in order to reduce the natural wine astringency. The influence of this oenological practice on the polyphenolic composition of Gaglioppo wines was studied during three vintages (2010–2012): the wines produced in the presence (WS) or absence (WOS) of seeds were compared for the physicochemical, polyphenolic and volatile composition, as well as for the sensory characteristics. Seeds removal did not cause any important modification in the general physicochemical composition of wines. Regarding polyphenols, no differences in total anthocyanins content were observed between the trials, but a significantly lower total polyphenols content was observed in the WOS wines, regarding in particular total flavonoids, low molecular weight flavans and condensed tannins. Qualitative variations in the composition of condensed tannins were also observed: the WOS wines had a higher mean degree of polymerization (mDP) and a lower galloylation degree. Finally, minor differences in the aromatic profile due to the seeds removal technique were observed between the trials. Despite the important modifications of the polyphenolic composition, the sensory characteristics of the wines, on the whole, were not affected: a significant decrease of the bitter taste in the WOS trial was noticed only in vintage 2010.

Effect of Reductive Pressing on the Concentration of Reduced Glutathione and Phenols in the Musts of Four Italian Cultivars

This research investigated the effect of pressing under air or nitrogen on the color and concentration of reduced glutathione (GSH), hydroxycinnamoyl tartaric acids (HCTA) and polyphenols in the musts of four Italian white grape cultivars: Arneis, Cortese, Moscato bianco, and Manzoni bianco. Grapes from different locations were pressed using a prototype press (500 kg capacity) under the same operating conditions as a commercial winery. The musts of the four cultivars were significantly different from one another. The trend of the measured GSH concentration in the musts was: Moscato bianco < Cortese < Manzoni bianco < Arneis, without any significant interactions between cultivar and year. The intake of oxygen during pressing in air caused large decreases in GSH concentration, yet its complete exhaustion was only observed in a few trials. When present, the residual GSH was proportional to the values observed in the respective trials pressed under nitrogen. The contact with air during pressing also lowered the amounts of total polyphenols and catechins. The loss of catechins did not depend on the composition of HCTA, GSH, and HCTA/GSH in musts, while color browning was influenced by the HCTA/GSH molar ratio. The color intensity of musts (A420) increased exponentially with the decrease in GSH: A420 values higher than 0.2 AU were observed for GSH concentrations less than 8 μM.

Validation of a rapid conductimetric test for the measurement of wine tartaric stability.

This work was aimed at optimizing a rapid and reproducible conductivity test for the evaluation of wine tartaric stability, in order to improve the practices for the prevention of tartaric precipitations during bottle aging. The test consists in measuring the drop of conductivity in wines kept under stirring for a fixed time, at low temperature, after the addition of micronized potassium bitartrate crystals (KHT). An experimental design was planned to study three factors affecting the test: temperature, duration and dose of added potassium bitartrate. A standard protocol was defined to produce a micronized potassium bitartrate starting from available commercial products, since the dimensions of the crystals can affect the final conductivity values. After the choice of the best conditions the method was validated. Two different stability thresholds were defined for white wines and for red/rosé wines by comparing the results of the mini-contact test with those of the cold test.