INFLUENCE OF VARIOUS PRESSING TREATMENTS ON THE QUALITY OF PINOT GRIS WINES

T. Steiner, J. Gallander and E. Firth The Ohio State University/OARDC Wooster, OH 44691

In recent years, whole-cluster pressing has become a popular vinification step in California among other top viticutural areas around the world for the purpose of improving white wine quality. Producers indicate that this technique minimizes maceration and provides more efficient extraction. Also, juices are lower in phenols, solids, pH values and have higher total acidity and better color. Winemakers generally consider wines from whole-cluster pressing more delicate and fruity. The objective of this study was to determine the effect of different pressing techniques including whole-cluster pressing on the quality of P. Gris wines.

MATERIALS AND METHODS

Pinot Gris grapes for this study have been harvested from the experimental vineyards of OSU/OARDC in Wooster each harvest year since 2001. After overnight storage at 35oF, the fruit for each season was exposed to the following treatments: 1) whole clusters were placed in a Willmes press, and the juice was extracted at 4-bars for 20 min. After releasing the pressure, the must was rotated for 2 min. and pressed again at the same pressure and time, and the extracted juice was treated with 50 ppm SO2; 2) light pressing was conducted on crushed grapes (treated with 50 ppm SO2) at 4-bars for 5 min. (Willmes press). After releasing the pressure and rotating for 2 min, the pressing procedure was repeated, and the extracted juice was treated with 50 ppm SO2; 3) heavy pressing was conducted as the extraction procedure for light pressing, but the pressing time was increased to 20 min. Again, the juice was treated with 50 ppm SO2. For the 2002, 2003 and 2004 seasons another treatment was added, 4) free run juice was collected from crushed grapes (treated with 50 ppm SO2) in a Willmes press during a 20 min. period.

After clarifying with a pectic enzyme (CinnFree), the clear juice was ameliorated with sugar to 22oBrix. the juices were analyzed for pH, total acidity, oBrix, and solids. The juice from each treatment was divided (triplicated), treated with DAP (3 g/gal), inoculated with o CY3079 yeast and fermented at 65 F. After additional racking and SO2 treatments (during a 6- month period), the wines were bottled and analyzed for pH, total acidity, volatile acidity, alcohol and total phenolics. The 2001 and 2002 wines were evaluated by a sensory panel consisting of 10 and 21 member panel respectively for aroma and taste. The 2003 wines were unfortunately tainted with the Lady Asian Beetle defect therefore were not evaluated on a sensory basis. The 2004 pressing fraction study has not been evaluated by a sensory panel at the present time.

RESULTS

The results of the must analyses indicated that juice from whole cluster pressing was generally lowest in pH and highest in total acidity. The whole cluster pressing also had

i significantly less solids then any of the other three pressing fractions for each harvest year (Table 1).

For the wines, there were generally only slight differences obtained for chemical constituents among the treatments (Table 2). Wines from whole cluster pressing were highest in total acidity and tended to be lowest in pH for all seasons. However, more significant differences are shown through the concentration of total phenolics. The whole cluster pressing in each season had the lowest concentration of total phenolics in comparison to the other three pressing fractions.

The 2001 results of the sensory evaluation indicated the judges preferred wines from whole cluster and light pressing. No differences in aroma and taste were obtained in comparison of these two treatments. The 2002 sensory evaluation showed similar data with the whole cluster and light pressing fractions preferred over the heavy and free run in all attributes. In addition, the sensory panel indicated the whole cluster pressing fraction most pleasing for all attributes in comparison to the light pressing treatment.

CONCLUSIONS

Preliminary data shows whole cluster pressed Pinot Gris grapes tend to have a lower must pH and higher acidity. The percent of juice insoluble solids are also considerably lower in whole cluster pressed grapes then any other pressing fraction studied. The amount of insoluble solids appears to be a major factor effecting the expression of Pinot Gris varietal aroma and flavor in this study. Examining the two extremes, the whole cluster pressed fraction described of having high fruit aroma and flavor intensity through sensory panel comments, contains considerably less insoluble solids then any of the other pressing fractions. In contrast, the free run pressing fraction contained the highest amount of insoluble solids, and was least preferred both years of sensory panel ratings. This may be attributed to the higher molecular weight solids masking varietal fruit expression in the production of higher alcohols in addition to other off byproducts.

Wines made from whole cluster pressed grapes also retain a higher acidity leading to a more crisp wine. This fits into the popularity of “Pinot Grigio” style wines which typically have higher acidities. In addition to a higher wine acid content, whole cluster pressed grapes also have the lowest concentration of total phenolics.. The lower concentrations of total phenolics in wines made from the whole cluster pressing fraction expressed more fruit forward aromas and flavors onto the palate as opposed to more of a harsh or bitter flavor profile as indicated in some sensory comments referring to the heavy and free run pressing fractions containing higher concentrations of total phenolics.

Sensory panel data for the year 2001 indicates that both the whole cluster and light pressing fraction was preferred over the Heavy or free run press fractions. The 2002 sensory data indicates a clear preference for the whole cluster pressed Pinot Gris for all sensory attributes evaluated. In both years, the free run fraction was chosen as having the lowest quality.

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Table 1. Effect of four pressing treatments on the must composition of Pinot Gris for 4 seasons, 2001-04.

Totalx Pressing acidity Solidsy treatment pH g/100 ml oBrix % (v/v)

2001

Whole Cluster 3.16 0.77 20.1 9.9

Light 3.23 0.71 20.9 14.5

Heavy 3.27 0.73 20.3 18.8

2002

Free Run 3.24 0.54 19.3 29.6

Whole Cluster 3.23 0.59 19.7 12.9

Light 3.26 0.57 19.9 20.0

Heavy 3.27 0.57 19.1 19.4

2003

Free Run 3.12 0.81 19.4 26.6

Whole Cluster 3.21 0.80 19.9 11.4

Light 3.21 0.78 19.8 16.5

Heavy 3.21 0.75 19.8 18.4

2004

Free Run 3.21 0.78 20.6 24.0

Whole Cluster 3.26 0.80 20.1 10.0

Light 3.24 0.75 21.1 16.0

Heavy 3.26 0.74 20.4 14.0 xTotal acidity as g tartaric acid per 100 ml.

iii yVolume of solids after settling for 14 hrs at 32oF.

Table 2. Effect of four pressing treatments on the wine composition of Pinot Gris for 4 seasons, 2001-04.

Totalz Pressing Alcohol Volatiley phenolics treatment pH TAx % (v/v) acidity mg/L

2001

Whole Cluster 3.07 0.87 13.7 0.04 165

Light 3.12 0.83 13.6 0.04 205

Heavy 3.02 0.82 13.6 0.03 185

2002

Free Run 2.96 0.63 12.9 0.04 245

Whole Cluster 2.96 0.67 13.0 0.04 236

Light 2.95 0.65 13.1 0.03 247

Heavy 3.00 0.65 13.2 0.04 244

2003

Free Run 3.22 0.84 13.5 0.04 183

Whole Cluster 3.18 0.88 13.6 0.04 170

Light 3.22 0.82 13.5 0.04 198

Heavy 3.21 0.79 13.7 0.04 187

2004

Free Run 3.19 0.82 12.5 0.05 236

Whole Cluster 3.21 0.83 12.7 0.05 197

Light 3.18 0.80 12.6 0.05 206

Heavy 3.27 0.77 12.7 0.04 213 xTotal acidity as g tartaric acid per 100 ml. yVolatile acidity as g acetic acid per 100 ml. zTotal phenolics as gallic acid, mg/L.

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