• WSU Horticulture and Landscape Architecture
• WSU Mount Vernon NWREC

Annual Report 2002

Evaluation of Wine Grape Cultivars and Selections for a Cool Maritime Climate

G.A. Moulton, J. King, L.J. Price, R.S. Darland and T.R. Bronkema
 

Introduction

Previous wine grape trials at WSU - Mount Vernon starting in the in the mid 1970s provided essential information to commercial wine grape producers in western Washington. Some of the best white grape varieties in this trial, such as 'Siegerrebe,' 'Madeleine Angevine' and 'Muller-Thurgau,' have already proven successful in area vineyards. In 2000 a variety trial was re-established consisting of recently introduced varieties, selections, and clones, including some previously unavailable material from certain areas of eastern Europe with similar climate conditions. The primary focus of this trial is red wine varieties, to broaden the range and increase the sales potential for the local wineries. In addition, the trial will test the effect of selected rootstocks on topworked Pinot Noir 2A to advance fruit maturity. Rootstocks may expand the range of areas where high quality red wine such as Pinot Noir can be produced.
 

Methods

Thetwo trial sites are located at Mount Vernon research station and at a vineyard near Everson, WA. The range of cumulative heat units in western Washington varies by location from 1400 to 2300, and the site at the Mount Vernon station is at the cool end of the scale (1600 annual heat units). The second site near Everson reaches the higher range of about 2000 annual heat units, at an elevation of 250' elevation on a southwest slope. Vines in both the varietal plot and the rootstock trial have been cane pruned and trained to wires in a vertical shoot position (VSP) system.

Thereplicated varietal trial consists of about 30 cultivars, selections, and clones (see Appendix A, Table 1). Early ripening red varieties are emphasized. The experimental design of the plots is a randomized block of 3 replications, with 5 plants per replication. At the station site, row spacing is 10' rows with 6' between plants. At Everson the spacing is 9' rows with 5' between plants.

A varietal pretest (see Appendix A, Table 3) evaluates other varieties, including new white wine grapes from cool climate areas in Europe. The varietal pretest consists of three plants per variety, replicated once. Promising varieties from the pretest will be multiplied, replicated and added to the main trial.

The rootstock trial of Pinot Noir 2A consists of seven rootstocks (see Appendix A, Table 2). They are being evaluated for their effect on maturity, yield, and quality compared with self rooted plants. Replications consist of five plants on each rootstock, replicated three times at the Everson plot and five times at the Mount Vernon plot.

At Mount Vernon the two additional replications have allowed comparison of the standard cultural treatment (control) with cultural methods that may advance maturity. In 2002 soil mulch, plastic tent/shelter applied both early and late in the season, and cluster number per shoot were examined.

A. Soil mulch/Early Plastic: In mid-April (4/18-19/02), before shoot growth occurred on the pruned vines, a solar ground mulch and plastic tents (a form of plastic cloche tented over the vines) were installed in specific plots. The treatments consisted of 1.) control, no mulch or plastic, 2.) mulch only, 3.) plastic tent only, and 4.) mulch and plastic tent. The mulch remained in place throughout the season; the plastic tents were redeployed in early May (5/06/02) as the shoots developed and removed in early June (6/10/02).

B. Late Plastic: On August 19 one replication was treated by applying a plastic sheet to the west side of the vine row in the area where the grape clusters were developing. This remained in place until harvest.

C. Clusters per shoot: After clusters were set in early July, fruit on vines was thinned to 1 cluster/shoot, except in Row 4 where all replications were left with 2 clusters/shoot.

Preliminary harvest evaluations were begun in 2002, and harvest data was collected. Cooperation of area winemakers is engaged in the post-harvest evaluation of varieties suitable for wine production. Individual wines are being made from grapes of Pinot Noir 2A from each of the 8 rootstocks harvested separately. Wine is also being made from several of the varieties, as well as a blend from the varieties with a partial first crop. Evaluation of the wines is estimated for spring-summer of 2003.
 

Results

In 2002 the first crop of grapes sufficient for evaluation was produced and data collected, although most of the vines have not yet reached full production capacity. (Data from the Everson trial are shown in Appendix B.) On October 8, an overall comparison of maturity for the varieties in the Mount Vernon trial was obtained by taking 10 sample berries from each vine (= 50 berries/plot) and testing for brix and titratable acid. At that date, heat units for the Mount Vernon site totaled 1520. Results of juice analysis for the variety trial and varietal pretest are shown in Tables 1 and 2, below.

Table 1. Variety trial, Mount Vernon 10/08/02 – Average pH, brix and titratable acid
(in ascending order by % titratable acid)

Table 2. Varietal pretest, 3 plants/plot, Mount Vernon 10/08/02 – Average pH, brix and titratable acid (in ascending order by % titratable acid)

At the same time, using the same sampling method as above, juice from the Pinot Noir rootstock trial was tested for brix, pH and titratable acid, with the results shown in Table 3. The Pinot Noir rootstock plot was nearly at full cropping capacity.

Table 3. Rootstock trial – Mount Vernon 10/08/02 – Average pH, brix and titratable acid
(clone Pinot Noir 2A, in ascending order by % titratable acid)

Yield and Crush Data

After taking sample juice for analysis from fruit in both the Mount Vernon and Everson trial plots, and in consultation with Tom R. Bronkema as wine manager, ripe grapes were harvested on October 17 and 18,2002 and processed at the Mount Vernon station on October 18 and 19. Yields were measured for the different varieties and for the eight different treatments of the Pinot Noir rootstock trial. Processing included stripping of berries from clusters in some instances, and crushing the grapes. After crushing, the juice Brix was measured using both a hygrometer and a refractometer, and the results recorded.

A few of the varietal plots were more advanced than others and yielded sufficient fruit for production of a varietal wine. Other varieties yielded enough fruit to combine for producing a blended wine. At Mount Vernon the Pinot Noir rootstock trial produced sufficient fruit to make a separate crush of wine from each of the eight rootstocks.

A yeast starter was prepared on October 17, using the following method: fruit of St. Laurent from Everson (19.2 brix) was crushed and added back with moldy discards from Zweigelt (17.0 brix) to total 1/2 gallon of juice with a combined pH of 3.2, then 6 fl oz of Assmanhausen from Wyeast(dated 3 Oct 2001) with yeast nutrients was added. On October 21, Wyeast ML culture was added to the yeast starter, 150 ml of yeast starter transferred to each 5 gallon fermenter, and 200 ml of yeast starter culture transferred to each 18 gallon tub.

Assmanhausen was selected to deal with the moldy Pinot. Moldy fruit was added to the yeast starter to proof the yeast with mold, and to balance the mold contribution in each wine,as a method of reducing some of the mold induced variation.

Table 4. Data from wine crush October 17, 2002

*Brix H = measured by hygrometer, Brix R = measured by refractometer, post crushing
 

Discussion

I. Rootstock trial

In comparing the juice samples from rootstocks on Pinot Noir 2A, those that were most successful in promoting overall earlier ripening were Millardet et de Grasset 101-14, Millardet et de Grasset 420A and Couderc 3309.

Comparison of juice samples indicates that with respect to pH value, the rootstocks 101-14, C3309 and 49-53 had significantly the highest pH at 3.275. All other rootstocks averaged 3.225, and self rooted vines had the lowest pH at 3.1.

Values for brix (soluble solids) showed 101-14 and 5BB with significantly higher brix than self rooted. Vines of 420A and Riparia Gloire were also higher in brix than the self rooted Pinot Noir, but was not statistically significant at the 5% level.

Mean values for percent of titratable acid (Table 4) indicated all rootstocks had significantly lower titratable acid than the self rooted vines. The outstanding performers again were 101-14, 420A and C3309 with the lowest levels. Plants grown on 101-14 were also more vigorous than those on 420A or C3309.

Table 5. Rootstock trial, Mount Vernon 10/08/02 – Mean values for titratable acid (LSD 0.1899)

A. Early Plastic: Where a plastic tent was applied early (April), initial observations showed an advanced bloom date of two weeks. Analysis of the juice indicated that initial pH was higher and titratable acid lower for the vines covered with early plastic but the levels were not significant at the 5% level. Brix registered higher for the vines with no plastic, but a variation occurred in the methodology, so that soluble solids readings for those treatments were not valid for comparison.

B. Late Plastic: In row 5 a plastic sheet was applied on the west side of the vine row in late August to see its effect. Analysis of data comparing these vines with the control (no plastic) resulted in no significant difference in the levels of initial pH or of brix. However, there was a significant reduction in titratable acid for the treated vines compared with the control (Table 5).

Table 6. Rootstock trial, Mount Vernon 10/08/02 - Mean values for titratable acid (LSD 0.0835)

C. Clusters per shoot: Data comparing the vines which were thinned to 1 cluster per shoot with those where two clusters were left on each shoot indicated no statistically significant differences in values for initial pH, brix and percent titratable acid. Though not statistically significant at the 5% level, values for brix and pH were higher and titratable acid lower for vines with 1 cluster/shoot than for vines with 2 clusters/shoot.

II. Variety trial and varietal pretest

Several of the varieties in the trial produced sufficient fruit both for sample tests and for wine making. Evaluating the performance in the first year of production resulted in several promising varieties (Table 6).

Table 7. Promising varieties tested at Mount Vernon (tested October 8, 2002- 1520 h.u.)

Table 8. Promising varieties from Mount Vernon, varietal pre-test (tested October 8, 2002)
(note that the pretest consists of 3 plants/cultivar vs 15 plants/cultivar in main trial)

* established varieties

On the basis of the 2002 results, these varieties from the pretest will be added to the varietal test for wine making: Perle of Csaba, Ortega, Muscat (Norwegian), Optima, Reichensteiner.
 

Appendix A – Cultivars/Selections and Rootstocks on trial

Table 1. Main variety evaluation (2002)

Table 2. Rootstock Trial (Pinot Noir 2A)

Table 3. Varietal Pretest (2002)

Appendix B – Everson Plot, 2002 Data

NOTE: Grape plants in this plot were moved in winter 2001–02 from a previous site where they had been initially planted in spring 2000. Heat units at Everson to October 8, 2002 were approximately 1900 (vs. 1520 at Mount Vernon). However, some effects of earlier ripening may be due to the stress of transplant, independent of the higher heat units at the Everson site. For this reason, data collected in 2002 on the fruit from the Everson plot is regarded as inconclusive. Seven gallons of wine from a mixture of Pinot Noir on the various rootstocks was made and will be sampled at the same time as the other wines.

Table 1. Variety trial, Everson 10/08/02 - Average brix and titratable acid (in ascending order by % titratable acid)

Table 2. Pinot Noir rootstock trial (clone Pinot Noir 2A), Everson 10/08/02 – Average brix and titratable acid (in ascending order by % titratable acid)

NOTES – October 25 Harvest and crush

Transferred to Mike L
Schonburger in two 5 gallon carbouys with bubblers
St. Laurent free run blanc de noir in one 1 gallon with bubbler
St. Laurent pink press wine in one 1 gallon with bubbler
St. Laurent blend free run / press wine in one 1/2 gallon with bubbler
Red Blend: Leon Millot, 39-X, Regent, Rubin T pressed with pommace of the others, in two 1 gallons with bubblers
This is more an inventory of hardware than wines, so the actual data for various wines should be obtained from Mike.