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Performance Of Certain Lesser Known European Wine Grape Cultivars Under South African Conditions
D. van Schalkwyk & A Schmidt ARC Infruitec-Nietvoorbij, Stellenbosch.
This article is an abridged version of a more comprehensive report available from: SAWIS Industry Library, PO Box 238, Paarl 7629 Tel: 021-8075756; Fax:021-8722354; library@sawis.co.za
Key words: lesser known cultivars, wine quality, production, Vitis vinefera
Introduction
According to the 2001 South African wine industry statistics 105 566 ha of all vine plantings in South Africa are wine grapes (SAWIS, 2001). These plantings are mostly made up of nine red wine and 12 white wine cultivars, with a few other cultivars making a small contribution. Approximately 59.6% of all these plantings is made up of the top six cultivars, namely, Chardonnay (5.7%), Sauvignon blanc (5.1%), Cabernet Sauvignon (8.1%), Merlot (14.0%), Pinotage (13.0%) and Shiraz (13.7%). Consequently there is not a big variation of cultivars that are being used for winemaking purposes in South Africa and the potential of other cultivars is being studied on an ongoing basis to determine whether they are not perhaps able to make a significant contribution to the expansion of the South African wine spectrum or the flavour profiles of wine blends.
Research procedure
In the quest for promising cultivars for South African viticultural conditions, ARC Infruitec-Nietvoorbij investigated the viticultural and oenological performance of 9 red and 17 white promising European wine grape cultivars at Nietvoorbij, Stellenbosch (Table 1) from 1993 to 2000. According to available literature, these cultivars produce high quality wines, while some have unique colour characteristics and others have good disease resistance.
Five vines of each cultivar were grafted onto Richter 99 RY 13 and evaluated for viticultural and oenological performance for eight consecutive years. The vines were planted 3.0 m x 1.5 m on Glencoe soil type (sandy loam soil with respectively 16% and 24% clay in the top and subsoil) and trellised on Five Wire Extended Perold. The resistance of the soil was above 2 000 ohm and the pH was adjusted during soil preparation to the norm of 6.0. Three supplementary irrigations (before budding, véraison and post-harvest) were applied by means of micro-irrigation. In order to evaluate all the cultivars on a homogeneous viticultural level, all the vines were pruned to 12 two-bud bearers (6 on each side of the cordon) and the bearers were spaced approximately 12.5 cm apart to ensure a good canopy microclimate. Standard canopy management practices such as tipping, topping and suckering were applied at all the treatments and leaves were removed as required. Phenological and viticultural data were collected and an attempt was made to harvest white cultivars at a sugar content of approximately 21 - 22°B and red cultivars at 23 - 24°B to eliminate differences in degree of ripeness. This was not always practical to implement, however. Wine was made according to standard Nietvoorbij experimental vinification methods. Red wines were fermented dry on the skins. Wines were evaluated six months after bottling for aroma and wine quality. Grape and skin colour of the red cultivars were determined at two absorbance levels, namely 420 nm and 520 nm. Chenin blanc 4/24 was included as a reference for the white cultivars and Blauer Spätburgunder (Pinot noir) for the red cultivars.
Results and discussion
Viticultural
If all the seasons are taken into account, Chenin blanc was the first to bud (3 August) and Fontanara the last (15 September). Based on the average of the 8 seasons, however, Chenin blanc (25 August) was the first and Deckrot (8 September) the last to bud. A fairly large variation in flowering, leaf drop and harvest dates occurred among the respective cultivars. Of all the cultivars, Aris was the first to ripen (25 January). Accurate ripening date could seldom be determined, however, due to serious bird eating damage. Most cultivars ripened before Chenin blanc (19 February), the earliest overall being Aris (25 January), Kanzler (27 January), Ortega (20 January) and Osiris (31 January). The red cultivars ripened more or less at the same time or slightly later than Chenin blanc, but all were later than Blauer Spätsburgunder (11 February) and earlier than Cabernet Sauvignon. Ripening ranged from 7 January in 1998 to 13 March in 1997. The 1994 and 1998 seasons were particularly early and 1997 was rather late. None of the cultivars experienced any difficulty ripening under the Western Cape weather conditions, but some ripened before any of the cellars in the Stellenbosch vicinity were prepared for the intake of grapes.
The evaluation of the general physical condition of the grapes during harvest showed that Optima, Forta, Osiris, Perle and Blauer Spätsburgunder are a lot more susceptible to dry Botrytis rot and sour rot than Chenin blanc. Aris, Comtessa, Forta, GM 6495-4, Ortega and Perle generally suffered severely from bird eating damage as a result of their early ripening and Aris was subject to as much as 80% bird damage. Cultivars such as GM 6495-4, Ortega Osiris, Perle, Blauer Spätsburgunder, Deckrot, Kolor and Müllerrebe WE 293 were the most susceptible to sunburn. Among the red cultivars there was often shrunken berries but this was not necessarily detrimental to vinification. Of all the cultivars Aris had the highest percentage of freerun and millerandage (7.6% & 14.5% respectively), which contributely largely to the low bunch, berry and crop mass of this cultivar (26.0 g, 43.9 g/100 berries & 1.2 t/ha respectively).
On the whole all the cultivars had lower productions than Chenin blanc (11.6 t/ha). Optima and Perle were the only cultivars with 19.6 and 18.0 t/ha respectively which produced crop masses equal to that of Chenin blanc 4/24 (19.8 t/ha) in 1994, whereafter their productions decreased drastically. In general Comtessa (9.2 t/ha), GM 7116-26 (8.8 t/ha), Ortega (8.7 t/ha), Regner (8.6 t/ha), Chenanson (8.4 t/ha) and Domina (8.6 t/ha) had consistently high productions, while the crop masses of Aris were considerably lower. Portan was the only cultivar with a higher bunch mass (208.9 g) than Chenin blanc 4/24, while Aris (26.0 g), Optima (83.5 g) and Blauer Spätsburgunder (82.3 g) had the smallest bunches. Bunch masses and size varied considerably from season to season and therefore also stalk masses. Differences in bunch compactness and berry masses from season to season therefore resulted in the heavest bunches not always having the highest stalk masses. In general the stalk mass of Portan (9.26 g) was the highest, while Aris (1.83 g), as could be expected in the light of its small bunches, produced the lowest stalk mass. On average Comtessa had the most berries per bunch (166) and Optima the fewest (71). The bunch mass of Aris (43.9 g/100 berries) was the lowest. Ortega (217.8 g/100 berries) and Helfensteiner (216.2 g/100 berries) had the heaviest berries. There was also a lot of variation in the vigour of the cultivars. Comtessa was the most vigorous grower with a shoot mass of 1.1 kg/vine and Aris the weakest with 0.1 kg/vine. Other cultivars such as Faberebe, Forta, GM 6495-4, Mariensteiner, Regner, Blauer Spätsburgunder, Chenanson and Domina also displayed relatively poor vigour. The vigour of the other cultivars compared more or less to that of Chenin blanc 4/24.
Grape and must quality
Although an attempt was made to harvest the white cultivars at 21 - 22°B and the red cultivars at 23 - 24°B, the acid concentration was also taken into account and grapes were harvested before the acid dropped too much. As a result, the degree of ripeness of the cultivars differed considerably. Aris produced good quality must despite low production and poor viticultural performance. The seasons did not all produce sufficient grapes for vinification, consequently this cultivar’s oenological potential could not be evaluated properly. Of the white cultivars Forta and GM 6495-3 produced the best quality must. With regard to the red cultivars, Deckrot stood out above the other cultivars due to its high total acid concentration (9.1 g/l). The total acid concentrations of Perle and Portan were the lowest (4.5 g/l & 5.1g/l). Other cultivars such as Ortega, Osiris, Regner, Septimer and Domina also produced relatively low total acid concentrations. The must of some cultivars, such as Ortega, Perle, Blauer Saint Laurent and Domina, also tended to have relatively high pHs.
Wine quality
Differences in must quality were apparent in the wine analyses. The average alcohol volumes ranged from 11.7% to 15.7%. Of the white cultivars Perle, and of the red, Chenanson, had the lowest average alcohol volume (12.0% & 11.7% respectively). The reason for the low alcohol volumes in the “lowest volume” column may be ascribed to season-specific development of shrunken berries and the grapes were therefore harvested before reaching the full ripe stage. Among the red cultivars Deckrot, Kolor and Müllerrebe WE 293 produced good extract concentrations (35, 36, & 34 g/litre respectively). The exceptionally high extract concentration in Optima was due to the wine not being filtered as a result of insufficient clear juice. Among the white cultivars only Forta (26 g/litre) had a higher extract concentration than Chenin blanc 4/24 (24 g/litre). Several of the cultivars’ wines had extremely low acid concentrations in some years as a result of the discharge of tartaric acid. The wines of the red cultivars Blauer Saint Laurent, Domina and Portan in particular, and the white cultivars Mariensteiner and Perle sometimes had extremely low acid concentrations which often resulted in thin wines with little aroma. Consequently these cultivars, and some of the others, did not have the potential to produce good quality wines with good lasting ability each season. The volatile acid concentrations were relatively high in some years, as much as 0.82 mg/l in Regner. Among the white cultivars the Perle wines generally tended to have a high pH (3.72), while the pH of Deckrot (3.48) in the red cultivars was fairly low compared to those of the other red cultivars. Deckrot and Kolor have an especially intense colour, which makes these cultivars ideal for use in blends with cultivars that do not provide satisfactory wine colour. The wine hue of Deckrot is so intense that the colour remains acceptable as red wine even when the wine is diluted up to 5 times with water. The good acid concentration of these two cultivars is beneficial to the improvement of the lasting ability of blended wines and in Germany they are used for this purpose.
None of the white cultivars evaluated produced better wine quality over the evaluation period than Chenin blanc 4/24 (Table 2). Aris, Kanzler, Mariensteiner, Ortega and Regner showed similar cultivar intensity in a few seasons, while Faberebe produced a considerably higher wine quality in a single season (73.3%). A number of the cultivars did produce comparable wine quality in individual seasons. If the average wine quality over the seasons is taken into account, a number of cultivars produced wines of a higher quality than Chenin blanc 4/24 and they have the potential to be used in blended wines. On the whole Kanzler showed the most promise and could possibly also be used as a cultivar wine. Must and wine analyses at which a number of cultivars produced the best wine quality, showed that several of the cultivars had the potential to produce good quality wine in specific seasons.
Among the red cultivars Deckrot and Kolor produced good quality wines throughout, while Domina, with an overall wine quality score of 73.1%, displayed the best wine quality, together with Kolor, in the 2000 season. Both the skin and wine colour of Domina were considerably less intense than that of the other two cultivars, but equal to the wine colour of Cabernet Sauvignon.. Both Deckrot and Kolor produced complex wines with a prominent berry character supplemented by a slight vegetal character. These two cultivars have a dark red juice, which results in the vinification of deep, dark wines. Both cultivars have good acid concentrations which should endow the wines with a good shelf life. Although the two cultivars are able to make their mark as cultivar wines, their extremely dark colour makes them more suitable for use in blended wines. The wine character of Domina is more like that of Cabernet Sauvignon, but the cultivar tends towards low acids. The results of the eight seasons have shown that cultivars must be harvested at different degrees of ripeness to ensure optimum wine quality. The optimum sugar:acid ratio among the red cultivars ranged from 3.0 to 4.5.
Summary
Some of the white cultivars such as Faberrebe, Kanzler, Ortega and Regner especially are probably able to make a contribution to the South African white wine spectrum as blending cultivars (Photos 1, 2, 3 & 4). Kanzler and Regner ripen very early in January, which may enable cellars to start pressing earlier and have their wines on the market sooner. Other cultivars, such as for example Forta and GM 6495-3, have better acid concentrations than Chenin blanc 4/24 and should also fare well in blends. However, most of these white cultivars have more or less the same sub-tropical character as Chenin blanc.
Of the red cultivars Deckrot, Domina and Kolor were the most promising and could be a good addition to red blends (Photos 5, 6 & 7). Deckrot and Kolor in particular may be used in instances where problems with wine colour are experienced, since both are red juice cultivars and make wines with an extremely intense dark red colour, even darker than those deriving from the locally developed red wine cultivar, Roobernet. Both cultivars also have high acid concentrations which may promote the maturation potential of red blends. Deckrot, Domina and Kolor have the ability to produce wine quality equal to Cabernet Sauvignon. Of the red cultivars Domina had the highest average production with 8.6 t/ha. These three red cultivars are also resistant to rot and all ripen earlier than Cabernet Sauvignon. It is recommended that the most promising cultivars be established on a semi-commercial basis to determine their true potential.
If the right wine style for each cultivar could be applied, more of these cultivars will probably make a positive contribution to the South African wine spectrum. The potential of other promising foreign white and red wine cultivars will be investigated further in an attempt to find cultivars that are able to make a positive contribution to the expansion of the wine spectrum potential in South Africa.
For more information contact Danie van Schalkwyk on 021 – 809 3156 or e-mail: danie@infruit.agric.za. Complete tables about the performance of the cultivars as well as photographs of the cultivars are available from the SAWIS web library: www.sawis.co.za.
ACKNOWLEDGEMENT
The technical assistance of Stawie Fouché, Kobus Theron, André Schmidt and Estelle Rhode from the Viticulture division, as well as the partial funding of the research by Winetech, are much appreciated.
REFERENCES
Alleweldt, G. & Dettweiller-Münch, 1992. The genetic resources of Vitis. Genetic and geographic origin of grape cultivars, their synonyms. 2nd edition. Institut für Rhebenzüchtung Geilweilerhof, 76833 Siebeldingen, Federal Republic of Germany.
Dettweiler, G., 2002. Vitis International Variety Catalogue. GENERES. Information Centre on Genetic Resources. An information service of the Information Centre for Biological Diversity (IBV). www.generes.de/eccdb/vitis.htm.
Galet, P.,1998. Grape varieties and rootstock varieties. Oenoplurimédia sarl Château de Chaintré, 71570 Chaintré, France.
Hildebrand, W., Lott, H. & Pfaff, F., 1987. Taschenbuch der Rebensorten. Fachverlag dr. Fraund GMBH. Rheinhessische Druckwerkstätte, 6508 Alzey.
SAWIS, 2001. South African Wine Industry Statistics. SAWIS, Po Box 238, 7620 Paarl.
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