Winetech Technical Yearbook 2022

PHOTO 4. Sap flows through the stem of a leaf inside the pressure bomb.

wines that score 16 or higher out of 20 (16 is the minimum score to be classed as a cultivar wine). • In table 3, the analyses of all seven blocks are given, along with their scores as evaluated by the panel. • Only two wines did not score the requisite 16 points, but these wines were still undergoing malolactic fermentation and will be judged again at a later stage. • The marketers, winemakers and producers are very optimistic and excited about the preliminary results. The results correlate with the research that too much water (in other words, no wa ter stress) is negative for wine quality.

PHOTO 3. Photo of a leaf covered with tin foil.

THE USE OF A PRESSURE BOMB The vine’s plant water status is determined through a pressure bomb (photo 2). The plant water status is not used to determine the size of irrigation but is useful to determine the replenishment lines in conjunction with soil water measurement. There is a protocol for using the pressure bomb, and it entails, among other things, the following: • For mid-day plant water measurements, the reading should be recorded between 12:00 and 14:00. • Pick/use undamaged mature leaves growing on the primary shoots. • The leaves must be in the bunch zone and receive good sunlight exposure. • Choose a leaf and cover it with a tin foil bag (photo 3). • The leaf can be folded to fit into the bag. • Place a paper clip over the bag to keep it in position. • The bagging must occur one to six hours before the measure ment occurs. • Calibrate the pressure bomb before use. • Cut the leaf with a surgical knife/blade at an angle of 90°. • Place the leaf inside the pressure bomb immediately/as soon as possible. • Use a magnifying glass to see the first signs of sap and record the pressure bomb reading (photo 4). THE STRATEGY OF UNIWINES VINEYARDS The plant water status can be divided into levels (table 2). Based on this data, uniWines Vineyards followed a moderate water stress approach. This, therefore, means that the replenishment lines would be determined on a plant water status of -1.2 to -1.4 MPa. The consensus was that this would be a safe starting point for all the relevant cultivars and that adjustments could be made over time. PRELIMINARY OBSERVATIONS AND FINDINGS • The 2020/21 season was late and challenging, with record yields for both the Worcester and Breedekloof regions. The average yield of the seven blocks was almost identical to that of the 2019/20 season. Except for one block, the yield was at least 25 t/ha. • uniWines Vineyards has a panel of eight winemakers who taste the wines blind and evaluate the quality. The goal is to identify

TABLE 3. Results of the first season.

Sugar (°B)

Acidity (g/L)

Wine score out of 20

Cultivar

pH

Chenin blanc

20.5

5.84 3.52

16

Sauvignon blanc

21.9

6.02 3.87

16

Cabernet Sauvignon 23.3

6.13 3.59

16

Chardonnay

24.5

4.96 3.73

16.5

Shiraz

24.6

4.21 3.94

15

Merlot

26.7

4.42 4.20

15

Pinotage

24.4

5.48 3.63

16

VISION FOR THE FUTURE uniWines Vineyards has taken an enormous step to reconcile production with quality. These are only the findings of one year. The ultimate expectation of the project is that guidelines around irrigation and fertilisation for each cultivar connected to a wine goal will simplify the producer’s management. The irrigation guidelines will be determined according to the cultivar, soil type and irrigation schedule. This will enable the producers of uniWines Vineyards with high-yielding blocks to produce wines of higher quality (in this case, cultivar wine goal). In a subsequent phase, the project will also focus on addressing fertilisation to refine the guidelines for sustainable wine quality. REFERENCE https://www.wineland.co.za/uniwines-vineyards-strategy-yielding-vine yards/

For more information, contact Pierre Snyman at pierre@vinpro.co.za.

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WINETECH TECHNICAL YEARBOOK 2022