Technical Yearbook 2024

the Swartland region. In contrast, the TTA of the Sauvignon blanc grapes at the shoulder site did not differ between the RF and SLD grapevines; however, TTA was higher for the DLD grapevines (Figure 4A; Table 3). These results were expected as the RF and SLD plots at the shoulder site experienced similar water constraints during the ripening period. 10 Similar results were reported for Sauvignon blanc grapes in the Coastal region, where lower acidity and higher pH were observed for grapevines that experienced water stress in a Glenrosa soil. 22 The TTA measured during the 2017/18 season followed similar trends to the mean TTA of the previous four seasons (Figure 4). On average, the different irrigation treatments did not affect the juice pH at harvest of either the Sauvignon blanc or Cabernet Sauvignon grapes (Table 3). Similar results were observed for the juice pH during the 2017/18 season compared to the previous four seasons (Figure 5). Except for the RF plots of the back- and footslope sites, juice pH was within the recommended range of 3.0 - 3.8. 23 High juice pH (e.g. > 3.8) is often associated with high juice K + concentrations, which may result in wines with poor colour stability and taste. 24 Previous studies have linked increased berry K + concentrations to increased K + supply to grapevines. 25,26 The pH in wines made from Shiraz grapes that received 135 L of municipal wastewater per week was higher compared to those irrigated with the same amount of fresh water. 6 The increased pH was attributed to greater K + concentrations, resulting in wines with poor colour, fewer anthocyanins and a greater “chemical age”.

10 12

A

2017/18 4-Year mean

0 2 4 6 8

TTA (g/L)

RF

SLD

DLD

10 12

B

2017/18 4-Year mean

0 2 4 6 8

TTA (g/L)

RF

SLD

DLD

10 12

C

2017/18 4-Year mean

0 2 4 6 8

TTA (g/L)

RF

SLD

DLD

FIGURE 4. Effect of rainfed conditions (RF) and irrigation with treated municipal wastewater via single (SLD) and double dripper line (DLD) on total titratable acidity (TTA) in (A) Sauvignon blanc on a shoulder, as well as Cabernet Sauvignon on (B) a backslope and (C) a footslope during the 2017/18 season compared to the mean for the 2013/14 to the 2016/17 seasons.

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TECHNICAL YEARBOOK 2024