Issue link: http://winesandvines.uberflip.com/i/137110
grapegrowing Depending on the variety, once a berry reaches 22°–25° Brix, it stops accepting sugar delivered by the phloem.1 Therefore, any increase in Brix during hang-time is due only to dehydration; there is no net gain of sugar content. From one of our experiments, we estimated that Merlot and Syrah berries gained 2.2° and 2.8° Brix per 10% weight loss, or had 4.7% and 3.9% weight loss to gain 1° Brix at ripeness. Therefore, it is important to evaluate the cost in yield to reach a certain Brix level if hang-time is required. ORGANIZED BY Berry transpiration and xylem backflow enhance ripening There is no doubt that getting stable supplies of water and sugar through the xylem and phloem is essential to the normal ripening of grape berries. However, what roles do berry transpiration and xylem backflow play during berry development? Should we stop berries from losing water to prevent any yield loss? In order to answer these questions, we conducted several experiments with three varieties (Concord, Merlot and Syrah) to learn what would happen if we artificially restricted one or both of these pathways. In a field experiment, commercial anti-transpirant was used to restrict berry transpiration. To stop xylem backflow, we carefully drilled through the peduncles of clusters to destroy only xylem tissue without damaging the phloem. 25TH EDITION INTERNATIONAL ENOLOGICAL AND BOTTLING EQUIPMENT EXHIBITION It is important to evaluate the cost in yield to reach a certain Brix level if hang-time is required. Treatments were applied just before véraison. Both treatments slowed color change and delayed ripening (Figure 3). By harvest, berries with either restricted transpiration or restricted xylem backflow had accumulated 33% less sugar compared with untreated berries, and the combination of these two treatments almost doubled the effect (65% less sugar). Besides less sugar accumulation, treated clusters also had much higher cracking incidence than untreated ones (seven-fold higher with restricted transpiration). In a separate experiment with potted vines, a custom-designed root-pressure chamber (Figure 4) was used to stop xylem backflow. Again, berry sugar accumulation decreased when xylem backflow was stopped. WORLD LEADER IN WINE TECHNOLOGY 12 —16.11.2013 Fiera Milano (Rho) Italy info@simei.it / simei.it pr actica l win ery & vin e ya rd JU LY 20 13 65