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Manipulating light in the fruit zone improves wine quality BY Katja Šuklje1, Nico Gobler 2,3, Zelmari Coetzee3, Klemen Lisjak 1 and Alain Deloire3,4* M and to show the complexity of the relationships between fruit composition and wine style (wine composition and wine sensory description by a trained panel), green/herbaceous and tropical flavors have been chosen as sensory attributes for Sauvignon Blanc. South Africa offers a great variety of Sauvignon Blanc wine styles, ranging from tropical to greener, herbaceous Methoxypyrazine Concentration Over Berry Development Methoxypyrazine Concentration Over Berry Development MP Concentration in Berries 1 Agricultural Institute of Slovenia, Central Laboratories, Ljubljana, Slovenia. 2 Eikendal Vineyards, Pty (Ltd.), Dennesig, Stellenbosch. 3 Stellenbosch University, Dept. of Viticulture & Oenology, Matieland, South Africa. 4 NWGIC-Charles Sturt University, Wagga Wagga, NSW, Australia. *Corresponding author: adeloire@csu.edu.au. Figure 1: Attributes commonly used to describe methoxypyrazines present in Sauvignon Blanc wine: green pepper, asparagus and green beans. to the diversity of the climate and soil of the Western Cape region. The greenness in Sauvignon Blanc could be considered a wine style up to the point where the green attributes dominate, resulting in a one-dimensional wine. In red wines, mainly Merlot and Cabernet Sauvignon, the perception of green attributes may be considered an undesirable aroma.3 The green aroma descriptors of Sauvignon Blanc, Merlot, Cabernet Sauvignon, Cabernet Franc and Carmenere grapes and wines originate from 3-alkyl-2-methoxypyrazines (MPs). The most important MP found in grapes and wine is 3-isobutyl-2-methoxypyrazine (IBMP), whereas 3-isopropyl-2-methoxypyrazine (IPMP) is rarely present in grapes at harvest. IBMP contributes to the green pepper, pea, and asparagus aromas while IPMP imparts earthier aromas.1,11 The sensory detection threshold for IBMP was found to be very low; 2 ng/L in water and white wines and around 15 ng/L in red Bordeaux wines.1,14 In some Merlot and Cabernet Sauvignon wines, aromatic attributes related to eucalyptus and mint are found, which results in the wine sometimes being described as green. These attributes are, in fact, not linked to IBMP, although further research is needed. IBMP in the grape berry is located in the skins (95%), seeds (4%) and pulp (1%).14 IBMP biosynthesis in the grape berry starts after flowering, reaching the maximum concentration two to three weeks before véraison, after which it declines during maturation, not only in concentration, but also on a per berry basis.13,16 Recent studies suggest that IBMP found in the berry is synthesized by the berry MP Concentration in Berries odified light and temperature in the fruit zone can have a positive role on the cluster microclimate, which consequently affect berry composition and therefore may improve wine quality or style. However, it is important to remember the following: • The relationships between fruit composition and wine quality or style are not direct. In other words, fruit analyses may give results on the concentration of a specific compound which will not reflect in the wine composition or in wine sensory analysis. Wine is a complex matrix within which numerous chemical compounds are interacting together and in addition, aromatic precursors present in the fruit are transformed during fermentation. • The positive role of increased light on fruit composition has been well described by numerous authors. It should be noted that this abiotic factor has to be managed very carefully to avoid damage to the fruit (sunburn, berry shriveling, etc.), negatively affecting the fruit composition. In this regard, the thresholds of light and temperature's effect on the fruit composition are not well known and need further investigations. • Fruit and canopy microclimates have to be managed to respect a specific site, canopy architecture and row orientation. To demonstrate the positive role of light and temperature at the fruit level w i n e G R O WIN G Berry Set Berry Set Veraison Veraison Maturity Maturity Berries harvested well before sugar maturity are widely reported to Berries harvested well before sugar have higher levels of methoxypyrazines.maturity are widely reported to have higher levels of methoxypyrazines. Figure 2: Opening the canopy at pea size (red arrow) affects the biosynthesis of IBMP in the berry, which in flavors.turn results in a reduced IBMP concentration in the wine (curve adopted from Roujon de This Boudee, 2000).14 can be related pr actica l win ery & vin eya r d JANUARY 20 14 27