ReviewChanges in vineyard establishment and canopy management urged by earlier climate-related grape ripening: A review
Introduction
Wine is etymologically defined as an alcoholic drink beverage made from the fermentation of grape juice (Oxford dictionary). Lawfully, the wine is instead defined in terms of different minimum and maximum alcoholic strengths according to countries. Thus, in all European Union countries and in Switzerland the lower and upper alcohol limit are established at 8.5% and 15% vol., respectively, with some exceptions (CE regulation n. 479/2008, art. 1 c and DFI 29/11/2013 art. 4); in South Africa table wine is required to contain less than 16.5% vol. alcohol and at least 6.5% vol. (South African Government 1990), while in USA the Federal Alcohol Administration Act established that the wine must have an alcohol content between 7% and 24% vol.
Traditionally, a general desirable target of wine grape growing worldwide has been to achieve high total soluble solids (TSS) (Kliewer and Weaver, 1971, Jackson and Lombard, 1993) since this parameter is the benchmark for the price-point of the grapes in several countries (Koblet, 1986). Today, though, this target is somewhat losing its appeal since an increasing number of consumers from both domestic and foreign markets prefers wines with moderate alcohol content (Salamon, 2006, Seccia and Maggi, 2011), which can naturally be obtained in vineyards through the reduction of TSS accumulated into the grapes. This new trend is also linked to the negative effects of the alcohol on human health and the more severe controls on vehicle drivers worldwide, as well as to significant changes in people life style and to organoleptic relishes requested in modern wines, such as freshness and tastiness. Ethanol can enhance the perception of sweetness and bitterness while reducing that of acid, saltiness and sourness (Martin and Pangborn, 1970, Fisher and Noble, 1994). Moreover, high alcohol content can negatively affect malolactic fermentation because Oenococcus oeni cells lose membrane stability, which, in turn, leads to a delay in wine stabilisation and ageing and an increase in undesirable sensory modifications (Graca da Silveira et al., 2002). High grape TSS concentration has also significant impact on the fermentation process and subsequent wine composition including changes in both sensory characteristics and in microbiological activity, linked mainly to growth inhibition or lysis of yeast cells, as well as sluggish and stuck fermentations. These latter phenomena are aggravated in hot years (Coulter et al., 2008) with a negative impact on wine composition. Lastly, high TSS stress was found to up-regulate glycolytic and pentose phosphate pathway genes (Erasmus et al., 2003) leading to the formation of undesirable by-products of fermentation, such as acetic acid and glycerol (Pigeau and Inglis, 2005).
The limitation of grape TSS concentration in the vineyard is also useful to minimize costly interventions in the winery aimed at dealcoholize the wines such as membrane techniques, supercritical fluid extraction and vacuum distillation. These physical techniques have recently become legal in the European Union (Council Regulation n. 606/2009) with a maximum alcohol reduction of 2% vol. Moreover, a major drawback of a too fast TSS development is that in several viticulture areas this process occurs during the hottest part of the season (Jones et al., 2005, Webb et al., 2012), when both color and aroma profile can be adversely affected (Lacey et al., 1991, Reynolds and Wardle, 1993, Mori et al., 2007). Under these conditions, grapes often combine an excessively low acidity and high pH, thus requiring the addition of tartaric acid before fermentation in order to avoid microbiological instability and improve mouth feel (Keller, 2010).
Over the last two decades a trend toward overly fast grape ripening with excessive TSS accumulation in the fruit and high alcohol in the resulting wine emerged in several countries (Duchene and Schneider, 2005, Godden and Gishen, 2005, Dokoozlian, 2009, Chaves et al., 2010, De Orduña, 2010, Keller, 2010, Jones, 2012). In many cases, irrespective of grape cultivar, such features matched with unacceptably low acidity, high pH and atypical flavors in the grapes (Keller, 2010). Webb et al. (2012) reported that in Australia wine grapes have undergone earlier ripening in recent years and, by using 64 years series, indicated that warming and reduction in soil water content are driving a major portion of this ripening trend.
Excessive TSS accumulation has been linked to several factors: (i) global warming and a rise in canopy photosynthetic potential due to a steady increase of CO2 concentration in the atmosphere (Schultz, 2000, Bindi et al., 2001, Ainsworth and Rogers, 2007); (ii) improvements in vineyard management; (iii) law-enforced yield constraints in several Appellation areas; (iv) adoption of grapevine cultivars characterised by low cluster weight and/or grafted on low-vigour rootstocks; and (v) improved sanitary status of the propagation material. In the medium-to-long term these factors will likely affect the geographical distribution of viticulture (Schultz, 2000, Jones et al., 2005, Keller, 2010, Caffarra and Eccel, 2011), whereas, in the short term, new management techniques able to mitigate these negative impacts are needed.
Section snippets
Future planning of viticulture according to global warming
The specific climate is crucial to the overall style of a wine produced from well-defined areas. The ability to reach complete grape maturation is fundamental in determining the best cultivar to be grown in a given climate and climate variability determines year-to-year differences in the grape and wine quality (Jones and Hellman, 2003). In particular, temperature and irradiance are critical because of their direct effect on the length of growing season, phenological stages, vine yield by means
Calibrated increase of vine yield
High yield per vine usually links to low leaf area-to-yield ratios, i.e. about 0.8 and 0.5 m2/kg for single and divided canopies, respectively, which in turn determine a lower capacity of TSS accumulation in the berries (Kliewer and Dokoozlian, 2005). In such situations, if needed, it is possible to accelerate and improve the berry ripening by increasing the leaf area-to-yield ratio through a reduction in yield per vine which can be easily achieved with bunch thinning (Ough and Nagaoka, 1984,
Post-veraison leaf removal apical to the bunch zone
Leaf removal is one of the most interesting canopy management practices due to its simplicity and suitability to mechanisation. Its impact on ripening, however, is controversial, as it seems to vary with timing and severity of application. Bubola et al. (2009) have reported a 1 °Brix increase after the removal of basal leaves at veraison in cv. Istrian Malvasia, but the same treatment did not significantly affect the TSS and phenolics content in grapes of several other cultivars (Bledsoe et al.,
Management techniques based on the use of growth regulators
In viticulture, hormone treatments have been mainly addressed to the reproductive developmental cycle, taking into account that grapevine vegetative activity can be successfully controlled by training systems and management practices (Botton and Bonghi, 2012). Albeit the use of plant growth regulators has faded over the last decades mostly due to more strict regulations in applying exogenous chemical compounds as well as still partial information on physiological processes regulation and
Early harvest
A quite challenging technique was proposed by Kontoudakis et al. (2011) who, in the attempt to elaborate red wines with a lower alcohol content and pH, yet with full phenolic maturity, used clusters of Grenache thinned at veraison to produce a very sour and harsh wine (TA = 17.8 g/L, pH = 2.64 and alcohol = 5% vol.), which was made odorless and colorless thanks to massive treatments with activated charcoal and bentonite. This wine was then blended with the wine made from Cabernet Sauvignon, Merlot and
Concluding remarks
The trends of climate change on the planet are now consolidated certainties and their impact on agriculture is increasingly evident. Viticulture certainly does not make exception to the new demands that the global warming imposes, particularly in the light of the increased frequency of extreme events during the summer, heat waves and long persistence of equatorial anticyclones on countries of medium latitude.
An adaptive strategy over the medium-to-long term will certainly need an upgrade of the
Acknowledgments
This research was partially funded by MIUR-Italian Ministry for University (PRIN 2009 Grant) and Biogard Division of CBC (Europe) (Grassobbio, BG, Italy).
References (138)
- et al.
Free air CO2 enrichment (FACE) of grapevine (Vitis vinifera L.): II. Growth and quality of grape and wine in response to elevated CO2 concentrations
Eur. J. Agron.
(2001) - et al.
Ethylene seems required for the berry development and ripening in grape a non-climateric fruit
Plant Sci.
(2004) - et al.
Genome-wide expression analyses: metabolic adaptation of Saccharomyces cerevisiae to high sugar stress
FEMS Yeast Res.
(2003) - et al.
Effects of plant hormones and shading on the accumulation of anthocyanins and the expression of anthocyanin biosynthetic genes in grape berry skins
Plant Sci.
(2004) - et al.
Canopy manipulation for optimizing vine microclimate, crop yield and composition of grapes
- et al.
Early source limitation as a tool for yield control and wine quality improvement in a high-yielding red Vitis vinifera L. cultivar
Sci. Hortic.
(2012) - et al.
The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactions
Plant Cell Environ.
(2007) - et al.
Effect of shading on the performance of Vitis vinifera L. cv. Cabernet Sauvignon
S. Afr. J. Enol. Vitic.
(1989) - et al.
Flavonoid biosynthesis-related genes in grape skin are differentially regulated by temperature and light conditions
Planta
(2012) - et al.
Delaying berry ripening process through leaf are to fruit ratio decrease