What is the expected impact of climate change on wine aroma compounds and their precursors in grape?

摘要

The intrinsic quality of a wine is strongly linked with its volatile compound composition involved in the complexity of wine’s subtle flavor nuances. Those reminiscent of green pepper, herbaceous, blackcurrant, blackberry, figs or prunes are strongly linked with the maturity of the grapes. Nowadays it is well accepted that macroscopic effects of climate change modify the environmental conditions of grape growing at local scale in all the vineyards across the world. The expected effects on grape and wine production can be positive when they increase the maturity of the grapes, but when the conditions are too warm and too dry they induce opposite effects producing grapes and wines with a lower intrinsic quality. These effects were perceived in young wines but also in older wines kept several years in bottle.In this article, we provide some examples of effects of climate change and growing conditions on grapevine and wine quality expressed as flavors and antioxidant composition. We also report some results associated with the incidence of grape growing conditions on white and red wine aging potential and on the composition of old wines.Finally, we discuss the opportunities for vine growers and winemakers to manage the quality of their grapes and wines in this climate change context. Introduction The aromatic component of wine is a decisive criterion of its sensory quality. This quality is based on the perception of aromatic nuances of varying intensity and complexity, often associated with the expression of a single grape variety or a mixture of grape varieties that is modulated by the soil and can thus contribute to the recognition of a typical or sensory identity (another word for typicality). The aromatic component is due to the presence in wine of many volatile compounds from families that contribute to the perception of aroma thanks to their vegetal, floral or fruity notes, or through complex sensory phenomena involving a mixture of the volatile compounds. Moreover, the preservation of this typical aromatic component during wine aging, possibly enriched by a "reducing" aging bouquet over time, is the signature and specificity of wines made from grapes that have ripened in temperate climates.The prospects of climate change over the next century raise questions about the potential impact of a global rise in average temperature on the aromatic potential of grapes and wine quality. This paper presents current knowledge about the impact of various eco-physiological parameters of the vine on the aromatic compounds of wines; the consequences likely to be observed for wines in the context of climate change are also discussed. The aromatic component of wines The aromatic nuances perceived when wines are tasted result from a combination of volatile compounds, at least fifty, in the headspace above a glass of wine. These compounds act as stimuli at the olfactory epithelium level before being converted into nerve impulses and becoming sensations in the mind (Shepherd, 2006). In the last forty years, almost 1,000 volatile compounds have been identified in wine; their contents range from several hundred milligrams per liter to levels likely below ten picograms per liter. The odor thresholds of these compounds are also highly variable and are mostly found in the picogram range and up to a dozen milligrams per liter for less odorous compounds. Thus, certain trace compounds can play an important role in wine aroma, while other much more abundant compounds yet play a minor role.A distinction has to be made between the groups of volatile compounds contributing to wine aroma. First, there are the strictly fermentative compounds produced by wine microorganisms (S. cerevisiae yeast, lactic acid bacteria) involved in the floral, fruity and milky notes of young wines, especially the major ethyl esters of fatty acids and higher alcohol acetates. Next, there are the compounds produced by the secondary metabolism of grapes present in wines such as derivatives of carotenoids [?-damascenone (apple sauce, floral), ?-ionone (floral, violet), TDN (1,1,6-trimethyl-1,2-dihydronaphtalene; notes of kerosene), vitispirane (woody nuances, camphor)], lactones (fruity, coconut, peach and apricot) and furanones (caramel, cooked sugar). This group also includes those specifically associated with the aroma of certain varieties: for example, monoterpenes, which contribute to floral characteristics of Muscat varieties, or sesquiterpenes such as (-) rotundone, which contribute to notes of black pepper. Volatile thiols (sulfur-containing compounds with grapefruit boxwood notes or passion fruit) are involved in the typical aroma of Sauvignon blanc wine and many white and red varieties like Colombard, Chenin, Gewürztraminer, Semillon, Petit Manseng, Arvine, Merlot, and Cabernet-Sauvignon. Certain compounds of this family can contribute to the toasted notes associated with wine aging bouquet. A member of the methoxypyrazine family, 2-methoxy-3-isobutylp