This review discusses the impacts of nitrogen addition in the vineyard and winery, and establishes the effects that nitrogen has on grape berry and wine composition and the sensory attributes of wine. Nitrogen is the most abundant soil-derived macronutrient in a grapevine, and plays a major role in many of the biological functions and processes of both grapevine and fermentative microorganisms. Manipulation of grapevine nitrogen nutrition has the potential to influence quality components in the grape and, ultimately, the wine. In addition, fermentation kinetics and formation of flavour-active metabolites are also affected by the nitrogen status of the must, which can be further manipulated by addition of nitrogen in the winery. The only consistent effect of nitrogen application in the vineyard on grape berry quality components is an increase in the concentration of the major nitrogenous compounds, such as total nitrogen, total amino acids, arginine, proline and ammonium, and consequently yeast-assimilable nitrogen (YAN). Both the form and amount of YAN have significant implications for wine quality. Low must YAN leads to low yeast populations and poor fermentation vigour, increased risk of sluggish/stuck/slow fermentations, increased production of undesirable thiols (e.g. hydrogen sulfide) and higher alcohols, and low production of esters and long chain volatile fatty acids. High must YAN leads to increased biomass and higher maximum heat output due to greater fermentation vigour, and increased formation of ethyl acetate, acetic acid and volatile acidity. Increased concentrations of haze-causing proteins, urea and ethyl carbamate and biogenic amines are also associated with high YAN musts. The risk of microbial instability, potential taint from Botrytis-infected fruit and possibly atypical ageing character is also increased. Intermediate must YAN favours the best balance between desirable and undesirable chemical and sensory wine attributes. ‘Macro tuning’, of berry nitrogen status can be achieved in the vineyard, given genetic constraints, but the final ‘micro tuning’ can be more readily achieved in the winery by the use of nitrogen supplements, such as diammonium phosphate (DAP) and the choice of fermentation conditions. This point highlights the need to monitor nitrogen not only in the vineyard but also in the must immediately before fermentation, so that appropriate additions can be made when required. Overall, optimisation of vineyard and fermentation nitrogen can contribute to quality factors in wine and hence affect its value. However, a better understanding of the effect of nitrogen on grape secondary metabolites and different types of nitrogen sources on yeast flavour metabolism and wine sensory properties is still required.

Implications of nitrogen nutrition for grapes, fermentation and wine

Plant secondary metabolites (SMs) are not only a useful array of natural products but also an important part of plant defense system against pathogenic attacks and environmental stresses. With remarkable biological activities, plant SMs are increasingly used as medicine ingredients and food additives for therapeutic, aromatic and culinary purposes. Various genetic, ontogenic, morphogenetic and environmental factors can influence the biosynthesis and accumulation of SMs. According to the literature reports, for example, SMs accumulation is strongly dependent on a variety of environmental factors such as light, temperature, soil water, soil fertility and salinity, and for most plants, a change in an individual factor may alter the content of SMs even if other factors remain constant. Here, we review with emphasis how each of single factors to affect the accumulation of plant secondary metabolites, and conduct a comparative analysis of relevant natural products in the stressed and unstressed plants. Expectantly, this documentary review will outline a general picture of environmental factors responsible for fluctuation in plant SMs, provide a practical way to obtain consistent quality and high quantity of bioactive compounds in vegetation, and present some suggestions for future research and development.

Response of Plant Secondary Metabolites to Environmental Factors.

Flavonoids are a large and diverse group of compounds that, by their presence or absence, contribute greatly to wine quality. While the flavonoid content and composition of a wine reflects the vinification process to some extent, the primary determinant is the composition of the grapes at harvest. Thus, considerable research has been directed toward understanding the nature of flavonoids in grapevines, the factors that influence their biosynthesis, and how this knowledge might be used to manage and manipulate the flavonoid composition of berries at harvest. This review examines the flavonoids as a class of compounds, the role these compounds play in the plant, their contributions to wine quality, and recent research on the impacts of environmental factors and cultural practices on the flavonoid content and composition of grape berries.

Cultural Practice and Environmental Impacts on the Flavonoid Composition of Grapes and Wine: A Review of Recent Research

Wine has been part of human culture for 6,000 years, serving dietary and socio-religious functions. Its production takes place on every continent, and its chemical composition is profoundly influenced by enological techniques, the grape cultivar from which it originates, and climatic factors. In addition to ethanol, which in moderate consumption can reduce mortality from coronary heart disease by increasing high-density lipoprotein cholesterol and inhibiting platelet aggregation, wine (especially red wine) contains a range of polyphenols that have desirable biological properties. These include the phenolic acids (p-coumaric, cinnamic, caffeic, gentisic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin, epicatechin, and quercetin). They are synthesized by a common pathway from phenylalanine involving polyketide condensation reactions. Metabolic regulation is provided by competition between resveratrol synthase and chalcone synthase for a common precursor pool of acyl-CoA derivatives. Polymeric aggregation gives rise, in turn to the viniferins (potent antifungal agents) and procyanidins (strong antioxidants that also inhibit platelet aggregation). The antioxidant effects of red wine and of its major polyphenols have been demonstrated in many experimental systems spanning the range from in vitro studies (human low-density lipoprotein, liposomes, macrophages, cultured cells) to investigations in healthy human subjects. Several of these compounds (notably catechin, quercetin, and resveratrol) promote nitric oxide production by vascular endothelium; inhibit the synthesis of thromboxane in platelets and leukotriene in neutrophils, modulate the synthesis and secretion of lipoproteins in whole animals and human cell lines, and arrest tumour growth as well as inhibit carcinogenesis in different experimental models. Target mechanisms to account for these effects include inhibition of phospholipase A2 and cyclo-oxygenase, inhibition of phosphodiesterase with increase in cyclic nucleotide concentrations, and inhibition of several protein kinases involved in cell signalling. Although their bioavailability remains to be fully established, red wine provides a more favourable milieu than fruits and vegetables, their other dietary source in humans.

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Wine as a biological fluid: History, production, and role in disease prevention

Climate change associated effects on grape and wine quality and production

The fruiting capacity of grapevines in a given climatic region is largely determined by their total leaf area and by the percentage of the total leaf surface area that is exposed to full sunlight, provided other factors are not limiting growth and the initiation of fruit primordia. A wide range of leaf area/crop weight ratios were investigated by pruning to different levels of buds per vine, by different degrees of defoliation, and/or by cluster thinning of grape cultivars Thompson Seedless, Tokay, Chenin blanc, and Cabernet Sauvignon located at Davis or Oakville, California. For single-canopy (SC) type trellis-training systems, the leaf area/crop weight ratio required for maximum level of total soluble solids, berry weight, and berry coloration at harvest ranged from 0.8 to 1.2 m2/kg, whereas for horizontally divided-canopy (DC) type trellis-training systems (GDC, lyre, wye), this ratio was reduced to 0.5 to 0.8 m2 leaf area per kg fruit. Optimal crop yield/pruning weight, pruning weight (kg) per m canopy length, leaf area (m2) per m canopy length, and leaf area density (m2/m3) for SC systems ranged from 4.0 to 10, 0.5 to 1.0 kg/m, 2 to 5 m2/m, and 3 to 7 m2m−3, respectively. Similarly, for DC systems these ratios ranged from 5.0 to 10, 0.4 to 0.8 kg/m, 2 to 4 m2/m, and 3 to 6 m2m−3, respectively. Grapevines with ratios that fell within the ranges given above for each of these five parameters were considered well balanced and capable of producing high-quality fruit and wines.

Leaf Area/Crop Weight Ratios of Grapevines: Influence on Fruit Composition and Wine Quality

Fruit coloration was investigated in Emperor vines grown in pots in sunlit phytotron, lathhouse, and field conditions under various temperature and light regimes in combination with different levels of nitrogen. At day/night temperatures of 37/32°C no anthocyanins were formed in fruits under either high light (HL; 66.5% sunlight) or low light (LL; 9.5% sunlight), whereas at field temperatures (FT; mean daily temperature 20.3°C), considerable anthocyanins formed under HL (100% sun) or LL (8.9% sun). At 37/32°C, soluble solids in fruits did not increase above 12.9° Brix, whereas at FT, 21° Brix was obtained under HL. The inhibition of anthocyanin formation and sugar accumulation in berries at 37/32°C and HL could not be reversed by transferring vines to temperature favorable for anthocyanin synthesis (FT), whereas when vines at 37/32°C and LL were transferred to FT at HL there was rapid accumulation of sugars but only slight formation of anthocyanin. Anthocyanin in berries decreased 59% in 20 days when the vines were transferred from FT-HL to 37/32°C-HL. Anthocyanin and soluble solids were significantly greater (P Fruit color and soluble solids were significantly less (P

Influence of Temperature, Solar Radiation and Nitrogen on Coloration and Composition of Emperor Grapes

Glucose, fructose, galactose, sucrose, maltose, melibiose, raffinose, and stachyose were identified in the leaves, bark, roots, and berries of Vitis vinifera L. var. Thompson Seedless. In addition to these sugars, verbascose and manninotriose were found in the leaves and bark. Malic, tartaric, citric, isocitric, ascorbic, cis -aconitic, oxalic, glycolic, glyoxylic, succinic, lactic, glutaric, fumaric, pyrrolidone carboxylic, α-ketoglutaric, pyruvic, oxaloacetic, galacturonic, glucuronic, shikimic, quinic, chlorogenic, and caffeic acids were identified in the leaves, bark, roots, and berries. Glucose, fructose, sucrose, malate, tartrate, and citrate were determined quantitatively in the leaf, petiole, xylem, bark, tendril, bud, puduncle pedicel, berry, lateral roots, and main roots at 4 separate physiological stages of growth. In addition, changes in the concentrations of fructose, glucose, malate, and tartrate in leaves were measured during a 36-day period starting from budburst.

Sugars and Organic Acids of Vitis vinifera.

The influence of two irrigation regimes (none and frequent), two levels of K fertilization (0 and 2.2 kg potassium sulfate per vine per year) and two crop levels (not thinned and thinned to one cluster per shoot) on grape and wine quality from field grown Carignane vines was studied at Davis, California, over a period of three years (1979 to 1981). Irrigation, K fertilization and crop level had a minor and inconsistent effect on petiole K concentration. Irrigation and crop level had no effect of lamina K concentration. Irrigation, K fertilization and crop level did not affect the rate of increase in berry weight after the data were transformed to remove the inherent variability of final berry size. Concentration of soluble solids in fruits was reduced by irrigation, but the pH and K concentrations were increased by irrigation. The rate of increase of berry juice K concentration with increasing soluble solids followed a sigmoidal pattern. K accumulated rapidly until fruit reached about 10°Brix, followed by relatively slow accumulation between 10° and 17°Brix, and then there was a second rapid period of accumulation during the final stages of ripening. The concentration of K in nonirrigated fruits at maturities greater than 10°Brix was less than in irrigated fruits. The increase in pH at soluble solids concentration greater than 17°Brix was associated with increase in K concentration. Crop level and K fertilization had no effect on grape juice pH, titratable acidity and K. Concentrations of arginine and proline in berry juice of nonirrigated vines were significantly less than in irrigated vines on a given date. Irrigation reduced the concentration of anthocyanins in berry skin and wine compared to nonirrigated fruit. Water stress was more important in regulating wine pH than crop level or soil K level, suggesting that irrigation management may be a useful method to help reduce high pH problems and improve wine quality.

Effect of Irrigation, Crop Level and Potassium Fertilization on Carignane Vines. II. Grape and Wine Quality

Total titratable acidity, pH, and concentrations of total tartrate and malate, tartaric and malic acids, and their acid salts in the fruits of 28 table varieties and 50 wine varieties of Vitis vinifera L. were determined at an early and at a late stage of fruit maturity for the 1966 season at Davis. Total titratable acidity of early- and late-harvested table varieties ranged from 0.38 to 1.12 and from 0.29 to 0.77, with averages of 0.60 and 0.49, respectively, Similarly, the pH ranged from 3.15 to 3.92 and from 3.60 to 4.36, with averages of 3.55 and 3.93. The ranges in total titratable acidity and pH were respectively 0.37 and 1.32 and 3.02 to 4.04 for earlyharvested wine varieties and 0.34 to 0.92 and 3.09 to 4.28 for late-harvested varieties. The concentrations of tartrates and malates in the fruits varied widely among varieties and usually decreased between the early and late harvests. For all varieties, the average percentages of the total titratable acidity due to tartrates and to malates were respectively 56 and 50% at the early harvest, and 57 and 45% at the late harvest. The varieties were divided into high, moderately high, intermediate and low malate groups based on the ratio of tartrates to malates. The concentrations of tartaric and malic acids in all varieties decreased between the early and late harvests, while those of tartrate and malate salts increased. The concentrations of acid tartrate and malate generally remained approximately the same between the two harvest dates. Concentrations of acid tartrate and tartrate salts were usually considerably greater than those of acid malate and malate salts. The average amounts of tartrates present as free acid at early and late harvests were respectively 23 and 11%. The average amounts of malates present as free acid at early and late harvests were respectively 45 and 27%.

W. Mark Kliewer

Papers

Leaf Area/Crop Weight Ratios of Grapevines: Influence on Fruit Composition and Wine Quality

Influence of Temperature, Solar Radiation and Nitrogen on Coloration and Composition of Emperor Grapes

Sugars and Organic Acids of Vitis vinifera.

Effect of Irrigation, Crop Level and Potassium Fertilization on Carignane Vines. II. Grape and Wine Quality

Concentrations of tartaric acid and malic acids and their salts in Vitis vinifera grapes