**1.4 Management of aroma in vineyards**

One of the main factors that influence the evolution of the aroma is management in vineyards. Viticulture practices, which include management of vineyard cultivation, are controlled by human beings and, may be used to change the quality of the wine. These practices involve very varied factors as for example those based on decisions affecting the orientation vineyards' rows, their training system, density, the calendar for pruning, trimming, fungicide treatments, or the way in which soil surface is managed, which includes its tillage, the manipulation of the canopy structure, the nitrogen fertilization [13]. Additionally, vineyard cultivation may be affected by sunlight and water, among others, which will determine the final quality of berries since they are very sensitive to the microclimate. All the factors could change year by year, so the potential aroma of the wine depends on the year.

The amount of light absorbed by the vine leaf area determines the rate of photosynthesis, hence its metabolism. Therefore, light influences the development of grape aroma compounds. This relation is complex, as direct sunlight induces beneficial changes in photosynthetic pigment levels, but can cause stress by dehydration or temperature increase. Excessive sunlight exposure may burn the grapes' skin, resulting in a bitter flavor and affecting the quality of the wine [9]. Several studies reflect that sun exposure plays an important role in the variations of the volatile composition of grapes [14–16]. Some authors [17, 18] reported that high levels of terpene precursors are produced in over-ripe grape. The concentration of free and bound terpenes can also be increased by exposure of grapes to the sun [19, 20].

Canopy management is also important. Limiting canopy growth by removing leaves and vine shoots allows the increment of glucose production in the fruit, improving fruit's sunlight exposure. Nowadays, different ways for canopy structure management have been developed. The most common one is the plucking of leaves. It improves the microclimate of the clusters, reduces grape rot (caused by different pathogenic bacteria, yeast and, fungi, such as *Botrytis cinerea*) and provides better fruit maturation since less shadow is generated and enhances the pass of the sunlight. Another technique is head trimming which consists of cutting growing shoot tips in order to remove non-photosynthetic leaves. This technique reduces transpiration and induces the lignification of the plant, balances the development of

## *Management of Wine Aroma Compounds: Principal Basis and Future Perspectives DOI: http://dx.doi.org/10.5772/intechopen.92973*

branches and increases airflow and insulation within the foliage [13]. Additionally, the removal of leaves may increase the content of total and phenol-free glycosides (one group of compounds that influence the aroma) [21]. In fact, wines obtained from defoliated grapes usually present higher fruity notes [22, 23]. Leaf-plucked grapes show the highest values of terpene and norisoprenoids compounds in Tempranillo, Merlot, and Gewürztraminer varieties where the synthesis of precursors is higher in warmest years and in grapes with more exposure to the sun [13].

As it has been previously described, soil and weather have an important effect on wine aroma, and this is mostly mediated by water. In general terms, water deficit has been proved to improve wine quality, enhance color, flavor and/or aroma [24]. However, no definitive scientific results can prove that the lack of water has such direct and positive impact on the quality since the effect of water depends on the species. For instance, during the maturation of Riesling grapes, the accumulation of terpene precursors is lower under irrigation [25]. In Tempranillo grapes, a positive correlation between irrigation and aroma potential at harvest has been detected [26, 27]. In Agiorgitiko grapes, precursors'synthesis is promoted by the limited availability of water [28]. There are several studies about the impacts of irrigation on fruit composition and wine sensory properties. However, the majority of these studies have been conducted in arid regions where irrigation is considered necessary and only a few have been carried out in humid regions where irrigation is mostly not necessary [29].

Among the nutritive compounds of must, the amino acids are of great importance. They can serve as precursors of esters and also may play an indirect role in supporting cellular metabolic activities [30]. Consequently, wine growers can also modify soil fertilization to change the aromatic profile of the resulting wine. The nitrogen soil composition can lead to excessive vine vigor and susceptibility to gray rot, but can also enhance aroma expression since yeasts use that same nitrogen [31]. Nevertheless, when juice presents a sufficient amount of nitrogen, the addition of amino acids does not improve the volatile composition of wine, therefore the excess of the amino acids will probably be consumed by other cellular processes [30].

As wine quality strongly depends on the grape quality, it is necessary to process healthy grapes at the correct ripeness stage in order to obtain high-quality wines. For this reason, winegrowers have to be especially careful in the prevention of parasite attacks on the grapevine. Fungicide treatments are applied to prevent diseases such as botrytis, powdery mildew or downy mildew, which cause serious problems in the production. However, these fungicides can pass to wines at trace levels and can affect the aroma, and also the safety of the wine [9]. In addition, pesticide residues on grapes can be transferred to the must and influence the selection and development of yeast strains. On the other hand, yeast can reduce the levels of the pesticides in the wine or adsorb them on the dregs of the wine. The persistence of pesticides depends on several factors such as the chemical characteristics of the active ingredients, photodegradation, thermodegradation, codistillation and enzymatic degradation [32]. However, more studies are needed to orient the preferences of winegrowers for one or another fungicide.
