**4. Future perspectives**

The most abundant lactones areγ-butyrolactone, 4-carbethoxy-8-butyrolactone and

**Chemical structure Olfactory**

**descriptor**

manure

**ODT (mg/l)**

0.620

The main volatile phenols produced by *Saccharomyces cerevisiae* yeasts are 4 vinylphenol and 4-vinylguaiacol. Within this group is also 4-ethylphenol, which is produced by yeasts belonging to the genus *Brettanomyces/Dekkera*. It is produced by

This type of aroma includes all volatile compounds formed throughout the aging of the wine, giving rise to what is called "bouquet". During the conservation of the wine, physicochemical and biological reactions transform the aromatic compounds produced in previous stages, so post-fermentative aroma suffers deep changes [79].

enzymatic decarboxylation of *p*-coumaric and ferulic acids during alcoholic

Depending on the type of aging, two types of bouquet can be distinguished:

• The bouquet of oxidation takes place in wooden barrels. It is produced by the synthesis of acetaldehydes and/or acetals, as well as by the extraction of a series of nuances from wood and the diffusion of oxygen through the wood

• The bouquet of reduction is characteristic of aging in the bottle, determined by the interaction between the wine compounds synthesized throughout the

During this stage, the fruity aroma of the wines disappears progressively, evolving towards a more complex aroma. These reactions are slow and limited, sensibly

In this type of wines, there are compounds given by wood such as furans (furfural, 5-methylfurfural, 5-hydroxymethylfurfural) which are responsible for the aromas of roasted almonds [81], phenolic aldehydes (vanilla), phenyl ketones (vanilla aroma), oxygenated heterocycles (caramel aroma), volatile phenols (toasted smell and burnt wood) [82], 4-vinylphenol (carnation aroma), 4-vinylguaiacol (clove aroma), whiskey-lactones (coconut aroma) [83].

4-ethoxy-γ-butyrolactone.

*Olfactory detection threshold (ODT).*

**Table 3.**

**Compound Molecular**

**formula**

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

*Relevant aroma compounds produced during wine fermentation [77, 78].*

4-ethylphenol C8H10O Medicinal horse

4-ethylguaiacol C9H12O₂ Wood 0.05

*3.2.2.7 Volatile phenols*

fermentation [69].

pores [79].

**62**

fermentation [80].

manifesting in the wines after several years.

**3.3 Post-fermentative aroma**

The complexity of wine's aroma has been considered more an art than a scientific fact since little knowledge of the mechanisms involved in the process is available. However, in the last decades, this situation is changing as more and more wine growers turn to science to improve their production. In the nearly future, winerelated genomic, proteomic and metabolomic research will be applied to *Vitis vinifera* cultivars (the important ones from a commercial point of view), to other *Vitis* species, as well as to the yeast strains employed in fermentation [9]. Nowadays, scientific research helps, for example, to understand the impact of wine microorganisms and their derivatives on varietal aromas. This allows winemakers to generate different wines with different characteristics (including aromatic ones) from the same matrix (same grapes), using different species of microorganisms.

The aromatic quality of wines in the near future will depend on climate change and the effect of greenhouse gases. The increment of these gases will carry an average raise on global surface temperatures, evaporative demand, and the frequency and intensity of drought. Studies about changes in the volatile composition, phenolic content and antioxidant activity of wines produced at elevated CO2 concentrations are very limited, so it will be necessary to optimize the quality of wine in a future scenario of climate change [9]. Climate change will also allow to cultivate vineyards in not cultivable areas until now. For instance, the viticulture sector of United Kingdom has undergone a rapid growth (148% during 2004–2013), in part attributed to a warmer temperature in the areas of England and Wales (13–15°C), deemed suitable for cool-climate viticulture [85].

There is a future concern about that wines in the future could being "manipulated" by using chemical additives to add enhance complexity and additional aromas to wine such as created a manufactured perfume. In fact, there have already been cases. In 2004, a South-African winery was found to have added illegal flavoring to their Sauvignon blanc to enhance the aroma [86]. Increasing the knowledge about the mechanisms and compounds responsible for wine aroma helps to develop new methods to allow the improvement of the quality of common wines to resemble high-quality wines. However, any artificial manipulation of wine aroma is currently forbidden, and there is a significant number of winemakers and consumers that prefer more natural wines, without or with minimum chemical manipulation. The wine is widely consumed around the world by its nice sensory taste and its natural origin from fermented grape juice. Change this view could be dangerous to the wine industry and can lead to a significant noteworthy wine devaluation towards by the wine consumers and connoisseurs.
