The turbidity of red wine during its ageing in oak casks has an influence on the accumulation of volatile compounds and, thereby, on the wine’s aroma, but not on the accumulation of biogenic amines. This is the conclusion of Nerea Jiménez Moreno in her PhD thesis defended at the Public University of Navarre. The PhD is entitled, “Ageing of red wine with different turbidity in barrels of oak. - the volatile composition and content of amines”.
After studying the ageing process of the same wine, filtered and unfiltered, over an eighteen-month period, Nerea Jiménez concluded that, in the unfiltered wine, the “lees” - the remains of yeasts, bacteria and other particles in suspension and that precipitate during the wine’s time in the cask – are able to retain certain volatile compounds that are responsible for the wine’s aroma. As regards the biogenic amines, the author explains that, during the ageing process of the wine, amines still continue to form but that the turbidity of the wine does not influence the accumulation of these compounds.
The aroma of the wine
Aroma is a highly important aspect determining the quality of wine. Primary aromas are those belonging to and characteristic of the variety of grape used for the elaboration of the wine. The compounds originating from fermentation – the most abundant – are responsible for the fruity and/or flowery aromas of wine and are known as secondary aromas. Finally, the compounds giving rise to the tertiary aromas come from the oak wood during the ageing process in the cask and subsequent evolution in the bottle.
With the ageing (crianza) of the wine in oak casks, not only is a greater aromatic and flavour complexity sought but, during this process, a series of simultaneous physical-chemical phenomena are produced that give the wine greater clarity and stability.
However, the ageing of wine in oak casks is an expensive process, largely due to the cost of acquiring the barrels as well as the time that the product has to remain stored in the wine cellar. Because of this, it is very important to know the factors influencing the maturing process of the wine and how to influence these in order to optimise the process.
In this sense, Ms Jiménez’s study has enabled the conclusion to be drawn that the turbidity of wine during the ageing process had influence both on the evolution of fermentation esters and on the accumulation of volatile compounds originating in the oak barrel; but that the fixation of the aromatic compounds of the lees depends on the composition of the latter and on the grape used.
As regards the sensorial implications of these findings, a wine-tasting session was carried out, with both filtered and unfiltered wines, after maturing between three and twelve months. The conclusion was that the filtered wines were more pleasant on the nose but more aggressive on the palate, while the unfiltered wines stood out for their qualities on the palate. In fact, the tasters were able to distinguish between filtered and unfiltered wines. The scientific literature coincides, effectively, in that the lees provide greater roundness and untuosity to the wine, which enhances the sensations on the palate of the consumer on drinking this product.
Another aspect related to the quality of wines that has sparked great interest over the past few years and that Ms Jiménez has studied for her research, is the presence of biogenic amines in this alcoholic drink. These nitrogenated compounds are mainly formed during the alcoholic and malolactic fermentations of the wine, their importance lying in the negative effects on human health that can arise with their ingestion. Consuming wine with high concentrations of these amines, principally histamine and tyramine, can cause headaches, allergic reactions, heart palpitations, high blood pressure, diarrhoeas, and so on.
Moreover, the presence of high concentrations of histamine in wines can give rise to export restrictions, as a number of countries are planning to place recommended limits on this histamine content in wines; in other countries, such as Switzerland, they have already imposed this limit. To this end, it is important to know the evolution of the biogenic amines during the cask maturing of the wine as their final concentration can determine its exportability.
In her PhD, Nerea Jiménez concluded that there exists a grand variety in the evolution of biogenic amines during the maturing process of the wine in the barrel. For example, histamine and tyramine, the most toxic, are formed at the beginning of the process and subsequently their concentration falls, possibly due to their degradation. Nevertheless, putrescine and cadaverine, both of which boost the toxic action of the former two amines, build up in the wine throughout the whole ageing process.
These findings are important in that they warn the enologist not to drop their guard in the control of these post-malolactic fermentation compounds, especially if part of the wine production is to be exported.
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