INFLUENCE OF THE THICKNESS OF OAK ALTERNATIVES ON THE COMPOSITION AND QUALITY OF RED WINES

Abstract

Aging red wines in oak barrels is an expensive and laborious process that can only be applied to wines with a certain added value. For this reason, the use of oak alternatives coupled with micro-oxygenation has progressively increased over recent years, because it can reproduce the processes taking place in the barrels more economically and quickly [1]. Several studies have explored how oak alternatives [2-5] can contribute to wine composition and quality but little is known about the influence of their thickness. The aim of this research was therefore to study how different thickness of oak alternatives would influence the color, phenolic compounds and volatile composition of a red wine, especially with regard to the substances released by oak wood. For that purpose, a red wine was introduced in twelve 100-L plastic tanks with an oxygen permeability similar to oak barrels (Flexcube, Quilinox). Three tanks were supplemented with 2.5 g/L oak chips (between 7.5x3x1.5 and 20x13x3 mm), other three with 5 g/L of thin staves (7x47x960 mm), other three with 10 g/L of thick staves (17x47x960 mm) and finally the last three were maintained as controls. These dosages were chosen based on an equivalent oak impact intensity according to previous experiences.
All the wood alternatives were made of French oak (Q, petraea) with origin and characteristics as similar as possible. The wines were analyzed at 2, 6 and 12 months of aging in that conditions. Wines were also tasted by a trained panel at the end of aging time. The color intensity (CI), the Total Polyphenol Index (TPI) and the total tannins quantified by the methyl-cellulose precipitation method were significant higher in all wines supplemented with oak alternatives in respect to the controls, and it was observed that all these parameters increased as the thickness of the alternatives increased. In contrast, anthocyanins showed the opposite trend, being lower in concentration when the thickness of the alternatives was greater. Both trends, higher CI and lower anthocyanin concentration as the thickness of the oak alternatives increases, can be explained by the formation of polymeric pigments. In fact, the PVPP Index (% of combined anthocyanins) and the Ionization index (% of colored anthocyanins) augment as thickness increases. In general, all the volatile compounds coming from the wood (furans, vanillin, volatile phenols and whiskey-lactones) increased throughout the aging time and this increase was more important when the thickness of the alternatives was higher. Finally, the trained panel considered that color, aromatic intensity and complexity, sweetness, mouthfeel, structure and persistence of the wine improved significantly as the thickness of the alternatives increased. In addition, the panel preferred the wine aged with thick staves, followed in decreasing order by the wines aged with thin staves, oak chips and control. It can be concluded therefore that the thickness of the oak alternatives seems to have a clear influence on the composition and quality of the wines, the effect being significantly better when the thickness is higher.