Ignacio Nevares

Effect of size, seasoning and toasting in the volatile compounds in toasted oak wood and in a red wine treated with them

The increasing demand for wood for barrel-making in addition to the rapid extension of alternative aging system, have led to looking into the possibility of utilizing Spanish oak. Quercus pyrenaica is the species that predominates in Spain, and the chemical composition of its heartwood (ellagitannins, low molecular weight phenolic and volatile compounds) and its incidence in characteristics of wine are similar to that of other species that are of recognized oenological quality for barrel-making, showing only quantitative differences with respect to French (Quercus petraea) and American (Quercus alba) species. However, at present, the quantity of good quality wood that we can obtain from the Q. pyrenaica Spanish forest is limited. Hence, in the short term, and considering the high chemical oenological quality of Q. pyrenaica wood, we propose the utilizing of chips, segments, staves, and other oak alternatives for wine aging, which would be obtained from wooden remnants from barrel-making as well as from trees with small diameters or physical defects which would normally be inappropriate for cooperage. With regards to the latter idea, studies on special chip-making processes, and other oak wood pieces are being carried out, especially focused on reducing seasoning time, and to toasting optimization as a function of wood piece size, in addition to its behaviour when incorporated into the different alternative aging systems. We present in this study the effect of seasoning way (traditional or unconventional) on volatile composition of Q. pyrenaica chips and staves at three toasting levels (light, medium and heavy), and the evolution of the wood-released aromatic composition of a Spanish artificially aged wine, using these alternative products. The wines showed in general small differences in their oak-derived characteristics, which were more related to the wood piece size and the toasting intensity than to the seasoning way, and they could be linked with the concentrations of compounds as eugenol, furfural, and the cis and trans isomers of beta-methyl-gamma-octolactone.

Aging markers from bottled red wine aged with chips, staves and barrels.

This paper shows the results of the experiments carried on Spanish red wines aged through alternative as well as traditional oak barrel systems, i.e., chips stainless steel tanks and staves stainless steel tanks, at the same time and under the same conditions. Wine aging through wood pieces is not accepted as an enological practice by the European Union and, in fact, it is considered a fraud. It is, then, of a great interest to identify those parameters able to establish the aging technique that had been used in a wine ready to be consumed. With this idea in mind, the development of the same wine has been studied while aging for 3 years in three different systems. During the first six aging months wines stored with staves obtained characteristics that were halfway between wines treated with chips and those aged in barrels. However, as wood contact period length increased so did the differences between wines stored in traditional and alternative systems (either with staves or chips). These differences grew during the bottling period, so that after a 2-year bottling period wines from the three systems became different enough to tell them apart. Discriminant analysis of the variables studied made it possible to establish these differences. The most meaningful variables were yellow colour component, anthocyanins (cyanidin-3-glucoside, vitisin A and sum of pcoumaryl derivates), vanillin acid, protocachuic aldehyde and epicatechin.

Measurement of dissolved oxygen during red wines tank aging with chips and micro-oxygenation

Nowadays, micro-oxygenation is a very important technique used in aging wines in order to improve their characteristics. The techniques of wine tank aging imply the use of small doses of oxygen and the addition of wood pieces of oak to the wine. Considering the low dissolved oxygen (DO) levels used by micro-oxygenation technique it is necessary to choose the appropriate measurement principle to apply the precise oxygen dosage in wine at any time, in order to assure its correct assimilation. This knowledge will allow the oenologist to control and run the wine aging correctly. This work is a thorough revision of DO measurement main technologies applied to oenology. It describes the strengths and weaknesses of each of them, and draws a comparison of their workings in wine measurement. Both, the traditional systems by electrochemical probes, and the newest photoluminescence-based probes have been used. These probes adapted to red wines ageing study are then compared. This paper also details the first results of the dissolved oxygen content evolution in red wines during a traditional and alternative tank aging. Samples have been treated by three different ageing systems: oak barrels, stainless-steel tanks with small oak wood pieces (chips) and with bigger oak pieces (staves) with low micro-oxygenation levels. French and American oak barrels manufactured by the same cooperage have been used.

Micro-oxygenation strategy depends on origin and size of oak chips or staves during accelerated red wine aging

The practice of wine aging in stainless steel tank involves storing wine in contact with wood and dosing it with small oxygen quantities in order to obtain a final wine more stable in time and with the same characteristics of barrel-aged wines. Oxygen dosing is a key factor and, to achieve a correct development of wine, needs to be applied according to wine necessities and to the kind of wood chosen. This paper shows the results obtained from the study of oxygen required by a same wine aged in tanks with different alternative products (chips and staves) made of American (Q. alba), French (Q. petraea) and Spanish oak (Q. pyrenaica), with a strategy of micro-oxygenation as required. The results indicate that the size and origin of the wood used determine the oxygen management during the process. In fact, wine treated with big pieces (staves) consumes more oxygen and, with regard to wood origin, wine aged with French oak (Q. petraea) products needs of a higher oxygen dosage.

Recent Advances in the Evaluation of the Oxygen Transfer Rate in Oak Barrels

The entry of atmospheric oxygen into wine barrels is a desirable characteristic of the wine aging process. The oxygen transfer rate regulates changes in wine affecting aging rates because some barrels may undergo a greater wine oxygenation. This study measured the transfer rate and oxygen distribution within a barrel. The analysis confirmed the presence of a dissolved oxygen concentration gradient in the liquid, with greater concentrations near the bung. The study of the transfer rate of oxygen over time, in 12 barrels of different types, showed that wetting wood reduces oxygen diffusion and the oxygen transfer rate (OTR). These results are the first to determine the kinetics of oxygen entry into wine barrels and can be used to quantify the annual rate of oxygen entry into wine barrels.

Dissolved oxygen distribution during micro-oxygenation. Determination of representative measurement points in hydroalcoholic solution and wines.

Red wine tank aging is monitored by organoleptic analysis, therefore, it is necessary to use an objective parameter representing the process. Among the possible parameters to be checked, it stands out the knowledge of dissolved oxygen because it offers the possibility of anticipating undesirable situations that bring about too much oxidation. Dissolved oxygen measurement, with non-intrusive luminescent technology is becoming an effective alternative. Uncertainty arises when trying to choose the measuring point able to represent the entire tank since previous works have considered the existence of gradients throughout the volume of the treated wine. This paper shows the results obtained from the study of the existence and the quantification of gradients of the dissolved oxygen in a 15% hydroalcoholic solution during the micro-oxygenation process. Different measuring point placements are studied and the solutions to monitor the process by controlling a representative point are set out. A successful monitoring of a red wine tank aging with alternative oak products and adaptative micro-oxygenation has proved that an objective control of the process is, indeed, possible.

Phenolic compounds and sensorial characterization of wines aged with alternative to barrel products made of Spanish oak wood (Quercus pyrenaica Willd.)

Wood of Quercus pyrenaica has suitable properties for the wine ageing process. However, the forest available for the barrel making from this particular type of tree is very limited. Nevertheless, it is highly advisable to use this kind of wood in order to manufacture alternative oak products. This study presents the results of ageing the same red wine using different pieces of wood (chips and staves) of Spanish oak (Q. pyrenaica), American oak (Quercus alba) and French oak (Quercus petraea) in conjunction with small, controlled amounts of oxygen. In addition, the phenolic parameters, colour and sensory analysis point out that wines aged with Q. pyrenaica pieces have similar enological characteristics to those aged with American or French oak pieces of wood (chips and staves). Furthermore, the total oxygen consumed and its relation with sensory properties also has been studied in this article in order to know how the oxygen behaves in these processes. Besides, it is going to put forward the fact that chips and staves from Q. pyrenaica oak are suitable for the ageing of red wines and better considered than American or French ones, showing higher aromatic intensity, complexity, woody, balsamic and cocoa. Finally, the tasters valued highly the wines with staves, pointing out its flavour and roundness in mouth.

Oak Stave Oxygen Permeation: A New Tool To Make Barrels with Different Wine Oxygenation Potentials

The aim of this study was to classify rough staves according to their permeability to oxygen by measuring their transmission rate to assess the capacity to build barrels with high and low oxygen transmission rates (OTRs). The ability to assess the OTR would be important for better understanding and controlling the aging process of wine in barrels. To accomplish this, we built a device that measures the OTR of rough staves under the same conditions as those in a full barrel, in which the stave is in contact with a liquid solution on one face and with a diffusing gas on the opposite face. A total of 69 rough staves were classified to yield a high-OTR group, with a mean 2.6 times higher than the mean of the low-OTR group. A high-OTR barrel and a low-OTR barrel were constructed, and we confirmed that the stave OTR decreased between 3- and 4.5-fold in the barrels and that the high-OTR barrel allowed the entry of twice the concentration of oxygen compared to the low-OTR barrel. These results confirmed the capacity to classify rough staves and build barrels with different OTRs.

Characterization of the Oxygen Transmission Rate of Oak Wood Species Used in Cooperage

The oxygen that wine receives while aged in barrels is of interest because it defines the reactions that occur during aging and, therefore, the final properties of the wine. This study is intended to make up for the lack of information concerning the oxygen permeability of eight different woods of Quercus alba L. and Quercus petraea (Matt.) Liebl. commonly used. In addition, it shows how oxygen transfer evolves with the liquid contact time during testing under similar aging conditions to those in wine barrels. French oak woods permitted a higher oxygenation rate than American ones in all cases. A decrease in the oxygen entry caused by impregnation of the wood during the process was observed in all of the species studied. This process is determined by the thickness of the flooded wood layer containing free water, although differently in the two species, possibly due to the anatomical structure and the logging process for each.

Investigation and correction of the interference of ethanol, sugar and phenols on dissolved oxygen measurement in wine

The dissolved oxygen in wine is routinely measured to control and monitor various oenological processes. The availability of devices based on different technologies and features allows a user to select a device that best meets their needs. However, grape must and wine samples each exhibit a complex composition that varies with time, which, along with atmospheric conditions, makes it necessary to evaluate the effects of these factors on dissolved oxygen measurements. This work evaluates the effects that ethanol, sugar, and phenols have on dissolved oxygen measurements in a model and real wine. The results suggest that significant errors are made in all studied systems and that the response of each device is different. Therefore, a compensation value was developed to take into account the sample composition. A compensation value was proposed to minimise the error made by each device based on the ethanol and sugar contents of the measured liquid. The best results are those obtained after using the compensation value to correct the data from the Pyro-Mini device. In all cases, errors made in DO measurements by optical systems were reduced by 50-82% by applying the compensation value for synthetic wines and 45-100% for real wines.