María del Alamo-Sanza

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.

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.

Evaluation of grape pomace from red wine by-product as feed for sheep

BACKGROUND This work aimed to study the chemical composition and in vitro digestibility of seeds and pulp from grape pomace. In sacco degradability, ruminal fermentation of grape pomace fractions and plasma lipid peroxidation were also studied in sheep fed with or without grape pomace. RESULTS Seed and pulp fractions of grape pomace had different values for cell walls (523 vs 243 g kg-1 dry matter (DM)), crude protein (CP, 104 vs 138 g kg-1 DM), ether extract (EE, 99.0 vs 31.7 g kg-1 DM), polyunsaturated fatty acids (PUFA, 69.6 vs 53.3%) and extractable polyphenols (55.0 vs 32.1 g kg-1 DM). The in vitro true digestibility, DM in sacco degradability and CP degradability of seeds and pulp were also different (0.51 vs 0.82, 0.30 vs 0.45 and 0.66 vs 0.39 respectively). The ammonia-N concentration and total volatile fatty acids (VFA) in ruminal liquid were significantly lower and plasma lipid peroxidation was also numerically lower in sheep that consumed grape pomace. CONCLUSION The nutritive value of grape pomace varies depending on the proportion of seeds and pulp. The interest of this by-product in sheep feeding could be related to its polyphenol and PUFA content, which could improve meat and milk quality.

On-line monitoring of oxygen as a method to qualify the oxygen consumption rate of wines

Measuring the oxygen content during winemaking and bottle storage has become increasingly popular due to its impact on the sensory quality and longevity of wines. Nevertheless, only a few attempts to describe the kinetics of oxygen consumption based on the chemical composition of wines have been published. Therefore, this study proposes firstly a new fitting approach describing oxygen consuming kinetics and secondly the use of an Artificial Neural Network approach to describe and compare the oxygen avidity of wines according to their basic chemical composition (i.e. the content of ethanol, titratable acidity, total sulfur dioxide, total phenolics, iron and copper). The results showed no significant differences in the oxygen consumption rate between white and red wines, and allowed the sorting of the wines studied according to their oxygen consumption rate.

Oak wine barrel as an active vessel: A critical review of past and current knowledge

ABSTRACT We review the role of the oak barrel as an active vessel for wine maturation. We present a historical background to highlight that previously established aspects of processes occurring with wine inside the oak barrel are still without confirmation. We argue that recently published new findings on the topic are determining factors in defining the manner in which the oak barrel works with wine. Several studies have been published reviewing how the wine barrel functions as an active vessel that releases chemical compounds into the wine, improving its physical, chemical, and sensory properties. Nevertheless, there are hardly any studies that describe how a wine barrel functions as an active vessel. The present review details the main factors affecting the gas exchange capacity of the barrel, such as the pressure drop generated within the barrel, the formation of a headspace, the effect of wood anatomy, the different oxygen entry routes, the role of wood moisture content and soluble ellagitannins, and the effect of barrel toasting on cooperage. Finally, a hypothesis is proposed regarding the function of the barrel as an active vessel, which determines the manner in which it interacts with the wine that it contains during aging.

Ratiometric Oxygen Imaging to Predict Oxygen Diffusivity in Oak Wood During Red Wine Barrel Aging

In this work, we present a high-resolution oxygen imaging approach to study the two-dimensional oxygen distribution inside an oak stave in contact with wine and that applies the series resistance model to explain the dynamic evolution of oak wood oxygen transfer rate (OTR). Oxygen flux throughout the oak stave has been studied by considering the wood as a permeable membrane with moisture content (MC) in a decreasing gradient from the wine-contacting side of the oak stave to the side in contact with atmospheric air in cellar conditions. The presence of different levels of liquid across the thickness of the wet stave modifies the oxygen diffusion flux, as the diffusion coefficient of oxygen in water is four orders of magnitude lower than in air. The stave resembles a multilayered membrane, where wood with an MC over the fiber saturation point represents a distinct layer. To that end, three simultaneous measurements were made, namely the MC profile of the wood within the thickness of the stave at different liquid-wood contact times, the OTR of the stave at those times, and finally the oxygen concentration profile within the thickness of the stave using planar optical sensors, a color camera, and ratiometric image analysis. The results show heat flux and oxygen flux that is analogous to that in a multilayer.

The influence of selected winemaking equipment and operations on the concentration of dissolved oxygen in wines

Oxygen has a determining effect on the quality and longevity of wines. In spite of its importance, there are only a limited number of reports examining the levels of dissolved oxygen during wine production and the enrichments produced by different operations. In this study, the contribution of selected winemaking equipment and operations ( i.e., pumping, centrifugation, tartrate stabilization, filtration and bulk wine transportation) on the concentration of dissolved oxygen in wines was assessed using a photoluminescence-based oxygen meter. For example, winemaking equipment such as diatomaceous earth filtration and membrane filtration caused dissolved oxygen increases between 0.100 and 0.200 mg L -1 , and pad filtration and centrifugation showed average oxygen enrichments of approximately 0.350 mg L -1 . However, operations such as filtration with rotary vacuum equipment and continuous tartrate stabilization produced oxygen enrichments up to ~2.8 mg L -1 . A better awareness of the levels of oxygen incorporated by different winemaking practices will help incorporate the necessary safeguards to protect wines from oxidation and estimate the magnitude of the cumulative exposure to oxygen during winemaking. El oxigeno tiene un efecto determinante en la calidad y la longevidad de los vinos. A pesar de su importancia, existe solo un numero limitado de investigaciones donde se analice la concentracion de oxigeno disuelto durante la produccion de vinos y los efectos de diferentes practicas de vinificacion sobre dichos niveles. En este estudio, se evaluo la contribucion de diversos equipos y practicas de vinificacion (ej. bombeo, centrifugado, estabilizacion tartarica, filtracion y transporte del vino a granel) sobre la concentracion de oxigeno disuelto en vinos, utilizando un medidor de oxigeno basado en el principio de fotoluminiscencia. Por ejemplo, equipos de soporte a la elaboracion de vino tales como filtros de tierras diatomeas y filtros de membranas produjeron de entre 0,100 hasta 0,200 mg L -1 , la filtracion por placas y la centrifugacion mostro enriquecimientos promedio de oxigeno de alrededor de 0,350 mg L -1 , mientras que el uso de filtros rotatorios al vacio y equipos de estabilizacion tartarica continua produjeron enriquecimientos de oxigeno de hasta ~ 2,8 mg L -1 . Un mejor conocimiento de los niveles de oxigeno incorporadas por las diferentes practicas enologicas ayudara a tomar las salvaguardias necesarias para proteger los vinos de las oxidaciones y estimar la magnitud de la exposicion acumulativa al oxigeno durante la elaboracion del mismo.

Wine evolution and spatial distribution of oxygen during storage in high-density polyethylene tanks

BACKGROUND Porous plastic tanks are permeable to oxygen due to the nature of the polymers with which they are manufactured. In the wine industry, these types of tanks are used mainly for storing wine surpluses. Lately, their use in combination with oak pieces has also been proposed as an alternative to mimic traditional barrel ageing. RESULTS In this study, the spatial distribution of dissolved oxygen in a wine-like model solution, and the oxygen transfer rate (OTR) of high-density polyethylene tanks (HDPE), was analysed by means of a non-invasive opto-luminescence detector. Also, the chemical and sensory evolution of red wine, treated with oak pieces, and stored in HDPE tanks was examined and compared against traditional oak barrel ageing. The average OTR calculated for these tanks was within the commonly accepted amounts reported for new barrels. With regards to wine evolution, a number of compositional and sensory differences were observed between the wines aged in oak barrels and those stored in HDPE tanks with oak barrel alternatives. CONCLUSION The use of HDPE tanks in combination with oak wood alternatives is a viable alternative too for ageing wine.