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38 p r a c t i c a l w i n e r y & v i n e ya r d J a n U a r y 2 0 1 5 P A C K A G I N G Paulo Lopes,* Maria Silva, Cédric Saucier, Pierre-Louis Teissedre, Yves Glories, UMR1219 Oenologie, Faculté d'Oenologie - ISVV, Villenave d'Ornon France. *Corresponding Author. Email: pdl@net.sapo.pt BY A chieving the optimum wine style is extremely dependent on the amount of oxygen a wine receives during the winemaking process. 1 In a complex matrix such as wine, oxygen can be involved in many reactions that affect compounds of sen- sory importance. Oxygen will have a great impact on consumer acceptance and preference .2,3 In a finished wine, the total package oxygen (TPO) consists of the oxygen concentration at the time of bottling plus any oxygen introduced after bottling. Oxygen at bottling represents the sum of dissolved oxygen in the wine plus any remaining oxygen present in the bottle headspace (dependent on variables of volume, pressure and gas composition). Oxygen ingress after bottling depends on the oxygen transmission characteris- tics of the closure. The latter depends on the inherent oxygen permeability of each wine closure. This article will summarize 10 years of research at the Bordeaux Faculty of Oenology to understand the oxygen transmission properties of different wine closures and assess their impact on the chemical and sensory qualities of wine during post-bottling. Method to determine closure oxygen transmission rate Ten years ago, there was little knowl- edge and understanding about the oxygen transmission of wine closures. There were no techniques and methods to measure the oxygen transmission rate (OTR) of closures under realistic bot- tling conditions. In 2005, the Bordeaux Faculty of Oenology developed a non-destructive method to determine the amount of oxy- gen entering the wine bottle according to the type of closure. This colorimetric method is based on the color change from the oxidation-reduction reactions of the Oxygen transmission through different closures into bottled wine This text edited and expanded by the authors from first publication: July/August 2007. between the headspace and outside air. As oxygen from the headspace dissolves into wine, the balance of concentra- tion changes and increases the rate of oxygen transmission. 7 The reaction of oxygen with the indigo carmine allows the colorimetric method to duplicate the change in concentration seen in actual wine storage. Initially, the method was used to moni- tor oxygen entering into wine from the external environment by permeation through the closures and/or between the closure-glass interface. 4,5 Subsequent work demonstrated the method also detects oxygen released by diffusion from air contained in the compressed closure itself. Several commercially available wine closures were tested: two natural cork stoppers (45 x 24 mm), the best grade ("flor"), and the intermediate grade indigo carmine. It allows a single bottle to be continually analysed over time, without compromising the closure seal. 4 The method measures oxygen ingress through a closure by direct colorimetric scan of colorless wine bottles (375 mL) con- taining indigo carmine solutions that grad- ually change color from yellow to indigo as oxygen reacts with the reduced indigo carmine. Details concerning this method- ology are provided in Lopes et al. 4,5,6 The great advantage of the colori- metric method is that it uses authen- tic closures and wine bottles stored under realistic wine conditions. One of the driving forces for oxygen transfer is the relative concentration of oxygen Figure 1: Kine cs of oxygen ingress through different closures into wine bo les stored in horizontal posi on (A) and ver cal posi on (B) over 36 months . Error bars represent the standard devia on of 4 replicates. 0.3 0.8 1.3 1.8 2.3 2.8 0 6 12 18 24 30 36 O 2 (mL) Ver cal storage (Months) Control Flor grade First grade Neutrocork Twin top Nomacorc 0.3 0.8 1.3 1.8 2.3 2.8 0 6 12 18 24 30 36 O 2 (mL) Horizontal storage (Months) B A Figure 1. Kinetics of oxygen ingress through different closures into wine bottles stored in horizontal position (A) and vertical position (B) over 36 months. Error bars represent the standard deviation of four replicates. Paolo loPes