Issue link: http://winesandvines.uberflip.com/i/235959
w i n e M A K IN G inant when oxygen exposure is lower. Overall, these observations seem to confirm that reductive and empyreumatic thiols are more responsive to oxygen exposure than fruity thiols, consistent with Figure 3. From a practical perspective, it is important to emphasize that the amount of oxygen needed to shift a wine aroma profile from fruity to more reductive or empyreumatic characters is rather small. This can be seen in Figure 5, where approximately 1 mg of oxygen was already sufficient to obtain these two distinct profiles after only six months in the bottle. In order to modulate the different thiol-related characters according to wine style, it is therefore necessary to precisely control oxygen ingress within a rather narrow range. Figure 6 shows data relative to oxygen ingress of different types of closures, expressed as the sum of oxygen released from the inner cavities of the closure after bottling compression (a process often referred to as outgassing), plus the oxygen entering through the closure due to its intrinsic permeability (commonly referred to as oxygen transmission rate or OTR). While OTR is commonly taken as the reference parameter for assessing the potential influence of a closure on a wine's post-bottling development, outgassing should not be neglected, as it can account for a significant portion of the oxygen entering the bottle in the first year (up to 50% or even higher depending on closure type), therefore influencing wine thiol composition even in the short-term. For example, we have observed that the amount of oxygen derived from desorption alone can account for a 50% loss of 3MH in six months of bottle storage (in 375 mL bottles). Consistent with other studies, the data in Figure 6 confirms that oxygen ingress is strongly dependent on closure type. However, for certain types of closures it appears not possible to define a specific oxygen ingress value, due to the large variability observed across the single batches analyzed. This is the case for natural cork and 1+1 closures, in agreement with the findings of other studies.2,5 Other types of closures are generally more consistent, although variations in the range of 2– 3 mg of oxygen over two years were still observed in the case of agglomerated or micro-agglomerated closures. Conversely, co-extruded synthetic closures (Nomacorc Select series) displayed 8 p ractic al w i ne ry & v i n e yard JANUARY 20 14 the most consistent oxygen ingress values, therefore offering improved performances in the management of volatile thiol evolution during wine bottle storage. Take-Home messages •Volatile thiols contribute to both pleasant/complex and negative/reductive aroma attributes. •Removal of reductive thiols by copper is likely to negatively impact fruity thiols. Moreover, copper addition at bottling can enhance H2S formation during bottle ageing. •Selection of closure with optimal oxygen ingress can allow removal of excess reduction. •A co-extruded synthetic closure allows precise and consistent oxygen ingress post-bottling, reducing the risk of bottleto-bottle variation in wine thiol profile. Conclusions Volatile thiols are powerful aroma compounds with a primary role in wine aroma composition. Their sensory contribution is rather diverse, ranging from pleasant passion fruit/exotic fruit (3MH and 3MHA) to complex smoky/mineral (furfuryl thiol and benzyl mercaptan), to unpleasant reductive (H 2S and MeSH) notes. Bottle ageing is crucial to formation and degradation of different volatile thiols, but achievement of an optimal balance remains challenging. Although often adopted to remove unwanted reductive aromas, copper addition also removes pleasant aromatic thiols and can have unpredictable effects during bottle ageing, including an increase in H 2S accumulation. Careful selection of closure oxygen ingress can allow winemakers to manage the different aroma nuances associated with varietal thiols, representing a valuable solution for management of wine volatile thiols. While preservation of volatile thiols generally requires closures with relatively low oxygen ingress, unpleasant reductive thiols seem to be the most responsive to oxygen, increasing the risk of reductive notes with closures allowing too little oxygen. In addition, a non-negligible variability of oxygen ingress values exists for certain types of closures even within the same production lot. This could lead to significant bottle-to-bottle variation and should therefore be carefully considered for wine styles that are closely dependent on volatile thiols. PWV Bibliography 1. Diéval, J-B., S. Vidal, O. Aagaard. 2011 "Measurement of the oxygen transmission rate of co-extruded wine bottle closures using a luminescencebased technique." Packag. Technol. 24, 375–38. 2. Faria, D., A. Fonseca, H. Pereira, O.M.N.D. Teodoro. 2011 "Permeability of cork to gases." J. Agric. Food Chem. 59, 3590–3597. 3. Goode, J., S. Harrop. 2008 "Wine faults and their prevalence: data from the world's largest blind tasting." Proceedings of LesXXes Entretiens Scientifiques Lallemand. 4. Nikolantonaki, M., I. Chichuc, P-L Teissedre, P. Darriet. 2010 "Reactivity of volatile thiols with polyphenols in a wine-model medium: Impact of oxygen, iron, and sulfur dioxide." Anal. Chim. Acta 660, 102−109. 5. Oliveira, V., P. Lopes, M. Cabral, H. Pereira. 2013 "Kinetics of oxygen ingress into wine bottles closed with natural cork stoppers of different quality." Am. J. Enol. Vitic. doi: 10.5344/ ajev.2013.13009. 6. Pasquier, G. 2013 "Mineralité. Avant de la comprendre il faut la définir." Rev. Oenol. 254, 48–49. 7. Tominaga, T., G. Guimbertau, D. Dubourdieu. 2003 "Role of certain volatile thiols in the bouquet of aged Champagne wines." J. Agric. Food Chem. 51, 1016–1020. 8. Ugliano, M., M. Kwiatkowski, S. Vidal, D. Capone, T. Siebert, J.B. Diéval, O. Aagaard, E.J. Waters. 2011 "Evolution of 3-mercaptohexanol, hydrogen sulfide, and methyl mercaptan during bottle storage of Sauvignon blanc wines. Effect of glutathione, copper, oxygen exposure, and closure-derived oxygen." J. Agric. Food Chem. 59, 2564–2572. 9. Ugliano, M., J.D. Diéval, T.E. Siebert, M. Kwiatkowski, O. Aagaard, S. Vidal, E.J. Waters. 2012 "Oxygen consumption and development of volatile sulfur compounds during bottle aging of two Shiraz wines. Influence of pre- and post-bottling controlled oxygen exposure." J. Agric. Food Chem. 60, 8561–8570. 10. Ugliano, M., J.B. Diéval, S. Begrand, S. Vidal. 2013a "Volatile sulfur compounds and 'reduction' odour attributes in wine. An update on why some wines 'stink,' some others have 'complex mineral aromas,' and what winemakers could do about it." Wine Vitic. J. 34–38. 11. Ugliano, M. "Oxygen contribution to wine aroma evolution during bottle aging." 2013b J. Agric. Food Chem. 61, 6125–6136.