WINETECH Technical Yearbook 2019

CARIEN COETZEE: Basic Wine, Stellenbosch KEYWORDS: Random oxidation, bottle dimensions, closures. DECEMBER 2019 RANDOM OXIDATION AND THE ROLE OF BOTTLE DIMENSIONS

As research and development projects increas ing l y focus on packag ing (especially closures) effects on random and premature oxidation of wine, it is timely to consider some recent findings regarding the role of bottle dimensions and their contribution to this issue. INTRODUCTION On 12 July, the South African wine industry gathered for the first-ever Oxygen in Wine workshop, hosted by S te l l enbos ch Un i vers i t y and sponsored by Cork Supply (Pty) Ltd. The speakers included renowned researchers, industry specialists, as well as students focussing on the topic at hand. All aspects of oxygen in wine, from random and premature oxidation, the effect of reductive winemaking, sparging techniques, bottling quality control protocols and the effects of oxygen and temperature, were covered in an interactive and lively

workshop with attendees from all disciplines of the wine industry. The presentations included results from various Winetech-funded projects. Prof. António Ferreira, a researcher and professor in wine flavour chemistry and product development and innovation manager at Cork Supply Portugal, de l i ve red a t hough t- p rovok i ng presentation regarding the effects of glass bottle variation on random and premature oxidation in wine. WHAT IS RANDOM OXIDATION? Random oxidation is bottle-to-bottle variation that exists due to certain factors that resulted in different amounts of oxygen in the packaged wines. This is a serious issue, especially in wines that are more susceptible to oxidation and/or wines that are intended to be aged. For these wines, a slight difference in dissolved oxygen and/or oxygen ingress can result in

random oxidation. When tasted in isolation, it is impossible to say if random oxidation took place, there needs to be a comparison of different bottles from the same batch. The formation and accumulation of various aroma compounds, as well as the deterioration of others, will inevitably occur due to random oxidation, leading to bottle-to-bottle aroma differences. Typical aroma compounds formed during oxidation reactions are acetaldehyde, as well as the Strecker aldehydes, such as methional (potato skin aroma) and pheny l aceta l dehyde (honey and floral aroma), and can play a major role in the perception of oxidation nuances. These aldehydes are often used as markers for oxidation and can be formed due to peroxidation of the corresponding alcohols by and/ or via Strecker degradation of the corresponding amino acid precursor.