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36 WINES&VINES May 2016 WINEMAKING PRACTICAL WINERY & VINEYARD B ottling is a complex and delicate step of the winemaking process that requires a lot of professional expertise. Maintaining wine quality during bottling, storage and shipping is one of the highest priorities, and the objective is clear: protect the wine from oxida- tion as long as possible. Implementation of good bottling prac- tices begins with preparation adapted to the type of wine and the marketing channel. It continues with careful monitoring of the bottling line and, most important, the oxy- gen intake (pickup). To obtain a full assessment of oxygen pickup, instrument manufacturers and wine experts have undertaken new efforts to mea- sure total package oxygen (TPO), 1 which is the sum of dissolved oxygen (DO) and head- space oxygen (HSO) in the bottle. Measuring HSO can be achieved using a needle that goes through the closure and is directly connected to an analyzer. 2 An alterna- tive method consists of estimating TPO by measuring DO only after shaking the bottle to obtain equilibrium of oxygen pressure between the headspace and wine. 3 With the development of non-destructive analytical instruments (PreSens, Noma- Sense), a complete assessment of the bottling process is now possible. Luminescence-based technologies allow for non-invasive measure- ment of dissolved oxygen and headspace oxy- gen through the glass bottle wall. 4 Oxygen can dissolve into the wine at every stage of the bottling process, and it can have an effect on wine composition, shelf life and consumer acceptance. During bottling, wine undergoes multiple operations: pumping, fil- tration, filling and corking or capping. These operations are particularly conducive to the dissolution of oxygen in wines. At each transfer, and with each treatment, oxy- gen may penetrate and dissolve in the wine, with an average pickup (introduction) of 1.6 mg/L. 5 As wine progresses through bottling, a so-called "U-curve" of dissolved oxygen occurs. High amounts of oxygen are introduced at the begin- ning and end of the bottling process, and lower and steady levels are common in the middle of a bottling lot. 6 According to Zoran Ljepović, Constel- lation Brands quality assurance director, the bot- tling process should start with a DO of less than 1 mg/L, and if any increase occurs throughout the run, it should be maintained below 0.3 mg/L. 7 At filling, oxygen concentration in bottle headspace can range from 1.5 to 2.5 mg/L. 1 The oxygen concentration depends on three factors: wine volume, headspace volume and oxygen concentration in the headspace. Thus, at the end of the packaging process, it is pos- sible to find wines with dissolved oxygen levels ranging from 2 to 4 mg/L and a final oxygen content approaching 8 mg/L. 8 Measurement of total package oxygen Dissolved in excessive amounts, oxygen can cause irreversible changes in the color of the wine and its flavor profile after packaging. The influence of oxygen on red wine aroma com- pounds and sensory properties has been more difficult to confirm compared to effects on wine color. In a two-year Cabernet Sauvignon wine closure trial, M.J. Kwiatkowski showed that, with larger headspace, significant losses of SO 2 are observed soon after bottling, and wines developed a higher oxidized aroma score. 9 White wines contain lower levels of poly- phenols than red wines (0.2 to 0.5 g/L), mainly hydroxycinnamic acids, but these remain very important for oxidation and hence contribute to browning and loss of varietal aroma. 10 Measurements can be performed in real time using specific equipment for assessing oxygen at critical steps (transfer, filtration, bottling and storage). These measurements can be performed directly on the transfer lines and in the bottles (dissolved oxygen in the wine and gaseous oxy- gen in the headspace). Ken Fugelsang, professor emeritus of enology at California State University, Fresno, recommended TPO levels below 1.25 mg/L in bottled red wines and below 0.6 mg/L for white and rosé wines at bottling. 11 Key Points of the Bottling Process Study at 17 wineries identifies impacts on total package oxygen By Hend Letaief Dissolved in excessive amounts, oxygen can cause irreversible changes in the color of the wine and its flavor profile after packaging.