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38 WINES&VINES May 2016 WINEMAKING PRACTICAL WINERY & VINEYARD The TPO was determined using a Noma- Sense O 2 P300 for dissolved oxygen (DO) and a piercing device for a destructive measure- ment of headspace oxygen (HSO). Bottle sampling for DO started from the beginning of the bottling run with samples taken in triplicate at each filling spout. Sam- ples were taken at Bottle 1, Bottle 50, Bottle 150, Bottle 300 and Bottle 500. Samples for HSO measurement were taken in the middle of the run, and DO was measured simultane- ously. At the end of the run, samples were taken when the bottling tank was empty, when one-half of the remaining wine reached the membrane, when all remaining wine reached the membrane, when the filler bowl was half empty and from the last three bottles. TPO variations Results varied considerably among bottling units, with TPO values ranging between 0.6 and 3.3 mg/L. Among the 18 audits, seven failed to achieve levels below 1.5 mg/L and four had considerable bottle-to-bottle varia- tions, as shown by the error bars in "TPO Variation Mid-Bottling Process" (page 37). With few exceptions where wine DO was high compared to HSO, we observed that TPO at bottling is mostly affected by the gaseous oxygen of the bottle headspace. In some audits, HSO reached levels close to 2.5 m g / L , w h i c h a g r e e s w i t h p r e v i o u s observations. 8 As the headspace is more saturated with oxygen than the wine, Henry's law of equi- librium 13 will favor the dissolution of gaseous oxygen, leading to an increase of TPO fol- lowed by an increase of DO during storage. 11 With a 30 mm fill height for screwcap clo- sures, the headspace can supply more than 2 mg/L of oxygen to the wine at a bottling temperature of 68° F. This may not be a problem if the sulfur dioxide level in the wine is adequate. The optimum level of sulfur dioxide for a wine is a complex function of several variables (pH, DO, oxidants and other wine elements such as carbonyls and polyphenols). As a general rule, 4 mg of free sulfur dioxide is required to neutralize 1 mg of dissolved oxygen. Thus, additional sulfur dioxide would need to be available to combine with the products of oxidation that would gener- ate from the dissolution of the gaseous oxy- gen during bottle storage. Survey results indicated several key areas of concern for excess oxygen pickup into wine during the bottling process. Contact with air at the time of bottling can be variable, de- pending on the care taken and equipment used. The most and least efficient bottling runs are reported in the table "Cellar Practices and TPO" (page 37). Among the 17 bottling audits, the lowest TPO level was recorded in Audit 11 and the highest TPO level in Audit 2. The two audits differ in both DO and HSO levels and management procedures. Generally, the type of wine and the hose length did not have a significant impact on oxygen pickup. An inverse relation between speed and oxygen dissolution was instead observed in this study. Slower bottling lines generally dissolved more oxygen than the high-speed units. Slower filling and corking or capping operations mean that the wine stays longer in the line, the filler and the bottle prior to filling, resulting in an in- creased pickup of oxygen. Bottling line rates should be maintained at sufficient levels to minimize this effect. Wine transfer and impact on DO As reported in the table "Cellar Practices and TPO," the potential for a higher DO level during bottling seems to decrease with the use of inert gas in the bottling tank and transfer line. If any headspace is present in the bottling tank, it is important that the surface is constantly treated with inert gas such as CO 2 , N 2 or argon to prevent oxygen from dissolving into the wine. Protecting the wine from oxygen during the transfer from the bottling tank to the filler is essential to minimize oxygen pickup. As seen in "U-Curve throughout the Bot- tling Process," audits 5 and 18 started with DO levels above 1.5 mg/L, and these levels were maintained throughout the bottling run. Wineries 4, 7 and 11 were able to elimi- nate the U-curve, maintaining a DO level below 0.5 mg/L. In the bottling tank, hoses and filler bowl are where the wine is most likely to come into contact with oxygen during pumping. Critical times for the dissolution of oxygen are the be- ginning and end of the transfer, because this is when the wine is most likely to come in contact with oxygen due to higher turbulence. U-CURVE THROUGHOUT THE BOTTLING PROCESS 3 2.5 2 1.5 1 0.5 0 Dissolved oxygen (mg/L) 1 50 150 300 500 Bottle Number n Audit 18 n Audit 5 Tank empty Half remaining wine reached membrane All remaining wine reached membrane Filler bowl half empty Last bottle n Audit 11 n Audit 7 n Audit 4 Effective DO management practices resulting in the lowest total package oxygen (Audits 4, 7 and 11) are compared with less effective DO management processes (Audits 5 and 18). MANAGING OXYGEN DURING AND AFTER FILLING Audit 1 (HSO=1.7mg/L) Audit 10 (HSO =1.6 mg/L) General features Wine type Red Red Closure type Natural cork Natural cork Methods for DO management Use of inert gas to inert the bottle N 2 (3 bars) Argon (0.5-1 bars) Technology of filling Vacuum Vacuum Methods for HSO management Use of inert gas after filling No Argon Use vacuum at corking -677 millibar -13.5 millibar Audits 1 and 10 resulted in similar levels of total package oxygen even though they had different manage- ment practices prior to filling, after filling and at corking.