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80 WINES&VINES December 2016 WINEMAKING WINE EAST levels at each storage interval (see "Influence of Low and High TPO Levels on Free SO 2 Content" on this page). Wines with the lowest TPO value (2.4 ppm) de- creased to 31 ppm FSO 2 in 126 days, a 28% drop. In contrast, the highest TPO amount (5.9 ppm) had a 42% decline in FSO 2 at the same storage times. Overall, these results showed that TPO has a primary role in FSO 2 de- crease in four months. The same conclusion was found in earlier studies, which also ob- served a gradual decline after four months. Their findings stated that another loss of 5 to 10 ppm will take place between four months and 12 months of storage. Much of this loss depends on the closure type, which influences the oxygen transfer rate (OTR). Keep in mind that 1 ppm O 2 consumes 4 ppm SO 2 . This ratio (O 2 : SO 2 ) can be used to estimate the decline of FSO 2 during storage. For example, the lowest TPO level (2.4 ppm O 2 ) in the figure "Influence of Low and High TPO Levels on Free SO 2 Con- tent" is multiplied by four (SO 2 ) to calculate the drop of 10 ppm FSO 2 at four months (126 days). Our actual reading (33 ppm) was close to the estimated value of 31 ppm. It is important to remember that the FSO 2 should not fall below 10 to 15 ppm during bottle aging. Lev- els less than this will result in wine oxidation and sensory property faults in addition to potential mi- crobial instability concerns. In general, we must not over- look the importance of TSO 2 in controlling oxidation. In this study, there was a noticeable trend among the TSO 2 levels with storage time. Although some inconsistency was observed, results indicated a de- crease during storage (zero to 126 days). An explanation for this vari- ability may relate to the forms of SO 2 in wine, particularly the bound species. These species include, of course FSO 2 , but also two bound forms with degrees of binding. One form has a lasting bond while the other dissociates and releases FSO 2 . This occurs when the initial wine FSO 2 drops to a certain level and lasts until the supply disappears. All forms depend upon the wine type and composition. A recent article from the Aus- tralian Wine Research Institute (AWRI) stated that SO 2 addition to wines should yield about 35% to 40% FSO 2 . Failure to reach these percentages is related to small SO 2 additions during vinification. It is best to treat wines with large amounts, but less frequently. This practice yields higher levels of FSO 2 , because a high TSO 2 ratio to bound was established. AWRI also mentioned that many problem wines were related to small SO 2 additions. Their FSO 2 percentages to the total SO 2 were less than 25%. This outcome was evident due to oxidation and spoil- age products binding with FSO 2 . For this study, calculating the per- centage of FSO 2 concentration to TSO 2 revealed that five Ohio wines were near 25%. Another important aspect of TSO 2 involves its influ- ence upon wine sensory properties. Past literature has suggested that wines approaching 200 ppm TSO 2 possess certain sensory faults. pH values The pH of wines has an important influence on many phases of the winemaking process. With regard to this study, low pH values are less susceptible to oxidation and more responsive to SO 2 . Wine pH levels between 3.1 and 3.6 are generally recommended. The majority of the pH values at bottling were within the acceptable range. However, wines from winer- ies B and D were somewhat low, 3.05 and 2.98, respectively. In con- trast, winery N was slightly above the suggested limit at 3.72. Also, a trend was observed for pH levels at the various storage intervals. These data showed a modest increase in pH from bottling to the last storage period, 126 days. An average pH rise near 0.2 with a range between 0.4 and 0.19 occurred in 13 wines of this study. Explanations for this pH increase may include: sulfur dioxide loss and extent of potassium exchange with wine acids during bottle storage. Also, the slight pH increase may suggest to the winemakers to add an extra amount of SO 2 before bottling. However, most Ohio win- eries are small and usually store their wines for a short time, three to four months. Thus, the SO 2 re- sults of this study indicate that SO 2 levels were adequate for brief storage times. On the other hand, prolonged bottle storage may ex- perience a significant FSO 2 de- crease with levels approaching the minimum guideline of 10 ppm. Conclusion Management of DO can affect wine quality during bottle aging. Wines in this study varied considerably with respect to their DO levels in the holding tank and at bottling. Most wines at these locations were above industry guidelines for DO. For example, only two wines of 14 measured were below the recom- mended level of 1.0 ppm. The same trend was found for HSO, with only six wines below the proposed level of 2.0 ppm. Also, the HSO percentage in the total wine oxygen content indicated that HS was an important source of oxygen in the wines. Most wines showed HSO percentages were above 50%, which may have a significant im- pact on the wine shelf life. It is evident that most wineries in this study need to employ tech- niques to better manage their oxy- gen levels. One specific issue that needs special attention is to im- prove the utilization of inert gas to remove wine oxygen at various steps of the vinification process. Another meaningful observa- tion in this study showed that the FSO 2 decrease during wine stor- age was related to the oxygen content at bottling. Wines with high O 2 amounts experienced the greatest loss in FSO 2 . With this in mind, a future study may answer the question, "Can winemakers compensate for high oxygen wines with FSO 2 without diminishing wine quality during bottle aging?" We believe that the results of this study would correlate with a majority of the wines from the Ohio commercial wine industry and throughout much of the coun- try. The study's results provide a stimulus for winemakers to review their winemaking and bottling protocols in providing best man- agement practices to limit un- wanted oxygen pickup in addition to appropriate sulfur dioxide use at critical times. If winemakers do that, it will help put the wine in- dustry on the right track toward producing premium quality wines with longer shelf life potential on a more consistent basis. The authors of this article are all in the Department of Horticulture and Crop Sci- ence at The Ohio State University, OARDC (Ohio Agricultural Research and Develop- ment Center). James F. Gallander is pro- fessor emeritus; Todd E. Steiner is enologist for the state of Ohio, and enol- ogy program manager and outreach spe- cialist; Patrick L. Pierquet is research associate, and Lisa R. Robbins is a gradu- ate student in the department. The rate of free SO 2 decline over time was shown to be related to the initial dissolved oxygen rate. INFLUENCE OF LOW AND HIGH TPO LEVELS ON FREE SO 2 CONTENT Free Sulfur Dioxide (ppm) 50 45 40 35 30 25 20 15 10 5 0 0 7 21 63 126 Storage Interval (Days) n TPO: 2.4 ppm (n=5) n TPO: 5.9 ppm (n=6)