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w i inneeGM A K IN GG w R O WIN Figure IV: Example of a sulfur dioxide addition calculation A Zinfandel has just finished aging in a barrel for one year and needs its sulfur dioxide level adjusted before it is ready to be bottled. It is dry and has completed malolactic fermentation and has very good clarity from setting during ageing. The analysis before the addition is pH 3.45, and the sulfur dioxide is 16/35 and there are 60 gallons of wine. Q: How many grams of KMB should be added to protect the wine after it has been bottled? A: Since the wine has completed both the alcoholic and malolactic fermentations a molecular SO2 level of 0.5 ppm should be adequate to preserve the wine. By looking at the chart in figure 3 you can see the free SO2 must be 23 ppm to have a molecular SO2 level of 0.5ppm. With the free SO2 currently at 16 ppm it must increase by 7 ppm to attain the desired amount. 23 ppm – 16 ppm = 7 ppm Since only a portion of the KMB that is added will be free SO2 it is necessary to estimate what the percentage that will become free SO2. Since the wine is clean and dry, we can assume that the ratio will be on the high side of the 35 to 75% range and for this example we will use 70%. 7 ppm ÷ 0.7 = 10 ppm To determine the amount of KMB when adding 10 ppm: (10 ppm) x (6,000 gallons) x (0.0066) = 3.96 grams of KMB If you wish to convert this to pounds (one pound is approximately 454 grams): 396 grams ÷ 454 grams per pound = .872 pounds For an aqueous solution of sulfur dioxide: volume of aqueous SO2 in mL = PPM addition 2.6 x gallons wine % SO2 solution For the wine used in the KMB example using 5% aqueous SO2. 10/2.6 x 6,000/5 = 4,615 mL There is a certain amount of guesswork in estimating just how much of a sulfur dioxide addition will be available as free SO2 and it is always best to be conservative you can always add more, but you — cannot add less. 58 p r acti c al w i ne ry & v i ne yard JANUARY 20 14 brownish hue. While this dark color may cause alarm, you should not be overly concerned because after fermentation the dark, oxidized phenols will settle out, leaving a wine that is much brighter and more appropriate in color for a white wine. Since the phenols that can oxidize have been removed from settling and racking, there is less of a potential for the wine to oxidize after fermentation and the wine will be more color-stable and better able to age. This method of pre-fermentation oxidation does diminish some of the fruity and floral aromas in the final wine. The absence of sulfur dioxide allows MLF to commence after primary fermentation is complete, lowering the acidity of the wine, and making it more microbiologically stable. After MLF is finished, sulfur dioxide should be added to protect the wine. If MLF is not desired, the wine should be adjusted with sulfur dioxide after primary fermentation is complete. For red wines, it is a good idea to add a small amount (about 30 to 40 ppm), of sulfur dioxide immediately after the grapes have been crushed. While not absolutely necessary, this will discourage the growth of spoilage organisms such as Lactobacillus and allow the yeast to get a good start on the fermentation without competition from other microbes. By the end of primary fermentation, the majority of SO2 will be bound up and there will not be so much residual SO2 that the growth of malolactic bacteria is inhibited. After MLF is complete, sulfur dioxide should be added to protect the wine during ageing. For both red and white wines, as they age, free sulfites are bound by other compounds or are oxidized to sulfate anion resulting in a gradual lowering of the effective amount of sulfur dioxide in wine. For this reason, it is always a good idea to monitor the SO2 level during ageing and to add more as needed. How much sulfur dioxide to add? Since it is the molecular form (SO2 ) of sulfur dioxide that has the most potent antimicrobial effect, and the percentage of sulfite that is in the molecular form is directly dependent on the pH, one must always consider both the pH and the free SO 2 when deciding how much sulfur dioxide to add to a wine. By knowing the pH, you can determine the percentage of free sulfur that is in the molecular (SO2 ) form by using Table I. For white wines, a level of 0.8 ppm molecular SO2 will slow down the growth of yeast and will prevent the growth of most other microbes. This level of sulfur dioxide will bind up most of the acetalde- hyde in a wine and reduce any oxidation aroma considerably. Therefore, 0.8 ppm is a good target level for molecular SO 2 immediately prior to bottling and will provide the maximum protection for the finished wine. However, sensitive tasters will be able to detect a slight burnt match aroma at 0.8 ppm SO2 . This is usually not a problem however because few consumers will be able to detect it. Additionally if the wine is bottle-aged for a few months before consumption, the SO 2 will decrease as more sulfites react with other chemical constituents in the wine and become bound. Thus, a wine bottled at 0.8 ppm will decrease to a lower level fairly quickly and there would be no detectable sulfur dioxide aroma. Winemakers who seal their wine with screw caps know that the sulfur levels diminish more slowly after bottling than wines sealed with corks. In this case, 0.7 ppm would be a better target for molecular SO2 at bottling. During storage, after all fermentations have completed, white wines should be adjusted to between 0.5 and 0.8 ppm molecular. If the wine is sweet or if you wish to prevent MLF, the wine should be kept at the high side of this range. Total SO2 should be kept below 110 ppm for table wines because, at higher levels, the wine can acquire off-flavors. For dessert and fortified wines, that are very sweet, it may be necessary to exceed this limit to obtain adequate free SO2. For red wines, a level of 0.5 ppm molecular SO2 at bottling is an appropriate target. You do not need to keep the molecular SO2 as high on red wines as you do white wines for several reasons: First, in most cases, MLF is complete in reds so there is no need to try to discourage it. Second, red wines are less sensitive to oxidation and their flavor is less dependent on fresh fruity aromas so sulfur dioxide's preservative effects are not as critical. Third, red wines usually have a higher pH than whites and often it is not possible to adjust the sulfur dioxide to a level that reached 0.8 ppm molecular SO 2 without having too much total SO2 . By knowing the pH of the wine and using the chart in Table I, it is easy to see what level of free SO2 is necessary to obtain a given level of molecular SO2 . However, it is more difficult to determine precisely what the ratio of free to bound sulfur dioxide level will be. When adding sulfur dioxide, the amount in ppm that you add should change the total SO2 by the same ppm. However, because some of the sulfur