Issue link: http://winesandvines.uberflip.com/i/840286
62 WINES&VINES July 2017 WINEMAKING WINE EAST portant first step in resolving high-pH wine- making challenges. Throughout our research work through Penn State University, we noticed that some of our most problematic fermentations tended to have high potassium concentra- tions in the leaf petiole during the growing season and in the fruit at harvest. Many of these wines resulted in large pH swings from the beginning of fermentation through the end of primary or malolactic fermentation. Red wines had uncharacteristic aroma and flavor profiles as well as odd color stability problems that were not amendable through post-fermentation acid additions. White wines were not quite stable through bottling, and many became undrinkable after a year in the bottle. After several years of producing odd wines and sharing them with regional wine- makers to troubleshoot the wines' problems, it was apparent that the important question was: How do we make quality wines from grapes high in potassium or experiencing a high pH? An approach to winemaking with high-potassium fruit Dealing with high potassium in winemaking is not a new problem. Other than addressing the issue in the vineyard, winemakers can utilize techniques such as ion exchange and acid adjustments in the must to address wine quality consistency complicated by high-potassium fruit. However, from a prac- ticality viewpoint, many regional winemak- e r s d o n o t b e l i e v e i o n e x c h a n g e i s a reasonable solution either due to difficulty finding available ion-exchange units or the associated cost. Upon reviewing literature, Mpelasoka et al. (2003) noted the costs associated with commercial Australian wineries making regular pre-fermentation tartaric acid addi- tions in an attempt to reduce potassium content in the juice to avoid a high pH by the end of fermentation. It is worth noting that potassium concentration influences buffering capacity and wine acidity. Addi- tionally, the binding of potassium and pre- cipitation of potassium bitartrate is also influenced by pH; potassium bitartrate be- comes more insoluble as ethanol concentra- tions increase during fermentation, and it is not unusual for titratable acidities (TAs) to decrease by the end of primary fermenta- tion due to the precipitation of potassium tartrate (Iland et al. 2012, Schneider 2012). International wine consultant and expert Volker Schneider has referenced reducing potassium content through precipitation of potassium bitartrate: "…addition of… 2.0 g/L tartaric acid, one has to accept a… loss of approximately 500 mg/L potassium" (Schneider 2012). Nonetheless, acid chem- istry should not be taken lightly, and wine- makers struggling with the topic should refer to modern wine chemistry texts. Because of the frequency of the high-pH problem, our research team at Penn State decided to run a trial on two red wine va- rieties that annually had pH greater than 4.0, color stability problems and had been previously tested for high concentrations of potassium in the petioles, fruit and previous wine vintages. Merlot juice from the research vineyard at Penn State Fruit Research and Extension Center in Biglerville, Pa., contained 1,682 mg/L K + , and Cabernet Sauvignon contained 1,668 mg/L K + in the juice prior to fermenta- tion in the 2015 vintage. Both samples were taken from the must and analyzed by atomic absorption analysis at Enartis USA, but we did not have the results until after we made acid additions and inoculated for primary fermentation. Both varieties contained potassium con- centrations that were considered relatively high (Somers 1975), indicating that high po- tassium may have been a potential culprit for some of our previous winemaking challenges. The tables on page 61 show additional chem- istry results for the Merlot and Cabernet Sau- vignon musts pre-fermentation. While we did not have replicate fermenta- tions as we sought potential production solu- tions for winemakers, we attempted a production trial on both Merlot and Cabernet Sauvignon musts to assess the potential im- pact of higher than normal tartaric acid ad- ditions pre-fermentation. For the Merlot, in addition to a 2 g/L tartaric acid addition, which in previous vintages appeared to have little to no impact on the wine quality com- pared to no tartaric acid addition, we tested 4 g/L and 6 g/L additions, both of which had potential to decrease potassium concentra- tions. Due to lesser volume of the Cabernet Sauvignon, we only tested 4 g/L and 5 g/L tartaric acid additions. Wines were all fermented in open-top fer- mentation bins, and primary fermentation was completed within approximately seven days. In hindsight, it would have been best to analyze pH and TA daily through primary fermentation to monitor changes in acidity. Pressing fol- lowed completion of primary fermentation, and wines were immediately inoculated with the Lallemand malolactic bacteria strain, Alpha. Malolactic fermentation (MLF) was tracked via paper chromatography. At completion of MLF, wines were moved to cold storage and treated with potassium metabisulfite with a dosage rate based on wine pH. Wines were later racked and final additions of potassium metabisulfite were made prior to bottling. Wines were left unfin- ished to emphasize the effect of the juice tar- taric acid treatments. The tables on page 62 show the differ- ences in pH and TA for each pre-fermentation 2015 CABERNET SAUVIGNON WINE CHEMISTRIES Pre-Fermentation Treatment Post-Primary Fermentation Post-Malolactic Fermentation pH TA (g/L) VA (g/100 mL) pH TA (g/L) VA (g/100 mL) Alcohol 4 g/L tartaric acid 3.57 7.70 0.021 3.82 7.31 0.038 13.3% 5 g/L tartaric acid 3.44 7.56 0.016 3.66 8.04 0.047 13.3% The pH, titratable acidity (TA), volatile acidity (VA) and alcohol concentration were measured post-primary fermentation and post-malolactic fermentation. 2015 MERLOT WINE CHEMISTRIES Pre-Fermentation Treatment Post-Primary Fermentation Post-Malolactic Fermentation pH TA (g/L) VA (g/100 mL) pH TA (g/L) VA (g/100 mL) Alcohol 2 g/L tartaric acid 3.79 6.02 0.014 3.96 5.21 0.045 11.1% 4 g/L tartaric acid 3.51 7.24 0.015 3.63 5.96 0.036 11.1% 6 g/L tartaric acid 3.27 7.84 0.015 3.40 7.17 0.032 11.2% The pH, titratable acidity (TA), volatile acidity (VA) and alcohol concentration were measured post-primary fermentation and post-malolactic fermentation. The Merlot wines treated with 4 g/L and 6 g/L tartaric acid had vibrant and red-hued color. The Merlot with a 2 g/L tartaric acid addition had a stronger purple-blue hue and appeared hazy.