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W i n e s & V i n e s n O V e M B e r 2 0 1 4 125 WineEast but they may also cause other—not neces- sarily positive—changes in the wine. Herbaceous aromas and flavors can come from other sources than grapes. Multicol- ored Asian lady beetles (MALBs) also pro- duce isopropyl methoxypyrazines and, when MALB get into grape must, they release the MP compounds that can give wines flavors that are described as asparagus, peanut butter or bell pepper. green June beetles can create a taint problem for winemakers in places such as Texas. green leaf volatiles are another class of compounds that may be a source of green flavors; they can be responsible for aromas of freshly cut grass. Fortunately, these compounds lose most of their potency during fermentation. Acid-pH balance As with much of winemaking, managing acidity and pH in wine begins in the vine- yard. Tartaric acid is the dominant acid in grape juice and wine, with malic acid being the second major acid. During malolactic fermentation, the malic acid is degraded into lactic acid. pH is a "resultant variable" in grapes, according to roger Boulton, pro- fessor of enology at the University of Cali- fornia, Davis. The level of pH is an outcome of the conditions of grapegrowing, and con- sequently it can be manipulated—at least to a certain extent. In his speech "Managing Acidity and pH in Wine," Boulton noted that measuring po- tassium might help explain more about pH in wines. He said that people who grow corn in the Midwest understand the relationship between pH and potassium, because if you plant corn in the same place for four years, it will pick up potassium through the roots and result in acidification of the soil. The same thing occurs with grapes: As the vines take up potassium from the soil, the potas- sium causes titratable acidity to decline and pH to get higher. According to Boulton, "Whenever you pick up a potassium, you lose a proton. The only question is: What are the conditions of berry size, tartrate and malate content as the consequence of that potassium uptake? And that will be different depending on the cultivars and different sites." For young vines with a smaller crop grow- ing on soils with a high potassium level, the amount of soil moisture and/or late harvest- ing can lead to higher pH levels in grapes. If the root system is pulling more potassium into the vine, increasing the crop level will cause there to be less potassium per berry, Vance_Jan11.qxp 11/23/10 9:29 AM Page 1 The amount of potassium uptake is critical in determining titratable acidity in berries. DAILY WINE INDUSTRY NEWS winesandvines.com