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70 WINES&VINES April 2018 WINEMAKING PRACTICAL WINERY & VINEYARD G reen, vegetal flavors in wine are typically associated with fruit that has not achieved the desired level of ripeness. Often such wines suffer from other quality issues linked to grape im- maturity, including high acidity, poor color and lack of varietal aroma. Thus, green flavors in wine are almost universally rejected by con- sumers. The exceptions are when these notes can be considered (at low levels) part of the expected varietal character, such as in cool- climate Cabernet Sauvignon, Carménère and Sauvignon Blanc. The main compounds eliciting green/ vegetal flavors in wine are alkl-methoxypyr- azines (also known as MPs, and often simply referred to as pyrazines), C6 green leaf vola- tiles (particularly hexanols and hexanals) and some thiols. MPs are the most important. In nature, they are produced by microbes, plants and insects. With the exception of some rare cork-taint issues from microbial contamination and even rarer cases of deliberate adulteration of wine, grapes and beetles from the Coccinellidae fam- ily are the most common sources of MPs in juice and wine. A fuller understanding of the impact of MPs and where they come from dur- ing winegrowing is important to prevent green- ness and remediate affected juice and wine. Methoxypyrazines The four MPs most commonly associated with greenness in wine are 3-isobutyl-2-MP (IBMP), 3-isopropyl-2-MP (IPMP), 3-secbutyl- 2 - M P ( S B M P ) a n d 2 , 5 d i m e t h y l - 3 - M P (DMMP). 7 All are capable of eliciting herba- ceous or vegetative aroma and flavor, al- though subtle differences in aroma quality have been noted; for example, IBMP is often described as more bell pepper-like than the others. While DMMP and IBMP are often the most prevalent in wine, the relative contribu- tion of each MP depends on its odor thresh- old, the grape variety, vinification practices and presence or absence of lady beetles dur- ing harvest. (See graph on this page) One thing shared by all MPs is their very low human detection threshold in wine, which for smell ranges from 320 pg/L for IPMP to 31 ng/L for DMMP. 3,18 As a means of reference, 1 picogram (pg) is one-trillionth of a gram, or the average weight of the DNA in one cell of a hummingbird. 11 Of interest to how we perceive greenness in wine, there is significant variation in sensitivity between individuals; for example, tasters report a 400-fold difference in IPMP thresholds for some white wines. (See "Sensi- tivity to Methoxypyrazines Varies Between Tasters" on page 71.) Also, greater familiarity with ladybug taint may be associated with higher sensitivity to IPMP. 20 What might smell or taste too green to you may be barely detectable to your colleague. This disparity has important implications for vintners assessing levels of greenness in wine and making decisions on treatment and market acceptability; it is important to know your own sensitivity and, if needed, use additional asses- sors to complement your perceptions. Sources of methoxypyrazines Grapes: MPs are secondary metabolites that accumulate early during berry development and likely serve to discourage frugivores (fruit eaters) from eating unripe grapes. They typi- cally reach maximum levels a few days before véraison, after which their concentration de- creases, particularly during early stages of Managing Green Flavors in the Winery Sorting, clarification and heat treatments are among the most successful options By Gary J. Pickering Data show dimethyl methoxypyrazine (DMMP), isopropyl methoxypyrazine (IPMP), secbutyl methoxypyrazine (SBMP) and isobutyl methoxypyrazine (IBMP) concentrations in a selection of international commercial wines. METHOXYPYRAZINE COMPOSITION OF WINE VARIES WITH GRAPE CULTIVAR 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 Cabernet sauvignon Merlot Cabernet Franc Pinot noir Sauvignon blanc Chardonnay Riesling Methoxypyrazine concentration (ng/L) n DMMP n IPMP n SBMP n IBMP ADAPTED FROM BOTEZATU ET AL. (2016).