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April 2018 WINES&VINES 71 PRACTICAL WINERY & VINEYARD WINEMAKING ripening. 25 Their distribution within grapes varies greatly, how- ever, with implications for how vinification decisions impact the final MP load in wines. In Cabernet Sauvignon, for example, stems contain approxi- mately 53% of the MPs, skins and seeds 46% and the pulp less than 1%. 24 Climate, terroir and viticul- tural practices all have been im- plicated in affecting grape MP concentration, however there is considerable debate in literature about the impact of specific fac- tors during the growing season (refer to D. Sidhu et al. [2015] for a review of these considerations). There is good agreement that the lowest MP levels are found in grapes exposed to techniques ap- plied pre-véraison that promote cluster exposure (such as leaf re- moval) and in fruit that has achieved full ripeness. Lady beetles: Recently, it has become clear that elevated MP levels in juice and wine can come from infestation of grapes by members of the Coccinellidae (lady beetle) family. If either Har- monia axyridis (multicolored Asian lady beetle) or Coccinella septempunctata (seven-spotted ladybird) are incorporated with the fruit into the processing stream, MPs contained in their haemolymph (the insect equiva- lent of blood) can produce green- ness in the final wine, a fault known as ladybug taint. 6 Harmonia axyridis in particular is becoming widely recognized as a significant problem for this rea- son. It is an invasive pest in many of the world's established and developing wine regions, where it tends to outcompete local lady beetle species and reach large populations rapidly. Typically, these beetles migrate from non- grape crops such as soy in the fall and take temporary residence in vineyards within grape clusters (see photos of seven-spotted lady- bird and multicolored Asian lady beetle above). Due to the high potency of MPs, as few as one beetle per vine can be sufficient to affect the final wine, with typical sensory descrip- tors of peanut and green pepper. Wines affected by ladybug taint have much higher levels of IPMP than found naturally in mature V. vinifera grapes. In fact, the ratio of IPMP to IBMP can be used as a chemical indicator that lady bee- tles are the source of the unde- sired greenness. 7 Adulteration: A much less common source of MPs is their deliberate introduction as fla- vorants during winemaking. Such practice is not permitted, yet it was documented in Sauvignon Blanc by the South African media in 2003 and 2004. 9,10,17 Adding MPs directly or in the form of green pepper extract, as sug- gested in these articles, would presumably increase the aromatic intensity and cool-climate nature of the wines, potentially confer- ring a competitive advantage in markets where this style of Sau- vignon Blanc is desired. Hope- fully tighter control by regulatory bodies and enhanced analytical techniques have led to cessation of the practice. Remediating green musts and wine Grape sorting: There are several interventions in the vineyard that can help reduce potential MP load the vintner might face when grapes arrive at the winery, and the reader (refer to D. Sidhu et al. [2015] and Botezatu and Pick- ering [2018]). In the case of harvested grapes that contain large numbers of lady beetles, shaker tables have proven particularly effective at separating them from the fruit, thus prevent- ing extraction of MPs from the beetles during grape processing. These tables are typically custom- built and consist of a vibrating metal mesh conveyor, along which clusters move. The shaking mo- tion forces beetles through the mesh into a collection and dis- posal area below. Several wineries also report that harvested grape clusters can be immersed in water, where beetles float to the surface and can be removed. Sorting is also important to remove leaves, which contain MPs and other compounds that can contribute to greenness. Crush, destem and juice treatment: Destemming is criti- cal, as the presence of stems dur- ing vinification significantly increases wine MP concentra- tion. 12 Given that about one-half of MPs are located in the grape skin, minimizing skin contact pre- fermentation is very important to reduce the potential for green wines. Thus, crushing should be avoided where possible. In the case of red grapes, this may even require serious consideration of making a white or blush wine rather than red, should the con- cern about potential greenness be sufficiently high. Data shown are orthonasal detection thresholds for isopropyl methoxypyrazine (IPMP) in a Gewürztraminer wine. SENSITIVITY TO METHOXYPYRAZINES VARIES BETWEEN TASTERS 6 5 4 3 2 1 0 Number of Subjects 0.26 0.48 0.65 0.94 1.13 1.61 2.82 4.03 95.4 IPMP Concentration (ng/L) ADAPTED FROM PICKERING ET AL. (2007). Both Coccinella septempunctata (seven-spotted ladybird, far left) and Harmonia axyridis (multicolored Asian lady beetle, center) can produce greenness in wine when they are incorporated in with grapes during harvest (right). KEVIN KER AND RYAN BREWSTER