IBMP
IBMP (2-Isobutyl-3-methoxypyrazine) is the main compound responsible for the “green bell pepper” aroma in wine. In Sauvignon Blanc, the compound adds an often desired “grassy” character. In red wines however, this flavor is largely unpopular. Excessive IBMP levels in red wines, typically Cabernets or Cabernet-based blends, can lead to disappointing ratings and mixed success in the marketplace. Because IBMP levels typically decrease as grapes mature, monitoring IBMP throughout ripening gives winemakers a unique tool to assess “aromatic maturity” along with berry maturity to target harvest dates based on their desired wine style. It is now believed that the IBMP decrease during ripening is caused by an active metabolic process, instead of degradation by sunlight. There is strong evidence that severe hydric and/or heat stress can trigger “maturity stops”, where IBMP degradation suddenly halts. This can result in shriveled, high-brix
Eucalyptol
Eucalyptus character is one of the industry’s most controversial aromas. On one hand, Eucalyptus traits are considered desirable in some “cult” wines; on the other hand, in excess this character can be overwhelming. ETS researched eucalyptol (1, 8-cineole) in wine, and discovered airborne transfer from eucalyptus trees growing near vineyards to grape berries. Eucalyptol can adhere to the wax on berry surfaces, and is then transferred into wine during extended macerations and fermentation on the skins. Eucalyptus character is rarely found in white wines due to minimal skin contact and extraction during production. The Australian Wine Research Institute also found that eucalyptol can be transferred through vine leaves and petioles, MOG, and from eucalyptus leaves and nuts that may end up in harvested grapes.
Invasive Insects
Ladybug taint first came to light in Ontario in 2001. Offensive off-aromas (described as vegetal, peanut, bell pepper, and asparagus) were often noticed in wines following a population explosion of Multicolored Asian Ladybeetles (MALB), originally introduced for biocontrol of aphids. Researchers at Brock University in Ontario traced the off-aromas to IPMP (2-isopropyl3-methoxypyrazine) released by the ladybugs when they were crushed during the winemaking process. As little as one beetle per vine may be sufficient to taint the resulting wine. Ladybug Taint appears to be a reoccurring problem on the east coast of the US, but so far has not had a significant impact on the west coast.
Photo: Thom Quine
raisins with concentrated IBMP, and cause discordant combinations of “green/herbaceous/unripe” and “jammy/overripe” flavors. Monitoring IBMP from the early stages of the ripening process provides a starting point to improve fruit quality from underperforming vineyards. Vineyard management decisions such as trellis types, fertilization, water availability, and early leaf removal are known to have a significant impact on IBMP. Once you have a better understanding of the kinetics of IBMP accumulation and degradation in a problem site, you can modify viticultural practices, and measure the impact in the following years. Testing grapes just prior to harvest is a useful tool for predicting IBMP levels in the resulting wine, since grapes do not contain any precursors or “hidden” sources of IBMP, and IBMP levels are not easily altered by standard winemaking processes.
Flavors perceived during tasting change with varying concentrations of eucalyptol. Trace levels close to 1 ppb are associated with “fresh”, slightly “minty” notes. In the low ppb range, “minty” or “fresh bayleaf ” aromas become stronger, and more easily identifiable as eucalyptus as concentrations increase. Wines with strong eucalyptus odors may contain more than 20 ppb of eucalyptol. Analysis of eucalyptol enables winemakers to objectively confirm and document their sensory impressions. It can also be used to assess the impact of eucalyptus trees near vineyards and the influence of winemaking practices such as fruit sorting at harvest. Winemakers can also minimize or maintain consistent levels of eucalyptus character by measuring eucalyptol concentrations in wine lots before blending.
released by these bugs may also taint wine. These odor compounds, identified in 2010 as unsaturated aldehydes by the University of Maryland, possess a “skunky”, “citrusy”, or “piney” odor, reminiscent of fresh cilantro. Preliminary research at Oregon State University in 2013 suggests that wines may become tainted at an infestation level of only a couple of bugs per vine. There is concern that Pinot Noir might be especially susceptible to the taint.
Another insect, the brown marmorated stink bug (BMSB) is an exotic species native to Asia that is now found in most of the US. Populations are established in Washington and Oregon, with occasional sightings in California. There are concerns that odor compounds
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