Monday, April 10, 2017

Stink Bugs Impact Red Wine Flavor

The brown marmorated stink bug officially known as Halyomorpha halys congregate in early fall in the afternoon waning sun. The stink bug is not harmful to people, houses, or pets, they do not bite, sting, suck blood or carry disease. They do not eat wood or bore into house. I thought of them as a nuisance, until I saw the damage they caused to tree fruit. To fruit growers and wine makers, stink bugs are much more than a nuisance- they are an economic disaster. A 10% infestation of stinkbugs can damage an entire tree fruit crop. These ¾ of an inch flying bug can hitch a ride on grapes going through the wine making process and foul the smell and taste of the finished wine.

The stink bugs are not native to the United States they arrived from China in the late 1990’s or around 2000 when they were first noted in Pennsylvania. In the United States they do not yet have any natural enemies and they have spread widely in the Mid-Atlantic States causing crop damage. In its native range of China, Japan, Korea it is known as an agricultural pest and has become a serious threat to the fruit, vegetables and farm crops of the Mid-Atlantic region here and has now spread to the northwest wine regions of the United States. Pesticides have very limited effect on the bugs.

The economic damage that the shield shaped bugs are causing in the United States has been a topic for the Department of Agriculture, USDA, and the Land Grant Universities to study. In vineyards, brown marmorated stink bugs feed on grapes, reducing their yield and quality. And because they are relatively small compared to a wine grape and they blend in, the insects hitchhike on the grapes and wind up in the winery. When the grapes are pressed the stink bugs give off their signature stress compounds, tridecane and (E)-2-decenal, that sometimes affecting the quality of the wine and juice.

Agricultural scientists at the USDA and University Agricultural Extension research centers have been unable to prevent the spread of the bug or eliminate the pest from agricultural fields, though work continues. If you are a fruit eater I’m sure you’ve seen the series of small blemishes on apples that sometimes appear at farmer’s markets. Now with the spread of the brown marmorated stink bug to the northwest the wine industry is threatened. In a new study published in the Journal of Agricultural and Food Chemistry:

Pallavi Mohekar, Trina J. Lapis, Nik G. Wiman, Juyun Lim, Elizabeth Tomasino, Am J Enol Vitic. August 2016 : Brown Marmorated Stink Bug Taint in Pinot noir: Detection and Consumer Rejection Thresholds of trans-2-Decenal, ajev.2016.15096; DOI: 10.5344/ajev.2016.15096

scientists investigate the impact of tridecane and (E)-2-decenal on the taste of wine seeking to find the number of stink bugs per grape cluster that will not impact the integrity of the wine. The scientists found that tridecane is odorless, and (E)-2-decenal produces an undesirable musty-like, coriander or cilantro aroma that can ruin a wine. Even if you like cilantro, it is not acceptable in a Pinot Noir. The main focus of this study was to estimate the level of contamination with the stress compounds that could be detected by both consumers and wine professional and the threshold of contamination with stress compounds where a consumer would reject the wine- in the study they used Pinot noir. Interestingly, white wine was contaminated less often than red. The researchers suggest that this is because these two wines are pressed at different points in the winemaking process. The scientists conclude that if winemakers could limit stink bugs to no more than three bugs per grape cluster, the levels of tridecane and (E)-2-decenal in wine would be below the consumer rejection threshold.

I love Pinot noir, and from my days on the west coast I have a deep affection for the Oregon wines. I have some lovely 2005, 2008 and 2010 Oregon Pinot Noir. I plan on keeping those to compare with more recent vintages. It could be an interesting taste test to see if my friends and I can taste any difference.

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