Tag Archives: viticulture

Wine Literature Review Lightning Round: 5th Edition

Posted on April 26, 2013 by Becca| Leave a comment

 

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Welcome to The Academic Wino! If you are new here, please read the “About Me” page to find out more about myself and the blog. If you would like to receive free updates on articles like this by email, then sign up here or you can subscribe to the RSS feed. Also, check us out on Twitter, Facebook, Google+, and or Pinterest. Thanks for visiting!

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There’s no way one single person can possibly review every single piece of peer reviewed literature related to wine that is published every day. This series presents multiple new papers (within the past year or two) in one post by briefly summarizing the research and linking to the source in order for you to pursue further if you’re interested. If there is enough reader interest, I can review any of the papers introduced to you in this post in a more critical assessment.

VITICULTURE/ENOLOGY

“Changes in sour rotten grape berry microbiota during ripening and wine fermentation”. This article, published in 2012, aimed to determine the community structures of yeasts, lactic acid bacteria, and acetic acid bacteria in healthy grapes and grapes afflicted with sour rot, and how the winemaking process does or does not change these populations. Using healthy and sour

NOBEL ROT (Not sour rot): Photo by davitydave (Flickr: IMG_0556.JPG) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

NOBEL ROT (Not sour rot): Photo by davitydave (Flickr: IMG_0556.JPG) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

rotten Trincadeira grapes from an experimental vineyard in Portugal, the researchers determined the microbiological composition of the grapes as well as the wines created from these grapes. Wines were made with either 100% healthy grapes, or with 70% healthy grapes plus 30% sour rotten grapes.

Results showed that sour rotten grapes showed significant increases in their populations and species diversity of yeasts and acetic acid bacteria counts, while lactic acid bacteria populations were low for both sour rotten grapes and healthy grapes. The bacterial species Acetobacter orleaniensis and Acetobacter syzygii were present only in sour rotten grapes. The yeast species Dekkera bruxellensis and Oenococcus oeni were found only after primary fermentation in all wines, and after malolactic fermentation, racking, and SO2 addition, the only yeast species found were Trigonopsis cantarellii and Saccharomyces cerevisiae (in all wines). The concluding results were that there are significant microbiotic changes in grapes that are afflicted with sour rot, with potential implications for early detection in the field for treatment or sorting purposes prior to winemaking.

Source: Barata, A., Malfeito-Ferreira, M., and Loureiro, V. 2012. Changes in sour rotten grape berry microbiota during ripening and wine fermentation. International Journal of Food Microbiology 154: 152-161.

CONSUMER PREFERENCES

“What matters to consumers of organic wine?”. This article, published in 2012, aimed to determine how important the distinction of “organic” of a wine is to consumers, and what other attributes of the wine are important to those that consume organic wine. To examine this issue, surveys were sent out to around 400 Swiss wine drinkers, which asked questions related to the judgment of different wine labels, how the image and make-up of an organic wine label influences their purchase behavior, and questions related to demographics of each survey participant.

The results showed that the most important attribute for these Swiss wine drinkers was price and country of origin (they preferred French over Swiss wine). The “organic” attribute was less important than price and country of origin; however, it was more important than the color of the wine. Those participants that considered themselves healthy, as well as urban residents and female consumers were more likely to consume organic wine than their other fellow participants. From these results, the authors suggest the Swiss wine market should focus their advertising on the healthy image of wine, as well as direct the marketing toward urban women in order to maximize likelihood of purchase for organic (and other) wines.

Source: Mann, S., Ferjani, A., and Reissig, L. 2012. What matters to consumers of organic wine? British Food Journal 114(2): 272-284.

HEALTH

“The antimicrobial effect of wine on Bacillus cereus in simulated gastro-intestinal conditions”. This article, published in 2012, aimed to determine if wine could protect against Bacillus cereus infection (i.e. results in food poisoning) in the human digestive system, using a simulated experimental design. Survival of Bacillus cereus when exposed to wine was first testing in inoculated TSB media (i.e. not simulated human conditions). Next, survival of B. cereus when exposed to wine was tested in simulated human digestive system conditions, by creating an environment very similar in chemistry to the inside of the human digestive system.

Results from the first test showed that B. cereus spores were resistant to wine exposure, however, B. cereus cells in the vegetative state were highly sensitive to wine and were significantly reduced when exposed to wine. The authors broke down the components of the wine to determine which components were responsible for this decrease in vegetative B. cereus cells, and found that wine

Photo by Flickr user Evil Erin

Photo by Flickr user Evil Erin

organic acids reduced B. cereus vegetative cells, which wine phenolic compounds had no effect on B. cereus vegetative cells. Similar results were found in the human digestive system simulation experiment, with wine (total wine, not just wine parts) significantly reducing B. cereus vegetative cells and somewhat reducing B. cereus spores. The authors concluded that wine therefore may have a protective/antimicrobial effect against the food poisoning causing B. cereus, and that it is the organic acids in the wine (and not the polyphenols) that seem to be providing that protection.

Source: Vaz, M., Hogg, T., and Couto, J. 2012. The antimicrobial effect of wine on Bacillus cereus in simulated gastro-intestinal conditions. Food Control 28: 230-236.

Posted in Literature Review Lightning Round

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Comparing Biogenic Amines and Polyphenols of Grapes and Wine After Conventional, Biodynamic, and Organic Practices: Which Method is Best?

Posted on April 15, 2013 by Becca| 4 Comments

 

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Welcome to The Academic Wino! If you are new here, please read the “About Me” page to find out more about myself and the blog. If you would like to receive free updates on articles like this by email, then sign up here or you can subscribe to the RSS feed. Also, check us out on Twitter, Facebook, Google+, and or Pinterest. Thanks for visiting!

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Biogenic amines are carefully monitored in the food and beverage industries, since if they are taken in at too high of concentrations, they can cause significant health problems including headaches, breathing problems, and cardiac problems. Biogenic amines are nitrogen-based compounds that are derived from amino acids and include compounds such as histamine, serotonine, tyramine, tryptamine, phenylalanine, agmatine, putrescine, cadaverine, spermidine, and spermine. Many of these compounds may be formed during the fermentation processes of food and beverage production, which are caused by interactions with the microbial population in the system.

In wine, several biogenic amines have been identified, with the most common being histamine, tyramine, and putrescine, and with concentrations reported up to 50mg/L. It has been shown that polyphenols in wine actually serve to keep biogenic amine levels in check, as some polyphenols in wine have been seen targeting the enzymes facilitating biogenic amine production, thus keeping amine levels relatively low. In essence, these polyphenols are providing protection to the wine so that these biogenic amine compounds don’t rise to potentially toxic levels.

Several studies have examined whether or not certain agricultural or processing techniques affect the balance of polyphenols and biogenic amines in a variety of food products with varied results. Studies have examined conventional, organic, and biodynamic agricultural methods only to come up short in terms of general

Photo By drdcuddy (Flickr: Italia 2010) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Photo By drdcuddy (Flickr: Italia 2010) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

observable trends. Some studies have shown that organic products have better biological activity than conventional products, while other studies have found no differences between conventional and organic agriculture and production methods. In general, it is assumed that organic and biodynamic agriculture and production methods are better for human health overall, though there is no solid scientific evidence to back that up quite yet (only mixed results).

Generally speaking, organic agriculture and biodynamic agriculture are very similar in that they both utilize composting and cover crops and prohibit the use of commercial pesticides, fungicides, herbicides, and other sorts of man-made chemicals. One major difference between the two practices is that biodynamic agriculture utilizes special preparations that use mineral and/or herbs, as well as various animal organs, which can be buried until the soil or made into a spray to apply to the foliage of the plants.

The study presented today aimed to compare conventional, organic, and biodynamic viticulture and winemaking practices for both red and white grapes and wine, and to determine if any of these methods differ from one another in terms of their polyphenol and biogenic amine content and particularly if one viticulture or winemaking method is ideal compared to the rest in terms of wine and human health quality.

Methods

Red and white grapes of the Sangiovese and Pignoletto varieties, respectively, were all grown in 2009 from vineyards in the Emilia-Romagna region of Italy. Conventional, organic, and biodynamic viticulture practices were performed for the different treatments.

Grapes were all picked on the same day from random locations throughout the vineyards and throughout the vines and clusters. 10kg of grapes were harvested from each treatment vineyard and were ground into a powder for chemical analysis.

Wine was made from the grapes at each of the treatment vineyards on site using conventional, organic, and biodynamic winemaking practices.

The following biogenic amines were measured for both grapes and wine: tryptamine, histamine, tyramine, diamine-propane, cadaverine, putrescine, spermidine, and spermine.

The following were measured for both grapes and wine: total polyphenols, individual polyphenols, anthocyanins, and antioxidant activity.

Results

Grapes

• Putrescine was the most abundant biogenic amine in all samples.
• Tryptamine was 4.7 times higher in Sangiovese grapes than Pignoletto grapes.
• Total biogenic amine levels in Sangiovese grapes were 5.5 times higher than in Pignoletto grapes.
• There were no clear trends or differences between viticulture methods in terms of biogenic amine levels.
• There were no significant differences between viticulture methods in terms of total polyphenol levels.
• Total anthocyanins were significantly higher in Sangiovese grapes compared with Pignoletto grapes (as expected).
• Total anthocyanin levels were highest using conventional viticulture methods, followed by biodynamic methods and finally organic methods.
• Catechins and stilbenes were significantly different between the Sangiovese and Pignoletto grape varieties (lower in Pignoletto grapes); however there were no significant differences between the two groups in regards to viticulture practice treatment.
• Resveratrol and trans-resveratrol were found in all samples, though cis-piceid and trans-resveratroloside were only found in Sangiovese grapes.
• Piceatannol was 2 times higher in Pignoletto grapes compared to Sangiovese grapes.
• Sangiovese grapes had 3 times greater antioxidant capacity than Pignoletto grapes.

Wine

• Biogenic amines were 3.6 times higher in Pignoletto wines compared with Sangiovese wines.
• There were no differences in biogenic amine levels between the different winemaking practices.
• Total polyphenols were 6.5 times higher in Sangiovese wines compared with Pignoletto wines.
• Sangiovese wines had the highest levels of anthocyanins and stilbenes compared with Pignoletto wines.
• Sangiovese wines had greater antioxidant capacities than Pignoletto wines.

Conclusions

The results of this study indicated that there were no significant differences in the chemical profile of Sangiovese and Pignoletto wines when treated with conventional, organic, or biodynamic viticulture and winemaking practices. The clear differences found in this study were in terms of grape variety (red versus white), and not viticulture or winemaking method, which was confirmed using Principle Components Analysis. Sangiovese grapes were found to have higher levels of biogenic amines, though none of the levels were high enough to cause a threat to human health. Conversely, after the winemaking process, it was found that Pignoletto wine had higher levels of biogenic amines compared with Sangiovese, which is likely due to winemaking technique and the interactions with the compounds present in the white must.

It seems as though reducing the levels of biogenic amines in wines may be difficult, as there are a number of factors that could be contributing to their

Biodynamic Composting. Photo credit: By Mark Smith [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Biodynamic Composting. Photo credit: By Mark Smith [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

levels (i.e. grape variety, winemaking technique, geographical growing area, etc), though this study shows that using biodynamic or organic viticulture or winemaking methods as opposed to conventional methods will not affect biogenic amine levels.

Of course, there are many environmental benefits of using biodynamic and organic viticulture and winemaking practices, so these results are certainly not meant to deter anyone from adopting these methods. It’s simply a matter of determining what viticulture or winemaking technique will help lower biogenic amine levels in wine, and it’s clear from the results that choosing biodynamic or organic methods over conventional methods will not help in this case. I encourage biodynamic and organic agriculture and production methods, though again if one is seeking to change practices just to lower biogenic amine levels, switching to either of these won’t make a difference (but it will make a difference in other areas!).

I’d love to hear what you all think of this topic! Feel free to share comments or stories with everyone!

Source: Tassoni, A., Tango, N., and Ferri, M. 2013. Comparison of biogenic amines and polyphenol profiles of grape berries and wines obtained following conventional, organic and biodynamic agricultural and oenological practices. Food Chemistry 139: 405-413.

Posted in Chemistry, Environmental Science

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Wine Literature Review Lightning Round: 4th Edition

Posted on March 18, 2013 by Becca| 4 Comments

 

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Welcome to The Academic Wino! If you are new here, please read the “About Me” page to find out more about myself and the blog. If you would like to receive free updates on articles like this by email, then sign up here or you can subscribe to the RSS feed. Also, check us out on Twitter, Facebook, Google+, and or Pinterest. Thanks for visiting!

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Normally, I save this series for Fridays, however, I was surprised by a marriage proposal (of which I said yes!) by my now-fiancé this weekend and didn’t end up having time to write anything else :)   Enjoy this post a few days early!

There’s no way one single person (even if that person is The Academic Wino!) can possibly review every single piece of peer reviewed literature related to wine that is published every day. This series presents multiple new papers (within the past year or so) in one post by briefly summarizing the research and linking to the source in order for you to pursue further if you’re interested. If there is enough interest, be it through comments or emails, I can review any of the papers introduced to you in this post in a more critical assessment.

WINEMAKING

“An assessment of using ground thermal inertia as passive thermal technique in the wine industry around the world”. This article, published in 2012, aimed to use a mathematical modeling approach to confirm the benefits of using underground cellars for aging wine, and to promote the use of this type of cellar when constructing new wineries. Basically, the model employed during this analysis used thermal inertia (i.e. how temperature moves in a given medium or space) of the ground in order to provide protection to the wines during the aging process. The characteristics of these underground cellars allow for good ventilation as well as good temperature control for the wines during the aging process.

By Philip Larson (originally posted to Flickr as DSC02022) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

By Philip Larson (originally posted to Flickr as DSC02022) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

According to the model results, the inputs of which were based on real underground wine cellars in Spain, the ideal temperature for storing wine is easily reached inside these underground cellars without the need for supplemental air conditioning. Eliminating the need for air conditioning is beneficial for multiple reasons, one being the savings on one’s electric bill, while the other being a savings for the environment in regards to a reduced carbon footprint. Finally, according to the authors of this study, the model the used in this analysis could be helpful for those designing or constructing new wine cellars, which based on the specific measurements and layout planned, could estimate the indoor temperature of the cellar and possibly allow for infrastructure changes if need be prior to completion of the facility if the temperature based on current specs was not up to acceptable standards.

Source: Mazarrón, F.R., Cid-Falceto, J., and Cañas, I. 2012. An assessment of using ground thermal inertia as passive thermal technique in the wine industry around the world. Applied Thermal Engineering 33-34: 54-61.

VITICULTURE

“Floral, spicy and herbaceous active odorants in Gran Negro grapes from shoulders and tips into the cluster, and comparison with Brancellao and Mouratón varieties”. This paper, published in 2012, aimed to examine the aromatic characteristics of Gran Negro grapes, and to specifically test if grapes from different parts of the cluster (shoulders and tips) would yield different aromatic compounds that could be taken advantage of when trying to create a unique wine in a highly competitive market. GC-MS spectroscopy was used to determine the aromatic chemical profile of the grapes from both the shoulders and the tips of the clusters.

The results of the study showed significant variation in aromatic compounds of grapes, depending upon where in the cluster the grape was located. For those grapes located at the tip of the cluster, volatile phenols and aromatic alcohols were 2 and 15 times higher in the flesh of the grape than in the skins, respectively, whereas for those grapes located at the shoulder of the cluster, volatile phenols were 2 times higher in the skins of the grapes compared with the flesh. Also, aldehydes and C6 alcohols were 4 and 3 times higher in the skin than in the flesh for those grapes located at the tips of the clusters. C6 alcohols were found to be 40% lower in the tips than in the shoulders.

Overall, this study showed that there is significant variation in the volatile composition of grapes, depending upon where in the cluster the grape is located, which could allow winemakers to create even more unique wines which could give them a market advantage in this competitive industry.

Source: Noguerol-Pato, R., Gónzalez-Barreiro, C., Cancho-Grande, B., Martínez, M.C., Santiago, J.L., and Simal-Gándara, J. 2012. Floral, spicy and herbaceous active odorants in Gran Negro grapes from shoulders and tips into the cluster, and comparison with Brancellao and Mouratón varieties. Food Chemistry 135: 2771-2782.

“RECYCLING”/ENVIRONMENTAL SCIENCE

“Wine grape pomace as antioxidant dietary fiber for enhancing nutritional value and improving storability of yogurt and salad dressing”. Grape pomace has already been shown to improve the shelf life and/or nutritional quality of many food products, including chicken, hotdogs, and green tea. This study, published in 2013, aimed to examine if grape pomace added to yogurt and salad dressing could be beneficial in this same manner, and whether or not consumers would actually enjoy the taste of these products after the pomace was added. Dried grape pomace powder was added to yogurt, Italian salad dressing, and Thousand Island salad dressing and stored for 3 weeks at 4oC.

By Tricia (Flickr: saladdressing) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

By Tricia (Flickr: saladdressing) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Results showed that adding grape pomace to all samples resulted in a 35-65% reduction in peroxide values, indicating the potential benefit of grape pomace as a preservative in all three products. The samples also showed dietary fiber levels of 0.94-3.6%; total phenolic content of 958-1340 mg gallic acid equivalent/kg product; and DPPH scavenging activity (i.e. antioxidant capacity) of 710-936 mg ascorbic acid equivalent/kg product. Sensory analysis revealed the products with grape pomace added were nearly universally accepted as “likable”. Overall, the study results indicated that grape pomace could be a good additive to yogurt and salad dressing in order to prolong shelf life and improve the nutritional content of the products.

Source: Tseng, A., and Zhao, Y. 2013. Wine grape pomace as antioxidant dietary fiber for enhancing nutritional value and improving storability of yogurt and salad dressing. Food Chemistry 138: 356-365.

I’d love to hear what you all think about any or all of these topics!  Please feel free to leave comments!

Posted in Literature Review Lightning Round

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Mealybug-Infested Grapes: How Do They Influence Wine Quality?

Posted on March 7, 2013 by Becca| 2 Comments

 

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Welcome to The Academic Wino! If you are new here, please read the “About Me” page to find out more about myself and the blog. If you would like to receive free updates on articles like this by email, then sign up here or you can subscribe to the RSS feed. Also, check us out on Twitter, Facebook, Google+, and or Pinterest. Thanks for visiting!

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There is a lot of research focused on the effect of various fungal agents on the quality of finished wine; however, to date there has been very little examining the effect of insects on wine quality. While some insects are considered to be beneficial (i.e. ladybugs; since they are known to prey on pest insects), many other are considered to be pests as a result of their contamination of the grapes which result in undesirable aromatic characteristics in the finished wine.

One insect pest of grapevines in particular is the mealybug (Hemiptera: Pseudococcidae). Certain species tend to be more problematic than others, though in general they aren’t exactly wanted ever in the vineyard. In California and Argentina, the most common species of mealybug is Planococcus ficus

By Tegermee (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

By Tegermee (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

(Signoret), whereas in Chilean vineyards, the most common species is Pseudococcus viburni (Signoret). As the grapes go through veraison and continue to ripen, the mealybug moves to the grape clusters where it continues to feed and reproduce. One problem with mealybugs in regards to grape health is that when they are going through the process of feeding, they excrete honeydew, which has been shown to act as a solid base for the development of sooty mold or other fungi. Also, it has been shown that mealybugs can carry and transmit grapevine viruses, including the leaf-roll virus.

Though it is generally understood that mealybugs (and other similar insects) are undesirable in the vineyard for the reasons mentioned above, there has been very little research done examining the effects of mealybug infestation on the quality of the wine produced from the exposed grapes. The goal of the study presented today was to test whether or not wine produced from different levels of mealybug infestation had different chemical and sensory characteristics for both red and white wines.

Methods

Grapes used were Chardonnay from the Casablanca Valley in Chile, and Carménère from the Colchagua Valley also in Chile. Mealybug damage on the grape clusters were based on a scale of 0-3; with 0 reflecting completely healthy grapes, 1 reflecting the presence of less than 5 mealybugs or a light bit of honeydew, 2 reflecting an infested cluster with only part of it useable, and 3 reflecting a completely infested cluster. After harvest, grapes were taken to the Enology lab at the Universidad Católica de Chile in Santiago, Chile.

180kg of grapes were harvested from the Chardonnay vineyard and another

Carmenere Photo Credit: By Lebowskyclone (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Carmenere Photo Credit: By Lebowskyclone (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

180kg from the Carménère vineyard, with approximately half the grapes being healthy, and the other half being infested with mealybugs.

Once grapes were brought to the laboratory, healthy and infested grapes were mixed together to create four different treatment types: 1) 100% healthy grapes; 2) 66% healthy and 33% infested grapes; 3) 33% healthy and 66% infested grapes; and 4) 100% infested grapes.

Wine was made using small-scale winemaking procedures. Chardonnay was not allowed to go through malolactic fermentation, while the Carménère was made as reds are made traditionally with malolactic fermentation. A total of 12 batches were made for each wine, representing the 4 treatments and 3 replicates each.

For the musts, the following were measured and analyzed: pH, sugar content, and titratable acidity.

For the finished wines, the following were measured and analyzed: free sulfites, total sulfites, pH, alcohol degree, titratable acidity, volatile acidity, residual sugar, and nitrogen content. For the Chardonnay, specifically, total polyphenols were also analyzed. For the Carménère, specifically; total polyphenols, hue, total anthocyanins, dimethyl amino cinnamaldehyde index, total tannins, and average degree of tannin polymerization were also analyzed.

Sensory analyses were performed by 20 people from the Pontifica Universidad Católica de Chile, including 2 enologists and 18 graduates of the ecology major program. Wines were randomly (and blindly) presented to the subjects in groups of 4, representing each of the 4 treatments. Tastings were done prior to the experimental tastings, in order to get a solid grasp of the taste descriptors that were being analyzed in this study. Flavors and aromas were scored on a 1-9 scale (1 being the worst and 9 being the best).

Results

• The chemical compositions of the musts were not different between mealybug infestation treatments.
• After the completion of alcoholic fermentation, there were no differences in chemical composition between the different treatments in the Chardonnay. However, in Carménère, pH and alcohol content were lower in the 100% infested treatment than all other treatment than all other treatments.
o Also, Carménère showed greater levels of nitrogen in the 66% and 100% infestation treatments than the 33% and 0% infestation treatments (no difference in Chardonnay).
• In Chardonnay, total polyphenols decreased as mealybug infestation proportions increased, with the 100% infestation treatment being statistically significant.
• In Carménère, total polyphenols, anthocyanins, tannins, and dimethyl amino cinnamaldehyde index all decreased in wines made from mealybug infested grapes.
• In Carménère, as mealybug infestation increased, total anthocyanins, malvidin, acetylated anthocyanins, non-acetylated anthocyanins and cumarilated anthocyanins all decreased.
• In Carménère, as mealybug infestation increased, total tannin content and the proportion of galiolated tannin decreased, whereas the average degree of tannin polymerization increased.

Sensory Analysis

• Principle Component Analysis on the sensory analysis results showed that Chardonnay made from the 100% mealybug infested grapes were associated with negative characteristics, including that of oxidation.
• Chardonnay wines from the 33% and 66% infestation treatments were associated with bitterness.
• Chardonnay wines from the 100% healthy treatment (0% infestation) were associated with positive flavor and aroma characteristics, as well as higher quality.
• Carménère wines from the 100% infestation treatment were associated with dry fruit and dry vegetable characteristics.
• Carménère wines from the 100% healthy treatment were associated with fresh fruit, body, and higher quality.

Conclusions

The results of this study indicate that mealybug infestation does, in fact, play a negative role in the overall quality of a wine created from infected grapes. The grape variety also seems to play a small role, as there were some differences between Chardonnay and Carménère when it came down to the changes in chemical composition and the sensory analysis of the wines. It was interesting to note that the musts of the wines actually did not differ in their chemical compositions, but throughout the alcoholic fermentation (and malolactic fermentation in the red) there appeared to be specific chemical composition changes related to the proportion of mealybug infested grapes used in the processing of the wines.

Specifically, the higher the proportion of mealybug infested grapes used to make the wine, the lower the phenolic content, which as the authors mention (and I

Leaf roll virus: Photo credit: William M. Brown Jr., Bugwood.org

Leaf roll virus: Photo credit: William M. Brown Jr., Bugwood.org

agree) could lower the overall quality of the wine. This lowering in quality was confirmed in the sensory analysis of the wines.

While it’s clear there is a negative effect of mealybug infestation on wine quality (at least with Chardonnay and Carménère), it is unclear exactly why. The authors mentioned the mechanism could be related to the insects themselves directly contaminating the grapes, or possibly indirectly through the honeydew left after feeding or through the fungus attracted to the grapes after mealybug feeding. Whatever the mechanism may be, it is clear that mealybug infestation should be controlled in order to avoid possible undesirable flavors and aromas in the finished wine, in addition to an overall decrease in the quality of the wine.

I would love to see more research focusing on determining the mechanism of this process, as knowing exactly what causes the lower quality wines would give vineyard managers a better idea of exactly how to target their protection and control defenses.

I would also like to see more research breaking down the influence of different species of mealybug and how infestations of one or the other (or both concurrently) affect the quality of finished wines. The authors made mention of differences between the two species in their introduction, however, these differences were not tested. I wonder if one species over another is more damaging to wine quality or if they are roughly equivalent in their harm.

What do you all think of this study? Do you have any experience with mealybug infestation? How have you been successful or unsuccessful in combating against these pests? Please leave these and any other general comments you have for discussion!

Source: Bordeu, E., Troncoso, D.O., and Zaviezo, T. 2012. Influence of mealybug (Pseudococcus spp.)-infested bunches on wine quality in Carménère and Chardonnay grapes. International Journal of Food Science and Technology 47: 232-239.

Posted in Chemistry, Viticulture

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