Category Archives: Enology

Using Carrageenan or Pectin as Possible Alternatives to Bentonite for Protein Removal in White Wines

Posted on April 10, 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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One very important step in the white winemaking process is the removal of proteins that cause a hazy appearance of the wine while in storage. Often, bentonite is used to remove these proteins, as the negatively charge bentonite will attract the positively charged proteins and settle out to the bottom of the tanks where they can be left behind. Though the use of bentonite is efficient in removing proteins from white wine, some claim it has less than desirable side effects, including the loss of wine since it can’t be reused, as well as the cost of its disposal and potential changes in the aromatic profile of the finished wine. Some studies have shown no effect on aromatics by bentonite, while others have shown it does negatively affect the aroma. As a result, finding an alternative to bentonite for removing proteins from white wines may be important.

Two possible alternatives to bentonite that are the focus of the study presented today are carrageenan and pectin. Carrageenan is a negatively charged polysaccharide that was originally extracted from red seaweed. The large number of sulfate groups on the compound gives it its negative charge and so

By Derek Keats from Johannesburg, South Africa (Red seaweed, Plocamium sp.) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

By Derek Keats from Johannesburg, South Africa (Red seaweed, Plocamium sp.) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

may function well to remove the positively charged proteins in white wine. Pectin, on the other hand, is a negatively charged heteropolysaccharide compound with many carboxylic acid groups that has been shown to be effective in acidic dairy beverages.

The goal of the study presented today was to determine if carrageenan or pectic could be good alternatives to bentonite in removing proteins from Australian Chardonnay wines and to determine how these possible alternatives affect the chemical and aromatic characteristics of the finished wine.

Methods

Small Experiment

4 unfined juices from the 2009 vintage using Chardonnay, Sauvignon Blanc, Riesling, and Semillon grapes, as well as 4 unfined finished wines from the 2011 vintage using two Chardonnays and 2 Sauvignon Blancs (all from Adelaide Hills, Australia) were used in the preliminary experiment.

1mL of each wine sample was mixed with 0.5g/L of carrageenan and left in contact for 18 hours before the carrageenan was removed by filtration. All samples were performed in triplicate.

Large Experiment

Chardonnay must from the Langhorne Creek region of Australia (2009 vintage) was used for the large-scale experiment. Twenty 20L fermentations were prepared for the experiment. 30mg/L of pectinase was added, cold settled for 24 hours at 0oC, and finally racked.

The following 6 treatments were tested: 1) pectin added pre-racking; 2) carrageenan added pre-racking; 3) pectin AND carrageenan added pre-racking; 4) pectin added post-racking; 5) carrageenan added post-racking; and finally 6) pectin AND carrageenan added post-racking. The concentration of pectin used was 2g/L, and the concentration of carrageenan used was 0.25 g/L. Controls without carrageenan and/or pectin were also produced and tested.

After racking, standard fermentation practices were used on all treatment wines.

After going through a cold stability test, wines were bottled and capped with screw caps 4 months after fermentation ended.

For all wines, protein and polysaccharide content were measured, in addition to undergoing a heat test (measuring the amount of haze produced). The following were also measured and analyzed for all wines: alcohol, specific gravity, pH, titratable acidity, glucose, fructose, volatile acidity, free SO2, total SO2, brix, organic acids, metal content, color, and finally sensory characteristics.

A separate test determined how much bentonite was needed to produce a heat-stable wine (i.e. no haze formation).

For the sensory analysis, wines were evaluated by 30 expert AWRI tasters 10 months after bottling. The panel wrote their own notes about the appearance, aroma, and flavor of each wine, as well as whether or not they noted any faults in the wine.

Panelists were asked to determine which wine was different from the rest in a sample set of 3 wines each. They were given 5 sets representing all of the treatment wines. Panelists were isolated in tasting booths for the sensory analysis. Panelists were allowed a 30 second break in between analyzing each set.

Results

Small Experiment

• Carrageenan significantly reduced the amount of protein in all samples in which the compound was present in the small-scale experiment.

Large Experiment

• The use of carrageenan resulted in a decreased fermentation rate (3-11 days slower than the controls).
• The use of pectin did not affect the fermentation rate of wines.
• All fermentations to which carrageenan was added had problems with frothing.
• At day 12, polysaccharide content was higher in all treatments than in the controls.
• After bottling, there were no differences between treatments and controls in regards to polysaccharide content.
• Free SO2, total SO2, specific gravity and residual sugar were not affected by any of the treatments.
• Ethanol content was about 0.15% v/v lower in carrageenan-treated wines.
• Volatile acidity was lower in pectin-treated wines.
• pH was higher and acidity lower in pectin-treated wines.
o Acidity was lower due to lower tartaric acid content (no other acids were affected).
• Acidity was not affected by carrageenan treatment.
• All metals were in range of those commonly found in white wines.
• Fe and Al were decreased in most treatment wines.
• Mn, Zn, and Mg were significantly decreased in pectin-treated wines.
• Na was significantly higher in all treatment wines.
• K was significantly increased in pectin-treated wines.
• Pectin added pre-racking removed the Al prior to the start of fermentation.
• Al content was nearly zero for all treatments at bottling.
• At bottling, pectin added pre-racking had significantly higher levels of Ca than the control.
• Fe and Zn levels were similar at bottling to what levels were in the must for most treatments.
• Zn was 30% decreased in pectin added pre-racking compared to all other wines.
• Mg and Mn levels were significantly decreased in all pectin treatment wines.
• Na was increased in all treatments at bottling.
• K levels increased by 20% in pectin-treated wines.
• B, Cu, S, and P levels were not affected by any treatment.
• Metal concentrations in wines were more affected by pectin treatment than by carrageenan treatment.
o The authors suggested that if either of these are used as alternatives to bentonite, winemakers may want to consider adding micronutrients to make up for the changes listed above.
• Color was largely unaffected by the treatments, with no differences detected using the naked eye.
• In regards to protein removal, adding both pectin and carrageenan after racking was most effective.
o Most of the protein was removed prior to fermentation.
• By itself, carrageenan was more effective at removing protein than pectin.
o Pectin did not remove as many chitinases or thaumatin-like proteins compared with carrageenan.
• Pectin added after racking reduced haziness in wine by about 50%.
• Carrageenan treatments reduced haziness in wines by between 58 and 72%.
• The bentonite control treatment reduced haziness in wines by between 38 and 76%.
• Sensory analysis confirmed a significant different between the control wines and the wines treated with carrageenan after racking. No other differences were noted.
o It was not determined if this difference was better or worse, just that it was different.

Conclusions

The results of this experiment showed that the addition of both pectin and carrageenan effectively reduced the levels of haze-causing proteins in white wines, though carrageenan was slightly more effective than pectin. It is possible

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

that adding them together might be more effective, though those numbers were not supplied by the authors. It appears as though they are as effective as bentonite in removing protein from wine, so from a simple protein removal standpoint, both pectin and carrageenan would be good alternatives to bentonite.

There were some negative aspects to using pectin and/or carrageenan, including slowed fermentation rates, slightly lowered ethanol content and frothing in carrageenan, and altered metal content in both treatments. Finally, when carrageenan was added after racking, there was a change in the sensory profile of the wine, which may or may not be desirable.

Overall, the results of this study showed that pectin and carrageenan, when used separately or in concert, where just as effective as bentonite in reducing the protein levels in white wine and thus the haziness of white wine. However, I don’t think I’m ready to say go ahead and make the switch, as there are a lot of questions still left unanswered. The slowed fermentation rate and the frothiness in all fermentation batches when carrageenan was concerning to me, as winemakers would need to come up with effective strategies to avoid or work with these issues.

I was also concerned with the results of the sensory analysis, as it was not clear to me how the aromatic profile of the wine with carrageenan added after racking was affected. It seems like a somewhat poor experimental design to have a sensory analysis that gathers information on differences between wines yet not describe which one actually tastes better. It’s a simple question that could have received a quick answer, yet it was somehow overlooked. For all we know, that wine could have tasted significantly better than all the other treatments and controls!

Further analysis should examine the sensory changes further, as well as possible mechanisms for combating the slow fermentation rates and frothing issues. It would also be interesting to see if pectin or carrageenan added at different doses would be more or less effective than the doses analyzed in this study, and if adding them together would be better overall than adding them separately. Finally, how effective are these treatments using different white wines? I’d like to see a range of white wines compared.

What do you think about this study? What would you have done differently? What would you like to see come next in this line of research? Please feel free to leave any comments or questions!

Source: Marangon, M., Lucchetta, M., Duan, D., Stockdale, V.J., Hart, A., Rogers, P.J., and Waters, E.J. 2012. Protein removal from a Chardonnay juice by addition of carrageenan and pectin. Australian Journal of Grape and Wine Research 18: 194-202.

Posted in Chemistry, Enology

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The Influence of Oak Chips Added at Various Stages of Winemaking on Sensory Characteristics of Wine

Posted on April 3, 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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As many of you may already know, using oak barrels in wine fermentation and aging increases wine aromatic complexity and improves overall quality. The use of oak in wine is and has always been very popular, despite the fact that it costs more money to produce an oaked wine than it is to produce a wine made in stainless steel tanks. As a result of this cost differential, some wineries as well as home winemakers have been searching for alternatives to oak barrels that give similar aromatic and quality characteristics to the finished wine without the high costs.

There is some experimental evidence suggesting that application of oak extract to the vines during the growing season may impart oak flavor characteristics into the finished wine, however, it’s a practice that is currently just in the research and development phase, and is not yet widely practiced or accepted. In recent years, the use of oak chips instead of oak barrels has become much more popular, as it has been shown that using oak chips in wine fermented and/or aged in stainless steel tanks results in finished wines that are aromatically similar to wines that are fermented and/or aged in oak barrels.

Oak chips may be added to the wine at any stage during the winemaking process, and will result in varied styles of wine depending upon exactly when the chips were added. The goal of the study presented today was to examine the sensory

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

characteristics of one particular type of wine (Bobal) when placed in contact with oak chips at different stages throughout the winemaking process and to identify when during the winemaking process oak chip exposure will create the wine most similar to a wine kept in oak barrels.

Methods

Bobal grapes from a vineyard in the La Mancha region of Spain were used for this study and were harvested at their optimal ripening time. Grapes were separated into 7 batches and were all processed the same up until right after skin maceration. The following treatments were applied to the grape batches:

1. Control Wine: wine without the addition of oak chips.
2. Addition of oak chips during alcoholic fermentation.
3. Addition of oak chips during malolactic fermentation.
4. Addition of oak chips post-fermentation (1 week contact time).

The three oak chip treatments were split into two sub-treatments: 3g/L dose and 6g/L dose (total 7 treatments including control).

The oak chips used were a mix of French and American oak and had medium toast.

The rest of the winemaking process was pretty standard and the same for all treatments: manual punch downs, malolactic fermentation, racking, filtering, bottling, and storing. Finished wines were stored at 16-18oC until sensory analysis was performed. All treatments were performed in duplicate.

For all wines, the following were measured and analyzed: total acidity, ethanol content, pH, volatile acidity, total SO2, and free SO2.

For the sensory analysis, a carefully trained panel of 15 judges between the ages of 24 and 50 years old from the University of Castilla in La Mancha, Spain was selected. Panelists were specifically trained to analyze flavor descriptors in Bobal wines (both oaked and unoaked).

20mL of each treatment wine samples were given to the judges in standard wine glasses and covered with a watch glass in order to avoid volatile loss to the air. Sensory analysis took place in individual booths in a sensory analysis chamber. Panelists smelled and tasted the wines and recorded the aromatic and flavor descriptors they noted in each wine.

Results

• There were no significant differences between samples in regards to total acidity, volatile acidity, and pH.

Nose:
• Aromas on the nose of control wines (no oak chips added) were: red fruit, fresh, liquorish, pepper, sweet spices, leather, tobacco, and cassis.
• Wines with oak chips added at alcoholic fermentation saw a significant decrease in red fruit, liquorish, cassis, and pepper aromas.
• Wines with oak chips added at alcoholic fermentation saw a significant increase in sweet spices and woody notes at the higher 6g/L dose compared with the lower 3g/L dose.
• Wines with oak chips added at malolactic fermentation saw significant decreases compared with all wines in red fruit, fresh, pepper, and cassis aromas.
• Adding oak chips during malolactic fermentation resulted in significantly higher intensities of oak-derived aromas at the 6g/L dose compared with the 3g/L dose.
• Wines with oak chips added post-fermentation for one week were similar in character to wines with oak chips added during malolactic fermentation, however showed decreases in intensity of woody, vanilla, coconut, toast, and toffee notes.
• Wines with oak chips added post-fermentation for one week showed increases in red fruit character compared with wine with oak chips added during malolactic fermentation.
• 6g/L oak chip wines generally showed greater oak character than wines treated with 3g/L oak chips.
• Principle component analysis (PCA) grouped wines most similar to each other into two groups: 1) both wines with oak chips added at alcoholic fermentation and control wines; 2) both wines with oak chips added at malolactic fermentation and both wines with oak chips added post-fermentation for one week.
o The second group showed significantly more oak character than the first group.
o In the second group, the two wines with chips added at malolactic fermentation were greater in oak aromatic intensity than the wines with oak chips added post-fermentation for one week.

Taste:
• Control wines (no oak chips) had flavors of red fruit, liquorice, clove, pepper, leather and tobacco.
• All oak chip wines had significantly decreased red fruit flavors, with the wine treated with oak chips at malolactic fermentation having the least red fruit flavors.
• All oak chips wines had flavors of cinnamon, vanilla, wood, toast, and chocolate that were not present in the control wines.
• Wine treated with 6g/L of oak chips during malolactic fermentation had the most oak-like qualities compared with all other wines.
• All oak chip treatments reduced astringency in the wines.
• Wines treated with oak chips during malolactic fermentation had greater body than all other wines.
• Principle component analysis (PCA) grouped wines most similar to each other into two groups: 1) both wines with oak chips added at alcoholic fermentation and control wines; 2) both wines with oak chips added at malolactic fermentation and both wines with oak chips added post-fermentation for one week.
o The second group showed significantly more oak character than the first group.

Conclusions

The results of this study showed that the addition of oak chips at different times during the winemaking process resulted in finished wines with significantly different aromatic and flavor profiles. The addition of oak chips at any time resulted in wines with more oak-like character, however the amount of oak character was dependent upon the dose of oak chips as well as when during the winemaking process the oak chips were added. It was noted that astringency was also reduced when oak chips were added, and body was only affected when the oak chips were added during malolactic fermentation.

The authors suggested that any of the treatments would be acceptable alternatives to using an oak barrel, however, depending upon what style of wine

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

you wish to create will determine how much and when the oak chips should be added. According to the results, adding 6g/L of oak chips during malolactic fermentation produced the wine with the most intense oak flavors, however, all oak chip treatments possessed some oak-like character.

One treatment that I feel was missing from this experiment was the oak barrel treatment control. The results showed that oak chip treatments resulted in “oakier” wines compared with the stainless steel control, however, how does it compare with wines that are actually fermented and/or aged in a barrel? Is it comparable? A lot less?

It would also be interesting to see how wines made from other grape varieties are influenced by oak chip addition at different stages during the winemaking process.  Will we see similar results?  Or will we see different treatments emerging as the “oakier” style wines?

One other thing I would have liked to have seen is preference scores by the sensory panel. They described the aroma and flavor characteristics of each sample; however, they did not score whether or not they preferred one particular wine over another. Everyone has different tastes and preferences, of course, but it would have been at least somewhat interesting to see if the panel actually liked these wines or not.

I’d love to hear what you all think of this topic! Do you have any personal experiences you can share regarding oak chip-treated wines? What sort of future research would you like to see coming out of this study? Please feel free to comment!

Source: García-Carpintero, E.G., Gómez Gallego, M.A., Sánchez-Palomo, E., and González Viñas, M.A. 2011. Sensory descriptive analysis of Bobal red wines treated with oak chips at different stages of winemaking. Australian Journal of Grape and Wine Research 17: 368-377.

Posted in Enology

Tagged , , , , , , ,

Examining Variations in Grape Phenolic Maturity and Ripeness at Harvest and How It Influences Wine Quality

Posted on March 25, 2013 by Becca| 5 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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It is well known among grape growers and winemakers that the phenolic maturity of the grapes at harvest significantly impacts the overall quality of the finished wine. Specifically, the aroma, flavor, mouth feel, and astringency (to name a few) are all tied in with the composition of phenolic compounds in grapes and wine, thus are strongly influenced by grape ripeness or a lack thereof. Studies have found that certain phenolics in the skins of unripe grapes are less extractable and certain phenolics in the seeds of unripe grapes are more extractable than those in the skins and seeds of fully matured grapes, thus resulting in altered flavor and aroma of the finished wine.

The current demand from consumers in terms of ideal red wine characteristics are wines with a dark red color, full body, soft tannins, and ripe fruit flavors and aromas. In order to create wines with these types of characteristics, winemakers need to use fully ripened grapes, specifically those grapes that have reached “phenolic maturity”. It is because of this that there has been a lot of work done looking for a method or system to test grapes in the field to determine their ideal harvest date when phenolic maturity has been reached. There has been some progress in this field of research, however, according to the authors of today’s paper, these methods rely on the average values of a sample of grapes in the vineyard, and don’t take into account the variability of the phenolic maturity of grapes within that sample. A large variability in grape phenolic maturities could spell trouble for a winemaker attempting to create the “ideal wine” for consumers.

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons

When grapes ripen throughout the season, each and every grape does not ripen at the exact same rate. A lot of factors go into this variability, from weather to vineyard management practices and even to the specific location on the cluster. As a result of this variability in ripening rates, there is the potential for there to be a large variability in phenolic maturities of the grapes at harvest, even when the average values indicate it’s about time to pick. According to the authors of today’s study, no one has ever looked at this variability (in other words, heterogeneity) of phenolic maturities in grapes, nor has it ever actually been quantified.

Thus, the goal of the study presented today was to evaluate the variability or heterogeneity of the degree of grape ripeness (degree of phenolic maturity) and how this variability affects wine quality and phenolic composition.

Methods

Grapes used for this study were Cabernet Sauvignon from experimental vineyards at Constantí owned by the Rovira i Virgili University in Spain. Grapes were studied during the 2007 and 2008 vintages and were harvested from the two central rows in this experimental vineyard.

600 grapes were collected randomly at 1, 3, 5, and 7 weeks after veraison (i.e. when the grapes start to change color) and analyzed. Sugar content, titratable acidity, pH, weight, and ripening heterogeneity of a portion of those grapes were measured.

Grapes were harvested 7 weeks after veraison for winemaking purposes and were separated into three different groups based on their densities. Grapes were then crushed, and then underwent typical red winemaking procedures (including a 14 day maceration period). After bottling, wines were stored at 15oC until ready for analysis.

The following were measured for grapes: sugar content, probable alcohol degree, titratable acidity, and pH; and the following were measured for the finished wines: ethanol content, titratable acidity, and pH. Also measured were: color intensity, lightness, chroma, hue, red-greenness, yellow-blueness, total color difference, total anthocyanin content, flavanol content (including catechins and oligomeric proanthocyanidins), total phenolic index, and astringency index.

A sensory analysis was performed on all wines by a panel of 10 “expert enologists” from Rovira i Virgili University after a 6 week storage period after bottling. Dark tasting glasses were used so the appearance of the wine color did not have any influence on the panel’s scores. Wines were compared in pairs, with the pairs being made up of two of the following: low density wine, medium density wine, and high density wine. The panel was asked to determine if they could tell a difference between the two samples and also what their favorite sample was and why.

Results

• As expected, during the growing season, sugar content, probable alcohol degree, pH, and berry weight increased, while titratable acidity decreased.
• The 2007 vintage grapes reached a greater phenolic maturity than the 2008 vintage grapes, though both years were considered “normal” years.
• Significant heterogeneity in phenolic composition and maturity of grapes was noticed from the start of the sampling period all the way through harvest.
o According to the authors, this means that are likely many unripe grapes mixed in at harvest prior to the winemaking process, which could increase bitterness and astringency due to lower sugar content, higher acidity, lower anthocyanin levels, and higher seed tannin levels, ultimately lower the quality of the finished wine.
o They suggest that these results indicate a significant influence of grape heterogeneity on phenolic composition of wine.
• As grape density increased, ethanol content and pH of wines increased, and titratable acidity decreased.
• Grape density significantly affected wine color.
o Higher density grapes resulted in wines with higher color intensity, chroma, and red-greenness as well as lower lightness levels.
o Hue and yellow-blueness levels were not consistent from year to year.
• The sensory panel was able to tell the different in wine color of wines from different grape densities just by using the naked eye.
o According to the authors, these results indicate that grape heterogeneity significantly impacts wine color.
• Grape density significantly influenced the anthocyanin content in the wines.
o As grape density increased, anthocyanin content increased (for both free and combined with flavanol forms)
o The authors noted that the presence of unripe grapes (i.e. less dense) at harvest could significantly impact the anthocyanin content of the finished wine.
• As grape density increased, proanthocyanidin concentrations and astringency increased.
o Denser grapes resulted in greater proanthocyanidin levels, which according to the authors could result in greater tannin levels, indicating a greater ability for aging than less dense grapes with lower levels of proanthocyanidins.
• As grape density increased, (+)-catechin decreased and (-)-epigallocatechin increased.
• Grape density significantly influenced proanthocyanidin monomer and oligomer concentrations.
o As grape density increased, monomers and dimers increased.
• Only 50% of the sensory panel could tell the difference between the medium and high density wines, while 100% of the panel could tell the difference between the low and high density wines.
o Overall preference was unanimous for the higher density wines, which the panel indicated had greater fruit and floral notes, as well as having better balance, lower acidity, and less bitterness than low density wines.

Conclusions

According to the results of the study and the author’s interpretations, grape ripeness heterogeneity has significantly more influence on finished wine quality than initially thought. Specifically, less ripe grapes (i.e. indicated by the lower density grapes in the study) can significantly influence the phenolic composition of the finished wine, and ultimately the overall quality of that wine. Basically, lower density grapes (i.e. less ripe grapes) lower the ethanol content, pH, anthocyanin concentrations, color intensity, total phenolic index, and proanthocyanidin concentrations, as well as increase the titratable acidity of the finished wine, resulting in an overall lower quality wine. By mixing in these lower density grapes in with the higher density grapes, the overall quality of the finished wine will most certainly be lowered some.

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons

Agne27 at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons

While only half of the sensory panel could differentiate between the medium and high density wines based on taste alone, 100% of the panel could tell the difference between the low and high density wines, indicating that grape ripeness heterogeneity is an extremely important factor in determining overall wine quality. Even though not all the panelists could tell the difference between the medium and high density wines based on taste alone, they were able to tell the difference based on color, so adding those two factors together could potentially decrease the overall acceptability and likelihood of purchase of even medium density (or not as many unripe grapes) wines (this was not tested—just my theory).

According to the authors, more research on grape phenolic maturity heterogeneity is needed, as well as methods or protocols for filtering out these less ripe grapes either in the field or just prior to the winemaking process. While the average phenolic maturity of the grapes may indicate it’s time to harvest, the fact that the grape to grape variability or heterogeneity is so vast indicates that there will likely be some lowering of quality if those grapes are mixed in with those truly ripe grapes.

Perhaps a method to quickly sort lower density grapes away from the higher density grapes would be most effective at reducing the heterogeneity of phenolic maturity of the grapes destined for making wine, be it through mechanical or digital means. My first thought was some sort of equipment or attachment to existing equipment that allows for density sorting in a similar manner that was done in this experiment. Those grapes with higher density would sink to the bottom of the machine, while those with less density would stay afloat, thus allowing someone to either scoop out the less dense grapes or have them funneled separately to a different container.

Overall, I thought this was an interesting study and certainly one that deserves follow up investigations based on its important findings. The entire concept of grape phenolic maturity variation and heterogeneity deserves more research, as well as applicable methods for sorting out these less ripe grapes either prior to harvest or just prior to the winemaking process in order to improve the chances of making a higher quality wine.

What do you all think of this study? Do you already employ methods for sorting out these less ripe grapes prior to winemaking? Please feel free to share your thoughts and/or experiences!

Source: Kontudakis, N., Esteruelas, M., Fort, F., Canals, J., De Freitas, V., and Zamora, F. 2011. Influence of the heterogeneity of grape phenolic maturity on wine composition and quality. Food Chemistry 124: 767-774.

Posted in Chemistry, Enology, Viticulture

Tagged , , , , , , ,

Wine Science Forum: Lessons in Oxygen Management from Industry Leaders

Posted on March 14, 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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Earlier this week, I had the pleasure of attending the first ever Wine Science Forum hosted by Nomacorc, a world leader in alternative wine bottle closure systems. The goal of this forum was to bridge the gap between what research has found regarding oxygen management in wine and what is currently in practice at wineries all over the globe. Roughly 200 people attended this event, with an estimated 80-90% of those attendees being winemakers.

Photo source: http://www.winescienceforum.com/

Photo source: http://www.winescienceforum.com/

The forum kicked off with an introduction by Malcolm Thompson, Vice President of Marketing & Innovation at Nomacorc, which essentially stressed why oxygen management is important in winemaking and how it is very important to manage oxygen exposure every step of the way. Mr. Thompson showed several figures on how oxygen management is basically “out of control” when considered on a global scale, and that there is an extreme level of variability in the industry in regards to how careful wineries are in protecting their wine against overexposure to oxygen. Specifically, Mr. Thompson focused on the variability in oxygen exposure to wine during the bottling process, when it’s essentially too late to “fix”.

Mr. Thompson also shared some statistics with the audience in regards to how common wine faults are in wines (and not just the cheap stuff!) and how much of that is related to the type of closure that was used. Specifically, since 2007, out of all wines entered into the London International Wine Challenge, 6.5% of the wines had some sort of fault, with about 3% of those succumbing to cork taint and another 3% showing reductive character (often occurs with screw caps). Mr. Thompson stressed how these numbers are simply too high, and that we, as an industry, must do a better job at reducing the frequency of faults in wine, and that proper oxygen management will help get that done.

Some may question whether or not most consumers can even taste these faults, or if it is just wine experts that have the palate to notice these quality reducers. Mr. Thompson provided us with results from a couple of studies examining this very question, the first study with a focus on Australian consumers (presumably more adept at tasting wine) and the second study with a focus on Chinese consumers (presumably more novice at tasting wine). It was clear from the study that both Australian and Chinese consumers could taste faults in the wine, and strongly preferred those wines that did not possess any of these faulty characters. These results helped provide support for Mr. Thompsons’ call to wineries to do better in reducing wine faults, particularly when it comes to oxygen management.

The rest of the Wine Science Forum was broken down into highly technical discussion related to specific subtopics in oxygen management and were led by speakers who have dedicated their careers to studying various aspects of winemaking, all specific tie-ins to oxygen management in wine and how oxygen management (or lack thereof) can affect the chemistry and stability of a wine, as well as its shelf life and overall quality.

In later posts, I will go into specific details regarding each and every one of these talks, but for now, I will simply introduce the speaker and the discussion topic, and promise more detailed follow-ups in the coming days and weeks.

Specific topics included:

Speaker: Dr. Maurizio Ugliano; Enological Research Manager at Nomacorc

Talk: “Oxygen and its influence on wine aroma development in-bottle. Facts and fiction around reduction, oxidation, minerality, and delivering to consumers the best possible wine”

Speaker: Dr. Andrew Waterhouse; Professor of Enology in the Department of Viticulture and Enology at the University of California at Davis

Talk: “The oxidation cascade in wine: How far are we from understanding and predicting SO2 loss and wine oxidation based on compositional data?”

Speaker: Dr. James Kennedy; Professor & Chair of the Department of Viticulture and Enology and Director of the Viticulture and Enology Research Center at Fresno State University

Talk: “Red wine color management: The influence of oxygen on pigments development during maturation and post-bottling phases”.

Speaker: Dr. Stéphane Vidal; Global Director of Enology at Nomacorc

Talk: “Wine and oxygen: Fundamental knowledge and the application in wine quality management” (also included a NomasenseTM demonstration)

Overall, I thought this was a very interesting and highly educational event that was successfully delivered to its target audience. Each of the speakers did a great job explaining their specific topics and research, and made convincing arguments for wineries to reevaluate their oxygen management techniques and improve wherever they see they are lacking. At the end of the talks, there was ample opportunity for the audience to ask questions, which was certainly taken advantage of by the many winemakers in attendance.

The event was well received among the audience members, and in my opinion, I think could be successful as a recurring forum. I believe it’s important for wineries to stay informed in regards to current research related to wine, and this kind of event would be a great resource for winemakers to improve upon their craft.

Please stay tuned for future posts, as I will be elaborating on each of the talks listed above in separate posts in the near future.

Did you attend this event? What were your thoughts? What other topics would you like to see covered next time? Please feel free to comment!

Disclaimer: I want to thank Nomacorc for giving me the opportunity to attend this event, and was to stress to all my readers that any opinions expressed in this post are completely my own and not influenced by Nomacorc or any other organization.

Posted in Enology

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