Tag Archives: oak chips

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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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

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Applying Oak Extract to Petit Verdot Vines: Making Oaked Wines Without Oak Barrels?

Posted on February 4, 2013 by Becca| Leave a comment

 

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About a year and a half ago, I reviewed an article that examined the effect of the application of an oak extract to Verdejo grapes on the potential oak flavor of the finished wine, in lieu of oak barrel fermentation or ageing, or the use of oak chips in stainless steel tanks (to read that full article, click here).  The main take-away from that article was that oak extract application on Verdejo grapes does, in fact, produce a finished wine that mimics the flavors and aromas of a wine that has been aged in oak barrels.

I had one reader comment: “who would want oak on Verdejo anyway?”; which is certainly a valid question!  Who knows! Maybe Verdejo was what the authors had at their disposal at the time.  Anyway, those same authors about a year later published a very similar experiment, however this time, focusing on a grape that is almost exclusively oaked: Petit Verdot.

By Eric 先魁 Hwang [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

By Eric 先魁 Hwang [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Studies (and experience) have shown that grapes exposed to smoke from wild fires result in wines with a burnt or smoky flavoring.  Taking this concept further, we’ve seen in the Verdejo study mentioned previously and other studies that certain compounds sprayed onto the grapes during the growing season (such as oak extract) result in wines with similar aromatic characteristics.  In addition to the grapes themselves, alcoholic fermentation, malolactic fermentation, and the aging process all have influence on the aromatic profile of the finished wine.

In regards to the aging process, oak aging in particular has a significant influence on the aromatic development of the wine (compared to the stainless steel alternative).  Sometimes aging in oak barrels can be problematic for some vineyards, due to the relatively high cost of a single barrel and the long periods of aging time required to produce a wine with certain aromatic characteristics.  Smaller wineries may not have enough money and/or time to be able to age their wines in oak barrels for these very reasons.

One alternative approach is to use oak chips in stainless steel tanks, though this practice is still thought of as poor-quality and less desirable (though in reality, most people can’t tell the difference).  Another alternative, which is the focus for today’s paper, is to instead apply oak extracts directly to the grapevine, which could result in wines retaining the characteristics of these extracts, thus eliminating the need to age the wines in relatively expensive oak barrels.  This

Photo by Bernt Rostad: http://farm4.staticflickr.com/3457/3246033875_f9556cf61b.jpg

Photo by Bernt Rostad: http://farm4.staticflickr.com/3457/3246033875_f9556cf61b.jpg

alternative is still relatively novel, and is still in a more experimental phase than a widely practiced phase.

Methods

The oak extract used was food quality French toasted aqueous oak extract from Protea France S.A.S.

The grapevines used were the Petit Verdot variety grown in La Mancha region of Spain (southeast Spain).

There were 4 different treatments used in this experiment: 1) a 25% dilution of the oak extract applied once on the 7th day after veraison (when the grapes start changing color); 2) a 25% dilution applied 4 times; on the 4th, 7th, 10th, and 13th days after veraison; 3) an undiluted (100% concentrated) oak extract solution applied once on the 7th day after veraison; and 4) an aqueous solution of eugenol and guaiacol standards applied once on the 7th day after veraison.  An untreated control was also used for this experiment.

Treatments were applied to 10 plants in the same row, with 5 plants left untreated between treatments in order to avoid contamination.  250mL of each treatment was sprayed on the leaves of each plant at around 7am and when the temperature was below 20oC.

After grapes were harvested at maturation, grape yield was calculated.  Winemaking took place in a multitube fermenter, which has been shown to reproduce actual cellar and winemaking conditions.  Wines underwent both alcoholic and malolactic fermentation, and were done in duplicate.  After malolactic fermentation was complete, wines were stored bottles at 14oC for 8 months.  Samples were taken at each fermentation step, as well as after the 8 months of storage time.

The following enological parameters were measured for each sample: yeast assimilable nitrogen (YAN), oBaumé, reducing sugars, alcohol degree, titratable acidity, volatile acidity, pH, malic acid, and lactic acid.  All parameters were measured in triplicate.  Volatile compounds were also measured and analyzed.

Results

Grapes

  • YAN, oBaumé, probable alcohol, pH, titratable acidity, and the ratio of oBaumé to titratable acidity of grapes from the oak extract treatments were not significantly different than the control grapes.
    • YAN levels were higher and oBaumé, pH, and probably alcohol levels were lower in grapes treated with eugenol and guaiacol compared with the controls.
  • No oak lactones or 6-methoxyeugenol were found in any of the grape samples.
  • Furfural levels were higher in oak extract treated grapes, with the 25% dilution extract treated four times throughout veraison having higher levels than the 25% dilution extra treated only once during veraison.
  • The lowest levels of acetovanillone, methyl vanillate, and guaiacol were found in the undiluted (100%) oak extract treatment.
  • The 25% dilution extract treated four times throughout veraison and the undiluted (100%) oak extract had lower levels of 4-vinylguaiacol and 4-ethylphenol compared with the control.
  • Syringol was lower in oak extract treated grapes.
  • The eugenol and guaiacol treatment grapes showed higher levels of eugenol and guaiacol (surprise surprise), as well as furfural, 4-vinylguaiacol, 4-ethylguaiacol, and syringol.
  • Discriminate analysis could not distinguish between the oak extract treated grapes and the control grapes, but could distinguish a difference in regards to the eugenol and guaiacol treated grapes.

Wine

  • Eugenol and guaiacol treatment resulted in the wine with the lowest alcohol level.
  • After alcoholic fermentation, titratable acidity was higher in all treatments compared to the control, however, after 8 months, titratable acidity was the same for all wines.
  • After 8 months, eugenol and guaiacol treatment wines had a lower pH than the control.
  • After alcoholic fermentation, volatile acidity was highest for control wines and lowest for eugenol and guaiacol treatment wines.
  • Malolactic fermentation progressed equally in all wines.
  • There were no oak lactones found in the control wines.
  • Oak lactones were found to be present in all oak extract treatment wines.
  • After alcoholic fermentation, the wine with the highest levels of oak lactones was the 25% dilution that was applied 4 times throughout veraison.
    • After 8 months, these levels decreased in these wines as well as the wines from the 25% dilution that was only applied once.  These levels increased for undiluted (100%) oak extract treatment wines.
  • Concentrations of oak lactones never reached sensory perception thresholds in any of the wines.
  • Furfural and 5-methylfurfural levels were higher in oak extract treatment wines compared with the control wines.
    • Over time, these levels decreased in all wines.
    • Levels of both these compounds were below their sensory thresholds in all wines.
  • After alcoholic fermentation, eugenol levels were higher in oak extract treatment wines compared with the control wines.
    • After 8 months, eugenol levels were actually higher in control wines than oak extract treatment wines.
  • 6-methoxyeugenol levels were higher in oak extract treatment wines than control wines, with the highest levels in the undiluted (100%) oak extract treatment wine. 
    • These levels increased during malolactic fermentation in all wines.
  • After alcoholic fermentation, guaiacol levels were higher in all treatment wines compared with the control wines.
    • These levels increased in the treatment wines after malolactic fermentation.
    • After 8 months of storage, guaiacol levels were 3x higher in treatment wines compared with the control wines.
    • Guaiacol levels were higher than their sensory threshold levels in all wines.
  • 4-ethylguaiacol levels were higher in oak extract treatment wines compared with the control wines.
    • Levels were found to be below sensory threshold in all wines.
  • Syringol levels were higher in oak extract treatment wines than in control wines (recall: this trend was the opposite in regards to the levels in the grapes).
    • Levels were found to be below sensory threshold in all wines.
  • Vanillin, vanillin derivatives, acetovanillone, and methyl vanillate were all higher in oak extract treatment wines compared with the control wines.

Conclusions

According to the results of this study, applying oak extract on Petit Verdot grapes during veraison resulted in changes in the aromatic profile of the finished wines.  Finished wines appeared to have many of the volatile compounds frequently found in wines that are fermented in aged in oak barrels.  It’s interesting to note that nearly all of the oak volatile compounds were not actually present in the grapes themselves, but were present after the fermentation and storage processes.  What is happening here is likely that the oak volatiles are present in grapes as non-volatile precursors, which undergo changes during the fermentation and storage processes that result in the formation of their volatile counterparts in the wine.

Photo by inspector_81: http://farm6.staticflickr.com/5165/5218552773_478a515be5.jpg

Photo by inspector_81: http://farm6.staticflickr.com/5165/5218552773_478a515be5.jpg

In addition to the oak extract treatments, I would have liked to have seen two more treatments:  1) fermentation in oak barrels and 2) fermentation using oak chips.  It would have been interesting to compare the oak volatile compounds from the oak extract treatment wines directly to those from oak barrel fermented or oak chip fermented wines.  How do the levels of the oak volatile compounds in these oak extract treatment wines directly compare with wines fermented in oak barrels or using oak chips?  Sure, the levels are increased with respect to the controls, but is it enough to produce a wine that would taste the same (or similar) to a wine produced in more traditional ways?

The above being said, it would have been interesting to see a sensory analysis of these wines, in addition to the chemical analysis that they performed.  How did the wines actually taste?  How do they actually taste compared to wines made in a more traditional manner?

The results of this study provide some evidence that the use of oak extracts on grapevines during the veraison process yields aromatic profiles similar to that of wines fermented in oak barrels, and thereby could be a good alternative to the more expensive and time consuming oak barrel fermentation methods.  However, before I can say that previous statement with complete certainty, I’d like to see a few more treatment comparisons.

How about you all?  What do you think of this study?  Please feel free to comment!

Source:  Martínez-Gil, A.M., Garde-Cerdán, T., Zalacain, A., Pardo-García, A., and Rosario Salinas, M. 2012. Applications of an oak extract on Petit Verdot grapevines. Influence on grape and wine volatile compounds. Food Chemistry 132: 1836-1845.

Posted in Chemistry

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The Influence of Oak Chips on Aromatic Quality of Wine

Posted on October 31, 2012 by Becca| 8 Comments

The use of oak in wine fermentation and aging is a very common practice that has an overall positive influence on the flavor and aroma of wine, as well as its complexity and overall quality.  Specifically, oak transfers many volatile and phenolic compounds into the wine, which individually and as a whole contributes to its complexity.  Aging in oak barrels also adds an additional level of complexity as due to the porous nature of the vessel; oxygen is able to slowly infiltrate the wine resulting in a reduction in astringency, stabilization of color, and reduction in certain aromatic characteristics.

Though fermentation and aging in oak barrels is desirable for many wineries, sometimes it is just not feasible due to many factors including financial

Photo by Bernt Rostad: http://farm4.staticflickr.com/3457/3246033875_f9556cf61b.jpg

constraints (oak barrels can be very expensive compared to stainless steel tanks), space limitations, or the need to purchase new barrels on a relatively frequent basis compared to stainless steel tanks in order to achieve the desired effect on the finished wine.  These issues present the need to utilize less expensive alternatives; specifically, oak chips.  Oak chips may be added to wine fermenting in stainless steel tanks, and have been found to impart similar characteristics into the finished wine as an oak barrel.

There are many factors that influence which volatile compounds are extracted from oak into wine, and how much of each compound is extracted, including (but not limited to) the length of time the wine is in contact with the oak, the geographic origin of the wood, the wood seasoning, and the toasting of the wood.  The type of wine (i.e., varietal or blend) can also have a major influence on the volatile extraction of the oak wood.  Volatiles most commonly extracted from oak wood that have a significant impact on wine aroma, flavor, and quality are: lactones, volatile phenols, and phenolic aldehydes.

In regards to the specific volatiles from oak that influence wine aroma and flavor, the following are most commonly found:

  • Furfurals (dried fruits)
  • Guaiacol (burnt tones)
  • Whisky lactone (woody and coconut)
  • Eugenol (cloves, smoke, spice)
  • 4-ethylphenol (barnyard, bandaid, mousy – Brettanomyces)
  • 4-ethylguaiacol (cloves, smoke, spice, etc)
  • Vanillin (vanilla tones)
  • Syringaldehyde (vanilla)

Photo by inspector_81: http://farm6.staticflickr.com/5165/5218552773_478a515be5.jpg

The goal of the study presented today was to examine the differences (if any) in volatile aromatic compounds of wine after using oak chips from different origins and under different toasting conditions.

 

 

 

Methods

Four wines were used in this experiment:

1) varietal Cabernet Sauvignon

2) varietal Blaufränkisch

3) red blend

4) white blend

Oak chips used in this experiment were:

1)      American oak

  • Medium toasting
  • High toasting

2)      German oak

  • No toasting
  • Medium toasting
  • Premium toasting

3)      French oak

  • Medium toasting
  • Medium-plus toasting
  • High toasting

Nine 1-liter glass bottles of each wine closed with crown cork were the vessels used in this experiment.  One of the bottles served as the no oak control, while the other 8 contained 1g/dm3 of each type of oak chip.  Oak chips were kept in the bottles for 30 days in the dark at 4oC. Bottles were shaken (not stirred….ha ha) twice a week to aid in the oak volatile extraction.

Volatile compounds were measured and analyzed using GC-MS techniques.

Results

Furfurals

  • Furfural concentrations varied the greatest out of all of the volatiles found in oak chip treated wines.
    • Furfural and 5-methylfurfural concentrations increased in all oak chip-treated wines.
    • The highest increase of furfural was detected in red wine samples treated with French oak chips with high levels of toasting.
    • The highest increase of 5-methylfurfural was found in wines treated with American oak chips under medium toasting, and French oak chips under high toasting.
    • The smallest increase and/or decrease in furfurals was found in wine samples treated with untoasted German oak chips.

Lactones

  • Trans-whiskeylactone increased in all wine samples treated with oak chips.
    • Cis-whiskeylactone levels were too small for statistical analysis.
    • The highest increase of trans-whiskeylactone was found in wines treated with medium toasted American oak chips.
    • The lowest increases of whiskeylactones were found in wine samples treated with high or premium toasted oak chips.

Eugenol

  • Levels of eugenol increased in all wines treated with oak chips with the exception of Cabernet Sauvignon.
    • Cabernet Sauvignon wines treated with untoasted and premium toasted German oak chips saw decreases in eugenol levels.
    • Eugenol increased in wines made from American oak chips with medium toast.
  • Trans-isoeugenol levels were highest in blended wine samples with French and American oak chips with medium and high toast.

Guaiacol

  • Levels of guaiacol were mostly affected by toasting level.
    • Highest levels of guaiacol were found in wine samples treated with high toasted oak chips, regardless of the origin of the wood.
    • Untoasted oak chips had no effect on guaiacol and 4-ethylguaiacol in wine samples.

Ethylphenol

  • Oak chips had no impact on 4-ethylphenol levels in wine samples.

What does this all mean?

According to the results of this study, which contradict the results of some other studies, the authors were not able to determine the origin of the oak chips used in a wine sample based on the volatile composition.  The largest influencer of volatile composition in the wine samples appeared to be the toasting levels.  Furfural, guaiacol, and whiskeylactones were influenced by the degree of toasting, while furfural and guaiacol increased with toasting intensity.

Though geographic origin of the oak chips did not have a significant influence on volatile composition of sample wines, the authors claimed that the highest

Photo by Franco Folini: http://farm1.staticflickr.com/113/294928909_01ab1f5696.jpg

increase in desirable volatile compounds in wine were found in wines made from French oak chips with high levels of toasting.  I’m a little perplexed by this statement, as when something is not significantly different, one cannot say with confidence that one treatment was superior to another.  It’s possible that the levels of these volatiles in wines treated with high toasted French oak chips trended toward having more desirable levels of volatiles than all other treatments, but other than this general statement in the conclusions, it was not immediately clear to me how this was true based on the reported results.

I’m also not entirely convinced that the results of this study are representative of a real world scenario.  First of all, the oak chips were placed directly into the bottle and left for 30 days.  Never would this method ever take place in the real world, with the addition of oak chips occurring at some point during the aging process while still in stainless steel tanks.  I suppose the shaking of the bottles was supposed to imitate the micro-oxygenation process in the tanks, but without evidence that this is an appropriate method substitution, I’m not convinced the wine is being exposed to the same amount of oxygen that it would be while aging in the tank.

I believe the conditions of the wine samples in this experiment are markedly different than samples that are kept in stainless steel tanks with micro-oxygenation.  This sort of variation would likely have a significant effect on the volatile composition of the finished wine, thus making the results of this study not repeatable in real world situations, and certainly not comparable to the volatile composition of wines made in steel tanks with micro-oxygenation.   I believe this is part of the reason why the authors were not able to detect differences in geographical origins of oak chips based on the volatile composition of the wine when other studies using more realistic methods could.

I don’t mean to sound all negative.  Clearly this study showed that oak chips and toasting do have influence on the volatile composition of wine, though again, I am not convinced the exact levels and trends are completely accurate based on the methods employed.  I think the study is a good start, but it needs to be repeated under more realistic aging conditions.

What do you all think of this study?  Do you agree or disagree with my thoughts on the study methods?  Do you see any other issues with the study that you’d like to discuss?  Maybe you loved the study—feel free to share that, too!  Please leave your comments and join in the discussion!

Source: Návojská, J., Brandes, W., Nauer, S., Eder, R., and Frančková, H. 2012. Influence of different oak chips on aroma compounds in wine. Journal of Microbiology, Biotechnology and Food Sciences 1(4): 957-971.

Posted in Chemistry

Tagged , , , , ,

Using Fungi-Treated Oak Chips to Increase the Extraction of Oak Character into Aging Wines

Posted on December 20, 2011 by Becca| 3 Comments

As a result of the relatively high cost of oak barrels, winemakers have been searching for a comparable alternative at a fraction of the cost.  Oak chips, while somewhat taboo in their earlier days, are gaining favor among winemakers as being a good alternative to the traditional oak barrel.  In blind taste tests, consumers showed no preference for wine aged in oak barrels versus wine aged with oak chips.  For the details of that particular study, click here to read a past review by The Academic Wino.

http://www.dehs.umn.edu/images/purpurogenum_cya6.jpg

Producing staves for barrel or oak chips is not a fast process.  One of the lengthiest steps is the outdoor seasoning process, which takes anywhere from 24 to 36 months.  It is during this time that the wood undergoes many biochemical transformations of biopolymers and other compounds by fungi and bacteria.  Studies have found the fungi population present during this seasoning process consists of Aureobasidium pullulans (83%), Trichoderma harzianum, and Trichoderma konigii (the latter two making up 15% of the population).  These fungi function to hydrolyze wood heterosides (including ellagitannins, coumarins, and polysaccharides) which result in a decrease in bitterness and astringency.

Over the 24-36 month seasoning time, the fungal community changes.  Over this time, fungi belonging to the genera Penicillum, Geomyces, and Geotrichum, with the species Penicillum purpurogenum the most represented.  In the internal layers of the staves, studies have found that the species Candida sp., Paecilomyces variotii, and Phialemonium sp. were the most represented molds.

Some scientists have hypothesized that by inoculating oak staves with certain fungi, they may be able to better control the metabolic reactions and therefore which wood compounds are hydrolyzed.  This could potentially lead to new seasoning places and greater customization of the desired flavors in the wine that is aged in a particular barrel or with particular oak chips.  Some studies have reported that by inoculating oak staves with fungi have increased the seasoning rate, thereby dropping the wait time for a finished staves or oak chips from 12-36 months to just one month.

The goal of the paper reviewed today, which was published last year, was to treat oak chips with certain combinations of fungi in order to potentially improve the impact of oak chips in red wine maceration, and to obtain effects comparable to wine aged in oak barrels.

Methods

The following fungi were used in this experiment:  Ph. chrysosporium Burds. (MUT 2660), P. purpurogenum Stoll (MUT 3316), A. pullulans (de Bary) G. Arnaud (MUT 3237), and Phi. obovatum W. Gams & McGinnis (MUT 2702).  The fungi used were all non-mycotoxinogenic.  After an incubation period, an agar plug (8mm in diameter from along the edge of an actively growing colony) of each fungus was used to prepare and inoculate the oak chips.  Each preparation used a different combination of fungi and growth medium.

Oak chips were toasted at a low degree and were of medium size.  A 3mL aliquot of fungi and growth medium preparations was added to a flask containing 4g of oak chips and either 12mL of laboratory medium or 12mL of saline solution.  Oak chips were sterilized either with the laboratory medium or the saline solution.

These cultures were incubated for 12 weeks in the dark under static conditions at temperatures optimized for each type of fungus.  In addition to each fungus by itself, a combination of A. pullulans and Ph. chrysosporium was studied.  For this combination, oak chips were first inoculated with A. pullulans for 6 weeks, then sterilized, then inoculated with Ph. chrysosporium for another 6 weeks.

Following the incubation period, oak chips were removed and brushed off to remove visible pieces of debris.  The chips were then used for aging of red wine using traditional winemaking processes.  The two grape varieties used were Montepulciano d’Abruzzo (70%) and Merlot (30%) from the 2006 vintage and originating from vineyards in San Severo, Apuila (southern Italy).  Artificial aging was done by placing 1g of oak chips in 500mL bottles containing the wine and storing them in a 20oC room (82% relatively humidity) for 17 days.

The following volatiles were measured and analyzed: furfural, furfuryl alcohol, guaiacol, syringol, cis-β-methyl-γ-octalactone, 2-phenylethanol, 4-vinylguaiacol, benzyl alcohol, 2,3-butanediol, γ-butyrolactone, benzylaldehyde, and 4-ethylguaiacol.  Gallic acid and ellagic acid were also analyzed.

Sensory Notes: 

  •        Furfural, furfuryl alcohol, guaiacol, syringol, cis-β-methyl-γ-octalactone are frequently present in wine after oak aging. 
  •       2-phenylethanol and 4-vinylguaiacol are known fermentation products, and have been shown to increase after oak aging.  
  •       4-ethylguaiacol is associated with Brettanomyces or Dekkera infections, and is associated with characteristic flavors such as “bacon” or “smoked”.  
  •       Cis-β-methyl-γ-octalactone is associated with oaky characteristics such as coconut and vanilla.
  •       Furfural contributes to characters such as “dried fruits” and “burned almonds”.  Studies have shown it does not play an important role in the aroma of wine, though it may strengthen the aroma of lactones.
  •       Guaiacol contributes to “burnt” overtones in wine aroma.
  •       Syringol is an indicator of the relative toast of the oak wood.  Compared to guaiacol, it has a weak odor and relatively little impact on the flavor of the wine.
  •       Benyzlaldehyde is associated with a “bitter almond” aroma.
  •       2,3-butanediol is odorless, though still contributes to the sweet taste of a wine.

Results

  •       Cis-β-methyl-γ-octalactone was present in all wine samples.
  •       The presence and concentrations of specific volatile compounds and phenols were influenced by the type of fungus and medium used for the particular oak chip treatment.

Furfural

  •       Concentrations of furfural were significantly affected by Ph. chrysosporium and P. purpurogenum by increasing in both laboratory medium and saline solution treatment.  Perception threshold was not reached.
  •       There were no significant changes with any other treatment.
  •       Furfural appears to be the most susceptible oak wood volatile compound to microbial transformations.

Guaiacol

  •       Fungal treatment of the oak chips resulted in a significant increase in the concentration of guaiacol.

o   For the saline solution, this increase was found in the treatments inoculated with P. purpurogenum, A. pullulans, and Phi. obovatum.

o   For the laboratory medium, this increase was found in the treatments inoculated with P. purpurogenum and A. pullulans.

o   For treatments with A. pullulans, guaiacol was above the perception threshold.

Syringol

  •       For the saline solution, there was an increase of syringol concentrations with the treatments inoculated with P. purpurogenum.
  •       For the laboratory medium, higher levels (above perception threshold) of syringol were found in the treatments inoculated with P. purpurogenum and A. pullulans.

Benzylaldehyde

  •       For the saline solution, fungal treatment decreased the concentrations of benzylaldehyde (except the treatment with Ph. chrysosporium).
  •        For the laboratory medium, there was a significant increase in benzylaldehyde concentrations.

2,3-Butanediol

  •       For both the saline solution and laboratory medium, there was a decrease in 2,3-butanediol levels in all fungal treatments except samples treated with A. pullulans.

Ellagic and Gallic Acids

  •       Ellagic acid and gallic acid were metabolized by the fungi, with the exception of wines treated with P. purpurogenum in the laboratory medium.

What do these results means?

The results of this study show that the fungal treatment of the oak chips significantly affected the chemical profile of the wine.  Based on principle components statistical analysis, the results showed two distinct groups that affected wines in specific ways.  Oak chips treated with Phi. obovatum, A. pullulans, and the combination of A. pullulans and Ph. chrysosporium (“Group A”) affected the chemical profile of wines in one particular way, and oak chips treated with P. purpurogenum and Ph. chrysosporium affected the chemical profile of wines in another way (“Group B”).

Group A treated wines showed increases in guaiacol and syringol concentrations, whereas Group B treated wines showed increases in furfural and benzylaldehyde concentrations.

Even though the effect of the fungi were variable depending upon what kind of medium was used for the chips (laboratory medium versus saline solution), Group B treated wines showed increases in furfural and benzylaldehyde regardless of the medium the chips were treated with.

Based on these results, the authors claim that the microfungal treatment of oak chips increases the concentrations of some volatile components in red wine during aging.  It may be possible, that with fungal treatment of oak chips for the aging of red wines, to tailor the flavors and aromas to those desired for a particular style of finished wine.  If the goal is to have a wine with greater “toasty” character, the use of fungi from Group A may be useful.  If the goal is to have a wine with more “dried fruit” or “almond” character, then a fungi of Group B may be better.

Of course, this research is in its infancy, and more work would need to be done, particularly in regard to examining the biology and enzymatic profile of the fungi, and any potential positive or negative health consequences of using it in the aging of wines.

I’d love to hear what you all think of the use of fungi in extracting more oak character from oak chips in the aging of wine.  Please feel free to leave your comments below!

Source:  Petruzzi, L., Bevilacqua, A., Ciccarone, C., Gambacorta, G., Irlante, G., Pati, S., and Sinigaglia, M. 2010. Use of microfungi in the treatment of oak chips: possible effects on wine. Journal of the Science of Food and Agriculture 90: 2617-2626.

DOI: 10.1002/jsfa.4130
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

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