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

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

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

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.