The Effect of High Hydrostatic Pressure Processing on Chemical Composition of Oak Chip-Macerated Wine

The use of oak barrels in wine fermentation and aging increases wine aromatic complexity and improves overall quality. This technique is often used in wines, 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 has been a lot of research on this topic, with many resulting products already available for purchase on the market, including oak chips, oak shavings, and oak extract.

The research on alternatives to oak barrels is certainly not dead yet, with newer technologies and combinations of older technologies studied every day.

One such newer technology that has up until now mostly been tested in the food industry for its use in food safety and preservation is High Hydrostatic Pressure (HHP) Processing. In essence, HHP works in food and wine preservation by improving the solid-to-liquid extraction process. In wine, HHP has been found to protect against harmful microorganisms with the possibility of the technology to be used as an alternative to SO₂ addition for preservation purposes, though more work is needed to confirm these findings.

Since HHP has been shown to improve solid-to-liquid extraction in both food and wine, a new study published in the journal Food Chemistry hypothesized that this same technology might be beneficial in extracting oak flavor and characteristics from oak chips into wine. Using HHP might help to improve the extraction of oak flavors and aromas into an aging wine using cheaper oak chips instead of oak barrels, and may cut down even further on the amount of time needed for this processing, thus allowing the wine to hit the store shelves earlier and potential profits seen quicker.

Brief Methods

Lightly toasted French oak chips were used in this study.

“Young red wine” made in Massa, Italy, (2012) from Merlot and Sangiovese grapes was used. After fermentation was complete, wine was transferred to stainless steel tanks with some SO₂ added to bring the final SO₂ concentration up to 50mg/L. Wine remained in the tanks for 6 months prior to bottling for this study.

For the High Hydrostatic Pressure (HHP) treatment, wine and oak chips were placed in a 50mL Teflon tube and subjected to various pressure and time treatments (all performed at 18^oC).

• The pressure treatments were: 250, 450, and 650 MPa.
• The time treatments were: 5, 15, 30, and 45 minutes.
• Each treatment was performed 3 times.

This experiment was considered full factorial, with a total of 36 experimental runs per wine and oak chip sample (3 pressure treatments x 4 times treatments x 3 replicates = 36).

It was noted that the temperature of the system increased slightly to 19.5^oC after starting the HHP treatment, though as the treatment progressed the temperature eventually decreased back down to the starting temperature of 18^oC.

An untreated wine was used as a control, as well as a wine treated with oak chips alone (no pressure treatment) for 45 minutes at 18^oC.

All wines were filtered after processing.

The following chemical analyses were performed on all samples: wine color (intensity), total phenolic content, total anthocyanin content, tartaric esters, flavonols, and antioxidant activity.

A sensory analysis was performed by 6 experienced judges following ISO standard protocol. Judges evaluated wine appearance, aroma, and taste. The judges only analyzed the following 3 wines: control (untreated) wines, HHP 30 minute samples, and the oak chips (no pressure) only samples. All wines were analyzed in duplicate.

Brief Results

• Oak chip maceration resulted in an increase in total phenolics, tartaric esters, and flanonols.
• HHP processing resulted in a faster “transfer” of oak characteristics into the wine samples.
• Tartaric esters and flavonol content were significantly higher in HHP wines treated for 45 minutes compared with untreated wines.
• The amount of phenols extracted from the oak chips was highest 15 minutes after the start of the 650MPa treatment.
• Total phenolics increased throughout the 45 minutes for the 250 and 450MPa treatments, while the levels were found to be significantly lower after the 650MPa treatment.
• Total anthocyanin levels were found to decrease in the first 5 minutes of treatment, but then increased throughout the remainder of the treatment for all pressures tested.
• After 45 minutes, anthocyanin levels were significantly higher in all pressure treatments compared with the untreated controls.
• HHP treatment significantly increased antioxidant activity of all samples.
• Antioxidant activity for the control (untreated) wine and the wine treated only with oak chips (no pressure) were statistically the same.
• Wine color was found to decrease in the first 5 minutes of treatment, but then increased throughout the remainder of the treatment for all pressures tested (corresponding nicely to the anthocyanin results).
• After 45 minutes, color intensity was higher in 250 and 450MPa treated wines compared with the control.
• After 45 minutes, color intensity was lower in 650MPa treated wines compared with the control.
• Statistical analysis revealed that pressure time was the most significant influence on the chemical composition of the wine samples, with pressure level was not as important.
• Although chemical analysis suggested there are color differences between the wines, the sensory panel could not tell any differences in the color of the samples.
• In general, the sensory panel could not tell many significant differences between the pressure treatment wines and control wines, other than the fact that there were obvious oak characteristics in all treatment wines and none in the untreated control wines.

Conclusions

According to the researchers, the results suggest that High Hydrostatic Pressure (HHP) treatment of wines causes some sort of structural damage, which effectively changes the concentration gradient of various compounds in the wine and increases extraction of

oak-derived compounds into the treated wines. In other words, High Hydrostatic Pressure (HHP) treatment breaks down the larger compounds in the oak chips into smaller chains that are responsible for various flavors and aromas, which interact with the various compounds in the wine (which have also been changed by the pressure treatment) and result in a more “oaky” wine.

In terms of pressure treatments, results showed that while total phenolics increased throughout the 45 minutes for the 250 and 450MPa treatments, the levels were found to be significantly lower after the 650MPa treatment. Similar results were seen in regards to color intensity. According to the researchers, this may be a result of the higher pressure damaging the structural integrity of the oak and wine compounds too much, thus degrading the overall total phenolic content of the samples. In other words, throwing too much pressure at the samples effectively beat the crap out of it instead of simply nudging the process along.

In terms of color, total anthocyanin levels were found to decrease in the first 5 minutes of treatment, but then increased throughout the remainder of the treatment for all pressures tested. The researchers suggested that perhaps this initial decrease resulted from the adsorption of anthocyanins by the oak chips, with the levels later increasing in solution after no more could be extracted and taken in by the chips. Interestingly, the sensory analysis did not confirm this finding, with the judges not being able to tell any differences in color between any of the wine samples. This suggests that while there are chemical differences between the different treatments, none of them were great enough to be perceivable to the naked eye.

Multivariate analysis of the results showed that pressure time was more important that pressure levels in terms of the chemical composition of the wine samples. The researchers could clearly see a different between the 5 and 15 minute treatments compared with the 30 and 45 minute treatments, with the longer treatments resulting in greater extraction of oak-derived compounds and antioxidant activity than the shorter treatments. The exact level of pressure was not as important, though the results did seem to suggest that 650MPa might be too high of a pressure to perform such a delicate extraction of compounds.

In general, the results seem to suggest that High Hydrostatic Pressure (HHP) treatment of wines with oak chips does influence the chemical composition of the sample, with significantly improved phenolic content and antioxidant activity. This result does not seem to be noticeable at the sensory level, however, could still be considered a justifiable treatment for a winemaker who wants to improve the time from processing to sales or who wants to produce a wine with nutritional value or health benefits than your traditional wines. The High Hydrostatic Pressure (HHP) treatment does not make the wine better in terms of sensory characteristics, but is more a means to arrive at a similar end point at a faster pace.

This is just a preliminary study, however, so certainly more work needs to be done. Namely, the researchers mentioned that the extraction time is sped up using High Hydrostatic Pressure (HHP) treatment; however, don’t go into detail regarding precisely how much time is saved using this method. More detailed time analyses would be interesting and potentially useful to see. It would also be very important to see how this treatment acts on a wine over time while in storage. Does the High Hydrostatic Pressure (HHP) treatment help with long term storage of these wines? Or not? More detailed aging studies are necessary to evaluate this idea.

How about you all? What do you all think of this study? What other questions would you like to see the researchers answer in a theoretical follow-up study? Feel free to share your comments!

Source:

Tao, Y., Sun, D-W., Górecki, A., Blaszcak, W., Lamparski, G., Amarowicz, R., Fornal, J., and Jeliński, T. 2016. A preliminary study about the influence of high hydrostatic pressure processing in parallel with oak chip maceration on the physicochemical and sensory properties of a young red wine. Food Chemistry 194: 545-554. (open access).