In winemaking, sulfur dioxide (SO2) is frequently utilized to protect wine against microbial attack, browning, and oxidation, to name a few.Â Somewhat recently, there has been pressure to reduce usage of added SO2, stemming partly from consumers and the finding that SO2 exposure could be a health risk for certain individuals.Â Most people who are not sensitive to SO2 can tolerate up to 5 parts per million (ppm), though those that are sensitive to SO2 can experience an array of symptoms at SO2 levels below 5ppm, including but not limited to abdominal pain, bowel problems, dermatitis, and trouble breathing.
Some alternative technologies to address this issue of SO2 sensitivity in some consumers have looked at replacing or
supplementing decreased concentrations of added SO2 in winemaking using hydrostatic pressure, pulsed electric fields, ultrasound irradiation, and/or UV (ultraviolet) irradiation.Â Unfortunately, while many of these technologies show protection of wine against many of the issues wines may face, none of them by themselves are as effective as using added SO2.Â It is possible that using these technologies with a lower dose of SO2 is as effective as a higher dose of SO2 by itself, but for those looking for completely added SO2-free wines, that approach simply wonâ€™t work.
The use of high hydrostatic pressure (HHP) has been used in recent years in food preservation and food processing, with pressures of 400-600MPa proving effective in eliminating spoilage microorganisms and enzymes, while minimizing any negative sensory effects on the food that is undergoing the treatment.Â In wine, some studies found that pressures of 200-500MPa are all that is necessary to inactivate spoilage bacterial in both red and white wines without having any significant negative sensory consequences.
As a result of the public pressure to find an alternative to SO2, and the knowledge that HHP has been successfully used elsewhere in the food preservation business and a couple of studies in wine, the authors of the study today aimed to determine if HHP could be a suitable alternative for SO2 in winemaking.Â In addition to determining the effectiveness of HHP compared with SO2 in winemaking, the authors also examined any potential changes in sensory and/or chemical characteristics of the wine after 12 months of storage time.
Red wine made from Touriga Nacional grapes from DĂŁo Appelation in 2010 and 2011 (producer DĂŁo Sul SA) was used in this study.
After alcoholic fermentation, wine was added to 250mL polyethylene bottles and pressurized for 5 minutes at 20oC at either 425 or 500MPa in a hydrostatic press for those wines undergoing pressure treatments.
The different treatments were as follows:
- Wine pressurized at 425MPa.
- Wines pressurized at 500MPa.
- Wines with 40ppm SO2 added.
- Untreated wines (no pressure or SO2 added).
All wines were stored in the dark at 80% relative humidity at temperatures between 10 and 15oC.
Wines were analyzed in triplicate.
The following were measured and analyzed for all wine samples: color, total phenolic content, total proanthocyanidins, and anthocyanin content.
Solid material found on the walls of the wine bottles after their time in storage was analyzed for total phenolic contents, proanthocyanidins, and anthocyanin content.
Blind sensory analyses were performed on all wine samples and were presented to panelists in random order.Â The sensory panel was made up of 5 men and 2 women, all of which were indicated as being â€śexpert panelists of the wine producerâ€ť.Â Panelists were told that the wines had undergone different treatments, but were not told the details of those treatments.Â Panelists were asked to score each wine in three different categories: color, aroma, and taste attributes, as well as an overall score from 0 to 20.
- All pressurized wines after 12 months of storage showed higher values of b*, a*, and L*, which led to a more orange-red hue in the wine.
- After 9 and 12 months, pressurized wines had color changes that were visibly different than untreated control wines (based on Î”E* values).Â Color differences were noticeable to the human eye.
- Î”E* values greater than 3 indicate a visual difference in color: 9 months after storage, the Î”E* value for the 425MPa wine was 4 and the Î”E* value for the 500MPa wine was 6 compared with the untreated control.
- 12 months after storage, the Î”E* value for the 425MPa wine for the 425MPa wine was 10, and the Î”E* value for the 500MPa wine was 8 compared with the untreated control.
- At the beginning of storage, there were no differences between wines in regards to their total phenolic and antioxidant activities.
- After 9 months of storage, total phenolic content decreased in pressurized wines by 9%.
- After 12 months of storage, untreated wines had antioxidant activity levels 21% lower than wines treated with SO2, 425MPa wines had levels 27% lower, and 500MPa wines had levels 15% lower than wines treated with SO2.
- Wines treated with SO2 had 15% higher antioxidant activities than they did at the start of the storage time.
- From 9 to 12 months of storage, individual and total anthocyanins decreased in pressurized wines.
- Â After 9 months of storage, pressurized wines had significantly lower monomeric anthocyanin (MA) levels than untreated wines.
- The 425MPa wines showed MA levels 56% lower than untreated wines, and 61% lower than wines treated with SO2.
- The 500MPa wines showed MA levels 45% lower than untreated wines, and 51% lower than wines treated with SO2.
- Final anthocyanin content was significantly affected by pressure treatments.
- According to Principle Components Analysis (PCA), at the beginning of the storage period, adding SO2 was the primary factor to differentiate the wines: high pressure had a lower impact on chemical characteristics of the wines.
- According to PCA, high pressure treatment wines were able to be differentiated from untreated controls by color alone after several months of storage.
- Results were very similar between the 2010 and 2011 vintages.
- High pressure treatments resulted primarily in an increase in an orange-red hue, a decrease in antioxidant activity, and a decrease in total phenolic content.
- Pressurized wines had greater numbers of solid particle deposits on the sides of the bottles (as well as lower total phenolic content) compared with untreated controlsĂ 4x higher for 425MPa wines and 13x higher for 500MPa wines.
- The decrease in total phenolic content correlated well with the increase in solid particle deposits on the sides of the wine bottles for pressurized wines.
- Solid particle deposits in SO2-treated wines were very low in total phenolic content as well as a lower rate of phenolic polymerization and precipitation.
- Pressurization treatments resulted in a more orange-red color, lower antioxidant activity, lower total phenolic content, and lower anthocyanin content, which may lead to the increase condensation reactions of polyphenols.
- The 425MPa wines had very similar aromatics to wines treated with SO2.
- The 500MPa wines had aromas of cooked fruit and spices.
- Untreated wines had less fruity and floral aromas and had increased metallic and leather aromas, as well as higher acidity and lower balance.
- Pressurized wines had high levels of brown and limpidity and low values of violet compared with untreated wines.
- After 9 months of storage, general scores for pressurized wines were very similar to SO2-treated wines, and were better than untreated wines.
Overall, the results of this study indicate that pressurization of wines influence both the chemical and sensory characteristics of a red wine, though it takes 6 to 9 months before these differences are detectable.Â Specifically, wines treated with high pressure show a more orange-red color, lower antioxidant activity, lower total phenolic content, and lower anthocyanin content compared with untreated controls.Â According to the authors, these changes are similar to those of wines that have been aged for a long period of time, so perhaps by applying pressure treatments to wines prior to storage; the resulting wines have similar characteristics as an aged wine, without compromising aroma, flavor, or overall sensory quality.
It was not clear from this study how well using high pressure protects against microorganisms or other similar â€śjobsâ€ť that SO2 does, though if it does provide some protection against these problems, it sounds as though using high pressure treatments could be a viable alternative to SO2 in winemaking.Â Future studies will need to examine the efficacy of high pressure treatments on microbial spoilage protection of wine, as well as optimizing the high pressure conditions that will allow for the best protection for the wine against these issues and throughout aging.
Iâ€™m curious to hear what you all think about this study.Â Is there anything the authors missed that you would have liked to have seen?Â What do you think high pressure treatments could be used for in winemaking that was not mentioned in this article?Â What other tests would you have liked to have seen done to be more convincing for you if you werenâ€™t totally on board?Â Please feel free to leave your comments!
Source: Santos, M.C., Nunes, C., Cappelle, J., GonĂ§alves, F.J., Rodrigues, A., Saraiva, J.A., and Coimbra, M.A. 2013. Effect of high pressure treatments on the physiochemical properties of a sulfur dioxide-free red wine. Food Chemistry 141: 2558-2566.