Phenolic Composition of Organically Grown Grapes Do Not Change with Different Winemaking Techniques

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It has been well documented that the phenolic composition of wine differs depending upon a variety of factors: including, but not limited to; the type of grape, environmental conditions, disease pressures, soil type, geographical location, and grape maturity status.  Studies have shown that different vinification techniques may also be a source of variation in regards to total phenolic composition of wine. 

For example, some studies have shown that by using extended maceration techniques, the extraction of phenolic compounds is improved.  Other studies have shown that the use of pectolytic enzymes, which function to improve juice yield and clarify the wine, shows mixed results, depending upon which study one looks at.  Some studies have shown that using pectolytic enzymes promote color and improve the quality of the wine, while other studies found that these enzymes result in a decrease in total anthocyanins and wine color.

In the short study reviewed today, published earlier this year in the Journal of Food Science, the authors examined organically grown Monastrell grapes, and whether there were any differences in phenolic composition of the resulting wine after using three different winemaking techniques.

Methods

The grapes used in this study were of the Monastrell variety that were grown under organic conditions in D.O. Jumilla. 

Three different vinification treatments were used in this study: 1)10 day maceration of the pomace (control); 2) 21 day extended maceration; and 3) 10 day maceration with the addition of 3g/100kg of enological enzymes.  All other vinification techniques were identical between treatments.

The first analysis of the wines was at bottling, then later every month for the next 3 months.

Standard physiochemical measurements of the wine were taken at analysis (pH, density, volatile acidity, total acidity, and alcohol degrees).  Total phenolic compounds were broken down into levels of anthocyanins, flavonols, hydroxycinnamic acids, and stilbenes.  All analyses were performed in triplicate.  Antioxidant activity was also measured.

Results

  •       Physiochemical

o   All physiochemical measurements were found to be in the normal range for red wine.

  •       Antioxidant Activity

o   No significant differences in antioxidant activity were found between any of the vinification treatments.

o   During the 3 month storing process, there were no significant changes in antioxidant activity between any of the vinification treatments.

§  These results agreed with some studies, yet disagreed with others.

  •       Phenolics

o   Average levels of phenolic compounds in the enzyme treatment equaled the average levels of phenolic compounds in the control treatment.

§  These results did not agree with some studies.

o   Average levels of phenolic compounds in the extended maceration treatment were similar to the average levels of phenolic compounds in the control treatment.

§  These results were opposite of some studies.

o   After 3 months of storage, there was a significant decrease in phenolic compound levels.  The control wines lost 43%; the enzyme treatment lost 35.1%; and the extended maceration treatment lost 31.9%.

§  These results agreed with some studies.

  •       Anthocyanins

o   Average concentrations of anthocyanins in the enzyme treatment were similar to the average concentrations of anthocyanins in the control treatment and the extended maceration treatment.

§  These results agreed with some studies, yet disagreed with others.

o   There was no correlation between anthocyanin content and antioxidant activity in any treatment.

§  These results agreed with some studies.

o   After 3 months of storage, there was a decrease of 40-50% in regards to anthocyanin concentrations, with no significant differences observed between any of the vinification techniques.

§  These results agreed with some studies.

  •       Hydroxycinnamic Acids

o   There was no difference in the concentration of hydroxycinnamic acids between the enzyme treatment wines and the control wines.

§  These results were opposite of some studies.

o   There was no difference in the concentration of hydroxycinnamic acid derivatives between the extended maceration treatment wines and the control wines.

§  The concentrations of hydroxycinnamic acids and their derivatives in this study were higher than some studies, yet lower than in other studies.

o   There was no correlation between hydroxycinnamic acid derivative content and antioxidant activity.

§  This result agreed with some studies.

o   After 3 months of storage, there were no significant changes in hydroxycinnamic acid concentrations for any of the treatments.

§  This result agreed with some studies.

  •       Stilbenes

o   The average concentration of trans-resveratrol-3-oβ-glucoside was similar in the enzyme treatment and in the control treatment, and the concentration in the extended maceration treatment was lower.

§  These values were higher than those found in some studies, yet lower than those found in other studies.

o   There was no correlation between stilbene concentrations and antioxidant activity in any of the treatments.

§  This result is opposite from some studies.

o   After 3 months of storage, there were no changes in the concentration of trans-piceid.

§  These results agree with some studies.

  •       Flavonols

o   There were no significant differences in flavonol concentrations between any of the treatments.

o   There was no correlation between flavonol content and antioxidant activity.

§  This result is opposite from some studies.

o   After 3 months of storage, there were no significant differences in flavonol concentrations in any of the treatments.

§  This result is in agreement with some studies.

What does this all mean?

The results of this study can easily be summed up in just a couple of sentences.  First, vinification technique had no effect on the antioxidant activity and the phenolic composition of organic wine.  Second, changes in phenolic composition over 3 months of aging were not related to vinification technique.

One thing I wanted to point out, if you haven’t noticed already, is that after nearly all of the results presented, I indicated whether other studies have found the same result.  One may have noticed that the results of this study were extremely variable in regards to how they compared with the results of this study.  Therefore, one must take the results of this study with a grain of salt. 

I have some confidence that the results of this particular study are accurate.  Though, how can it be that their results at times are so different than the results from other studies?  I think what it boils down to what was briefly mentioned in the introduction of this post.  Phenolic composition of wine differs depending upon a variety of factors: including, but not limited to; the type of grape, environmental conditions, disease pressures, soil type, geographical location, and grape maturity status.  If any of these conditions (or other conditions not described) are different between studies in any way, it is likely that the results may be different.  There can be no blanket statement regarding how phenolic composition will change using certain vinification techniques, since almost any difference in production will cause huge variation in results.

Therefore, I conclude to say that vinification technique had no effect on the antioxidant activity and the phenolic composition of organic wine made with Monastrell grapes.  This may not be the case for other grape varieties undergoing different vinification techniques than those studied here, but alas, I suppose that is not the point of this short and sweet study!

I’d love to hear what you all think!  Please feel free to leave any of your comments below!

Source: Mulero, J., Zafrilla, P., Cayuela, J., Martínez-Cachá, A., and Pardo, F. 2011. Antioxidant Activity and Phenolic Compounds in Organic Red Wine Using Different Winemaking Techniques. Journal of Food Science 76(3): C436-C440

DOI: 10.1111/j.1750-3841.2011.02104.x
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!