Is There a Difference?

The Academic Wino

Dissecting Current Research Related to Wine

Phenolic Content of Wines Made From Organic Versus Conventionally Grown Grapes: Is There a Difference?

Organic foods, once only spotted in health food stores, are becoming increasingly popular and are found all over the grocery store aisles. While it is unclear whether or not organic foods are higher in nutritional content than more conventional foods, there is a clear difference between the ways in which organic foods are produced. Overall, organic agriculture results in far less pollution to the environment, compared to conventional methods which include potentially harmful chemical pesticides, herbicides, and insecticides, in addition to growth hormones and other additives and preservatives.

Organic agriculture not only functions without the potentially harmful products mentioned above, but also promotes and enhances biodiversity, biological cycles, and soil biological activity.  In a sentence, organic agriculture aims to “optimize the health and productivity of interdependent communities of soil life, plants, animals, and humans”.  In the growing of grapes, often (in more humid climates, particularly), more conventional agricultural methods are employed, including herbicides, fungicides, etc.  One question is whether or not conventionally grown grapes contain differing chemical compositions than organically grown grapes, which is what the study reviewed today aimed to discover.

Grapes have many phenolic compounds in the skins and seeds, which act as health-beneficial antioxidants, as well as the contribution of color, taste, mouthfeel, oxidation, and other reactions in the finished wine.  These phenolic compounds, including flavonoids, have important antioxidant health benefits, which have been shown to protect against many diseases, including arteriosclerosis and coronary heart disease.  The climate of the region in which grapes are grown has significant impacts on the phenolic composition of the grapes, as well as berry size and yield.  Even within the same variety of grape, climate and other environmental factors, in addition to disease, soil type, geographical location, and maturity level, will all have significant effects on phenolic levels of the grapes. 

Today’s study, which was published in the Journal of Food Composition and Analysis in 2010, aims to investigate the behavior of these phenolic compounds and their antioxidant activities during the ripening and processing of conventional versus organically grown grapes.

Methods

Grapes

Grapes were sampled 30 days before harvest, 14 days before harvest, and the point at which the grapes were technologically mature.  100 berries were randomly selected from every vineyard and processed in the laboratory the same day.  Two vineyard parcels were treated using conventional methods, while two neighboring vineyard parcels were “treated” using organic methods.  The closeness of the vineyards allowed the scientists to control for soil and climate variations.

The organic grape vines were treated with natural pesticides, including dry flowable sulfur, copper salts, and oligoelements. Conventional grape vines were treated with chemical fertilizers and pesticides, in order to control for weeds, pests, and various diseases.

Winemaking

After the grape clusters were squeezed through a squeeze roller, the stalks were removed and the squeezed grapes and juice were transferred into fermentation tanks.  80mg/kg and 70mg/kg of SO₂ was added to the conventional and organic viticulture methods, respectively.  The must-wine was kept in vats at 25^oC for 10 days while undergoing fermentation and maceration.  Daily mass homogenizations were performed.  After maceration, the must-wine was pressed, and wine was recovered 10 days later. The wine was subsequently bottled.  (Note:  this is as much detail as the study gave, so more specific questions you may have regarding the methods, I may not be able to answer).

Chemical Analysis

For the grape samples; Baumé degree, pH, and total acidity were measured.  Phenolic compounds were measured from the grape skins using HPLC-DAD methods.

For the finished wine; pH, density, volatile acidity, total acidity, and alcoholic degree were measured.  Phenolic compounds were measured after filtering, using HPLC-DAD methods.

Results

Physiological Parameters

•       Grapes: No significant differences were found in physiological parameters (Baumé degree, pH, and total acidity) between conventional and organically grown grapes.

o   This result is consistent with other studies.

•       Wine: No significant differences were found in physiological parameters (pH, density, volatile acidity, total acidity, and alcoholic degree) between wines made from conventional and organically grown grapes.

o   This result is consistent with other studies.

Antioxidant Properties

•       Grapes:  The antioxidant activity of organic grapes 30 days before harvest was higher than conventionally grown grapes.  However, this difference disappeared over time, and at harvest, there were no significant differences in antioxidant activity of organic versus conventionally grown grapes.

o   The antioxidant levels reported were higher than in some studies, and lower than in other studies, with the changes over time consistent with yet other studies.

•       Wine:  There were no significant differences in antioxidant activity of wines made from organic versus conventionally grown grapes.

o   The antioxidant levels reported were lower than in some studies.

Anthocyanins

•       Grapes:  The concentrations of anthocyanins of organic grapes 30 days and 14 days before harvest were higher than conventionally grown grapes.  However, these differences disappeared over time, and at harvest, there were no significant differences in anthocyanin concentrations of organic versus conventionally grown grapes.

o   These results were consistent with other studies.

•       Wine:  The average anthocyanin concentrations were lower in wine made from conventionally grown grapes than wine made from organically grown grapes. (Unclear if these differences are significant, but since the authors did not specify that it was, I’m going to assume the differences were not significant).

o   These values were higher in this study than in other studies.

Hydroxycinnamic Acids

•       Grapes: The concentrations of hydroxycinnamic acid derivatives were higher in organic grapes than conventional grapes 30 days before harvest through harvest itself, though this difference was not significant.

o   These values were lower than reported in some studies.

•       Wine:  There were no differences in hydroxycinnamic acid derivatives in wines made from conventionally or organically grown grapes.

Flavonols

•       Grapes:  Flavonol concentrations were higher in organic grapes 30 days before harvest was higher than conventionally grown grapes.  However, this difference disappeared over time, and at harvest, there were no significant differences in the concentrations of flavonols of organic versus conventionally grown grapes.

o   These values are consistent with other studies (though slightly higher than one other study).

•       Wine:  Concentrations of flavonols was lower in wine made from conventionally grown grapes than organically grown grapes, however, this difference was not significant.

Total Phenolic Content

•       Grapes:  Total phenolic content was higher in organic grapes 30 days before harvest was higher than conventionally grown grapes.  However, this difference disappeared over time, and at harvest, there were no significant differences in the total phenolic content of organic versus conventionally grown grapes.

o   These values were lower than reported in some studies.

•       Wine:  Total phenolic content was slightly higher in wine made from organic grapes than wine made from conventionally grown grapes, however, this difference was not significant.

Conclusions and Thoughts from The Academic Wino…

The results of this study seem to suggest that when it comes down to phenolic composition of wine, there are no differences between wine made from organically grown and conventionally grown grapes.  Some significant differences of certain phenolic compounds were noted in the early stages of ripening, which over time disappeared and “evened out”.  One explanation is that phenolics play an important role in the protection of the developing grapes, including UV protection, disease resistance, and defense against herbivory (a.k.a insect attacks).  Conventionally grown grapes are treated with chemicals that also protect against these various elements, thereby the plant itself likely responds by not producing the necessary phenolics to do the job, since something else is already doing that for it. 

Plants and animals are energy-efficient machines (for the most part), so if the plant does not need to waste the energy on producing compounds that will protect it against attacks and diseases, then it will not.  The results showing that in the early stages of ripening, when the grape is more vulnerable to attack and disease, phenolic composition is lower in conventionally grown grapes than organically grown grapes, likely due to the decreased need for the plant to produce the compounds themselves, since they were already being protected by the conventional treatment methods.  These differences do decrease in significance over time, which could simply be a result of low sample size, or some other mechanism that is unbeknownst to me at this time.  Larger sample sizes may retain the significant differences, though more studies are needed to confirm or refute this.

The values presented in this study were often consistent with other studies, though at time were lower or higher than studies done previously.  This could be due to a multitude of factors, including different collection and chemical analysis methods, or simply due to the geographical location of the study vineyards, which has already been shown to have significant differences in chemical compositions of the same grape varieties.  I’m confident that the methodology they were using in this study was sufficient to attain the answers they needed, however as mentioned previously, it may have been better to take more samples.

One final beef I have with the study is that it was never made clear to me what variety of grapes they were actually dealing with during this study.  Was it one variety?  Or many?  Which type?  Knowing this could be very important, as it is possible that some grapes are more sensitive to conventional agricultural methods than others.

The results of this study indicate that there are no significant differences in phenolic compound composition of wine made from conventionally grown grapes or organically grown grapes.  This may not be a consistent result across all grape varieties over all types of climates and even more so with all winemaking procedures.  These results are interesting in and of themselves; however, more work should be done to achieve a more comprehensive understanding of these differences.