March Dreer Fellowship Report

From Vine to Wine
The Implications for Health and Extension

A joint research venture between the University of California, Davis and the University of Adelaide, Australia recently identified the enzyme – and the encoding gene – which converts vitamin C in grapes to tartaric acid, the key acid in wine. Such a discovery is leading researchers to question whether, with genetic manipulation, a high vitamin C wine may be produced that could further enhance the healthful properties associated with this drink known the world over.

Since the 1990’s, scientists have extensively examined wine – specifically red types – for its health advantages. Flavanoids have been shown to act as anti-oxidants and may lower the risks of coronary heart disease and certain types of cancers. Other health benefits associated with wine consumption include lowering bad cholesterol levels, postponing the development of Alzheimer’s disease, and reducing the risk of developing diabetes. All of these discoveries spurred the U.S. Food and Drug Administration to remove a line from their 1995 revision of the Dietary Guidelines for Americans which denied the health advantages of wine.

The healthful properties of moderate wine consumption are attractive pieces of news, especially for health-conscious consumers with a trained palate. Nevertheless, what many of these people may not realize – as the general consumer grows distant from the food supply and food processing systems – is that these healthful properties may be linked directly to crop cultivation, pest management, and post-harvest conditions. Thus, it is not only the responsibility of the enologist for making a fine wine; much also rests in the hands of the viticulturist. Attentive to soil conditions, climate, and variety – factors collectively known as “terroire” or “of the earth” – the management strategies of the viticulturist are equally important to the procedures in the winery. Thus, consumption – both of product and news – is the result of this translation from vine to wine.

Laboratory Analyses

I have been working under the direction of Dr. Álvaro Peña, a professor in the Agriculture Industry and Enology department at the University of Chile. Álvaro’s research involves understanding how grape quality translates into wine quality. Grape samples are received from field experiments and then processed in the laboratory. A primary task in the laboratory is quantifying phenolic compounds – like anthocyanins and tannins – for comparison and observation. Upon my arrival at the university, Álvaro and I discussed what would be the nature of my work during my stay. He suggested that I gain experience in the laboratory, understanding the procedures by which these properties are measured, their importance to health, and their attractiveness as health news. The knowledge and experience would help to link me as an agriculturist to the consumer, which as a future extension educator is valuable insight. Thus, I joined the laboratory team and began to acquaintance myself with the routine. When grapes are brought to the laboratory – for each set of samples – skins and seeds are separated, macerated into slurries, and then the slurries are filtered for clarity (Figure 1). These samples, now transformed to liquid, are used for the analyses of total phenols, total tannins, total anthocyanins, and color.

The compounds responsible for the healthful properties of wine are the phenols. Present in the skins, stems, and seeds of grapes, phenols contribute color, astringency, bitterness, and aromatic properties to wine. Crop processing and fermenting influence the final wine phenolic content, with pH, temperature, degree of skin and seed maceration, and length of skin contact time being important.

To ascertain the total phenolic content in the samples, a spectrophotometer is used to measure the absorption of a given light frequency – 280 nanometers – by the liquids (Figure 2). At this frequency, all phenolics of any type of wine and regardless of pH, can be quantified. The optical density measurement obtained from the spectrophotometer is inserted into a formula, and the milligrams of phenolics per gram of seeds or skins is calculated.

Tannins and anthocyanins are two types of phenols. Tannins provide physical stability to a wine and are recognized as the agents causing astringency or bitterness. This is because as wine ages, tannins bind with proteins and precipitate, resulting in a bitterly-flavored wine. To analyze tannin content, concentrated acid is added to paired, diluted samples. One of the pairs is set-aside, while the other is heated (Figure 3). The action of the acid and heat separates the tannins from anthocyanins and other compounds. Again, the spectrophotometer is used to measure the absorption of both the heated and non-heated solutions, using a light frequency of 550 nanometers. The difference in absorption between the two is then used in a formula to obtain the milligrams of tannins per gram of seeds or skins.

Anthocyanins are found in various red, purple, and blue fruits – including red apples, cherries, blueberries, prunes, and red grapes – and influence wine color. To measure anthocyanins, paired samples are prepared, with one sample having sodium bisulfite. The sodium bisulfite changes the color of the sample to clear (Figure 4). Using a frequency of 520 nanometers, the absorption of both samples is measured. The difference in absorption between the colored and clear samples is then used in a formula, and total anthocyanin content, in terms of milligrams per gram of skins, is calculated.

The final analysis conducted in the laboratory is for color. Color implicates both health characteristics, given its relation to anthocyanins, and wine quality. Again, the spectrophotometer is used. Yellow is absorbed at 420 nanometers, and both the skin and seed samples are analyzed for yellow color. The skin samples are also measured for red (520 nanometers) and blue color (620 nanometers).

The series of analyses for a set of samples takes about a week and a half to complete. Once one set of samples is analyzed, it is usually time to begin the next set. The final set of samples is that obtained from the harvest. Periodic analyses are important because phenol levels generally decrease with crop maturity due to enzyme degradation. Finding the balance between desired sugar level and phenolic content will result is a quality wine, but it is not an easy balance to achieve. As field conditions change from year to year, a new balance must be struck each year. These field conditions, previously described as “terroire,” are the subject of the field research from which our samples were taken.

Field Experiment

A trip to northern Chile provided the opportunity to see production systems and understand the cycle of our work from field to laboratory. I ventured five hours northwest of Santiago with Álvaro and his cooperator from the Department of Plant Physiology, Dr. Claudio Pastenes, to the one-road town of Punitaqui. Punitaqui is located in an inland valley surrounded by Atacama hillsides. The valley is literally an oasis amidst the parched desert, as irrigation has allowed agriculture to thrive (Figure 5). Water is the lifeblood of the annual vegetable crops and wine grapes, which, given the arid climate, generally mature weeks ahead of those from the central valley near Santiago.

The University of Chile conducts field research at the private, biodynamic vineyard of the Soler family. Dating back to 1924, and predating organic farming by 20 years, biodynamic farming is surging in popularity worldwide. It was developed by Austrian scientist/philosopher Rudolph Steiner and, like organic farming, emphasizes environmentally-sustainable practices like composting, soil fertility, crop rotation, and plant diversity. Nonetheless, biodynamic farming goes further than its organic counterpart by integrating crops and livestock and by using life forces – like seasonal events and cosmic rhythms – in coordinating planting and composting. In other words, biodynamic farming could be described as a “whole farm approach” (Rieger, 2005) to farm management.

These biodynamic principles were evident at the Soler vineyard. A man-made lake augmented flora and fauna diversity. A chicken coop was positioned within the vineyard for the birds’ contribution to pest management and soil organic matter. Compost is made on-site and applied to the land to enhance soil nutrition, and of course, no chemical pesticides are used on their Cabernet Sauvignon vines, which are irrigated by drip (Figure 6).

All else being equal, what the Soler family cannot control are their soil conditions. The primary focus of the “terroire” experiment is the tremendous variability of the vineyard soil profile. The site has been divided into six sectors, and differences in soil texture are obvious. All points of the soil texture triangle, and points in between, are illustrated in the soil trenches. Rocky soils, sandy soils, and clayey soils are all present in this one vineyard site (Figures 7 and 8). These differences in soil are translating into differences in vine vigor. Stronger, greener vines are found in the rich soil, while weaker vines – verging on chlorotic – are found in the porous ones (Figure 9).

This relation between soil quality and vine vigor may have interesting inference for berry composition. Vine vigor and the resulting microclimate have been shown to effect berry phenolic levels. According to an Australian study by Haselgrove et al. (2000), grapes in exposed light generally had higher sugars, an improved acid balance, and higher phenolics than those in shaded regions of the canopy. Light was recognized as the factor influencing anthocyanin production in the early stages of berry ripening. Temperature, however, was the more important factor in later stages, with temperatures higher than 26°C inhibiting anthocyanin production. The information presented from this study could have implications for the “terroire” experiment at the Soler family vineyard. Do the weaker vines have a warmer canopy microclimate? Is this warmer microclimate inhibiting anthocyanin production? If so, a diversified management strategy may be in order for the future – based on field sector – in an effort to maintain a consistent crop and high-quality wine.

Conclusion

When striving to create a quality wine, many factors must be considered. From the field factors collectively known as “terroire,” to those studied in the laboratory which impart healthful properties, wine-making has its intricacies, and there is more to think about than merely how it feels on the palate. From the viticulturist to the enologist to the consumer, many parties are interested in the product and will read news about it, especially if it has health inferences. In a world where the general public has little knowledge about where their food comes from, we as agriculturists can take advantage of this interest in health news to extend our own areas of specialty from seed to grain, stock to fruit, and vine to wine.

References

Bailey, Pat. 2006. Wine with a double shot of vitamin C? UC Davis News and Information. Viewed March 23, 2006. http://www.news.ucdavis.edu/search/newsdetail.lasso?id=7676.

Haselgrove, L., D. Botting, R. van Heeswijck, P Hoj, P. Dry, C. Ford, and P. Iland. 2000. Canopy microclimate and berry composition: The effect of bunch exposure on the phenolic composition of Vitis vinifera L cv. Shiraz grape berries. Australian Journal of Grape and Wine Research. 6(2): 141-149.

LaMar, Jim. 2006. Wine and health. Professional Friends of Wine. Viewed March 27, 2006. http://www.winepros.org/wine101/wine-health.htm.

Rieger, Ted. 2005. New roots in Lake County: Ceágo Vinegarden. Vineyard and Winery Management. 31(4): 52-63.

Zoecklein, B.W., K.C. Fugelsang, B.H. Gump, and F.S. Nury. 1990. Production Wine Analysis. Van Nostrand Reinhold: New York.