Growing & Winemaking


A Conversation with James Kennedy

February 2015
by Laurie Daniel
James Kennedy
James Kennedy specializes in tannin chemistry.

Dr. James Kennedy, chair of the Department of Viticulture and Enology at California State University, Fresno, was raised near another famed wine school, the University of California, Davis. Growing up near the university’s farm, Kennedy says he was “fascinated with the grape and wine industry at a young age.”

Although he says wine “was just in my bones,” there were a lot of detours in his career. When he left high school, Kennedy intended to become a forester and studied at Sierra College in Rocklin, Calif. But his love of fermentation science never left him, and Kennedy transferred to UC Davis. He earned his bachelor’s degree in chemistry in 1987 and went to work in the pharmaceutical industry.

As much as Kennedy enjoyed the chemistry, he missed agriculture, so one day he answered an ad for a job at a winery. That winery turned out to be Ridge Vineyards in the Santa Cruz Mountains. After a few years there, he went back to school and earned his Ph.D. in agricultural and environmental chemistry at UC Davis in 1999. He went on to do postdoctoral research on grape and wine phenolic chemistry at the University of Adelaide in Australia, then worked at Oregon State University and the Australian Wine Research Institute before becoming chair at Fresno State.

Kennedy is most widely recognized for his research on grape and wine tannin chemistry, and he has published numerous articles about tannins and proanthocyanidins. He is a past president of the American Society for Enology and Viticulture and is on the board of directors for the California Raisin Marketing Board and San Joaquin Valley Winegrowers Association. He will be among the speakers at the Wines & Vines Oak Conference on Feb. 11 in Napa, Calif.

Q: Please give us a preview of your upcoming presentation about oak and tannin for the Wines & Vines Oak Conference.

James Kennedy: My plan for this talk is to update the audience on work from around the world with regard to oak and tannin and to relate this information to wines and their aging. One of the major goals is to provide quantitative information about what oak barrels “give” to wine. As an example, although oak barrels do not contribute much tannin to red wine, the structure of oak-derived tannins is different than grape-based tannins and interacts differently with oxygen. Does that unique chemistry impart special qualities with regard to wine quality? My talk will explore this question and more.

Q: If oak barrels aren’t directly contributing much tannin to the wine, what role do they play in the development of red wine?

Oak barrels are critically important to wine aging for a number of reasons. First is that different interaction of oak-derived tannins to oxygen. Second, as an oxygen-permeable storage vessel, the oak barrel allows for controlled oxidation of wine, which is very important to development. Finally, oak barrels provide aroma and flavor to wine.



    One area of research at California State University, Fresno, involves “forced cropping.” Professor James Kennedy says his colleague, Dr. Sanliang Gu, is researching use of the Roseworthy double-pruning system to improve grape quality in warm to hot climates like those found in the San Joaquin Valley, where sugar ripeness often outpaces phenolic ripeness.

    The RDP technique was developed by Peter Dry and Richard Smart at Roseworthy Agricultural College in South Australia in the late 1970s (read Smart’s column on page 54). The first crop is removed, which makes the vines push another crop. “Hence, the grapes ripen during a cooler portion of the growing season,” Kennedy says. “The wines that have been produced from grapes using RDP are consistent with grapes grown in cooler climates.”

    There is, however, the question of economics. Producers in the San Joaquin Valley operate on slim margins. “Every time you walk in a vineyard, it costs money,” Kennedy says. “Any new operation you put on a vineyard is costing money.” So getting rid of the first crop is an expense that could be hard to recoup.

    Kennedy says that smaller producers are interested in the technique, but they’re also looking at alternative varieties that are better suited to their hot climate.

Q: How did you get interested in studying tannins in red wine?

My fascination with red wine tannins can be traced back to a couple of people. The first person was Dr. Vernon Singleton. I took a class in wine aging from Dr. Singleton at UC Davis in the mid-1980s, and I was absolutely blown away and became fascinated with age-worthy red wines. A large part of that fascination was the chemistry of red wine tannins and their role in the aging process.

The second person was Paul Draper of Ridge Vineyards. I worked at Ridge in the mid-1990s and again was blown away by the ageability of the wines that had been produced by this winery. Paul specifically instilled in me the appreciation for craftsmanship in wine production.

By 1995 I was hooked on the chemistry of red wine tannins. These are amazingly interesting molecules that have tremendous importance in red wine quality and yet in so many ways are still a mystery. My initial interest stemmed from the idea of tannin “ripeness.” While working at Ridge, I became fascinated with the quality of tannins coming into the winery and the notion that tannin perception and astringency quality was changing in the vineyard. At the time, we knew very little about how precisely tannins were changing during berry development, and that thought intrigued the heck out of me. Imagine that something that is so sensorially apparent, and the chemistry is poorly understood. I wanted to understand that at the chemical level. I’ve scratched the surface, but there’s still so much that’s not understood. I am keen on tannin chemistry ( thank you, Dr. Singleton) and appreciate that the finest red wines are crafted not assembled (thank you, Paul Draper).

Q: Where is your current research focused?

My current area of research is focused on understanding tannin structure-activity relationships as they relate to red wine production. Activity in this case is how we perceive tannins. Imagine chewing on a green banana or an unripe persimmon. What you feel when you do this is astringency or what we call the response when tannins “stick” to and precipitate salivary protein. We all know anecdotally that wine-production practices influence tannin perception: Whether it is the source of fruit, different types of maceration or aging in an oak barrel, we all know that tannin perception is impacted. My research is very much focused on understanding how tannin structure changes during operations such as these and determining the effect of structure on activity. The newest tool in the toolbox for me is an analytical method that has been developed in my lab. This method measures tannin activity so that we can now more effectively investigate the role of tannin structure.

Q: As a graduate of the University of California, Davis, and now chairman of the Department of Viticulture and Enology at Fresno State, you are in a unique position to talk about how the programs differ and how they complement each other. How is Fresno State different from UC Davis and other such programs? Does it attract a different type of student?

Those are great questions. I grew up in Davis, was educated at UC Davis, and it goes without saying (although I will!) I am an Aggie, through and through. With that, I have been at Fresno State for a while now, and as hard as it may be for some of my Aggie compatriots to hear, I have become a tremendous supporter of Fresno State. The beauty is, these programs are not mutually exclusive. They are unique in their own ways and very much complementary. Given the size of our industry, there is clearly a need for both programs.

How are they different? With regard to instruction, I guess the simplest way to state it is that UC Davis stresses science and Fresno State stresses practice. Both programs deliver instruction in the science and practice of grape and wine production; we just emphasize different aspects. With regard to research, I believe that Fresno State stresses near-term solutions and UC Davis stresses long-term understanding. From my experience, I do think that UC Davis and Fresno State attract different students, but they’re equally passionate about their chosen profession.

Currently Fresno State has about 170 students, and of that number about two-thirds of the students want to become winemakers and the remaining students plan to work as viticulturists. The program is growing by about 10% per year, and virtually all of our graduates are finding employment after they complete their course of study. Fresno State also offers a certificate program for those students who would like to return to school for specialized training in wine production. These students generally come from a previous career, and they already possess an undergraduate degree.

I have also been fortunate enough to work at Oregon State University, the Australian Wine Research Institute and the University of Adelaide. From this collective experience, I have come to believe that grape and wine industries are healthiest when they are supported by dedicated viticulture and enology education and research centers. In California, we are fortunate in having viticulture and enology programs at all tiers of our higher education system, and this is a good thing. Our industry is stronger and more sustainable because of this.

Q: You have a faculty member who is studying berry structure and extractability. What can you tell us about that research?

Our most recent faculty addition is Dr. Hend Letaief. Hend grew up in Tunisia, was trained in France and Italy, and is very interested in the relationship between berry physical properties and wine composition. This area of research has the potential to make the objective assessment of fruit more rapid.

As winemakers make harvesting decisions, there are many characteristics that you need to evaluate. We all know that pH, TA and Brix are not sufficient when determining ideal ripeness. The challenge is that our understanding of the relationship between berry characteristics and wine characteristics is incomplete. So we chew on seeds and skins, look at stem color and do all of these other things to correlate berry physical properties with wine composition. The challenge here is that humans are subjective and not as reproducible as an instrument. This is where Dr. Letaief’s line of research comes in.

A resident of the Santa Cruz Mountains, Laurie Daniel has been a journalist for more than 35 years. She has been writing about wine for publications for more than 21 years and has been a Wines & Vines contributor since 2000.

Currently no comments posted for this article.