Enology Notes #109, December 19, 2005
To: Regional Wine Producers
From: Bruce Zoecklein, Head, Wine/Enology-Grape Chemistry Group, Virginia Tech
1. Argentina and Chile Trip Postponed until November 2006. The study tour to Argentina and Chile scheduled for March 1-14, 2006 has been postponed. While being in those countries during the harvest would be interesting, we could not guarantee the chance to visit with important grapegrowers and winemakers during this busy time. The rescheduled study tour will be sometime between November 10 and Thanksgiving.
As before, the trip will be limited to approximately 20 people and is being organized by Eric Henderson. We will spend several nights in Buenos Aires, and fly to Mendoza, Argentina, for three days and nights of vineyard and winery visits. We will then fly from Mendoza to Santiago, Chile, and visit Vina del Mar, Valparaiso, the Casablanc, Maipo Valley, Aconcagua Valley, and go to the Colchagua on the wine train. Departure back to the US will be from Santiago. Details regarding this trip will be posted on the Enology-Grape Chemistry Group website at www.vtwines.info.
2. Chile 2005. I recently participated in a VinoTech Chile-sponsored symposium in Santiago, Chile, titled Winemaking from a Viticultural, Oenological and Microbiological Perspective. After the symposium, I visited several of the important wine-producing regions of the country.
The Chilean wine landscape has changed considerably since my first visit in 1996. The country is not the land of sleepy bodegas, but a vibrant, international wine community with an annual production of more than 900 million hL/year. Investments from Mondavi, Château Mouton-Rothschild, Miguel Torres, and Antinori, among others, have set a tone of technical advancement.
Chile is a country of extremes. This includes grape and wine technology. There are very technically advanced, very modern wineries, and those that are much less so. The following is an update of the review I posted after my trip to Chile in 2003.
Climate. Chile, a country squeezed between two barriers, the Andes and the Pacific Ocean, is roughly 2700 miles long, but only 96 miles wide at its narrowest point. The northern hemisphere's latitude counterparts to Chile’s wine-growing regions are Northern Africa/southern Spain. Thanks to the moderating effect of the ocean and mountains, the temperature rarely exceeds 90°F in most of the valleys. Chilean wine producers describe their climate as somewhere between Napa and Bordeaux.
The country's wine-producing regions are composed of numerous valleys, some of which are reaching relative fame. The most important of these are the Aconcagua and Casablanca, north of the capital, and the Maipe, Rapel, Curico and Maule valleys in the center of the country. These central valleys, collectively know as the Valle Central, are separated by rivers from the Andes, which provide ample irrigation water. The soils are mostly alluvial, with clay and some tuffeau in the southern Rapel and Maule. Soils in the Maipe suffer from excessive salt, with potassium deficiency not uncommon.
In most of these valleys, the summers are dry and generally mildew-free. In the Casablanca region, which is near the coast, vineyards are cooled by morning fog, which slows ripening. This is a UCD region 1. It has about 180 days of sunshine, vs. the interior valleys which have 240-260. Almost all of the vineyards in this region have wind machines to help reduce the potential from late spring frost, which can be a large problem.
More than twenty varieties of wine grapes are grown in Chile. The largest planting is Pais (Mission), but that is rapidly changing. Sauvignon blancs produced in the Casablanca have varietal intensity and integration, reminiscent of New Zealand wines. Edward Flaherty, the winemaker for Robert Mondavi's Errazuriz winery, suggested that their varietal intensity was a result of fewer daytime temperature spikes, compared with many other wine regions.
This may be a very important issue. What are the effects of short-term temperature spikes on grape aroma/flavor? It may not be realistic to rely too heavily upon the maximum and minimum temperatures to describe the thermal characteristics of a region or site. As suggested by Happ at our American Society for Enology and Viticuture-Eastern Section meeting in Roanoke, VA, in 2004 (Grapes, Wines and the Environment Symposium), if the movement of temperature between the daily max. and min. exhibited the properties of a straight line, the mean would provide the average temperature experience. However, the true average lies away from the mean.
The rise in a temperature curve is asymmetrical, and changes with cloud cover, wind, etc. The optimum temperature for enzymatic reactions which govern aroma/flavor development and retention is about 22°C. Therefore, it has been suggested that the periodic difference between the temperature experienced throughout the day (for example, every twenty minutes) and 22°C, is the true measure of site climate. An issue may be the consistency of temperature during the entire day, for the final 28 days or so before harvest.
Happ (1999) has calculated a heat load index, which takes into account that a fruit temperature rise does not necessarily have a linear effect on aroma/flavor. For example, a temperature increase to 25°C does not have the same impact on aroma/flavor as a rise to 35°C.
Cost of Production. Chile’s standard of unmatched quality for the money has been somewhat eroded. There are a lot of players in the $6-12 per bottle market. Most industry members we visited expressed the importance of maintaining a low production cost. This philosophy has limited the widespread use of enzymes, membrane filtration, etc., in the past, but that is changing rapidly.
Yield and Vigor. The average Chilean vineyard yield is well over 70 hL/ha (4 tons per acre), but that is rapidly changing. Like most premium wine producers around the world, Chileans are concerned about yield, as it may relate directly to quality, and/or as a function of delaying maturity. The question of how yield impacts quality is complex, due to the interactions of growing season, vineyard site, vine density, clone, variety, pruning, crop thinning and timing, fruit weight/exposed leaf area, solar exposure, etc.
Traditionally, many vineyards in Chile were planted on a Tendone system in a high, arbor-like trellis which provides shade, similar to the Parral used extensively in traditional Argentine vineyards.
Almost all of the new plantings are on VSP. There were a few vineyards planted on various divided canopy systems, however these are not common due to establishment costs. I saw a few vineyards on Gobelet.
Most of the Chilean vineyards are planted on the very fertile alluvial soils of the valley floors. This has resulted in excess vine vigor, which many growers suggested was their primary viticultural concern. They are attempting to control the vigor by the use of irrigation. Most were well aware of the research conducted on the use of deficit irrigation, both to help control vigor and improve quality. Now about half of the vineyards are irrigated and vineyards are being planted on hillsides.
Organic Farming. The interest in organic farming is universal. As I reported in Enology Notes #75, many of the Loire Valley producers believe that organic farming increases wine quality. The Chileans perhaps agree, but also see a rapidly-increasing market for such products. Their generally dry climate will allow them to take advantage of this trend. The Maipo averages about 300 mm of rainfall (about 12 inches).
Maturity Gauges. For the reds, notably from the Maipo Valley which is planted to 50% red, 50% white varieties, winemakers place a primary importance on phenolic maturity. As such, virtually all the red wines evaluated were supple, with "new world" round, soft palate profiles. The concern with phenolic maturity has resulted in wines with high to very high alcohol levels (14 - 15+%).
At our pre-harvest workshop in 2005, Patricia Roca from VinoTech Chile showed data on the changes in the alcoholic concentration of "new world" wines from 1985 to 2005. In 1985, the average alcohol content was 12.5, whereas today it is about 15% (v/v).
The universal problem of high alcohol stems from extra “hang time” to obtain seed, stem and skin phenolic maturity. This problem is the result of the asynchrony among sugar development, aroma/flavor, and phenolic maturity, as discussed in several past editions of Enology Notes.
Elevated pH values reduce longevity, a feature that most Chilean winemakers seem to be willing to live with. It is not uncommon to find red wines with pH values above 3.6. This problem is somewhat offset by the alcohol concentrations.
Some producers appear to ameliorate with water, to help assure that fermentation goes to completion, and resulting in lower alcohol. The amelioration volume is calculated from the loss of berry weight due to dehydration. This remains as controversial in Chile as elsewhere.
Protracted Cold Soak. Uninoculated fermentations are common. These are not without risk, particularly when used in conjunction with protracted prefermentation cold maceration. Many Chilean producers use multiple days of prefermentation maceration, sometimes up to 20. This is somewhat surprising, given the cost of keeping a tank below 10°C for that long a period. Temperatures warmer than 10°C run the risk of growth of Kloeckera spp., a cold-tolerant yeast present on the fruit.
In a study conducted by our group (The effects of prefermentation maceration temperature and percent alcohol (v/v) at press on the concentration of Cabernet Sauvignon grape glycosides and glycoside fractions, McMahon et al., 1999), prefermentation maceration at 10°C increased the glycosides extracted into the juice by 103% vs. control non-cold-soaked wines. Cold soaking increases long-term color stability and may increase aroma intensity. Several winemakers reported that cold soak helped to assure the completion of MLF.
After my visit in 2003, the Enology-Grape Chemistry Group conducted a study to evaluate the effects of time of cold soak on several red wine components. The impact of prolonged cold soaking is likely be dependent upon the cultivar, maturity, and degree of berry breakage (see Enology Notes # 61, 62).
Figure 1 illustrates a comparison between copigmented anthocyanins, total anthocyanins, flavone cofactors, polymeric pigments and total phenols in wines 4 months post-fermentation that were produced with either 4 or 20 days of cold soak at 7°C. This study was conducted by graduate student Kerem Baki. Differences were noted, the most significant of which is in the concentration of total phenols. The significance of these parameters to red wine production will be discussed in depth at the Tannin and Color Management and Measurement short course (see below).
Figure 1 – Effect of 4-Day vs. 20-Day Cold Soak at 7°C of Prefermentation Must on Cabernet Sauvignon Wine Chemistry
It is likely that prolonged cold soaking would have an influence on red wine color, among other things. Color is a function of three components, anthocyanins, color cofactors, and the degree of polymerization. Figure 2 demonstrates the color intensity and hue of wines produced by 4 and 20 days prefermentation cold soak, analyzed four months post-fermentation.
Figure 2 – Effect of 4-Day vs. 20-Day Cold Soak at 7°C of Prefermentation Must on Cabernet Sauvignon Wine Colors
The extended cold soak wine has less spectral red color. The 20-day cold soak wine has a hue reminiscent of an aged wine, with an increase in the brown tones absorbed at 420nm.
Fermentation. Many ferment their red must uninoculated, relying on the native flora of the winery. In a study from our group (Quantification of glycosidase activities in selected yeasts and lactic acid bacteria, McMahon et al., 1999), we evaluated the hydrolytic activity of 32 strains of yeasts isolated from wineries and vineyards. Several of these had a significant ability to hydrolyze glycosides, that is, convert grape-derived aroma/flavor precursors to their odor-active forms. This work, and that of others, suggests the possible benefits of uninoculated fermentations. There are, however, some substantial risks of microbial and oxidative degradation.
There are all the standard cap management procedures utilized in Chile, including a few uncommon methods. Several producers use the Australian Red approach, e.g., cold soak with enzymes and dejuicing into barrels at about 7-5 Brix. This has the advantage of softening wood phenols and integrating wood components into the wine (see previous editions of Enology Notes).
Carmenere. One possible advantage that Chile has is that it is the leading producer of the variety Carmenere. After the Phylloxera crisis, the production of Carmenere in Bordeaux declined, as a result of its late ripening and frequent degradation due to late season rains.
It has found a home in Chile, producing well-structured red wines. Most suggested that the variety has some significant potential, but that a lot of work remains. Where it should be planted and optimal clone are open questions. It is the last to ripen, frequently has uneven development, and is a rather reductive grape. The interest in this variety seems to be overshadowed by those who are focusing on the so-called international varieties.
The question for many is, to what extent should this variety be developed. In the world of international marketing, how important is it to have a single identity? New Zealand is known for Sauvignon blanc, Oregon for Pinot Noir, Uruguay for Tannat, etc. Regional distinction is an important marketing consideration, one that we in Virginia have been considering as well.
Finally, there was one very interesting point stressed several times: that the industry would only reach its full potential with greater unity among producers. In order to help reach that goal, the Chilean Winemakers Society, as a group, visits wine regions around the world. They have been to California, Europe, and other South American countries.
The Chilean wine industry, like any other, will only reach its full potential through the cooperative interaction of its producers.
3. Tannin and Color Management and Measurement, an Advanced Short Course. The Enology-Grape Chemistry Group will offer a one-day advanced Tannin and Color Management and Measurement short course February 27, 2006, at White Hall Vineyards from 10:30 AM to 4:30 PM.
We have some common beliefs regarding grape and wine phenols. Are they true?
- Grape and wine color strongly correlate to aroma/flavor?
- Anthocyanin concentration strongly correlates to aroma/flavor?
- Color is a good indicator of yield?
- Aged red wine color is directly related to young wine color?
To succeed in any business requires three things: To be well informed, to think laterally, and to question established practices or beliefs. This practically-oriented, advanced program will explore these and other questions to help winemakers determine what the influences of various phenolic compounds are, which could/should be monitored, and how. Sensory analyses will be highlighted, and chemical analyses that can be conducted at the winery will be discussed and compared.
The topics will include the following:
Grape and wine phenolic compounds
- Types and classes of phenols
- Grape-derived phenols
- Processing-derived phenols
Nature of grape and wine color
- Color stability
Viticultural factors impacting grape phenolic compounds, including color
- Vine nutrition
- Climate: macro-, micro-
Enological factors impacting phenols
- Cold maceration
- Short vatting, Australian red, extended maceration
- Enological tannins/wood fermentation
- Thermal processing, impact of temperature
Sensory analysis techniques with the following examples
- Phenolic standards
- Delestage vs. cap punch
- Short vatting vs. extended maceration
- Total vs. partial destemming
- Yeast strains
Phenolic measurement at the winery
- Wet chemistry and spectrophotometric procedures will be compared.
- Measurements, such as tannins, color density, hue, total pigments, polymeric pigments, copigmented anthocyanins, etc., will be outlined, and their significance discussed.
Pre-registration is required BEFORE Monday, February 20, 2006.
COST: $45 per person, due by Monday, February 20, 2006.
Make checks payable to: Foundation Account, Virginia Tech.
Mail to: Terry Rakestraw
Department of Food Science & Technology
Virginia Tech - 0418
Blacksburg, VA 24061
Please bring a bagged lunch, since food will NOT be provided.
4. Sixth International Cool Climate Symposium. Sixth International Cool Climate Symposium for Viticulture and Oenology is scheduled for February 5-10, 2006 in Christchurch, New Zealand. The theme for this event is Wine Growing for the Future. Keynote speakers with cover the following areas:
- Managing viticulture and oenology for quality and sustainable outcomes
- New technologies for cool climate wines
- Marketing cool climate wines
- Forging new frontiers and meeting new challenges
A three day Otago Pinot Noir tour starts on Thursday, 2 February, and includes visits to seven of the region’s top vineyards and wineries. The tour to the Marlborough winegrowing area starts on Saturday, 11 February, with an optional train, plane or drive to Blenheim for the BMW Marlborough Food and Wine Festival.
Workshops will take place on Wednesday, 8 February. Workshops include:
- Phylloxera Identification and Management, Devin Powell and Carolyn Trethowan
- Wine Microbe Management, Lisa Van de Water, Paul Grbin and Bruce Zoecklein
For additional details on the ICCS see their website: www.iccs2006.org.nz
5. Enology Service Lab Update. As many of you know, The Enology-Grape Chemistry Group at Virginia Tech is establishing a fee-based, full service enology laboratory. This will have the full range of analytical services, and is being supplemented by the College of Agriculture and Life Science at Virginia Tech and the Virginia Wineries Association.
The expected outcomes of this effort are increased technical support, which will translate into increased wine quality, increased wine sales, and an overall increase in economic activity within this vital sector of agriculture.
We are in the process of hiring a lab director and renovating a separate lab for this purpose.
This service will be available to wineries in any state, including importers and wholesalers. The prices will be competitive, with profits designed to help support extension activities of the Enology-Grape Chemistry Group. The goal is for very rapid turn-around time, with optimum precision and accuracy. Look for details regarding this service in upcoming issues of Enology Notes.
Subscription to Enology Notes. All past Enology Notes newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.vtwines.info/.
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Professor and Enology Specialist Head Enology-Grape Chemistry Group
Department of Food Science and Technology, Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: http://www.vtwines.info/
Phone: (540) 231-5325
Fax: (540) 231-9293
Cell phone: 540-998-9025