Enology Notes

Enology Notes #126, February 19, 2007

To: Regional Wine Producers

From: Bruce Zoecklein, Head, Enology-Grape Chemistry Group, Virginia Tech

Subject: New Edition of Winery Planning and Design CD Available; Winery Planning and Design Workshop; Dragon Wines – The Chinese Wine Industry (continued); Virginia Tech’s Enology Service Laboratory: Precision and Accuracy as a Function of Method and Equipment.

1. New Edition of Winery Planning and Design CD Available.  Edition 12 of the Winery Planning and Design CD is available through Practical Winery and Vineyard magazine. Email them at , or call (415) 479-5819.

2. Winery Planning and Design Workshop.  A Winery Planning and Design Workshop is scheduled for March 5, 2007 in King of Prussia, PA, one day prior to the start of this year’s Wineries Unlimited program. The Valley Forge Convention Center is just outside of Philadelphia. Registration information is available at www.wineriesunlimited.com.

Please note: Pre-registration deadline is Monday, February 26.

Please note: The Winery Planning and Design CD (see above) is NOT included with registration. A hard copy manual specific to the course topics will be provided.

3. Dragon Wines – The Chinese Wine Industry (continued). In November 2006, I was invited to lecture at two universities (Agricultural Research Station of Guangdong Province in Guangzhou, and the China Agriculture University in Beijing) and tour Chinese wine regions. The following is a continuation from Enology Notes #125, a review of that visit and the Chinese wine industry.

From Guangzhou, I traveled some 2400 km by train to the Chinese Agricultural University in Beijing. In 2003, the university established the country’s first PhD program in Enology and Viticulture. With extensive support from some of the major wine producers in the country, including Great Wall Winery, this program is thriving. The university has a pilot winery and research facilities that are quite impressive. With four full-time faculty and about 50 graduate students, the program is providing the industry with the technically-trained personnel needed to grow and develop production.

I lectured on aroma and flavor management, and evaluated many of their experimental products. I also lectured to the graduate students in English. English competency is a requirement for the Chinese Agricultural University Enology and Viticulture program.

From Beijing, I visited several wine regions. China has more than 300 wineries. Most of this development has been in the North Central Heartland areas near Beijing, in the eastern maritime region of Shandong, and in the Inner Northern region of the country.

The industry is dominated by six large producers who account for about 55% of the total production. The average capacity of Chinese wineries is approximately 2000 tons, with 70% of the producers under 1000 tons. The more predominant wineries include Changyu, Great Wall, Dynasty, and Dragon Seal, all producing over 10,000 tons.

Wine production in China in 2005 was 434,000 tons, an increase of 14% from 2004. While small compared with other alcoholic beverages, it represents a substantial increase.

Some wineries still use flavor essence, ethyl alcohol, sweetening agents, and water additions to produce wines. This has been the motivation to attempt to establish standards. At a wine conference in Shandong Province, participants discussed the establishment of an AOC-type system.

New standards are evolving, including premium wine and ice wine; the latter, produced in the extremely cold Xinjiang Region, is abundant in stores in most big cities. Regulations are being put into effect to control raw materials, regional identity, variety, and vintage.

Despite some opposition to geographic indicators as a means of wine classification, local branding has become a trend, with the expansion of some estate-branded wines. One winery I visited, Great Wall, is leading the market in estate wines.

Domestic wine producers are starting to change marketing strategies. Changyu Wines has established the first estate wine club in China. They and others are attempting to break out of the traditional, for example by selling entire barrels of wine at a time. The Huadong Winery, established in Shandong Province in 1985, was one of the first wineries to attract attention, being the first Chinese winery with a varietal label, and the first to vintage date.

China reportedly has 26 indigenous vine species and hundreds of grape varieties. These are used to produce mainly low-end wines. Widespread introductions from Russia, including Muscat Hamburg and Rkatsiteli, along with Italian Riesling, make acceptable, if not noteworthy, products.

In Shandong Province, early vineyards were developed from a diverse selection of wine grapes introduced mainly from Europe. Among the most common are Cabernet Sauvignon, Cabernet Franc, and the mysterious Cabernet Gernischt and Welchriesling. Cabernet Gernischt is a red wine grape variety used in China and believed to be of European origin, similar, if not identical, to Cabernet Franc. The name may be a misspelling of the Cabernet Gemischt, once used in Europe. It was imported into China in 1892, and is used both as a varietal wine and a blending component.

Shandong Province is at roughly the same latitude as California. Cool Pacific breezes moderate the temperature, which ranges from about 3C in winter to 26C during the summer. Monsoons come from the South China Sea, although spring is usually dry, and summer and autumn wet. Therefore, fungal growth is a problem, with rainfall averaging about 700 mm (27 inches) between June and August.

Like many regions in the world, China’s initial plantings were on flat land with fertile soil, poor drainage, and poor ventilation. Overcropping is a large problem, impacting quality.

In the Shandong peninsula at Pingdu, the eastern range of the Dazashen Mountains, with its south-, southeast-, and southwest-facing slopes, is being planted. This area is gaining a lot of attention due, in part, to decomposed granite soils overlaying a limestone bed which, for the most part, is low in nutrients and well drained.

China’s parallel systems of market-driven and controlled economy, along with very strong farmer traditions, may limit the pace of change. Traditionally, all grape varieties (for wine and table) were grown in a fan-type trellis system with little canopy management. On the fertile valley floors, this results in dense foliage. High humidity and excessive yield increase the fruit rot potential, which motivates growers to harvest immature fruit.

The vast majority of vines I saw were ungrafted. Grapes are supplied by individual farmers who usually work less than an acre. With the abundance of cheap labor, as expected, all viticultural activities are performed manually.

In Hebei Province, not far from Beijing, vines are trained to a single and double cordon system, and buried in the winter, due to temperatures between -10 and -20C. The soil in this region is very sandy, with a high pH. Rainfall is about 400 mm. Here they use the so-called Dragon system. Vines are trained to single or multiple cordons just above ground level. Each cordon, or dragon body, bears dragon claws (canes) which are trained vertically about 50 cm apart.

More to follow.

4. Virginia Tech’s Enology Service Laboratory: Precision and Accuracy as a Function of Method and Equipment. While creating the Enology Analytical Services Laboratory website, it was suggested that we list legal limits and typical values for wine chemical parameters. Legal limits, such as those for Alcohol, VA, and SO2, are established by the TTB for taxation and health/safety. The desired ranges for some wine parameters were established by convention (8,000 years of winemaking), literature review, and experience of the Enology-Grape Chemistry Group.           

The detection limit of a wine parameter, the smallest amount of the chemical that can be accurately and precisely measured, is determined by the method used for analysis and the type of equipment. Our lab service can perform most chemical analyses using at least two different methods; for some parameters, we have 4 or more different methods available to us. A good example is malic acid. Malic acid levels, which are a matter of wine stability and stylistic winemaking, can be determined by paper chromatography, IR spectrometry, HPLC, or enzymatic analysis.

The choice of method for any wine parameter is a combination of accuracy, precision, time, and total cost. Paper chromatography for malic acid requires only a few chemicals and essentially no equipment. It is employed in some small wineries to monitor malolactic fermentation (MLF), but the accuracy can vary widely, even under the best circumstances. The lowest limit of detection under the best circumstances is approximately 100 mg/L. Because of the inherent flaws of this method, it is not one we use or recommend.

HPLC analysis is essentially the complete opposite of paper chromatography; it is very accurate, very precise, and also very expensive due to equipment, chemical, and operator cost. Our lab relies primarily on IR Spectrometry and enzymatic analysis for malic acid quantitation.

Even under these circumstances, the analysis is performed at least twice. Infrared spectrometry is fast, accurate, and precise, but only to a level of approximately 500 mg/L. Below this level, enzymatic analysis is our method of choice, due to accuracy, precision, and sensitivity.

As stated above, accuracy, precision, and sensitivity are functions of method and equipment. Enzymatic analysis sensitivity can vary, based on the equipment used. We use a benchtop spectrophotometer and 1cm pathlength cuvettes. As a general rule, the accuracy of a standard spectrophotometer is limited to the third decimal place in absorbance, i.e. +/- 0.005 AU.

This means that the minimum detectable level of malic acid is typically 2.5 mg/L, but to have confidence in the accuracy and precision, the absorbance must be 0.010 AU. With our equipment, the minimum detectable level of malic acid is therefore 0.005 g/L (5 mg/L), which under special circumstances can be reduced to 0.0005 g/L (0.5 mg/L) through the use of larger volumes or methods to concentrate the sample.

We were considering using high-throughput methods of analysis, but typically these instruments use shorter pathlength spectrophotometers, which present a mathematical change in detection limit, so that if the pathlength drops in half, the limit of detection doubles. Some automated equipment, such as robotic systems or microplate readers, used by some labs, drop the pathlength 5- to10-fold, which can raise the detection limit as high as 50 mg/L. This is an instance where we have sacrificed efficiency and time (robotic/automated systems) for low detection limits, and precision at these low values.

With such a range of precision and accuracy, one might consider MLF complete, because no malic acid was detected by paper chromatography, when an enzymatic analysis performed by our lab can detect malic acid at a level that is 20 times lower.

For any analysis performed by any laboratory, winemakers, as consumers of services, should question the method, accuracy, and precision of the tests performed on their behalf, so that accurate and informed decisions can be made, based on the results.

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Dr. Bruce Zoecklein
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