Vol.15, No. 3 May - June, 2000

Bruce W. Zoecklein

Department of Food Science and Technology

VPI & SU - 0418

Blacksburg, VA 24061, E-mail: bzoeckle@vt.edu

www.fst.vt.edu/Zoecklein

Table of Contents

I. Management of red wine phenols, Délestage 1

II. Aroma/Flavor Trapping Research Continued 3

III. Upcoming events - Synergy of Food and Wine, Annual ASEV-ES Meeting 4

IV. Enology - Grape Chemistry Group Web Site 4

V. Extension Laboratory Analysis 4

VI. Wine Industry Friend Departs 4

Phenols are important grape metabolites composed of many types of compounds with different chemical and sensory properties. Understanding the qualitative and quantitative nature of grape phenols (including tannin phenols) is important to premium red wine producers. In the past, the goal of many was to achieve a high concentration of tannins without regard to tannin quality. That goal has been modified due to our increased understanding of tannins and the factors influencing tannin quality. As discussed in previous editions of the Vinter's Corner, tannin quality can be loosely defined as suppleness. What is desired is a wine with a positive tannin profile as depicted in Figure 1. According to Delteil (1998), a preferred red wine profile has the characteristics of high volume or body in the foremouth with supple, fine-grained tannins. What should be avoided are overly astringent and bitter tannins, including those which can be described as dry or dusty.

A positive tannin profile can be achieved only with a complete understanding of tannin management from vineyard to bottle. There are a number of factors which influence a wine's tannin profile including: fruit maturity and uniformity of maturity, fruit handling, sulfur dioxide, oxygen, yeast species and strain, and must nitrogen status. Processing variations such as cold soak, the use of maceration enzymes, tannin addition, and alcohol content at dejuicing can also influence a wine's tannin profile. Each of these has been discussed in previous editions of the Vintner's Corner which are available on-line at www.fst.vt.edu/Zoecklein.

One of the most important aspects influencing red wine structure is fruit maturity. Evaluation of grape maturity should involve a review of the maturity of the individual grape components- the grape skin, the stem (including the cap stem), the pulp and the seeds. These do not mature at the same rates and, therefore, may not reach optimum maturity at the same time-yet they all go into the fermenter. Seed maturity has gained attention due to the fact that seeds have a relatively high concentration of bitter and astringent tannins. As discussed during recent winemaker roundtable meetings, increasing fruit maturity coincides with decreasing extractable tannin concentration of the seeds. Immature seeds provide a high level of astringent and bitter tannins. Even red wines fermented with mature seeds contains seed tannins.

Délestage. At a winemaker roundtable meeting in early 1998, I recommended a cap management procedure known as délestage. This procedure involves rack and return during fermentation. Occurring as often as once per day, délestage allows the cap to drain relatively dry. During this process, as much as 40% of the grape seeds can be deported from the fermenter. Seed removal plus oxidative polymerization of tannins result in a positive change in the tannin profile of the wine. There is a reduced concentration of astringent, bitter and dusty tannins. Several Virginia wineries are using this cap management method.

The Enology-Grape Chemistry Group at Virginia Tech has been conducting applied research on délestage in conjunction with White Hall Vineyards and has evaluated some of the chemical and sensorial differences of wines produced by this rack and return method. To help quantify the structural influences, we analyzed Merlots produced by délestage and conventional punch-down using several phenol indices developed by Professor Y. Glores. Results are shown below.

Index Control Délestage

Gelatin 43 36

PVPP 63 60

Ethanol 11 10

The gelatin index can be considered an indication of the astringency of a wine. The higher the value, the greater is the astringency or coarseness of the wine. During aging the index is relatively constant and begins to diminish after long storage. While it is not an exclusive measure of condensed phenols, it does demonstrate the percentage of tannins likely to give an astringent sensation.

The PVPP index represents the percentage of anthocyanins combined with tannins. These include anthocyanins in tannin- anthocyanin complexes and anthocyanins polymerised with condensed tannins.

The ethanol index is related to the organoleptic characteristics of the tannins, most specifically the softness and fullness. Higher values are associated with wines that require more age.

Volatile compound analysis. Délestage wines have a significantly different palate structure or profile. We are also interested in the olfactory influcences of this treatment. An analysis was performed on the volatile compounds of délestage vs control wines using solid phase microextraction (SPME) and gas chromatography/mass spectometry (GC/MS). Those compounds significantly influenced by treatment are listed in Table 1. A negative sign before a compound indicates it was present in lower concentration in the treated (délestage) wines.

Table 1.

Ethyloctanoate 31.1% Fruity

Furfural -100.0% Odorless

Ethyldecanoate 53.7% Fruity

Diethylsuccinate 23.9% Odorless

2-phenolethanol -35.2% Rose-honey

Sensory analysis. We also conducted a duo-trio difference test on wines produced by délestage vs conventional cap management. Three wines were provided to evaluators, two the same and one different. The judges were asked to identify the different wine based only on odor. The results were that 11 of 18 judges could distinguish the wines by odor alone, a statistical difference at the 95% confidence level.

Wines produced by this method have a different palate profile than conventionally produced wines. Délestage wines have a lower perception of astringent, bitter and dry tannins. Délestage produced wines also differ in their volatile components and these differences appear to be sensorily significant.

II. Aroma/Flavor Trapping Research continued

The Effects of Flavor Trap Methodology on Chardonnay (V. vinifera L) Aroma and Flavor. Anna Katharine Mansfield, Master's Candidate, Enology-Grape Chemistry Group, Virginia Tech

Previous editions of the Vintner's Corner have oulined our research efforts on aroma and flavor trapping (Vol. 14 No.5). The following is a research update.

Compounds such as ethyl and acetate esters are produced during fermentation and play a positive role in the perceived flavor and aroma characteristics of wine. These compounds are fairly volatile and have little solubility in must or wine. Consequently, they are swept away or entrained with the carbon dioxide during fermentation. The extent of this transfer is temperature dependent: greater loss occurs at higher temperatures. Assuming a similar production of these compounds, losses at 20ºC can be expected to be about twice those at 10ºC. This is a primary reason why white wines are traditionally fermented at low temperatures--to reduce such loss. Given the wide temperature range for white wine production (8 to 25ºC) there is potential for considerable variation in ester composition through entrainment loss. The most volatile and sensorily important compounds (esters) incur the greatest losses, while the long-chained alcohols, generally, are retained.

The technology for the capture of emission control volatiles has long been implemented in the petroleum and chemical industries, which operate under strict governmental regulation. Most of the work done in the wine industry has involved selective capture and return, using carbon filters and solvents. These methods are not easy, inexpensive, or, in most cases, practical. The Enology-Grape Chemistry Group has been evaluating a new method for selective capture and return in various wines.

Our most recent work centered around Chardonnay production. Pairs of Chardonnay wines, with designations of clone or location, were produced using both standard and flavor trap fermentation methods. Each set contained one control wine and one treatment, both produced from free-run juice. Standard fermentation locks were fitted to oak puncheons containing control wines. Treatment wines were fermented under conditions identical to the control wines, but experimental filters were fitted to the bunghole of each treatment puncheon to capture and condense volatiles, allowing them to drip back into the wine. A total of eight volatile compounds were found to be significantly different in the control versus flavor trap wines. Most notably, ethyllactate increased after treatment, while ethyl acetate and decanoic acid decreased. In the sensory analysis, this should translate to an increase in the butterscotch flavor consumers appreciate in chardonnay, and a decrease in the unpleasant rancid notes of decanoic acid and nailpolish remover scent of ethyl acetate.

Triangle difference tests were performed with both inexperienced and experienced panelists. Chardonays designated as North (1999) and West (1998) were found to be significantly different (Table 1). In addition, of the panelists who correctly identified the odd sample, 100% preferred the treated wine to the control. While there can be several reasons for this preference, it must be noted that these wines had a lower concentration of higher alcohols and a higher concentration of esters due to the flavor trapping.

Table 1: Results of Triangle Sensory Tests on West and North Chardonnays

Modified Quantitative Descriptive Analysis (QDA) was used to create aroma and flavor profiles for some of the wines (Meilgaard et al., 1999). This procedure involves the selection and subsequent training of individuals for the comprehensive evaluation and description of specific product attributes (Vintner's Corner, Vol. 12 No. 4). In QDA analysis, panelists are asked to rate a characteristic on an unstructured line scale, anchored with "weak" and "strong," by placing a vertical mark on the line for each characteristic. These marks are later converted into a measurement of intensity, and analyzed with simple statistics. In this case, a trained and experienced panel was presented with sensory standards representing key aroma and flavor characteristics for Clone 96, North, and West Chardonnays. Spider plots were developed from the data generated (Figures 1,2)

It can be concluded, based on volatile analysis, that the potential for flavor and aroma differences exists in the flavor trap and control Chardonnays. The triangle tests bore out this reasoning, as wines were found to be significantly different in aroma and flavor by both trained and untrained panels. Preference tests indicated that flavor trapped wines showed increased customer acceptance when compared to control wines of the same type. With further investigation, flavor trap methodology may provide an affordable and time-effective means of increasing flavor complexity and varietal intensity in wines.

This research has been funded, in part, by the Virginia Winegrowers Advisory Board. We appreciate their support, and will continue to bring you information on selective aroma/flavor capture and return.

References:

McMahon, H. 1997. Sensory Evaluation in the Winery. In: Vintner's Corner, Vol. 12, #4.

Meilgaard, M., Civille, C.V., and Carr, B.T. Sensory Evaluation Techniques, 3^rd ed. Boston, MA: CRC Press, Inc.

Zoecklein, B.W. 1999. New Technologies. In: Vintner's Corner, Vol. 14, #5.

III. Upcoming events - Synergy of Food and Wine, Annual ASEV-ES Meeting

The 25th Anniversary Conference and Symposium of the American Society for Enology and Viticulture-Eastern Section will be held July 19-21 at the Clarion Inn and Conference Center in Ithaca, New York. The symposium topic this year is the synergy of food and wine-the science of creating and marketing wine as food. The purpose of the Society is to promote the development of your industry. Plan on attending this interesting and informative meeting (see attachment for details or call my office for additional information).

IV. Enology - Grape Chemistry Group Web Site

The Enology-Grape Chemistry Group web site now has an active job posting listing employment opportunities in the industry. Additionally, there is a complete listing of all past newsjournals and abstracts of published research.

V. Extension Laboratory Analysis

The Enology-Grape Chemistry Group provides free chemical, physical, microbiological and sensory lab services to the Virginia wine industry. A full description is listed in the group's web site: www.fst.vt.edu/Zoecklein. Due to the high volume of samples submitted, please email the lab prior to sending samples. In the email indicate the wine(s) to be sent, when we should expect them and the desired analyses. This will help to assure timely results! The email address: ldouglas@vt.edu .

VI. Wine Industry Friend Departs

Dr. Cameron Hackney, Head of the Department of Food Science and Technology at Virginia Tech has accepted the position of Dean and Director of the College of Agriculture, Forestry and Consumer Science at West Virginia University.

In his roll as Department Head at Virginia Tech, Dr. Hackney has been instrumental in the University's expanded research and extension programs for the grape and wine industry. His extensive background in research, extension and teaching (he has won awards in each area) gave him a unique perspective as to how each relate to the primary goal of industry development. As a member of the Winegrowers Advisory Board he has helped provide the technical perspective so important for the industry to remain competitive. Through his tireless energy and support, the College and University leadership have an enhanced understanding of the importance of the grape and wine industry to Virginia and the vital roll that Virginia Tech plays in its development. His departure is a loss to Virginia Tech and the Virginia wine industry. His leadership, insight, compassion, and enthusiasm will be missed by all!