Enology Notes

Enology Notes #111, January 30, 2006

To: Regional Wine Producers

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

Subject: Virginia Tech Enology Service Lab; Tannin and Color Management and Measurement Short Course; Prebottling Considerations

I. Virginia Tech Enology Service Lab.  As reported in the previous edition of Enology Notes, The Enology-Grape Chemistry Group at Virginia Tech is establishing a fee-based, full-service enology laboratory. This lab will provide chemical, physical, microbiological and sensory analyses, including standardized reagents.

This service will be available to wineries in any state, and to importers and wholesalers. The prices will be competitive, with profits designed to help support extension activities of the Enology-Grape Chemistry Group.

The goal of this analysis program is to provide very rapid turn-around, with optimum precision and accuracy.

A note from Ken Hurley, Enology Service Lab Director:

The purpose of the lab, in my view, is two-fold: to support the wine industry by supplying the best in analytical services, and to foster the laboratory abilities of the winemakers, themselves.

Toward the analytical services goal, the Enology Service Lab is currently being set up. As equipment is obtained and quality control methods put in place, we will provide a list of available analytical services, which will be posted on the Web at www.vtwines.info. The more common services will be available in the coming weeks.

To foster the analytical services that winemakers can do in-house, we will be developing standard sets, available for distribution, which can be used to practice and evaluate the analytical abilities of winery lab technicians. Questions about the lab service, or comments about what services are most important for your vineyard, can be sent to .

II. 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, beginning promptly at 10:30 a.m.

Enology Notes 111 Figure 01

This practically-oriented, advanced program will explore the various influences of phenols listed above, and others. Also discussed, which phenols could/should be monitored, and how they are monitored.

Sensory analyses will be highlighted, and chemical analyses that can be conducted at the winery will be discussed and compared. 

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.

For details, see Enology Notes #109.

III. Pre-bottling Considerations.  This is the time of year when winemakers begin to consider bottling. This last step in the process is the one that can take a well-made, palatable product and turn it into something much less.

There are a number of evaluations (chemical, physical, sensorial and microbiological) that must be conducted prior to bottling. These tests are necessary to ensure maximum quality, stability and longevity.        

Oxidation Potential. You should review your bottling system (including pre-bottling filtration) to know the extent of oxygen pick-up. Optimally, the oxygen pick-up during any transfer, including bottling, should be less that 0.2 mg/L. Oxidation potential can be minimized by bottling with some dissolved carbon dioxide in the wine, and the use of displacement gas in the bottle. Particulates, such as case dust, adsorb air (oxygen) and increase the potential for oxidative degradation. Naturally, the use of vacuum corkers, closure types, fill height, and the temperature of the wine at bottling impact the oxygen pick-up.

Sulphur dioxide. Different wines, bottled under different conditions (including closures), with different release dates and aging expectations, may require different levels of sulfur dioxide at bottling. The concentration of free sulfur dioxide that provides an anti-microbiological impact is determined by the pH.

Most make their additions just prior to bottling, to aid in binding aldehydes and to maintain as much free sulfur dioxide during the bottling as possible. How much is added should be determined, based on the wine’s biological content, wine chemistry, and how much free sulfur dioxide is lost during your bottling operation. Excessive oxygen pick-up during the filtration and bottling, including from not using a vacuum system, reduces the sulfur dioxide concentration notably. Note that sulfur dioxide is not a very good oxygen scavenger (see Enology Notes).

Untypical /Atypical Aging Test of White Wines. Grape nitrogen appears to be related to a sensory phenomenon known as untypical (UTA) or atypical (ATA) aging. This topic has been reviewed in previous editions of Enology Notes (#14, 77, 107).  Some Virginia vineyards experienced moisture stress conditions in 2005, that may increase the incidence of ATA in wines produced from those vines.

Wines with this taint lose varietal character very early, and develop atypical aromas and flavors, described as naphthalene (moth balls), dirty dish rag, wet towel, linden, floor polish, etc., and are characterized by an increase in a metallic-like bitterness that can be associated with reductive-odor defect.

A screening test was provided in Enology Notes #110. If the test is positive, the best course of action is to prevent oxidation, and to add ascorbic acid to the wine after the free sulfur dioxide level has stabilized. Do not use ascorbic acid in the presence of copper. When in doubt, consult my office. Ascorbic acid may, in some circumstances, encourage oxidation.           

Stability Testing. This commonly includes protein, bitartrate and microbiological  reviews. Check heat and cold stability for white wines, as well as pinking potential where there may be a likelihood of pinking. A quantitative test for L-malic acid (vs. paper chromatography) will help assure that wines do not undergo MLF in the bottle (see Zoecklein et al., 1999). If there is a potential for Brettanomyces growth, a biological screening should occur.

Turbidity Testing. Membrane filters are designed only to lower the biological titer. If a wine is not brilliantly clear, it will likely plug membrane filters. Equally important, particulates in the wine impact your perception of the structural and textural elements. This may distort your perception of the wine’s balance, and can be a large palate modifier. Wines that do not clarify naturally should be tested for pectins and/or glucans (see Zoecklein et al., 1999).

Sensory Evaluation, Including Sulfide Screen. Wines should be evaluated with their intended purpose, which is usually as a food complement. In order that this evaluation be a true gauge of the structural, textural and aromatic elements, proper serving temperature and optimal glassware should be used.

Naturally, prior to bottling a sulfite screen should be conducted on all wines, red, white and rosé.

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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