Enology Notes # 98 February
17, 2005

To: Regional Wine Producers

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

Subjects: Wine Closures, continued; American Society for Enology and
Viticulture-Eastern Section; Annual meeting of the American Society for
Enology and Viticulture; Juice and Wine Fining Workshop

I. Wine Closures. As discussed in Enology Notes # 97, as wines age in the
bottle, the oxidation-reduction potential decreases until it reaches a
minimum value, which is largely dependent on the wine and how well it is
sealed.

The nature and intensity of bottle bouquet is, in part, dependent on the
redox potential. Thus, variations in closures and/or closure performance
can impact the redox potential and the sensory characteristics of a wine.
This issue continues the discussion of wine closures and the role of
oxygen.

As discussed in Enology Notes # 97, the ullage space in bottles can be
substantial. I reported that 30-mm headspace for screwcap closures was an
international standard. Such a headspace could provide 9 mL of volume.
However, Bruce Scott of Scott Labs reports that North American standard
cork-finished bottles have fill heights ranging between 61 and 67 mm, with
an average of about 64.

Bruce Scott notes that using a 45- or 49-mm cork in a bottle with a 64-mm
fill height at 20°C provides an ullage space of 19 or 15 mm, respectively.
The throats of bottles average approximately 0.3 mL per mm. This would
result in a 5.7 or 4.5 mL volume at 20°C, using a 45-mm or 49-mm cork,
respectively. If this volume is composed mainly of oxygen (air) it could
impact wine development. Naturally, variation in the oxygen concentration
in the ullage space can result in bottle variation.

Sulfur Dioxide. The free sulfur dioxide and optical density (OD) at 420 nm
are perhaps the best predictive measures of how wines will hold up
post-bottling, regardless of closure type. For example, there is a
non-linear relationship between oxidized character development and the
concentration of free sulfur dioxide. The cut-off appears to be about 13
mg/L free sulfur dioxide for white wines.

As wines develop in the bottle and retain a level of free sulfur dioxide
exceeding 13 mg/L, the likelihood of developing oxidized aroma/flavors is
minimized and the wine will usually remain sound. When the free sulfur
dioxide level drops to less than about 13 mg/L, we can expect perceptible
"developed" and/or oxidative aromas.

A level of 13 mg/L or more free sulfur dioxide should be considered an
average concentration. Naturally, different wines have differing oxidative
buffering capacities due to their redox potential, which is impacted by the
total antioxidant concentration.

Antioxidants include phenols, ascorbic acid, glutathione, sulfur dioxide,
etc. Regardless, small differences in post-bottling sulfur dioxide has been
found to be strongly correlated to later sensory scores (Godden et al.,
2001). Such differences can result from different oxygen levels as
suggested by Brajkovich (2004):

a.. Wine absorbs oxygen at bottling, dependent on the bottling equipment.
b.. Wines continue to absorb oxygen from the ullage gas in the bottle.
c.. With corks and synthetics, this absorption can be from within the
closure.
d.. Oxygen absorption ends within several months if the closure makes a
complete seal.
The ratio of free to total sulfur dioxide may also be important. When there
is a large difference in this ratio, the free is being bound. Several
compounds in wine are active in binding free sulfur dioxide, including
sugars, anthocyanins and acetaldehyde.

Acetaldehyde formation is a direct result of oxygen exposure. Differences
in ratios of free to total sulfur dioxide have been observed in studies
comparing screwcaps with natural and synthetic closures. Presumably, these
differences are due to oxygen.

Monitoring the free sulfur dioxide concentration could be an effective means
of reviewing both the impact of different closures, and how a wine bottled
with a particular closure is holding up. This may allow for a periodic
review of longevity so as to aid in wholesale and retail distribution as
suggested by Godden et al. (2001).

A periodic evaluation of the free sulfur dioxide level from an adequate
number of randomly selected bottles is an effective gauge for monitoring
wine development. Again, if the free sulfur dioxide level in a white wine
is maintained at 13 mg/L or above, oxidative aromas will be minimal.

Naturally, measuring sulfur dioxide concentration and the change in
concentration over time to predict wine longevity implies a certain level
of analytical accuracy and precision. Note that the Ripper titration
method, and associated kits that may employ the same chemistries, may not
be sufficiently accurate for such a review. I suggest using the Aeration
Oxidation method (see Zoecklein et al., 1999), with reference standards.

The Wine/Enology-Grape Chemistry Group is currently evaluating the impact of
accelerated aging, as a means of determining shelf life and differences
among closures. This follows a study conducted by one of our students
several years ago (Mansfield and Zoecklein, 2003). This will be discussed
at the Wine Closure Roundtable to be held this spring (Check future Enology
Notes and my website for the date, time, and location).

It is likely that critical loss of antioxidant levels relate, at least in
part, to oxygen and oxygen permeability via closures. This will relate to
the development of oxidized aroma and flavors, and the variation among
wines bottled with different closure types. More to follow.


II. The American Society for Enology and Viticulture-Eastern Section. All
wineries, regardless of size, operate within the global marketplace. This
marketplace has been subject to a steadily increasing disparity between
wine production and wine consumption.


This disparity (currently estimated at 50 million hectoliters) has resulted
from a dramatic decline in consumption in traditional European
wine-producing countries, and increased production in ever-increasing "new
world" regions and subregions.


What does this imbalance in supply and demand mean to the eastern US wine
industry? It is safe to say that market forces will promote additional
competition, and some producers that do not adjust will not survive. Our
challenge is not unique: like all regions, we need to retain current
customers and persuade potential new ones. How do we do this?


To increase consumption of our region's wines, we need wines with desirable
sensory characteristics, products that present no risk, perceived or real,
to the health of individuals and the environment, and distinctive wines
that are of a competitive price per quality, while remaining profitable.


There is no question that the development and application of new
technologies can assist the industry in meeting these challenges.
Winemakers in our part of the world must become more sophisticated in
applying new technologies, when appropriate, while maintaining the cultural
and traditional nature of our industry.


Through the exchange of scientific research findings, student scholarships,
and practically oriented industry symposia, the American Society for
Enology and Viticulture-Eastern Section has been working to aid the
industry in meeting today's challenges.


A significant portion of the Society's revenues go toward providing
scholarships to viticulture and enology students working throughout the
region. In virtually every state in the Midwest and East, ASEV-ES students
are engaged in practical research studies that could impact our industry.
Most of these students are training to become our industry's future grape
growers and winemakers.


In recent years, the Society has sponsored symposia on a broad range of
practical vineyard and winery issues, including a cork symposium, and
programs on varietal wine production, sparkling wines, wine taints, and
grapes, wines and the environment. The purpose of these programs has been
to provide the best technically oriented information available, to allow
our industry to reach its full potential.


The American Society for Enology and Viticulture-Eastern Section is the
professional society for your industry. Your support of the Society helps
to assure that all of us meet the challenges of today and the future. If
you are not a member, I urge you to become one today. Membership is very
inexpensive.

III. Annual Meeting of the American Society for Enology and Viticulture,
2005. I am pleased to announce that the 2005 annual meeting of the American
Society for Enology and Viticulture-Eastern Section will be held July 13-15
in St. Louis, Missouri, at the Millennium Hotel. This spectacular facility,
on the banks of the Mississippi, is within walking distance of the Arch and
downtown cultural attractions.

The meeting will involve technical presentations, the Viticulture Consortium
East research summit, wine industry trade show, annual banquet, local wine
industry tour, and a symposium.

This year's symposium will involve viticulture and enology discussions, and
sensory evaluations, on the Cutting Edge Varieties: Norton, Pinot Gris,
Traminette, and the cold-hardy Frontenac and La Crescent. Speakers from the
academic community, commercial growers, and winemakers will present
practical information and extensive sensory evaluations. For information,
see the website at www.nysaes.cornell.edu/fst/asev/.

IV. Juice and Wine Fining Workshop. The Wine/Enology-Grape Chemistry Group,
in conjunction with Scott Laboratory, will offer an afternoon advanced
workshop on juice and wine fining, February 28, 2005, at White Hall
Vineyards, from 12:30 to 4:30 pm. Fee is $30. See Enology Notes # 95for
details.

Enrollment for the program is limited. For registration and questions,
contact Terry Rakestraw at 540-231-6805 or .

All past Enology Notes newsjournals are posted on the Wine/Enology - Grape
Chemistry Group's website at: http://www.vtwines.info

To be added to (or removed from) the Enology Notes listserv, send an email
message to with the word ADD or REMOVE in the subject line.

Dr. Bruce Zoecklein

Professor and Enology Specialist

Head, Wine/Enology - Grape Chemistry Group

Department of Food Science and Technology

Virginia Tech, Blacksburg, VA 24061

Wine/Enology - Grape Chemistry Group website:

www.vtwines.info



References

Brajkovich , M. 2004. Bottle maturation. In: New Zealand Screwcap Wine Seal
Initiative. First New Zealand Screwcap Symposium, Marlborough, New Zealand,
November 10-13.

Godden, P., Franccis, L., Field, J., Gishen, M., Coulter, A., Valente, P.,
Hoj, and E. Robinson. Wine bottle closure. 2001. Aust. J. Grape and Wine
Research.

Mansfield, A.K. and B. W. Zoecklein. 2003. Effect of fermentation,
post-fermentation and post-bottling heat treatment on Cabernet Sauvignon
glycoconjugates. Am. J. Enol. Vitic. 54: 99-104.

Zoecklein, B., Fugelsang, K.C. and B. H. Gump. 1999. Wine Analysis and
Production. Kluwer Academics, New York, New York. pp 621.