Department of Food Science and Technology
VIRGINIA POLYTECHNIC INSTITUTE
AND STATE UNIVERSITY
Dr. Bruce W. Zoecklein
Wine/Enology-Grape Chemistry,
Blacksburg, VA 24061
Office phone: (540) 231-5325
Fax: (540) 231-9293; e-mail:
www.vtwines.info
Virginia Sauvignon blanc and Pinot Gris
Bruce Zoecklein
Professor and Head, Enology-Grape Chemistry Group
Virginia Tech
www.vtwines.info
The following is adapted from Enology Notes electronic technical bulletins,
available at www.vtwines.info.
Many factors impact the varietal aroma, aroma intensity, and stability of
Sauvignon blanc and Pinot Gris. Of these must composition, yeasts, and oxygen
are of particular interest.
Aroma/flavor. Sauvignon blanc and Pinot Gris juice have simple aromas that
develop considerably during fermentation, and are dominated by relatively few
volatile compounds. The volatiles that contribute to the varietal character are
formed during winemaking from specific aroma/flavor precursors present in the
grapes.
Thios, or complex sulfur-containing compounds, such as 4-MMP, 4-MMPOH and
3-MH, contribute to Sauvignon blanc varietal character. In wines, they provide
odors described as box tree/bloom, citrus zest, and grapefruit/passion fruit,
respectively.
Sauvignon blanc varietal character is produced from S-cysteine (a sulfurcontaining amino acid) metabolism in the plant, and is impacted by the following:
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Soil and climate
Rm 14
bzoeckle@vt.edu
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Fruit maturity
Juice processing
Yeast species and strain
Malolactic fermentation
Aging
Cool nighttime temperatures are important for production and retention of fruit
volatiles in Sauvignon blanc. Ideal conditions reported in parts of the Loire Valley
are 25-27°C daytime temperatures, and 10°C at night, from véraison to harvest.
Nitrogen. There is a relationship between fruit nitrogen and the production of the
aroma precursors for Sauvignon blanc and Pinot Gris. Too little fruit nitrogen
substantially reduces the production, resulting in wines which are described as
less fruity and aromatic, sweaty, and cheesy in character.
The level of fermentable nitrogen for optimizing aroma/flavor is reported to be
between 175 and 300 mg/L (Dubourdieu, 2004). The Enology Service Lab has
been providing the analysis of nitrogen components for the industry as a means
of helping to increase varietal character.
Maturity Evaluation. Aroma precursors are not uniformly distributed in the fruit.
The relative ratio in Sauvignon blanc skins and pulp, respectively, is as follows
(Dubourdieu, 2004):
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4-MMP – 7% and 92%
4-MMPOH – 15% and 85%
3-MH – 50% and 50%
Due to the distribution between skin and pulp, some prefer to taste Sauvignon
blanc whole fruit for maturity evaluation, rather than simply evaluating juice
aroma and aroma intensity. A portion of each of these sulfur-containing
compounds is in the free form, and a percentage bound to other components.
When the whole berry is put into the mouth, some of the bound forms are
believed to be released, making the fruit seem more intense in aroma/flavor than
simply the juice. The obvious problem is the variation in maturity level among
individual Sauvignon blanc berries.
Juice Oxidation. A number of Sauvignon blanc producers blanket their juice with
carbon dioxide during pressing, helping to keep the juice green by minimizing
oxidative degradation. There is an age-old debate regarding the merits of brown
vs. green juice in the fermentor. As new research comes to light, we find that the
dichotomy between green vs. brown relates not simply to style, but also variety.
Both Pinot Gris and, notably, Sauvignon blanc varietal compounds are easily
oxidized. Therefore, protecting them from the impact of molecular oxygen makes
sense. Maximizing the passion fruit notes requires the limitation of oxidative
degradation. Indeed, this is a primary reason why some also add ascorbic acid to
the juice. Ascorbic acid is a very good oxygen scalper, acting much more rapidly
than sulfur dioxide.
Glutathione. Glutathione is an important sulfur-containing compound in grape
juice. This tripeptide is by far the most abundant source of reduced sulfur in the
grape berry. It acts as an antioxidant and helps to stabilize 4-MMP, 4-MMPOH,
and 3-MH. Lees contain glutathione, one reason why lees storage keeps wines
from oxidative degradation.
There are some important steps known to have a positive impact on minimizing
oxidation and the loss of aroma/flavor. These include the following:
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No copper
Low concentration of phenols
Protection from oxidation, via sulfur dioxide, glutathione, and/or lees
storage
Copper is a strong inorganic oxidative catalyst. Copper in the must, from lateseason Bordeaux mix vineyard sprays or any other source, can lower the
longevity of wines like Sauvignon blanc. Copper inactivates glutathione.
The role of glutathione as an oxidative buffer is receiving considerable attention.
Glutathione is produced by the grapevine, and by yeast at the end of
fermentation. Research has shown that grape glutathione concentration declines
at the beginning of fermentation, and then increases again at the completion of
fermentation. The following are important relationships regarding glutathione:
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There is a positive correlation between glutathione and the freshness and
longevity of Sauvignon blanc wines.
There is a positive correlation between the concentration of glutathione in
the must and concentration in the young wine.
There is a positive correlation between the juice free amino nitrogen
concentration and the glutathione concentration at the end of alcoholic
fermentation.
Yeast. Yeast species and strains vary in their abilities to hydrolyze or release
bound compounds to their odor-active forms. In a study reported by de Barros
Lopes (2004), commercial wine yeast strains differed by a factor of 20 in their
release of free 4-MMP from the bound form.
Work by a number of research groups, including ours, suggests that it may be
desirable to have the fermentation conducted by several yeasts, one for the basic
fermentation, and one for increasing the aromatic nature of the wine. This may
be the most effective means of maximizing the grape’s potential.
It is believed that thios, like 4-MMP, are hydrophobic enough to get inside the cell
without an active transport system. Yeasts differ notably in their ability to convert
thios to their odor-active form. Different strains have different genes for cleavage
enzymes, and the enzymes for precursor cleavage of compounds, such as 4MMP and 3-MH, may be different. This may suggest the merit of fermentations
conducted by multiple vs. single genera or strains.
Currently, our processing is a very inefficient means of optimizing aroma/flavor.
Regardless of yeast, it appears that only about 1-5% of the precursor compounds
get converted to their odor-active forms.
Both Pinot Gris and Sauvignon blanc have relatively labile varietal aromas. The
distinctive varietal character of both of these grapes ins a result of careful
management of the must composition, yeasts, and oxygen.