Several factors can influence this
crystallization rate, including: 1) nucleation
(the number of nuclei on which
crystals can form and grow); 2) diffusion
(the rate at which the dissolved
potassiumbitartrate comes into contact
with the crystal formations); 3) the rate
at which crystals grow; and 4) the
grape variety.
There are three methods, or
enhancements, that expedite the stabilization
process:
In the Contact Process, chilled wine
is seeded with potassium bitartrate,
which hastens the crystallization rate.
The crystals left behind are ground and
reused to seed the next batch.
In the Filtration Process, the wine is
filtered through a potassium bitartrate
bed where faster crystallization occurs.
Wine is sometimes passed through this
crystal bed several times until stabilization
is reached.
In the Crystal Flow Process, wine
is chilled to its freezing point,
between 14°F and 21°F, which generates
potassium bitartrate and ice crystals.
These crystals act as nuclei for
further crystal growth. This process
requires the use of scraped-surface
heat exchangers
There are various methods used to
determine stability with respect to
potassium bitartrate crystallization
and they vary depending on the winemaker.
Some of these methods
include:
- Chill proofing followed by a Concentration Product test
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- Chill proofing followed by visual inspection
- Filtering at 25°F for 24 hours followed by visual inspection
- Wine freeze/slush test
- Conductivity test
Electrodialysis -
A technology with legs
In an electrodialysis system, tartaric
acid is removed as the wine passes
through an electric field and separates ions
on anionic and cationic membranes. The
ions are potassium (K+), calcium (Ca++),
and negatively-charged tartaric acids.
In this electrical and chemical
process, the cationic membrane
allows positively-charged calcium
and potassium to pass through, while
the anionic membrane allows negatively-
charged tartaric acid ions to be
removed. One chamber holds the
wine; a second chamber contains a
solution of potassium and calcium
ions that have been extracted by
applying an electric field across the
wine. Water flows through the second
chamber, creating a brine solution
made up of the potassium and calcium
ions.
Electrodialysis technology is used in
a variety of other applications, including
seawater desalinization and food
processing.
Putting electrodialysis to the test
From January through April 2007,
PG&E's Emerging Technologies
Group commissioned BASE Energy to
perform a test at Fetzer Vineyards.
This study assessed the electrical
energy and demand savings of electrodialysis
versus cold stabilization.
For each method, around 20,000 gallons
of 2006 Pinot Grigio
|
| Table I: Cold vs electrodialysis wine stabilization |
|
Cold Stabalization |
Electro-dialysis |
| Energy Consumption |
26,891 kWh |
165 kWh |
| Average demand |
24 kW |
5 kW |
| Increase in water consumption** |
baseline |
3,010 gallons |
| Adjusted energy consumption* |
22,965 kWh |
170 kWh |
| Stabilization period |
1,108 hours |
31 hours |
| Initial conductivity drop |
14.8% |
14.6% |
| Final conductivity drop |
3.4% |
2.5% |
| Volume of stabilized wine |
18,500 gallons |
21,500 gallons |
| Energy intensity |
1,200 Wh/gal |
7.9 Wh/gal |
* The adjusted cold stabilization energy consumption
considers the added tank and bare
pipe insulation. The adjusted electrodialysis
stabilization energy consumption considers
the extra energy needed for wastewater treatment.
The energy consumption for the
increased electrodialysis water consumption is
based on the Secondary Wastewater Treatment
(activated sludge system) Baseline Study.
** Cold stabilization uses water during
clean-in-place and through evaporation; not
measured for this study.
|
were stabilized
in uninsulated, indoor, jacketed
stainless steel tanks. To accurately
compare the electrical energy consumption
of
both systems, it was
determined that use of the
Conductivity Test, wine reaching
2.5% conductivity would be considered
stable.
The study took into account many
testing parameters, including electrical
energy consumption, temperatures,
wine tank levels, water consumption,
flow rates, and wine
conductivity. Each of these items were
monitored and logged for the duration
of the study. A detailed description
of measurement points is
described in Tables III and IV. The
refrigeration required to keep the
wine cool at its baseline temperature
was not subtracted.
|
STARS ED-1600 electrodialysis unit on-site at Fetzer Vineyards. This unit, with a nominal flow
rate of 1600 gallons per hour, was used for production-scale trials at Fetzer during 2007.
Photo courtesy of WineSecrets.
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