Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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September/October 2008
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
  • 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.
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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.