Caustic soda, also known as sodium hydroxide (NaOH), caustic, and lye, is a strong metallic base. It is used in a wide variety of industries and by consumers for cleaning. Caustic soda is highly corrosive and reactive. In its pure form it is a white solid, however it is sold in the form of flakes, pellets and in a 50% liquid solution with water. It is highly hygroscopic so readily attracts water molecules from the air through absorption and adsorption. If not stored in an air tight container, it will begin to dissolve in the water it attracts. Caustic soda also readily dissolves in ethanol and methanol, though it is less soluble in these than in water. The largest application of caustic soda world-wide is in the paper and pulp industry where it is used to de-ink paper, for bleaching and so on. Other industrial applications include processing of textiles, bleach manufacture, petroleum production and products, aluminum production, chemical processing, water treatment and in detergents. In detergents, caustic is used in soaponification reactions and for anionic surfactants. Caustic soda is a common base in laboratories and used for cleaning in homes. The industrial manufacture of caustic soda involves a chlor-alkali process. Electrolysis is used to separate chlorine and sodium hydorxide. The overall reaction is as follows;
2NaCl (aq) + 2H2O -----> Cl2 (g) + H2 (g) + 2NaOH (aq)
with chlorine at the anode and sodium hydroxide and hydrogen at the cathode. It is imperative that the chlorine and sodium hydroxide are kept separate so that they do not react. This is done in a variety of ways. The three most common are the membrane cell process, the diaphragm cell process, and the mercury cell process. The latter is more controversial in its use due to the environmental and health problems associated with mercury. The largest producer of caustic soda is the Dow Chemical Company which employs the use of the former two in the production of caustic. Due to its high reactivity and corrosiveness, caustic soda must be used carefully by people as it will burn skin and damage eyes. When using caustic soda, individuals need to use safety precautions, such as gloves and glasses.
Application in Wine Microbiology:
In the wine industry, caustic soda is used as a cleaning and sanitation agent and in laboratories. In laboratories and wine testing, sodium hydroxide is used as a base for various tests such as titrations. In wineries, it is used to clean and sanitize surfaces. One application is to clean winery floors, or other surfaces, to prevent corrosion by organic acids from wine. Wine spilled on the winery floor can corrode the floor. Caustic soda, in liquid or flake form, can be put on the floor to neutralize the acid. This is mostly commonly employed on concrete and other porous surfaces. Caustic soda is used to clean and sanitize tank exteriors, usually in a 5% liquid solution. It is also used to remove cells and biofilms from winery surfaces. One study found that of the commonly used detergents tested, caustic soda was the most effective in the removal of cells and biofilms from plastic and metal surfaces. While effective for plastic and metal, caustic soda cannot be used for some winery surfaces, such as oak barrels.
- Foller, P. C. and R. T. Bombard. Processes for the Production of Mixtures of Caustic Soda and Hydrogen Peroxide via the Reduction of Oxygen. J. of Applied Electrochemistry. 1994, 25(7): 613-627.
- Holstein, John. Winery Buildings Sanitation Problems and their Solutions. Am. J. Enol. Vitic. 1960, 11(2): 92-94.
- Joseph, C.M. Lucy, et al. Adhesion and Biofilm Production by Wine Isolates of Brettanomyces bruxellensis. Am. J. Enol. Vitic. 2007, 58(3): 373-378
- “Product Safety Assesment: Caustic Soda.” Dow Chemical Company. http://www.dow.com/productsafety/finder/caustic.htm. Accessed February 20, 2010.