• Surface Composition. Stainless steel is the preferred surface for food equipment and is specified in many industry and regulatory design and construction standards. For example: 3-A Sanitary Standards (equipment standards used for milk and milk products applications) specify 300 series stainless steel or equivalent. Other grades of stainless steel may be appropriate for specific applications (i.e. 400 series) such as handling of high fat products, meats, etc. For highly acidic, high salt, or other highly corrosive products, more corrosion resistant materials (i.e. titanium) is often recommended.

• Surface Finish. Equipment design and construction standards also specify finish and smoothness requirements. 3-A standards specify a finish at least as smooth as a No. 4 ground finish for most application. With high-fat products, a less smooth surface is used to allow product release from the surface.
• Surface Condition. Misuse or mishandling can result in pitted, cracked, corroded, or roughened surfaces. Such surfaces are more difficult to clean or sanitize, and may no longer be cleanable. Thus, care should be exercised in using corrosive chemicals or corrosive food products.

Environmental Considerations
Detergents can be significant contributors to the waste discharge (effluent). Of primary concern is pH. Many publicly owned treatment works limit effluent pH to the range of 5 to 8.5. So, it is recommended that in applications where highly alkaline cleaners are used, that the effluent be mixed with rinse water (or some other method be used) to reduce the pH. Recycling of caustic soda cleaners is also becoming a common practice in larger operations. Other concerns are phosphates, which are not tolerated in some regions of the U.S., and the overall soil load in the waste stream which contributes to the chemical oxygen demand (COD) and biological oxygen demand (BOD). 

Chemistry of Detergents
Detergents and cleaning compounds are usually composed of mixtures of ingredients that interact with soils in several ways:

• Physically active ingredients alter physical characteristics such as solubility or colloidal stability.
• Chemically active ingredients modify soil components to make them more soluble and, thus, easier to remove.

Physically Active Ingredients
The primary physically active ingredients are the surface active compounds termed surfactants. These organic molecules have general structural characteristic where a portion of the structure is hydrophilic (water- loving) and a portion is hydrophobic (not reactive with water). Such molecules function in detergents by promoting the physical cleaning actions through: emulsification, penetration, spreading, foaming, and wetting. The classes of surfactants are:

• Ionic surfactants which are negatively charged in water solution are termed anionic surfactants. Conversely, positively charged ionic surfactants are termed cationic surfactants. If the charge of the water soluble portion is depended upon the pH of the solution it is termed an amphoteric surfactant. These surfactants behave as cationic surfactants under acid conditions, and as anionic surfactants under alkaline conditions. Ionic surfactants are generally characterized by their high foaming ability.
• Nonionic surfactants, which do not dissociate when dissolved in water, have the broadest range of properties depending upon the ratio of hydrophilic/ hydrophobic balance. This balance is also affected by temperature. For example, the foaming properties of nonionic detergents is affected by temperature of solution. As temperature increases, the hydrophobic character and solubility decreases. At the cloud point (minimum solubility), these surfactants generally act as defoamers, while below the cloud point they are varied in their foaming properties.

Chemically Active Ingredients
Alkaline Builders
Highly Alkaline Detergents (or heavy-duty detergents) use caustic soda (sodium hydroxide) or caustic potash (potassium hydroxide). An important property of these highly alkaline detergents is that they saponify fats: forming soap. These cleaners are used in many CIP systems or bottle-washing applications. Moderately Alkaline Detergents include sodium, potassium, or ammonium salts of phosphates, silicates, or carbonates. Tri-sodium phosphate (TSP) is one of the oldest and most effective. Silicates are most often used as a corrosion inhibitor. Because of interaction with calcium and magnesium and film formation, carbonate-based detergents are of only limited use in food processing cleaning regimes. 

Acid Builders
Acid Detergents include organic and inorganic acids. The most common inorganic acids used include: phosphoric, nitric, sulfamic, sodium acid sulfate, and hydrochloric. Organic acids, such as hydroxyacetic, citric, and gluconic, are also in use. Acid detergents are often used in a two-step sequential cleaning regime with alkaline detergents. Acid detergents are also used for the prevention or removal of stone films (mineral stone, beer stone, or milk stone). 

Water Conditioners
Water conditioners are used to prevent the build-up of various mineral deposits (water hardness, etc.). These chemicals are usually sequestering agents or chelating agents. Sequestering agents form soluble complexes with calcium and magnesium. Examples are sodium tripolyphosphate, tetra-potassium pyrophosphate, organo-phosphates, and polyelectrolytes. Chelating agents include sodium gluconate and ethylene diamine tetracetic acid (EDTA). 

Oxidizing Agents
Oxidizing agents used in detergent application are hypochlorite (also a sanitizer) and -- to a lesser extent -- perborate. Chlorinated detergents are most often used to clean protein residues. 

Food Equipment Cleaning and Sanitizing Continued: Water Chemistry and Quality Page 3