Detergents are chemicals designed to assist in the removal of soil from a surface and are available as powders, liquids, foams or gels. Detergents have two modes of action (physical & chemical) depending on their makeup and the soil they are acting upon.
When selecting a detergent, the following points should be considered:
- Type of soil to be removed
- Cleaning method required
- Cleaning equipment available
- Will disinfection be required
- Time window
- Water hardness
- Chemical concentration required
- Water temperature
- Materials of construction
- Operator safety
- Risk to food safety
- Cost
Detergent Components
Surfactants (Surface Active Agents) are an important part of any detergent as they enable the detergent to increase the “wetting power” of water by reducing its surface tension. This ability increases the contact between the soil and the detergent solution and allows it to penetrate the minute irregularities of the dirt more effectively. Four types of surfactants are available, which are:
Anionic - the active part is negatively charged and generally is a good foamer and has good wetting properties.
Cationic - the active part is positively charged and generally is biocidal.
Amphoteric - which is cationic in acid medium and anionic in alkaline medium. Can sometimes be biocidal.
Non-ionic surfactant, these have no overall charge but are very good emulsifying agents.
Sequestrants counteract the effect of water hardness salts, preventing the formation of scale drop out. Scale drop out on surfaces provides a barrier to cleaning and a place where microbes can reside and grow.
Sequestrants bind the calcium/magnesium ions in the hard water to form soluble complexes and thereby prevent scale formation. The level of sequestrant in the detergent and the detergent concentration must be matched to the water hardness and mineral salts that may be present in the soil to be removed.
The base of a detergent will determine what type of detergent it is – alkaline, acid or neutral. For example in an alkaline detergent, the base is usually caustic soda (sodium hydroxide).
In some cases, the detergent may have a chlorine donor that is added to assist in protein and stain removal. The chlorine donor is there primarily for this purpose and not as a biocide.
Inhibitors are sometimes added to detergents to reduce the attack on the metal surface (for instance inhibitors added to hydrochloric acid formulations - Descaler). Alternatively, the formulation may be designed to prevent attack on soft metals such as aluminium, tin and brass (Silicated alkaline products - Chlorfoam 2000).
Alkaline and Caustic detergents are probably the most common detergents used throughout the food industry as they have good fat and protein removal properties and they can be used across a wide spectrum of food manufacturing environments. Both contain sodium hydroxide boosted with surfactants and sequestrants. Caustic detergents contain higher levels of Sodium Hydroxide and generally have higher risk classifications than alkaline detergents. They are corrosive to skin and should always be used in conjunction with the correct Personal Protective Equipment. They may also attack soft metals such as aluminium, tin, brass etc.
Acid Detergents
These are used mainly for protein, mineral and vegetable deposit removal and typically contain phosphoric acid. Acids must never be allowed to come into contact with chlorine compounds because of the consequential release of chlorine gas, which can prove to be fatal.
Neutral Detergents
These are generally blends of surfactants used for manual dishwashing and manual cleaning. They are generally safe to use and are found predominantly in domestic and light industrial use. Gloves should still be worn to avoid de-fatting of the skin and to reduce the risk of dermatitis.
Types of Soil
There are essentially two types of soil:
Organic – These are derived from living matter and include animal fat, vegetable oils, starch, sugars, and proteins from milk, egg, meat or blood. Normally they can be removed by using neutral or alkaline detergents, but if heated, dried or allowed to remain for a prolonged period then caustic detergents may be required to remove them.
When removing liquid protein deposits such as egg, blood or meat it is best practice to begin with a cold water rinse first to prevent “cooking” of the protein. When grease or oil is heated it will form a resolute, dark, sticky polymerised deposit, which can generally be removed with an alkaline detergent. If the polymerised deposit is heated further it results in the formation of carbon, which generally has to be removed by a more aggressive caustic alkali detergent such as sodium hydroxide.
Inorganic – These include water hardness salts (scale), oxidised metals (rust), uric acid salts (urinal stains), beerstone and calcium salts deposited from milk (milkstone). These types of soils are usually removed with acids such as hydrochloric and phosphoric.
Soils are very rarely made up of one component, for example a hard scale in a meat processing area may be a complex of a mineral scale and protein.
Water Chemistry
All water used for domestic and industrial purposes will have hard water salts (calcium and magnesium ions) present.
Water hardness is a measurement of the level of these dissolved solids in the water. These solids may come out of solution and precipitate as a scale under certain conditions; namely:
An increase in water temperature – highest effect as water is raised to boiling point.
As the pH of water is increased; e.g. by adding an alkaline detergent.
The level of hard water salts varies from area to area in the UK, for example, water used in some areas of the north of Scotland will have less than 60ppm (parts per million as CaCO3) hard water salts because the water is generally surface water held in reservoirs and has not passed through limestone deposits. In areas such as the South East where the underlying rock is limestone, water hardness can easily be over 600ppm.