Role of Chemistry in Cleaning
The four primary components of cleaning are:
- Chemical Action
- Mechanical Action
With the exception of Time, each component may be considered a type of energy. Mechanical Action is energy added to the system by scrubbing or spraying, Temperature is heat energy that is added to the system, and Chemical Action is energy added to the system through the use of a chemical cleanser. The chart to the right shows how each of the components adjusts for each other and how increasing the amount of Chemical Action or Temperature may lower the need for Mechanical Action.
There is also a crossover effect in the chemistry involved in almost any cleaning process. Sometimes chemical interactions are actually physical interactions on a very small scale. Silicates are a good example of this — the silica portion of a complex silicate acts physically to break apart flocculated soils but does not interact with the soil in a reactive manner. These types of physical interactions are referred to as physico-chemical and will be discussed below, along with what are considered “typical” chemical interactions, such as the neutralization of acidic soils.
Wetting is responsible for what is often called “the peel-up effect.” Water has an attraction to itself due to hydrogen bonding and that results in a high surface tension. This surface tension causes water droplets to form rather than water simply wetting many surfaces as a sheet of fluid. The surface tension makes it difficult for water to penetrate the space between a soil and a hard surface.
Lowering the surface tension of water will allow it to more easily move between the soil and surface to be cleaned and the soil can then be lifted off. Many things will lower the surface tension of water, but the most efficient materials for doing this are surfactants or detergents. Most cleaning compounds used in brewing or winemaking will have a very low level of surfactant present for this purpose. Although it is strongly advised that you never use a detergent such as a dishwashing soap for cleaning equipment due to the difficulty of completely removing it (even with copious rinsing), the surfactants that you will find in typical cleansers for our industry are at an extremely low level and are selected for their ability to rinse easily.
Deflocculation occurs when large soils that have an affinity for themselves are broken apart. This is an excellent example of a physico-chemical interaction when it is performed by silicates, although alkalis such as soda ash and caustic will also aid this process through chemical degradation.
Smaller soils are more easily removed, suspended, and rinsed by cleansers.
Suspension is the act of keeping dissolved or broken down soils in solution. This is performed by nearly every component of a cleanser although in different ways, either through charge modification, neutralization, dissolution, or emulsification. The bottom line is that suspended soils are easy to remove simply by emptying the container that you are washing and following that with a rinse.
Dissolution occurs when water-soluble soils such as sugars and smaller proteins are dissolved by the cleaning solution. It also refers to what happens when things that aren’t normally soluble in water alone are dissolved. An excellent example of this is when the mineral component of beerstone is dissolved by an acid.
Emulsification is performed by surfactants and alkalis. It occurs when oils and fats are broken into small globules and suspended in the solution (and are thus removed via emptying and rinsing).
Neutralization describes the chemical character change that takes place in acidic soils when they react with the alkaline cleaning solution. Often, acidic soils are not soluble in the cleaning solution or water, but the act of neutralizing them changes the character so they can be dissolved. A more specific term for this reaction is saponification — fatty acids are neutralized into soaps. This is how soaps are formed industrially, and by people who make lye soap.
Oxidation is the last type of reaction that we will discuss here. Free oxygen is provided via an oxidizing agent (if one is contained within the cleanser that you are using) or bleach. Sodium hypochlorite (chlorine bleach) and hydrogen peroxide are both examples of how free oxygen can be brought into a cleaning system. The reaction that follows will both decolorize (bleach) stained substrates as well as break down protein soils so that they may be more easily deflocculated, suspended and dissolved.
An aside on chlorine bleach: Although we tend to think of it primarily as a chlorinated substance (and it is), the strength comes from the alkali used to stabilize it as well as the oxygen entrained by the chlorine and hydrogen atoms (OCl-is effective simply because it aggressively hands off the oxygen). While it is much more aggressive in terms of oxidizing power than hydrogen peroxide (oxygen bleach), it works via the same mechanism. The aggressiveness does count — chlorine bleach can be very detrimental to stainless steel over time, but oxygen bleach is generally harmless.