Cleaning is a pretty straight-forward process. Add some soap, scrub and rinse. That’s really all it takes to clean most surfaces. But when it comes to the chemical processes involved in the act, things can get fairly complicated. In fact, soil formation is a pretty complicated process, especially when we talk about brewing. That’s when chemistry becomes even more important because the right chemistry can reduce the amount of energy required to complete the cleaning process, and when “energy” means “elbow grease,” you can see how chemistry makes things easier.
Our goal here is to help you understand the soiling that occurs in brewing, how chemistry can be used to remove it and how the right chemistry can make the process environmentally safe and friendly for you, the people who consume what you brew and the community at large.
Let’s talk about what types of soils occur in the process. You know that quality wort or must is critical to your end result, but these consist of a number of substances that change as the boiling and/or fermentation progresses. You’ve probably noticed that some vessels (like mash tuns, presses, or totes) are fairly easy to clean with a water rinse and a sponge or scrub pad, while boiling vessels and fermenters take a lot more effort. The reactions that result in a hot and cold break are partially to blame, but there is also the association and deposition of minerals and macromolecules that must be considered because they are increased by the heat differential between the fluid and the environment of the vessel, whether it's during a boil or simply during a long fermentation.
Coagulated proteins cling to hard surfaces, such as metal, glass or plastic. Imagine the proteins as being kind of web-like and you can see how they can start to trap minerals, fats or oils. In fact, it is this interaction and trapping that gives rise to complex biofilms, which can be very difficult to remove; a perfect example of this for brewers is beerstone.
Think of soil films as painted surfaces, or at least surfaces that are well-painted. The first coat or primer lays the foundation and gives all future coats a surface to which they will adhere. The second coat and each subsequent coat provide more complete coverage and a thicker layer over the painted substrate. Each of these coats make water, sunlight, and all other sources of weathering less effective in getting to the painted or protected surface.
Unfortunately, the same type of action occurs in your boiling kettle, fermenter and other vessels. This coating occurs as solids settle out from your wort or must and, over time, will lay coating after coating over the surface. It gets worse with a greater temperature difference between the two sides of the surface like, for instance, if you are cooling a fermentation vessel. The bottom line is that soil builds up and if it is not removed completely each time your equipment is used, it will just get harder and harder to remove.
The Role of Chemistry in Cleaning
A well-known graphic in the cleaning industry that is used to describe the major players involved in cleaning a surface is shown in the figure below. It uses a pie-chart to represent each portion of an optimized cleaning system. The pie-chart is important because it shows that each time one of the aspects is changed, the other s must be altered to compensate for that. If the water is hotter, you don’t have to use as much mechanical action (elbow grease), and vice-versa.
The “Cleaning Pie-Chart”
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 actually 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.
Wetting is responsible for what is often called “the peel-up effect.” Water has an attraction to itself due to hydrogen bonding and it results in a high surface tension. This surface tension causes water droplets to form rather than water simply wetting a surface as a sheet of fluid. The surface tension also 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 will have a very low level of surfactant present for this purpose. Although it is strongly advised that you never use a detergent for cleaning brewing equipment due to the difficulty of completely removing it (even with copious rinsing), the surfactants that you will find in typical brewing cleansers 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 in 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.
Choosing a Cleanser
Clearly there is a lot going on when you use chemistry to clean your equipment, but not all cleansers are created equal. The simplest way to determine if the cleanser you are using is helpful is to try multiple products and brands, but there are easier ways. If the cleanser lists the ingredients, look at the label.
Most quality cleansers will incorporate silicates and phosphates that are very helpful, although you may choose not to use a phosphated product. (The problem with phosphates and some other chemicals are discussed below.) Soda ash is generally a large component because it contributes alkalinity and serves as a good “filler.” (“Filler” in the cleansing industry is a substance that allows users to measure out a tablespoon of a reasonably priced product at a time rather than using an eighth of a teaspoon of a very expensive product. Soda ash is called filler because it is inexpensive, not because it is ineffective.
You may also see polyacrylates and surfactants on the label, although they are generally in such small quantities that the manufacturer will not bother to add those to the label.
Finally, you may see a chemical with either “oxygen” or “per” as part of its name, which means that you are getting a product that incorporates oxygen bleach into the system. This can be very helpful, but it will also increase the expense.
(Personal Note: This is an expense that I believe is worthwhile in my own brewhouse.)
Environmental Considerations in Cleaning
Phosphates used in cleaning compounds once had a bad name in environmental circles because they are excellent micronutrients. Too much phosphate can cause algae blooms that will suck the oxygen out of water bodies. “Greening” waterways became a problem of great public concern in the 1970’s and ‘80’s and resulted in heavy-handed phosphate bans. The problem, though, is that phosphates have a singular role to play in cleaning operations and industry was forced to devise new compounds to take their place.
Unfortunately, some of the replacements for phosphates are no better and are sometimes worse. Ethylenediamine Tetraacetatic Acid (EDTA) works very well in handling the mineral component of soils, but it also plays a large role in mobilizing heavy metals. In other words, the biggest problem with EDTA (to date) is that when it finds its way out into nature, it will help mercury to move into active water rather than remaining undisturbed. Other compounds, such as Nitrilotriacetate (NTA) are suspected carcinogens and are banned in some states.
Despite the black eye that phosphates received, they remain one of the best components to use in cleaning. In the European Union (which have banned many cleaning compounds that we use in the States), phosphates are still viable as a cleaning compound in many industries! The bottom line is that phosphates should not be dismissed out of hand if they are present in a quality cleanser. Having said that, we do not use phosphates in our products because we sell our products across the US and in other countries. We cannot anticipate the issues that are facing a particular region and do not wish to contribute to a problem if we can easily avoid it.
Generally speaking, powdered cleansers tend to break down easily into naturally occurring components over time. In fact, breweries have a much harder time in dealing with the actual waste streams from their brewing than with the waste streams from cleaning.
If your concern is minimizing the environmental impact, which is certainly admirable, avoiding the compounds mentioned above -- NTA, EDTA, and phosphates – is a reasonable first step. Using a cleanser with oxygen present would be helpful because that will encourage aerobic organisms to digest the discharged soil and cleaning solution. As a side note, these types of cleansers will have negligible impact on septic systems simply because of the sheer volume of waste typically in a tank and drainage field.