by Lance Renfrow and Sofia Herrera
History of Cleaning Products
Currently in the brewing industry, clean-in-place (CIP) clean-ers are vital to preserve the quality of the beer produced. The history of proper cleaning actually goes back to the late 1960s. This primarily dealt with the food and beverage industry. The food and beverage industry has used strong acids and alkali products for cleaning for many years. Caustic soda had been the product of choice because of its excellent organic dissolving and saponification powers. Over the years, compounders have formulated a wide variety of cleaning compounds, with the end user being sold a commercially available concentrated cleaner. When this occurs, many people are unaware of how the additives are used. It is for this reason that the key is to fully understand what these “additives” are and how they function.
Liquid Caustic Soda
The base of many cleaning solutions is caustic soda. Typically, the concentration of a CIP cleaner is 90% caustic soda that is 50% “active” sodium hydroxide. The remaining 10% is often a mixture of other chemical components. Commercially, there are several methods of producing liquid caustic soda. Sodium chloride brine is reacted in a cell with a strong current. This electrolytic reaction with water and salt yields caustic soda, hydrogen, and chlorine. The industry terminology is known as diaphragm, mercury cell, and membrane grade (Fig. 1). The specifications vary by process because the different grades produce low salt, carbonates, and iron.
The current U.S. market for liquid caustic soda is approximately 11 million short dry tons, with a world market of approximately 43 million short dry tons. The market is generally sold on a dry ton basis and is generally billed on the active NaOH content. Most formulators, distributors, or manufacturers, when blending, will sell product on an “as is” pound basis or by the gallon. Some brewers will use high-purity (mem-brane-grade) material because the high chloride content of the lower grades of caustic soda has a long-term detrimental effect on stainless steel.
Formulation of CIP Solutions
Some companies such as Clear Solutions USA blend what is called an “additive package” into the caustic soda to create more effective and efficient CIP solutions. These additive packages often consist of a chelant, a scale inhibitor, a dispersant, and a surfactant. Some ingredients can be multifunctional (Fig. 2).
The CIP formulation should vary from brewery to brewery because the effectiveness of this package depends on operating conditions of temperature, water hardness, pH range, and, lastly, the final percentage of the working solution or the “set point” (Fig. 3).
The operating temperature should be known because certain chemical components are affected by the temperature and may not clean as well in high or low temperatures. The water hard-ness is also important because different amounts of chelating agents and scale inhibitors should be added depending on how high the water hardness. The seasonal variances of the water hardness should also be noted, and the maximum value should be considered in formulating to maximize cleaning efficiency. The pH range determines the type of chelation package. Certain chelators are pH sensitive and should not be used. As an example, ethylenediaminetetraacetic acid (EDTA), which is a common chelant, does not work well in highly alkaline solutions, primarily due to what is known as the equilibrium constant. The final set point should also be known because it determines the final concentration of caustic soda and the additive package. The use of an additive package often will decrease the set point because the additive package greatly increases the cleaning capability of the CIP solution.
Many CIP formulations are considered trade secrets. Once the operating conditions are known, the proper additive package can be determined. This was done by many major breweries and is currently being used today.
Additive Package Components
The word chelant is from the Latin word chela meaning “claw.” Chelants are materials that work in aqueous solutions to tie up metal ions so that they are no longer effective. The term “chelating agent” refers to a molecule that contains two or more complexing sites or claws capable of coordinating around a metal ion. In technical terms, chelation is a kind of sequestration process whereby the chelating agent forms a nonionic ring structure with a dipolyvalent cation by ionic valence bonding. Sequestration, on the other hand, is a generic term that covers all the ways in which chemical species may be protected from unwanted chemical reactions in their solution environment.
Chelation is important because the chelating agents tie up the metal ions in hard water and inhibit their ability to interact with the other cleaning agents. The concentration of chelating agents needed is directly related the water hardness. The harder the water, the higher the concentration required. When formulating a CIP additive package, it is important to note the water hardness as well as the fluctuation of the water hardness in the brewery.
Common chelating agents include gluconates and phospho-nates. Gluconates are very effective at tying up metal ions but their ability to do so is greatly affected by the temperature of the solutions. An increase in temperature decreases the chelation ability. Phosphonates, on the other hand, do not have these temperature dependencies and, thus, are often included in formulations in addition to gluconates to produce a more stable formulation.
Scale is defined as deposit adhering to a surface. The scale inhibitor virtually modifies and attacks the crystal growth by changing the structure and prevents the scale from forming. In the brewing industry, scale can be formed with the presence of calcium, magnesium, iron, and other trace minerals. The most commonly formed scale is calcium carbonate, followed by calcium oxalate (beerstone). Iron is traditionally found in the northeastern part of the United States.
Dispersants attack the undesired species by using a high negative charge. This works much like two magnets with like charges (the magnets repel one another). The charge of the dispersants causes the contaminants to be more suspended within the solution, which allows for easier washing.
The real breakthrough in CIP formulations was the addition of surfactants. Surfactants effectively lower the surface tension of a given solution. The decrease in surface tension allows for easier wetting of a surface as well as easier rinsing. The effect of an increase in wetting can be noted in Figure 4. This increase in wetting allows for less product use because the low surface tension allows for more spreading across a given surface as well as easy removal with a water rinse. Together, this also amounts to a decrease in cleaning time because the product is able to spread across the surface quickly as well as rinse easily.
When first introduced, surfactants led to large amounts of foaming during the cleaning cycle. Over time, new low-foaming surfactants were developed and have eliminated the foam problem. Many of these surfactants are patented or considered trade secrets.
Surfactants are more generally known as synthetic detergents, of which there are four types: anionic, cationic, nonionic and amphoteric. The anionic types are more commonly used in detergent formulations, the most important being the sulfated alcohols and alkyl arylsulphonates. The principal nonionic wetting agents are polyethylene oxides, which are compatible with anionic and cationic types but, unfortunately, can cause excessive foaming. Both anionic and nonionic surfactants have very good wetting, dispersing, and rinsing capabilities but are of little use against most deposits.
The use of surfactants has been limited over the years due to caustic soda’s high concentration (50%). The high concentration of caustic soda limits the ability of the surfactants to couple and causes the product to have difficulty going into solution. Over the years, various surfactants have been created. One in particular, patented by Clear Solutions, is able to re-duce the surface tension of caustic soda from 72 to 19 dynes/cm. One important thing to note about surface tension is that the scale is logarithmic, and a small change in surface tension is actually a large change with respect to wetting capacity.
Benefits of Additive Package
There are numerous benefits to using the additive package, many of which were stated above. Together, the four components allow the alkaline CIP solution to work well in the working conditions of the plant. In summary, the benefits of using properly formatted CIP solutions include:
- Less product use. The consideration of pH, temperature, and water hardness during formulation leads to less product being used because the product is formulated to be more efficient in the working conditions. The surfactant also allows less product to be used because the lower surface tension allows the reduced amount of product to cover a larger area (Fig. 4).
- Less water use. Less water is used because the surfactant allows for easier and faster rinsing, which leads to less water use.
- Shorter cleaning times. Because the cleaning solution has a lower surface tension, it spreads over the surface faster and rinses faster, which ultimately leads to an overall faster cleaning cycle.
- Elimination of beerstone. Perhaps most importantly, when used correctly, the correct CIP formulation will eliminate the problem of beerstone. Many of the calcium ions of hard water are tied up with the chelating agents so that they cannot precipitate out and form calcium oxalate (beerstone). The scale inhibitors as well as the surfactant also make sure there is no surface for the crystal growth.
The elimination of beerstone leads not only to a cleaner tank but also to better tasting beer, which then translates to more profit because customers will always buy the better-tasting beer. The presence of beerstone can lead to poor taste of the product due to its potential effect on the microbiological stability of the system. Beerstone normally has to be removed with the use of an acid beerstone remover such as EDTA, sulfamic acid, or citric acid, among other examples. Once the tanks have been destoned, the incorporation of our CIP product eliminates the need for future removal procedures because our products will prevent beerstone build-up.
CIP Case Study: Clear Solutions USA, LLC
An Arizona-based company called Clear Solutions USA, LLC, has developed a CIP additive package that has been used with major breweries as well as in dairy and other related industries. In particular, a major dairy has utilized these CIP products for over 7 years and has found that the cleaning products result in a 50% decrease in product use and cleaning time. Similar results have been seen in the brewing industry (Fig. 5).
A key component of cleaning is ensuring that the surface is, in fact, clean. Hygiena’s adenosine triphosphate (ATP) sanitation monitoring system effectively measures the cleanliness of a surface. A sample of the contamination of a surface is obtained by wiping a MicroSnap swab across the surface. The swab is then placed in the ATP device, which measures the amount of ATP that is on the surface (Fig. 6). ATP is found in most living organisms and is representative of the amount of contaminants on a given surface.
The effectiveness of our cleaning products has been tested using the universal ATP testing device, with resulting levels of ATP after using the Clear Solutions product being lower than 5 relative light units (RLU). This is significantly lower than the accepted standard for food production of 30 RLU. Please note that different ATP meters have different scales.
To have an effective additive package, CIP must be formulated to address:
- Water hardness
- Maximum temperature in cleaning cycle
- Percent NaOH in working solution
Once properly formulated and included in the CIP cleaning process, shorter wash times can be achieved while using less product.
In summary, the addition of an additive package greatly increases the effectiveness of NaOH in the CIP process. In order to have an efficient additive package, water hardness, maximum temperature of cleaning cycle, and percentage of NaOH in the final solution must be considered. Once properly formulated, the CIP cleaning process can utilize less product and shorter cleaning times.
As far as the brewing industry is concerned, these well-developed CIP products can lead to more efficient use of water be-cause the cleaning cycles are shorter as a result of easier rinsing. The use of these products also prevents the build-up of scale, which ultimately leads to a more efficient brewery and better-tasting beer. The cleanliness of any brewery can then be verified using ATP meters to ensure that great-tasting beer is being brewed.