Lesson 2 - Cleaning Systems and Control
This lesson explores the concepts of hygienic design and the Cleaning-in-Place (CIP) systems in the brewery. We examine the nature of soils, the chemicals used to remove them and how we can validate cleaning effectiveness. We also consider the optimisation of modern cleaning systems within the brewery.
Acids
In the beverage industry, acid detergents are used for descaling. Scale is composed of metal salts of oxalates, phosphates, carbonates, and silicates, but in reality, is often a complex of inorganic and organic soil. The acid detergent should be able to penetrate the scale, dissolving and lifting it. For this to occur, a strong acid component is required. To facilitate the lifting of scale complexes, a component of the acid formulation is required that will attach itself to metal ions and act as a sequestrant.
Mineral acids, such as nitric and phosphoric acids, are commonly used. Most other mineral acids, such as sulphuric and hydrochloric acid, are extremely corrosive and leach nickel from stainless steel. They are also incompatible with other active components commonly used in cleaning products. Sulphuric acid, however, is better for removing beer stone than nitric and phosphoric and can be used in diluted form on stainless steel for this purpose.
Most acid detergents are made of a blend of phosphoric acid and nitric acid. Nitric acid is a strong hydrolysing and oxidising acid that is good for penetrating scale, particularly scales of inorganic and organic composition.
Phosphoric acid removes scale through hydrolysis and has sequestering properties for easy removal of the dissolved scale. It is also less corrosive than nitric acid.
Acids with a higher level of nitric acid than phosphoric acid are recommended for passivation of stainless steel.
Passivation of new stainless steel means removing the free iron from the surface of the metal using an acid solution. When the surface iron is removed, the other components of the alloy (primarily chromium, often nickel as well) are left behind as a surface layer over the underlying steel. Upon exposure to air, these elements react with oxygen to form an oxide layer that protects the rest of the steel from corrosion.
Formulating acid detergents with wetting agents improves both the penetration of and removal of scale, especially when the soil is mixed organic and inorganic scale. Corrosion inhibitors may be added to reduce the risk of corrosion.