Food Safety and Environmental Services

Food Equipment Cleaning and Sanitizing: Water Chemistry and Quality (Page 1)

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Water comprises approximately 95-99% of cleaning and sanitizing solutions. Water functions to:

• carry the detergent or the sanitizer to the surface;
• carry soils or contamination from the surface.

The impurities in water can drastically alter the effectiveness of a detergent or a sanitizer. Water hardness is the most important chemical property with a direct effect on cleaning and sanitizing efficiency. (Other impurities can effect the food contact surface or may effect the soil deposit properties or film formation.) Water pH ranges generally from pH 5 to 8.5. This range is of no serious consequence to most detergents and sanitizers. However, highly alkaline or highly acidic water may require additional buffering agents. Water can also contain significant numbers of microorganisms. Water used for cleaning and sanitizing must be potable and pathogen-free. Treatments and sanitization of water may be required prior to use in cleaning regimes. Water impurities which affect cleaning functions are presented in Tables 1a and 1b.

Properties of Food Soils
Food soil is generally defined as unwanted matter on food-contact surfaces. Soil is visible or invisible. The primary source of soil is from the food product being handled. However, minerals from water residue and residues from cleaning compounds contribute to films left on surfaces. Microbiological bio-films also contribute to the soil buildup on surfaces. Since soils vary widely in composition, no one detergent is capable of removing all types. Many complex films contain: combinations of food components, surface oil or dust, insoluble cleaner components, and insoluble hard-water salts. These films vary in their solubility properties depending upon such factors as heat effect, age, dryness, time, etc. It is essential that personnel involved have an understanding of the nature of the soil to be removed before selecting a detergent or cleaning regime. The rule of thumb is that acid cleaners dissolve alkaline soils (minerals) and alkaline cleaners dissolve acid soils and food wastes. Improper use of detergents can actually "set" soils, making them more difficult to remove (e.g., acid cleaners can precipitate protein). Many films and bio-films require more sophisticated cleaners which are amended with oxidizing agents (such as chlorinated detergents) for removal. Soils may be classified as:

• soluble in water (sugars, some starches, most salts);
• soluble in acid (limestone and most mineral deposits);
• soluble in alkali (protein, fat emulsions);
• soluble in water, alkali, or acid.

The physical condition of the soil deposits also effects its solubility. Freshly precipitated soil in a cool or cold solution is usually more easily dissolved than an old, dried, or baked-on deposit, or a complex film. Food soils are complex in that they contain mixtures of several components. A general soil classification and removal characteristics is presented in Table 2.

Fat-based Soils
Fat usually is present as an emulsion and can generally be rinsed away with hot water above the melting point. More difficult fat and oil residues can be removed with alkaline detergents which have good emulsifying or saponifying ingredients.

Protein-based Soils
In the food industry, proteins are by far the most difficult soils to remove. In fact, casein (a major milk protein) is used for its adhesive properties in many glues and paints. Food proteins range from more simple proteins, which are easy to remove, to more complex proteins, which are very difficult to remove. Heat-denatured proteins can be extremely difficult. Generally, a highly alkaline detergent with peptizing or dissolving properties is required to remove protein soils. Wetting agents can also be used to increase the wettability and suspendability of proteins. Protein films require alkaline cleaners which have hypochlorite in addition to wetting agents. 

Carbohydrate-based Soils
Simple sugars are readily soluble in warm water and are quite easily removed. Starch residues, individually, are also easily removed with mild detergents. Starches associated with proteins or fat-scan usually be easily removed by highly alkaline detergents. 

Mineral Salt-based Soils
Mineral salts can be either relatively easy to remove, or be highly troublesome deposits or films. Calcium and magnesium are involved in some of the most difficult mineral films. Under conditions involving heat and alkaline pH, calcium and magnesium can combine with bicarbonates to form highly insoluble complexes. Other difficult deposits contain iron or manganese. Salt films can also cause corrosion of some surfaces. Difficult salt films require an acid cleaner (especially organic acids which form complexes with these salts) for removal. Sequestering agents such as phosphates or chelating agents are often used in detergents for salt film removal. 

Microbiological Films
Under certain conditions, micro-organisms (bacteria, yeasts, and molds) can form invisible films (bio-films) on surfaces. Bio-films can be difficult to remove and usually require cleaners as well as sanitizers with strong oxidizing properties. 

Lubricating Greases and Oils
These deposits (insoluble in water, alkali, or acid) can often be melted with hot water or steam, but often leave a residue. Surfactants can be used to emulsify the residue to make it suspendable in water and flushable. 

Other Insoluble Soils
Inert soils such as sand, clay, or fine metal can be removed by surfactant-based detergents. Charred or carbonized material may require organic solvents. 

Quantity of Soil
It is important to rinse food-contact surfaces prior to cleaning to remove most of the soluble soil. Heavy deposits require more detergent to remove. Improper cleaning can actually contribute to build-up of soil. 

Food Equipment Cleaning and Sanitizing Continued: Water Chemistry and Quality Page 2