Module 7. Cleaning and sanitation

Lesson 12

12.1 Introduction

Cleaning is the process of removing food and other types of soil from a surface, such as utensils and equipments used in dairy and food industries etc. Cleaning is accomplished using a cleaning agent that removes food, soil, rust stains, minerals, or other deposits. The right cleaning agent must be selected because not all can be used on food-contact surfaces. (A food-contact surface is defined as a surface of equipment or utensil with which food normally comes into contact or a surface of equipment or a utensil from which food may drain, drip, or splash into a food or onto a surface normally in contact with food.) Sanitation of a food-processing plant involves keeping product con­tact surfaces of utensils and equipment clean and sterile. Clothing, air, packing materials, and product non contact surfaces of equipment, floors, walls, and ceilings must be sanitized to minimize contamina­tion of the products from these sources. The bodies, particularly the hands, of employees are also sources of contamination, therefore high standards of personal health and cleanliness must be insisted upon. Moisture and heat contribute to microbiological insanitation of both product and environment. Moisture on product contact surfaces and in the products provides a medium through which nutrients become available to microorganisms and in which microorganisms may find other conditions suitable to their life processes. The physiological processes of viable microorganisms can adversely affect the safety and quality of milk and milk products.

12.2 Types of Soil

The types of soil which the dairy-processing industry must remove from its equipment are as follows:
  • Liquid milk films,
  • Air-dried films,
  • Heat-precipitated films,
  • Heat-hardened films,
  • Milk stone, and
  • Miscellaneous foreign matter.
Microorganisms are not included separately here as a type of soil to be removed. Any viable microorganisms in the dairy-processing equip­ment constitute a distinct danger. Such microorganisms must be destroyed by proper sterilization or removed. Otherwise, the sanitizing process is incomplete. "Viable microorganisms" should therefore be added to this list.

Cleaning or sanitizing product contact surfaces of dairy apparatus, utensils, and equipment involves washing, or cleaning, and sterilizing; sanitizing includes both. Care must be taken to protect the surfaces from undue wear, erosion, or corrosion which shorten their useful life.

Soluble soil will dissolve and carried out in rinse or wash water. Insoluble soil components may have to be treated with a chemical detergent to make them soluble or to soften them so they are more easily removed.

12.3 Sanitizing Material

12.3.1 Water

As a solvent, water carries both dissolved materials in solution and suspended materials including soil components. Water serves as a means of applying physical force during rins­ing, surging, and jetting. It is the medium through which heat is applied during cleaning. The physical, chemical, and microbiological properties of the water supply are important when used for the sanita­tion of the dairy-processing plant.

12.3.2 Heat

It is important in cleaning and sterilizing dairy equipment. It increases both the speed of chemical actions and the dissolving capacity and solute holding capacity of water. If present in sufficient quantities, heat can destroy the viability of microorganisms. In hand washing procedures the amount of heat must be rigidly limited to prevent dis­comfort or injury to the workers hands. In mechanical washing procedures more heat is used. Its use must be controlled; however, to assure that cleaning is not made more difficult by hardening any soil on the product contact surface, and that the equipment surface or surface materials are not damaged. The cleaning solution is warmed or heated with steam. Steam can be used either to heat product contact surfaces so they dry quickly after washing or to sterilize such surfaces. A jet of steam is sometimes used to provide physical force surge and mix washing solutions in addition to heating them.

12.3.3 Chemicals are used in sanitation procedures for two principal reasons

1. To change soil so as chemically to soften, disperse, or dissolve it.

2. To destroy the viability of microorganisms. These chemicals are either detergents or sterilants.

12.3.4 Detergents

Detergents include soaps, inorganic alkaline materials, acids, organic surface active or wetting agents, chelating chemicals, sequestering agents, sterilants, emulsifiers, colloids, abrasives, and inhibitors. The detergents to be used are selected according to the type of soil to be removed, the characteristics of the materials of which the soiled surface is made, the cleaning facilities and procedures to be employed, the characteristics of the water, and the cost of the detergents.

12.3.5 Soaps

Soaps are used mainly for washing clothes, floors, walls, and win­dows. They are not suitable for product contact surfaces because they leave a film which is difficult to remove and which may leave undesirable flavors of odors which are absorbed by the product. Mild soaps are excellent for washing hands, and should always be available in the milk-processing plants for this purpose.

12.3.6 Alkaline detergents

These are generally available and economical. The more common of these are sodium hydroxide or caustic soda (NaOH); sodium bicarbonate, (NaHCO3); sodium carbonate or soda ash (Na2CO3); sodium sesquicarbonate (Na2CO3 ·NaHCO3 ·2H2O), and trisodium phosphate (Na3PO4 ·12H2O). Others have more recently come into use for specialized cleaning purposes. Two of these are sodium meta silicate( Na2SiO3 ·5H2O); and sodium hexametaphosphate, (NaPO3)6.

12.3.7 Acids

Acids have come into increasing use as dairy detergents. They are generally used in weak solutions of about 0.1 % or slightly more. Those more commonly used are phosphoric and nitric acids.

12.3.8 Surface active agents

Surface active agents are those which include such materials as sodium alkyl sul­phates and quaternary ammonium compounds. These materials help a detergent solution at surfaces or interfaces to spread the solution and to penetrate the sole.

The penetration of the soil carries the detergent not only into the soil, but also to the equipment surface beneath the soil. While both these actions assist the cleaning process, the latter is particularly important for it is the equipment surface that must be cleaned. These materials may also assist in stabilizing dis­persions and emulsions, helping to keep particles of undissolved soil, once that soil is physically removed from the equipment surfaces, from settling out and returning to that surface during cleaning. The wetting property of a material can be illustrated by plac­ing a drop of petrol in the palm of the open band. The petrol instantly spreads over a portion of the palm surface. In contrast, a drop of water similarly placed in the hand will usually remain as a high compact drop, drawn by its own surface tensions as it is repuls­ed by the naturally oily condition of the skin surface.

12.3.9 Chelating agents

These are used along with other detergents, especially in hard water. They react with metallic ions, particularly Iron and copper, to form soluble compounds. Ethylene diamine tetra acetic acid and its sodium salts are frequently used as chelating agents. Chelation can be thought of as a selective form of sequestration. The action of sequestering agents is similar to chelaters, but involves a greater variety of ions including heavy metals and earth alkalies. Polyphosphates are often included in dairy detergent formulae for then sequestering properties.

12.3.10 Emulsifiers

Emulsifiers strengthen the ability of the solution to hold unsaponified fat which may be released from the product contact surface during the cleaning process. Materials which are suspended and emulsified pass out readily with the wash or rinse water.

12.3.11 Abrasives

These are irregular hard particles of sand, pumice used for grinding, abrading, or polishing. They might be included in a detergent mixture for very special uses such as cleaning floors or walls. Unless properly selected, especially for particle size, and properly used, they will etch and abrade most surfaces making many of them more difficult to clean properly thereafter. This action is particularly undesirable on a product contact surface.

12.3.12 Inhibitors

Inhibitors prevents chemical action between two materials. They are used in dairy detergents to protect aluminum and tin surfaces from alkali or acid detergents. Sodium metasilicate is used to protect aluminum; concentrations of up to 0.5% in the washing solution are suggested. For the protection of tin, sodium sulphite can be used in concentrations of 0.25% or slightly more in the washing solution.

Chemicals and heat are sterilants widely used in dairy and other food industries for the microbiological sanitation of product contact surfaces. Chlorine, in solutions of sodium or calcium hypochlorite, is the most widely used of the chemical sterilants. For proper micro­biological sanitation the chlorine solution used in dairy-cleaning operations should contain between, 50 and 300 ppm available chlorine. Equipment can be immersed in, or rinsed with; the chlorine solution or the solution can be sprayed on product contact surfaces. Contact of the solution with the entire surface involved must be assured. Chlorine is effective over a wide range of temperature. Hydrogen peroxide has been used to sterilize packaging material surface in aseptic packaging of heat-treated milk. Where available, quaternary ammonium compounds and iodophore might be used for sterilizing equipment. The causticity of several alkaline detergents gives them some germicidal property, but this is not sufficient to assure adequate microbiological sanitation in the dairy. Care must be taken in using any chemical in dairy equipment to assure that residues which may be carried into the product do not exceed legal limits.

12.4 Heat in Sanitation

In sterilizing equipment, heat is applied by using hot air hot water, or steam. Some laboratory apparatus can be sterilized in hot dry air. The exposure recommended is 160°C for two hours or more. This procedure is not common for utensils and equipment used in the procurement, processing, packaging, and storage of dairy products. Because the thermal death point of microorganisms found in milk and milk pro­ducts and dairy equipment, and their ability to survive high tempera­tures, Surfaces should be exposed to water hot enough to maintain a surface temperature in excess of 85°C for at least five minutes. If a higher degree of sterility is required steam must be used instead of hot water. The nutrient media and certain other materials used in microbiological tests of milk and milk products must be heated with steam in an autoclave up to 121°C for at least 20 minutes; this requires 1.055 kg/cm2g of steam pressure. Milk lines should be heated to 112°C, requiring about 0.5 kg/cm2 of steam pressure in the lines. Steam can be applied by directing steam into the equipment long enough for product contact surfaces to be heated to at least 100°C. Where it is possible to check the temperature of the condensate flowing from a piece of closed equipment into which steam flows, sterility is considered complete when the condensate temperature reaches 100 °C.

12.5 Sanitizing Equipment

The bare hand is perhaps the oldest "tool" or "piece of equipment" used in washing procedures, but its use is increasingly limited in modern dairy plant sanitation.
  • A piece of cloth held in the hand may be used for washing. How­ever, the cloth can be source of microbiological contamination or of odors. These preclude its use.
  • Brushes are commonly used in dairy-cleaning operations to apply physical force to surfaces, particularly to corners not easily reached. Their bristles physically remove particles of soil which otherwise might remain. The composition of the cleaning solution and the temperature at which it is used as well as the shape and size of the item being cleaned are some of the factors involved in selecting the right brush. If a brush is not properly selected or used, its bristles might abrade equipment surfaces, or it may prove of no use in the cleaning procedure.
  • Scouring pads, that is pads or wads of shavings or shreds of metal or plastic, are not regularly used in dairy-plant cleaning, but can be useful for specific purposes. Such pads must be used cautiously for they can badly damage a finely polished product contact surface.
  • Movement of solutions during the washing process, if rapid enough, can provide effective physical force during the cleaning operation.The surging of the solution helps to keep freed soil particles in sus­pension so they are removed with the washing solution. This action also facilitates dissolution of any soluble materials present.
  • Water or washing solution is often applied in a high speed stream produced by forcing the material through a small opening or jet. Such force is very effective in dislodging materials adhering to surfaces. The pressure on the washing solution the diameter of the jet orifice, the distance from the tip of the jet to the surface being cleaned, the extent to which the jet stream is diverted or dissipated by any liquid through which it must flow, and other factors determine the effectiveness of a jet stream as a physical force in cleaning operations. Smaller items of equipment are usually washed and/or soaked in a special wash tank or vat which holds a quantity of the washing solution.
12.5.1 Sanitizing procedures

Sanitizing the surfaces of dairy apparatus, utensils, and equipment involves certain well-defined steps: 1. Drain 2. Rinse 3. Wash 4. Rinse 5. Sterilize 6. Drain 7. Dry.

Initial draining removes some of the product or soil residue. Residue loosely adhering to the soiled surface will be flushed out with the rinse water. Ordinary water is used for rinsing since it is plentiful and inexpensive. This rinse water might be warmed slightly to soften and remove fat along with other residues. Cold water hardens the fat and causes it to adhere more firmly to the surfaces. If the rinse is too hot, however, it will harden some of the nonfat soil, making it more difficult to remove later on.

The wash water is warmed to a temperature the hand will tolerate for hand washing, or to a temperature near boiling for mechanical washing. The wash water shall contain the selected detergents in a con­centration appropriate for the particular cleaning task. Washing in­volves the use of both chemical and physical forces. The chemical pro­perties of the detergent in warm or hot solution when in contact with the soil is the chemical force. The manner in which the deter­gent solution and physical forces are applied must be regulated accord­ing to the soil involved. Soaking softens and dissolves fractions of most soil.

After washing, the wash water or detergent solution is drained out and the cleaning surface rinsed with clean warm water to remove remnants or traces of both the soil and the detergent solution. The order of the steps which then follow will depend upon the choice of sterilants. The problem with using a detergent which contains a sterilant is that of assuring the rinse which follows washing does not defeat what the sterilant accomplished. For the final rinse, water which is micro­biologically clean and is therefore not a possible source of recontaminate is required. Separate sterilization might follow the use of a detergent, even one which contains a sterilant, to assure microbio­logical sanitation.

When hot water or a solution of chlorine is used, draining and drying follow the rinsing or the sterilization. When steam is used for sterilization, as in the mechanical can washer, it should be dry steam to facilitate the evaporation of any moisture adhering to the cans. When properly used, steam helps dry the can as well as sterilize it. The direct use of steam for sterilizing bottles is not advisable, as they susceptible for breakage thermal shock

Many variations in the washing materials and cleaning equipment will be employed, and sanitation procedures will differ with the type of soil and the type of equipment being cleaned. More detailed infor­mation for each of many specific problems of sanitation encountered in the dairy-processing industry may be found elsewhere.

Last modified: Friday, 5 October 2012, 6:47 AM