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Cleaning technology and hygiene in food industry - module 2

This module gives an overview on cleaning technologies for cleaning of facilities, machines and other equipment in food industry. We recommend to study the slides presentation of the module first, as it provides the basics within this subject. For students and apprentices, the presentation is available as a PDF file. Teachers should have a look at the summary of didactical components before downloading the original PowerPoint presentation from the restricted area. When you have used the module, we would appreciate your feedback submitted in the online evaluation form. Filling in the module evaluation form will help to improve the quality of the training course. The advanced learners will find on this page a detailed discussion on the types of soil, principles of soil removal. Definitions

Hygienic design and properties of surfaces

Surfaces in food premises should be plain and easy to clean. Additionally, the material should be robust, durable, and resistant to disinfecting agents. Many surfaces in food industry therefore are made of stainless steel, which properties are defined in DIN EN 1672-2. In addition, the European Hygienic Engineering and Design Group developed standards for the design of equipment and machine components (EHEDG Guide No. 8 and 10). According to EHEDG guidelines, average roughness of stainless steel should be at RA 0.8 µm. Surfaces smoother than RA 0.8 µm do not improve cleanability, because particles and bacteria might adhere better onto such surfaces. Cleanability of surfaces is decreased at RA value of 1.0, e.g. at locations with scratches and big pores. Interactions between soil and surface (e.g. repellent coatings) also might be used to improve cleanability.

Soil types in food premises

The soil types found in food premises can be various in nature and can be categorised into soil consisting of:

Cleaning strategies

Depending on the production line and their components, the building cleaner will have to apply a number of different cleaning and disinfection methods. For example do surfaces subjected to regular heating, like surfaces in heat exchangers require another type of cleaning than cold surfaces in storage rooms, pipes, and storage tanks. Alkaline cleaners might be appropriate for cleaning cold stainless steel surfaces but not for removal of mineral and protein encrustations. The choice of cleaning method therefore always is a combination of the type of surface to be cleaned, the type of soiling to be removed, and the geometry of the areas and machines to be cleaned.

Adherence of soil particles on surfaces can be reversed by the impact of the energy. The amount of energy needed is the same as the amount of energy that was released upon adsorption on the surface and can be added by mechanical, chemical, and thermal forces. The type of energy to be employed depends on the type of soiling, strength of interactions between soil and surface, and susceptibility of the surface towards chemical, mechanical and thermal forces. Most cleaning technologies apply a combination of different energies, e.g. a combination of chemical and thermal energy. For industrial cleaning in food industry, mechanical energy is mainly applied by accelerated pellets and fluids, whereas chemical energy is embodied by use of surfactants, and thermal energy by heating. Manual cleaning with wipes and brushes is only applied, if there is no better method, because manual cleaning does not give reliable and reproducible results.

Cleaning in place (CIP) technologies

Cleaning in place denotes a technology applied at closed circuit systems. It denotes cleaning of internal surfaces in tubes, valves, and switch over elements by pumping a cleaning fluid through the system. In general, the pipes are completely flooded without a headspace. Due to the low velocity of cleaning solutions (0.5 – 3 m/s), the energy for soil removal has to be provided by chemical agents of the solvent. The mechanical energy of the solvent pumped through the system however must be sufficient to remove loose soil.

Until the 1950’s cleaning in place was conducted locally with on site filling of liquids into the tube system, manual preparation of working solutions, and discarding of cleaning solvents after one passage. Today’s CIP systems are filled automatically and are characterised by an upstream flow of cleaning solutions, allowing reuse of cleaning solution. Freshwater is only applied for final rinsing. Additionally, heat exchangers are applied for recollection of thermal energy. Depending on the distance between the different CIP units, heating may be conducted locally, avoiding loss of thermal energy caused by long range transportation.

With the computer based control of parameters like time, temperature, concentration, velocity, and pH, cleaning of a CIP system can easily be controlled by machine operators and cleaners.

Cleaning in open CIP systems (OCIP)

Closed systems like storage tanks with big open volumes are denoted as open CIP systems. Such systems are present in the beverage industry. Cleaning of such systems is achieved by spraying and sprinkling systems, which distribute cleaning solution over inner surfaces. Depending on the type of soil spray nozzles are either fixed (many holes covering an angle of 360°) or rotating.


Cleaning of bottles and barrels

An important task in food industry is cleaning of reusable bottles and barrels. It is a delicate task, because small amounts of a contaminant may interact with a relatively huge volume over a long time. The hygiene requirements heavily depend on the type and amount of soil present in the vessels. The soil removing capacity of a cleaning process for used bottles is much higher than the capacity of a cleaning process for unused bottles. Cleaning in automated cleaning systems contains the steps of emptying, pre-rinsing, pressure jet cleaning, alkaline cleaning, rinsing, disinfection, and final rinsing with sterile water. The bottles are mostly submersed into a water bath of cleaning solution. For rinsing steps, water is injected with pressure jet cleaning methods. Cleaning of transportation containers and trading units may be performed using a combination of different techniques such as submersion, pressure jet cleaning. Cleaning of trays used for transportation of unpacked meat generally would include a disinfection step.

Cleaning of open surfaces: Cleaning off place (COP) technologies

Pressure jet cleaning

In this type of cleaning soil is removed by water being forced through a jet nozzle at pressures at 20 – 40 bar. In this range of pressure, elevation of water does not result in aerosols, which is important, because small water droplets may re-contaminate already cleaned surfaces. The cleaning effect is mainly based on mechanical forces, although cleaning detergents can be added. The mechanical forces depend on the angle, pressure, and the distance.


Foam cleaning

Cleaning off place is more and more conducted as low pressure foam cleaning. In this technology a  pre-rinsed surface (jet cleaned with water pressures of up to 30 bar) is covered with a thin layer of foam. After 10 – 20 minutes, dispersed soil is removed with water at temperatures above the melting points of fats (e.g. 60°C in the meat industry). Foam consists of air enclosures coated by a thin layer of surfactant solution. The air enclosures disintegrate upon contact with the surface, thereby forming a thin layer of cleaning liquid. The foam can act as a carrier for cleaning agents, as well as disinfection agents. Because of the adhesive forces, the foam supports the application of liquids on walls and ceilings. A prerequisite is the stability of air bubbles, which should last for at least 10 minutes. The foam acts as a pool that constantly re-generates the liquid layer running off. Foam cleaning can be applied in mobile, manually operated jet pressure units or automated systems, which are for instance used for the cleaning of transportation belts.

High pressure cleaning

In contrast to pressure jet cleaning, high pressure cleaning uses pressurised hot water at short distances (70° C, 40 – 130 bar, 10 – 30 cm). This means that the cleaning effect is predominantly caused by mechanical forces. The energy of a sharply defined aerosol free jet of water hits the surface and virtually chops off the soil. Systems with pressures of more than 2,000 bar can be in operation for cleaning of clogged tubes in heating units for high temperature treatment of milk in dairies. Due to the safety risks, of operating at such high pressures, this type of cleaning can only be conducted by specialised firms.  

Dry ice cleaning

Cleaning without water, using carbon dioxide pellets (CO2 at - 78°C) is an established method for the removal of sticky soils like dough or chocolate. Another application is the cleaning of coffee soils. The technology shoots small pellets at velocities of 400 m/s onto the soiled surface. The cleaning effect is based on the physical properties of the carbon dioxide ice which

The energy released while hitting the surface transforms the ice pellet into CO2 gas (sublimation). As the sublimation rapidly expands the volume of CO2 by a factor of 700, the soil breaks into pieces which are easily removed by the air flow. See also the video on dry ice cleaning by Danduct.

Supersonic cleaning

Cleaning with ultra sonic waves is a procedure for delicate surfaces that can not be cleaned by normal mechanical or chemical means. It is also used for objects with a complex geometry (outlets, cones, undercuts. Knives and saw blades at meat cutters are efficiently and gently cleaned by ultrasonic cleaning in a water bath. The application of sound waves at frequency at 16 kHz – 1 GHz with intensities of more than 1 W/cm2 primarily generates and destroys small air bubbles in the water medium. The water running back into the imploding voids - causing microscopic jet streams - has enough velocity to remove soil from surfaces. The technique is used for the cleaning of knifes, boxes, and casting moulds for cheese.

Assessment of cleanability

Cleanability of process equipment and components can only be evaluated by microbiological investigations. A method for the investigation of pumps has been published Benetzech et al [A new test method for in-place cleanability of food processing equipment, Journal of Food Engineering No 54(1), 2002]. A good source for current methods for the evaluation of food processing equipment (pipe coupling, membrane filters, etc.) is the web page of the European Hygienic Engineering & Design Group (http://www.ehedg.org/).