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Food-Info.net> Topics > Food Engineering > Hygienic Engineering > EHEDG Documents

Hygienic Design Guidelines

(As published by EHEDG)

The EHEDG (European Hygienic Engineering and Design Group) is a consortium of equipment manufacturers, food industries, research institutes, universities and public health authorities, founded in 1989 with the aim to promote hygiene during the processing and packing of food products.

European legislation requires that handling, preparation, processing, packaging, etc. of food is done hygienically, with hygienic machinery in hygienic premises. How to comply with these requirements, however, is left to the industry.

To assist in the design of safe and hygienic machinery, EHEDG has published a number of guidelines. In co-operation with Food-Info.net and Elsevier Scientific Publishers, the summaries of the guidelines are published here. The full documents are available on the EHEDG website.

The published guidelines are shown in the table below.
( Please click on the titles, if underlined, to read the summary)

 

Guideline Title
1 Microbiologically safe continuous pasteurisation of liquid foods, 1992
2 A method for assessing the in-place cleanability of food processing equipment.
3 Microbiologically safe aseptic packing of food products, 1993
4 A method for the assessment of in-line pasteurisation of food processing equipment.
5 A method for the assessment of in-line sterilisability of food processing equipment.
6 The microbiologically safe continuous flow thermal sterilisation of liquid foods.
7 A method for the assessment of bacteria-tightness of food processing equipment.
8 Hygienic equipment design criteria, 2004
9 Welding stainless steel to meet hygienic requirements, 1993
10 Hygienic design of closed equipment for the processing of liquid food, 1993
11 Hygienic packing of food products, 1993
12 The continuous or semi-continuous flow thermal treatment of particulate foods, 1994
13 Hygienic design of equipment for open processing, 1996
14 Hygienic design of valves for food processing, 2004
15 A method for the assessment of in-place cleanability of moderately sized food processing equipment.
16 Hygienic pipe couplings, 1997
17 Hygienic design of pumps, homogenisers and dampening devices, 2004
18 Passivation of stainless steel, 1998
19 A method for assessing the bacterial impermeability of hydrophobic membrane filters.
20 Hygienic design and safe use of double-seat mixproof valves, 2000
21 Challenge tests for the evaluation of the hygienic characteristics of packing machines, 2000
22 General hygienic design criteria for the safe processing of dry particulate materials, 2001
23 P roduction and use of food -grade lubricant s, 2002
24 The prevention and control of Legionella spp (incl Legionnaires Disease) in Food Factories, 2002
25 Design of Mechanical Seals for hygienic and aseptic applications , 2002
26 Hygienic Engineering of Plants for the Processing of Dry Particulate Materials, 2003
27 Safe Storage and Distribution of Water in Food Factories, 2004
28 Safe and hygienic water treatment in food factories
29 Packing systems for solid foodstuffs
30 Air Handling in the Food Industry
31 Hygienic Engineering of fluid bed and spray dryer plants
32 Materials of construction for equipment in contact with food
33 Hygienic Engineering of Discharging Systems for Dry Particulate Materials
34 Integration of Hygienic and Aseptic systems, March 2006.
35 Welding of Stainless Steel tubing in the food industry
36 Hygienic engineering of transfer systems for dry particulate materials

 

1. Microbiologically safe continuous pasteurisation of liquid foodsid soil to drop or to be drawn into the main product or container.

There are many reasons why, in practice, pasteurised products sometimes present a microbiological health hazard. Due to distribution in residence time, not all products may reach the temperature required for pasteurisation or may do so for too short a time. Further, there may be a risk of contamination with a non-pasteurised product, or the cooling medium. This document describes the requirements particularly for liquid foods without particulates.

 

2. A method for assessing the in-place cleanability of food processing equipment.

The method is intended as a screening test for hygienic equipment design and is not indicative of the performance of industrial cleaning processes (which depend on the type of soil). See Doc 15 for a test procedure designed for moderately sized equipment. cleanability trials.

 

3. Microbiologically safe aseptic packing of food products.

This guideline stresses the need to identify the sources of micro-organisms that may contaminate food in the packaging process, and to determine which contamination rates are acceptably low. It clarifies the difference in risk of infection between aseptic processing and aseptic packing and recommends that aseptic packing machines be equipped with fillers that are easily cleanable, suitable for decontamination and bacteria-tight. Requirements for the machine interior include monitoring of critical decontamination parameters. See also Doc 21 on challenge tests. Extended summary (pdf)

 

4. A method for the assessment of in-line pasteurisation of food processing equipment.

Food processing equipment that cannot be or does not need to be sterilised may need to be pasteurised to inactivate relevant vegetative micro-organisms and fungal spores. It is important to test the hygienic characteristics of such equipment to ensure that it can be pasteurised effectively. This document describes a test procedure to determine whether equipment can be pasteurised by circulation with hot water. Extended summary (pdf)

 

5. A method for the assessment of in-line sterilisability of food processing equipment.

Food processing equipment may need to be sterilised before use, and it is important to ensure that the sterilisation method applied is effective. Thus, it is necessary to determine under which conditions equipment can be sterilised. This paper details the recommended procedure for assessing the suitability of an item of food processing equipment for in-line sterilisation. It is advisable to conduct in-place cleanability trials (see Doc 2) prior to this test in order to verify the hygienic design of the equipment. Extended summary (pdf)

 

6. The microbiologically safe continuous flow thermal sterilisation of liquid foods.

Thermal sterilisation is aimed at eliminating the risk of food poisoning and, when used in conjunction with aseptic filling, at achieving extended product storage life under ambient conditions. Whereas pasteurisation destroys vegetative micro-organisms, sterilisation destroys both vegetative micro-organisms and relevant bacterial spores. This document presents guidelines on the microbiologically safe continuous sterilisation of liquid products. The technique of Ohmic heating was not considered in this paper but may be included in an update being prepared. See Doc 1 for guidelines on continuous pasteurisation of liquid foods. Extended summary (pdf)

 

7. A method for the assessment of bacteria-tightness of food processing equipment.

This document details the test procedure for assessing whether an item of food processing equipment, intended for aseptic operation, is impermeable to micro-organisms. Small motile bacteria penetrate far more easily through microscopic passages than (non-motile) moulds and yeast. The facultative anaerobic bacterium Serratia marcescens (CBS 291.93) is therefore used to test bacteria-tightness or the impermeability of equipment to micro-organisms. The method is suitable for equipment that is already known to be in-line steam sterilisable (see also Doc 5). Extended summary (pdf)

 

8. Hygienic equipment design criteria.

This guideline describes the criteria for the hygienic design of equipment intended for the processing of foods. Its fundamental objective is the prevention of the microbial contamination of food products. It is intended to appraise qualified engineers who design equipment for food processing with the additional demands of hygienic engineering in order to ensure the microbiological safety of the end product. Upgrading an existing design to meet hygiene requirements can be prohibitively expensive and may be unsuccessful and so these are most effectively incorporated into the initial design stage. The long term benefits of doing so are not only product safety but also increased life expectancy of equipment, reduced maintenance and consequently lower operating costs. This document, first published in 1993, describes in more detail the hygienic requirements of the Machinery Directive (98/37/EC ref. 1). Parts of it have subsequently been incorporated in the standards EN1672-2 and EN ISO 14159.

The full text of Guideline 8.

 

9. Welding stainless steel to meet hygienic requirements.

This document describes the techniques required to produce hygienically acceptable welds in thin walled (<3 mm) stainless steel applications. The main objective was to convey the reasons and requirements for hygienic welding and to provide information on how this may best be achieved. This document is superseded by Doc 35, recently published. The subgroup will continue with a guideline on inspection of the quality of welds in food processing machinery. Extended summary (pdf)

 

10. Hygienic design of closed equipment for the processing of liquid food.

Using the general criteria for the hygienic design of equipment identified in Doc 8, this paper illustrates the application of these criteria in the construction and fabrication of closed process equipment. Examples, with drawings, show how to avoid crevices, shadow zones and areas with stagnating product, and how to connect and position equipment in a process line to ensure unhampered draining and cleaning in-place. Attention is drawn to ways of preventing problems with joints, which might otherwise cause leakage or contamination of product.Extended summary (pdf)

 

11. Hygienic packing of food products.

Products with a short shelf life, or whose shelf life is extended by cold storage or in-pack heat treatments, do not have to conform to such strict microbiological requirements as aseptically packaged foods (Doc 3 discusses aseptic packing). This paper discusses the packing of food products that do not need aseptic packing but which nevertheless need to be protected against unacceptable microbial contamination. It describes guidelines for the hygienic design of packing machines, the handling of packing materials and the environment of the packing machines. See also Doc 21. Extended summary (pdf)

 

12. The continuous or semi-continuous flow thermal treatment of particulate foods.

Thermal sterilisation is a process aimed at eliminating the risk of food poisoning and, when used in conjunction with aseptic filling, it aims to extend product storage life under ambient conditions. This is achieved by the destruction of vegetative micro-organisms and relevant bacterial spores. Liquid foods containing particulates are inherently more difficult to rocess than homogenous liquids due to heat transfer limitations in particulateeliquid mixtures and the additional problems of transport and handling. This paper presents guidelines on the design of continuous and semicontinuous plants for the heat treatment of particulate foods. Ohmic heating techniques are not covered. See also Doc 1 on continuous pasteurisation and Doc 6 on sterilisation of liquid products without particles. Extended summary (pdf)

 

13. Hygienic design of equipment for open processing.

It is important that the plant design takes into account factors affecting the hygienic operation and cleanability of the plant. The risk of contamination of food products during open processing increases with the concentration of micro-organisms in the environment and their opportunity to grow in poorly designed equipment. This means that in open plants, environmental conditions, in addition to appropriate equipment design, have an important influence on hygienic operation. The type of product and the stage of the manufacturing process must also be taken into consideration. This paper deals with the principal hygienic requirements for equipment for open processing and applies to many different types, including machines for the preparation of dairy products, alcoholic and non-alcoholic drinks, sweet oils, coffee products, cereals, vegetables, fruit, bakery products, meat and fish. It describes methods of construction and fabrication, giving examples as to how the principal criteria can be met. See also guidelines on hygienic design criteria (Doc 8), hygienic welding (Doc 9), and the hygienic design of equipment for closed processing (Doc 10). Extended summary (pdf)

 

14. Hygienic design of valves for food processing.

Valves are essential components of all food processing plants and the quality used strongly influences the microbiological safety of the food production process. These valves must
therefore comply with strict hygienic requirements. The guidelines apply to all valves used in contact with food or food constituents that are to be processed hygienically or aseptically. Aside from general requirements with regard to materials, drainability, microbial impermeability and other aspects, additional requirements for specific valve types are also described. See also Doc 20 on double-seat mixproof valves. Extended summary (pdf)

 

15. A method for the assessment of in-place cleanability of moderately sized food processing equipment.

This document describes a test procedure for assessing the in-place cleanability of moderately sized equipment, such as homogenisers. The degree of cleanliness is based on the removal of a fat spread soil, and is assessed by evaluating the amount of soil remaining after cleaning by visual inspection and swabbing of the surface. This method is not as sensitive as the microbiological method described in Doc 2. Extended summary (pdf)

 

16. Hygienic pipe couplings.

This paper identifies and defines critical design parameters for welded pipe couplings: easily cleanable in-place; easily sterilisable in place; impervious to micro-organisms, reliable and easy to install. Gaskets of various types were tested for reliability and hygienic aspects using EHEDG cleanability test methods and repeated sterilisation. The objective was to provide a reliable dismountable joint which is bacteria-tight at the product side under the conditions of processing, cleaning and sanitation. Extended summary (pdf)

 

17. Hygienic design of pumps, homogenisers and dampening devices.

This paper sets the minimum requirements for pumps, homogenisers and dampening devices for hygienic and aseptic applications. The scope includes all pumps intended for use in food processing, including centrifugal, piston, lobe rotor, diaphragm, screw and gear pumps. The requirements also apply to valves integral to the pump head and the complete homogeniser head. Design aspects and the characteristics of materials, surfaces and seals are discussed and additional requirements for aseptic equipment are identified. Extended summary (pdf)

 

18. Passivation of stainless steel.

Passivation is an important surface treatment that helps assure the successful corrosion resistant performance of stainless steel used for product contact surfaces (e.g. tubing/piping, tanks and machined parts used in pumps, valves, homogenisers, de-aerators, process monitoring instruments, blenders, dryers, conveyors, etc.). The purpose of this document is to provide manufacturers, users and regulatory personnel with basic information and guidelines relative to equipment passivation. The complete passivation process is described and environmental, as well as safety, concerns are discussed.

 

19. A method for assessing the bacterial impermeability of hydrophobic membrane filters.

Research has shown that hydrophobic membrane filters, with a pore size of 0.22 mm, do not retain micro-organisms under all process conditions. Investigations were conducted in risk assessment of sterilising hydrophobic membrane filters, evaluating the performance of the filters under a range of operating conditions. To validate the bacterial retention ability of sterilising grade hydrophobic membrane filters, a bacterial aerosol challenge test methodology was developed. Extended summary (pdf)

 

20. Hygienic design and safe use of double-seat mixproof valves.

This document describes the basic hygienic design and safe use of single-body double-seat mixproof valves. Today, food process plants incorporate various multifunctional flow paths. Often one piping system is cleaned while another still contains product. This simultaneous cleaning can potentially result in the dangerous situation where product and cleaning liquid are separated by just one single valve seat. Any cleaning liquid that leaks across such a seat will contaminate the product. Therefore, often two or three single seat valves in a ‘‘block-and-bleed’’ arrangement are applied. Extended summary (pdf)

 

21. Challenge tests for the evaluation of the hygienic characteristics of packing machines for liquid and semi-liquid products, 2000.

After documents 3 and 11, this is the third test method in the series. It discusses how packing machines should be designed to comply with hygiene design criteria and thereby with the requirements specified in Annex 1 of the Machinery Directive.1 To determine whether those criteria are met requires validation of the design and measurement of essential parameters. Proven methods for testing the performance of the various functions of packing machines are described. These methods may also be used by the manufacturer to optimise or redesign a packing machine and by the food processor who may want to compare different packing machines. Upon delivery, a packing machine needs to be checked by a commissioning procedure to be agreed in advance between the food processor and the supplier. Commissioning may include physical as well as microbiological tests. Additional tests are specified for commissioning of machines for aseptic packing. Extended summary (pdf)

 

22. General hygienic design criteria for the safe processing of dry particulate materials.

Dry food processing and handling requires equipment that are different from those typically associated with wet and liquid products. This is the first in a series of documents that go beyond equipment design and covers installation and associated practices. In the case of dry materials, other considerations include material lump formation, creation of dust explosion conditions, high moisture deposit, formation in the presence of hot air, and material remaining in the equipment after shutdown. Appropriate cleaning procedures are described, dry cleaning being favoured to reduce risks of contamination. Extended summary (pdf)

 

23. Production and use of food-grade lubricants.

Lubricants, grease and oil are necessary components for the lubrication, heat transfer, power transmission and corrosion protection of machinery, machine parts, instruments and equipment. Incidental contact between lubricants and food cannot always be fully excluded and may result in contamination of the food product. This risk applies equally to food-grade lubricants or ‘‘lubricants for incidental food contact’’ and conventional lubricants. This guideline will assist manufacturers to understand better their responsibilities, based on the principles of GMP, by laying down the general requirements and recommendations for the hygienic manufacture and supply of food-grade lubricants. It also assists operators by explaining the hazards that may reasonably be expected to occur during the use of food-grade lubricants and the actions required to eliminate these hazards or to reduce their occurrence to acceptable levels. Extended summary (pdf)

 

24. The prevention and control of Legionella spp. (incl legionnaires’ disease) in food factories.

There are many locations in food industry sites where the potential for the proliferation of Legionella spp. in water systems exists. These bacteria can give rise to a potentially fatal disease in humans, which is identified as legionellosis or legionnaires’ disease. This document applies to the control of Legionella spp. in any undertaking involving a work activity and to premises controlled in connection with a trade, business or other undertaking where water is used or stored and where there is a means of transmitting water droplets which may be inhaled, thereby causing a reasonably foreseeable risk of exposure to Legionella spp. The guidelines summarise the best practice for controlling Legionella in water systems. It consists of two parts, namely, Management Practices and Guidance on the Control of Legionella spp. in Water Systems. The first section describes a management programme: risk identification and assessment; risk management (incl personnel responsibilities); preventing or controlling risk of exposure to the bacteria; and record keeping. The second part provides guidance on the design and construction of hot and cold water systems as well as the management and monitoring of these systems. Water treatment programmes, with attention to cleaning and disinfection, are also discussed. Extended summary (pdf)

 

25. Design of mechanical seals for hygienic and aseptic applications.

This guideline compares the design aspects of different mechanical seals with respect to ease of cleaning, microbial impermeability, sterilisability or pasteurisability. It can serve as a guide for suppliers and users of this important component. Using EHEDG definitions, mechanical seals are classified according to use in the food industry into three categories: Aseptic, Hygienic equipment Class I, and Hygienic Equipment Class II. Both single and dual mechanical seals fall under the first two categories, which by definition, are subject to more stringent hygienic demands. General design criteria and basic material requirements for food applications are explained. Materials covered include carbon-graphite, ceramics, elastomers and metals. Hygienic implications of seal elements and components are also discussed. Finally, installation requirements are described and illustrated, taking into account the product environment side, the flushing side and the cartridge design. Extended summary (pdf)

 

26. Hygienic engineering of plants for the processing of dry particulate materials.

This document describes general engineering guidelines to be applied to ensure that buildings, individual equipment items and accessibility of equipment when integrated within the plant layout are designed so that aspects of the process operation, cleaning and maintenance comply with hygienic design standards. It details requirements related to plant enclosure, including hygienic zoning, building structures and elements (from floor to ceiling) as well as process line installation. Attention is also given to air stream and water related aspects within the plant as well as cleaning and contamination aspects. See also Doc 22.

 

27. Safe storage and distribution of water in food factories.

Water is a vital medium used for many different purposes in the food industry. Systems for storing and distributing water can involve hazards, which could cause water quality to fall below acceptable standards. It is therefore critical to ensure that water storage and distribution in a food manufacturing operation takes place in a controlled, safe way. This guideline summarizes the best practice for three water categories used in the food industry: product water, domestic water and utility water. See also Doc 24. Extended summary (pdf)

 

28. Safe and hygienic water treatment in food factories.

This guideline summarizes the best practice for the management and operation of water storage and distribution systems in a food manufacturing plant. System requirements are described for three categories of water used: domestic, product and utility water. The product water distribution system within the plant must be hygienically designed. Water storage tanks should be enclosed, fitted with an air vent and a backflow prevention device and be completely drainable. A suitable-sized tank based on water consumption is essential to minimize stagnation. Chemical or thermal disinfection is recommended. Hazards and risks associated with utility water can have significant implications on process reliability. The document provides some recommendations with regard to specific utility water applications in the food industry, both for hot water and cold water. Attention is given to once through cooling systems, those using cooling towers and some examples of closed circuit systems. Extended summary (pdf)

 

29. Hygienic design of packing systems for solid foodstuffs.

This document addresses packing systems of solid food products and supplements earlier guidelines. Solid food is characterised as having a water activity of >0.97, low acid, not pasteurised or sterilised after packaging, and distributed through the cool chain. Examples include fresh meat and some meat products, cheeses, ready meals, cut vegetables, etc. Hygiene requirements of the packaging operations, machinery as well as personnel, are described and reference is made to the American Meat Institute’s principles of sanitary design. See also Docs 3 and 11. Extended summary (pdf)

 

30. Guidelines on air handling in the food industry.

The controlled properties of air, especially temperature and humidity, may be used to prevent or reduce the growth rate of some micro-organisms in manufacturing and storage areas. The particle content (dust and micro-organisms) can also be controlled to limit the risk of product contamination and hence contribute to safe food manufacture. Airborne contaminants are commonly removed by filtration. The extent and rate of their removal can be adjusted according to acceptable risks of product contamination and also in response to any need for dust control. These guidelines are intended to assist food producers in the design, selection, installation, and operation of air handling systems. Information is provided on the role of air systems in maintaining and achieving microbiological standards in food products. The guidelines cover the choice of systems, filtration types, system concepts, construction, maintenance, sanitation, testing, commissioning, validation and system monitoring. They are not intended to be a specification for construction of any item of equipment installed as part of an air handling system. Each installation needs to take account of local requirements and specialist air quality engineers should be consulted, to assist in the design and operation of the equipment. Extended summary (pdf)

 

31. Hygienic engineering of fluid bed and spray dryer plants.

Because these plants handle moist products in an airborne state, they are susceptible to hygiene risks, including a possible transfer of allergens between products. It is therefore critical to apply hygienic design considerations to both the process and machinery to prevent occurrence of such risks. Starting from the basics with regard to design, construction
materials, layout, and zone classification of the drying systems to meet hygienic requirements, this paper outlines component design aspects of the processing chamber, with
particular attention to the atomization assembly and the distribution grids for fluidization. Systems for both supply and exhaust air should operate in a hygienic manner and recommendations for the use and installation of various types of filters are listed. Finally, operational aspects, including sampling, control and general housekeeping are briefly
discussed.

 

32. Materials of construction for equipment in contact with food.

This guideline aims to offer a practical ‘handbook’ for those responsible for the specification, design and manufacture of food processing equipment. It offers guidance on the ways in which materials may behave such that they can be selected and used as effectively as possible. The properties and selection procedures with regard to metals, elastomers and plastics are covered in detail. Potential failure mechanisms and influences of manufacturing processes are also discussed. A more general overview of composites, ceramics and glass and materials is provided. The guideline can serve as an aide-memoir during the design process, so that equipment manufacturers and endusers can together ensure that all aspects of materials behaviour are taken into account in designing safe, hygienic, reliable and efficient equipment which can be operated, maintained and managed economically.

 

33. Hygienic engineering of discharging systems for dry particulate materials.

The introduction of the product into the processing system is a key step in maintaining the sanitation and integrity of the entire process. Discharging systems are designed to transfer, in this case dry solids, from one system into another without powder spillage, contamination or environmental pollution. Many dry systems do not have any additional protective heating steps, as they are merely specialty blending processes. Therefore, any contamination that enters the system will appear in the finished product. Guidelines for the design of bag, big bag, container and truck discharging systems are presented. They are intended for use by persons involved in the design, sizing, and installation of bag, big bag and truck discharging systems operating under hygienic conditions.

 

34. Integration of hygienic and aseptic systems.

Hygienic and/or aseptic systems comprise inter alia individual components, machinery, measurement systems, management systems and automation that are used to produce, for example, food products, medicines, cosmetics, home and personal products, and even water products. This horizontal guideline is about the hygienically safe integration of hygienic (including aseptic) systems in a food production/processing facility. Systems and components are frequently put together in a way that creates new hazards, especially icrobiological
ones. Deficiencies during the sequence of design, contract, design-change, fabrication, installation and commissioning are often the cause of these failures, even when specific design guidelines are available and are thought to be well understood. Errors in sequencing and content can also result in major penalties in terms of delays and in costs of components and construction. This document examines integration aspects that can affect hygienic design, installation, operation, automation, cleaning and maintenance and uses system flow charts
and case studies describing the integration processes and decision steps. It does not provide detailed guidance on specific manufacturing processes, products, buildings or equipment. Extended summary (pdf)

 

35. Welding of stainless steel tubing in the food industry.

Abundantly illustrated, this paper provides guidelines for the correct execution of on-axis hygienic (sanitary) welding between pipe segments, or between a tube and a control component (e.g. valve, flow meter, instrument tee, etc.). It deals with tube and pipe systems with less than 3.5 mm wall thickness, built in AISI 304(L) (1.4301, 1.4306 or 1.4307), 316(L) (1.4401, 1.4404 or 1.4435), 316Ti (1.4571) or 904L (1.4539) and their equivalents. The requirements for a weld destined for hygienic uses are first described, then the possible defects which can affect the weld are listed, and at the end the procedure for a state-of-the-art welding execution is illustrated, including preparation of pipe ends, final inspection and a trouble shooting guide. It mainly refers to the part of the weld in contact with the finished or intermediate product and the only welding method considered is the GTAW (Gas Tungsten Arc Welding, commonly known as TIG) without filler material (autogenous weld), since this technique is capable of assuring the best performance in the execution of welds for the fabrication of thin wall stainless steel tubing. Inspection of welds will be covered in more detail in the next project.

 

 



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