5 Temperature monitoring and measurement M. L. Woolfe, Food Standards Agency, London 5.1 Introduction The practice of measuring and keeping records of temperatures is not new to the food industry, and has been undertaken by certain sectors, e.g. canning, for many years. However, its widespread application in the refrigerated food sector, other han fitting temperature measurement equipment to chill stores, is relatively recent. The prime factor focusing attention on temperature monitoring was the concern about food poisoning and the introduction of new legislation covering temperature control of chilled foods, where temperature abuse and likely growth of pathogens could be a problem. However, national changes were overtaken by developments in the European Community where a harmonised hygiene directive was developed and agreed. This coupled with vertical hygiene directives on animal based foods laid more emphasis on risk management. Thus the practic and use of temperature monitoring has matured quite rapidly over the last te years and become more integrated into quality and safety management systems 5.1.1 Changes in legislation Both the Food Hygiene(Amendment) Regulations 1990and the Food Safety Act 1990- produced a significant change across the chill chain. The Food Hygiene(Amendment)Regulations 1990 introduced temperature controls for certain types of chilled foods which applied at all stages of the chill chain Further minor amendments were made in 1991.Up to this date very few end users of refrigerated systems practised regular temperature monitoring, however The views expressed in this Chapter are those of the author and should not be regarded as a statement of official Government policy
5.1 Introduction The practice of measuring and keeping records of temperatures is not new to the food industry, and has been undertaken by certain sectors, e.g. canning, for many years. However, its widespread application in the refrigerated food sector, other than fitting temperature measurement equipment to chill stores, is relatively recent. The prime factor focusing attention on temperature monitoring was the concern about food poisoning and the introduction of new legislation covering temperature control of chilled foods, where temperature abuse and likely growth of pathogens could be a problem. However, national changes were overtaken by developments in the European Community where a harmonised hygiene directive was developed and agreed. This coupled with vertical hygiene directives on animal based foods laid more emphasis on risk management. Thus the practice and use of temperature monitoring has matured quite rapidly over the last ten years and become more integrated into quality and safety management systems. 5.1.1 Changes in legislation Both the Food Hygiene (Amendment) Regulations 19901 and the Food Safety Act 19902 produced a significant change across the chill chain. The Food Hygiene (Amendment) Regulations 19901 introduced temperature controls for certain types of chilled foods which applied at all stages of the ‘chill chain’. Further minor amendments were made in 1991.3 Up to this date very few end users of refrigerated systems practised regular temperature monitoring, however, 5 Temperature monitoring and measurement M. L. Woolfe, Food Standards Agency, London The views expressed in this Chapter are those of the author and should not be regarded as a statement of official Government policy
100 Chilled foods when they began to apply it they realised the concurrent benefits of process and quality control it brought The Food Safety Act 1990 gave Ministers additional powers to legislate in many new areas. One significant change in the 1990 Act is found in Section 2 This describes the conditions under which a defence to charges brought under the Act can be offered. The warranty'defence under the 1984 Act has been substituted by a due diligence defence. In order to show due diligence companies have to demonstrate that they took all reasonable precautions'and exercised'all due diligence in their operations. Many companies have moved to better systems of control and inspection on the basis of parallel case law of 'due diligence in other legislation A harmonised horizontal Hygiene Directive 93/43/EEC- was agreed and implemented in the UK in 1995(The Food Safety(General Food Hygiene Regulations). These laid emphasis on a risk or HACCP(Regulation 4(3) pproach to hygiene rather than giving prescriptive or detailed rules about hygienic requirements and practices. There is a general requirement that temporary premises and equipment for transport must be capable at maintaining the food at appropriate temperatures and where necessary their design must allow those temperatures to be monitored The requirements of the Directive relating to temperature control are enacted in the Food Safety (Temperature Control) Regulations 1995. In addition, the Government was able to take advantage of the computer model developed over five years(MAFF Micromodel)to look at predictions of microbiological growth under the different temperature conditions to ensure safe food, and as a result the earlier temperature control regulations were simplified Controls already existed in European Community legislation in the trade of animal-based foods, e.g. meat, meat products, poultrymeat, etc. In order implement the Single Market after January 1993 some ten vertical directives were agreed dealing with the hygienic production of animal products from fresh meat to bivalve molluscs Some of these were new and others re-negotiated from intra- community trade directives. All of these Directives have some temperature control requirements. Work is in progress to consolidate all the vertical hygiene directives and the horizontal Hygiene Directive into one simplified directive. The only mandatory requirement for temperature monitoring and keeping records is based on a European Community measure which requires monitoring equipment to be fitted to cold stores and vehicles which store or transport quick-frozen foods ( Commission Directive 92/1/EC). This same requirement has also been adopted in the UN/ECE agreement which facilitates cross-frontier traffic in perishable foods(ATP) in order to harmonise EC requirements for third-country vehicles 5.1.2 Risk and quality management systems nce companies began to investigate and implement temperature monitoring stems. it soon became evident that there are derived benefits to offset the incurred capital costs and effort. Better control of temperature underpins both
when they began to apply it they realised the concurrent benefits of process and quality control it brought. The Food Safety Act 1990 gave Ministers additional powers to legislate in many new areas. One significant change in the 1990 Act is found in Section 21. This describes the conditions under which a defence to charges brought under the Act can be offered. The ‘warranty’ defence under the 1984 Act has been substituted by a ‘due diligence defence’. In order to show ‘due diligence’, companies have to demonstrate that they took all ‘reasonable precautions’ and exercised ‘all due diligence’ in their operations. Many companies have moved to better systems of control and inspection on the basis of parallel case law of ‘due diligence’ in other legislation. A harmonised horizontal Hygiene Directive 93/43/EEC4 was agreed and implemented in the UK in 1995 (The Food Safety (General Food Hygiene) Regulations).5 These laid emphasis on a risk or HACCP (Regulation 4(3)) approach to hygiene rather than giving prescriptive or detailed rules about hygienic requirements and practices. There is a general requirement that temporary premises and equipment for transport must be capable at maintaining the food at appropriate temperatures and where necessary their design must allow those temperatures to be monitored. The requirements of the Directive relating to temperature control are enacted in the Food Safety (Temperature Control) Regulations 1995.6 In addition, the Government was able to take advantage of the computer model developed over five years (MAFF Micromodel) to look at predictions of microbiological growth under the different temperature conditions to ensure safe food, and as a result the earlier temperature control regulations were simplified. Controls already existed in European Community legislation in the trade of animal-based foods, e.g. meat, meat products, poultrymeat, etc. In order to implement the Single Market after January 1993 some ten vertical directives were agreed dealing with the hygienic production of animal products from fresh meat to bivalve molluscs. Some of these were new and others re-negotiated from intracommunity trade directives. All of these Directives have some temperature control requirements. Work is in progress to consolidate all the vertical hygiene directives and the horizontal Hygiene Directive into one simplified directive. The only mandatory requirement for temperature monitoring and keeping records is based on a European Community measure which requires monitoring equipment to be fitted to cold stores and vehicles which store or transport quick-frozen foods (Commission Directive 92/1/EC).7 This same requirement has also been adopted in the UN/ECE agreement which facilitates cross-frontier traffic in perishable foods (ATP8 ) in order to harmonise EC requirements for third-country vehicles. 5.1.2 Risk and quality management systems Once companies began to investigate and implement temperature monitoring systems, it soon became evident that there are derived benefits to offset the incurred capital costs and effort. Better control of temperature underpins both 100 Chilled foods
Temperature monitoring and measurement 101 the safety and quality of the food product, and can bring economic benefits of energy efficiency The changes in legislation also necessitated the setting up of appropriate systems to ensure the safety of foods. All food businesses have the responsibility of identifying critical steps in their own processes. The approach adopted nationally and internationally is HACCP (Hazard Analysis and Critical Control Point). This identifies the risks and the critical control points in the process to control the risks. The important issue is that a HACCP plan is unique to a particular product and process, and it should be continually assessed. Help in implementing HACCP has been given by provision in the Hygiene Directive which encourages sectorial guidelines, and to date six guides have been published Temperature monitoring may or may not be part of the HACCP plan depending on the product and process involved. There is no specific requirement to keep records of temperature checks, but records may be helpful to show that egal requirements have been met. More importantly temperature monitoring is put into context with all the other control points, and integrated into the overall HACCP system It is clear that HACCP is rarely implemented in isolation but combined with uality systems to ensure that a production unit manufactures food that is safe and is of consistent quality for the consumer. There are many systems of quality assurance,and the most widely used ones are based either on Iso 9000 or on TQM ( total quality management ) ISo 9000 series has two main standards (Iso 900 and 9002)and various guidelines, and companies achieve accreditation when they have implemented the standards. TQM is more a cultural approach involving all members of an organisation in achieving consistent quality and consumer satisfaction and also has the concept of continual improvement 5.1.3 Improvement in technology The ability to produce microelectronics relatively cheaply has enabled the manufacture of relatively small devices that store large amounts of data. These are now routinely integrated with computerised management systems. The last few years have seen an enormous advance in computer and communications technology. Now satellite tracking systems can follow a vehicles position and give total information about the refrigeration and engine systems to its depot Retail display cases can also have integrated temperature and humidity control to ensure full shelf-life of non-pre-packed foods. Thus where temperature measurement is part of the integrated safety and quality, new technology lends tself to the storage and processing of the data 5.2 Importance of temperature monitoring Temperature control requirements for England and Wales apply to food which is ikely to support the growth of micro-organisms or the formation of toxins
the safety and quality of the food product, and can bring economic benefits of energy efficiency. The changes in legislation also necessitated the setting up of appropriate systems to ensure the safety of foods. All food businesses have the responsibility of identifying critical steps in their own processes. The approach adopted nationally and internationally is HACCP (Hazard Analysis and Critical Control Point). This identifies the risks and the critical control points in the process to control the risks. The important issue is that a HACCP plan is unique to a particular product and process, and it should be continually assessed. Help in implementing HACCP has been given by provision in the Hygiene Directive which encourages sectorial guidelines, and to date six guides9 have been published. Temperature monitoring may or may not be part of the HACCP plan depending on the product and process involved. There is no specific requirement to keep records of temperature checks, but records may be helpful to show that legal requirements have been met. More importantly temperature monitoring is put into context with all the other control points, and integrated into the overall HACCP system. It is clear that HACCP is rarely implemented in isolation but combined with quality systems to ensure that a production unit manufactures food that is safe and is of consistent quality for the consumer. There are many systems of quality assurance, and the most widely used ones are based either on ISO 9000 or on TQM (total quality management). ISO 900010 series has two main standards (ISO 9001 and 9002) and various guidelines, and companies achieve accreditation when they have implemented the standards. TQM is more a cultural approach involving all members of an organisation in achieving consistent quality and consumer satisfaction and also has the concept of continual improvement. 5.1.3 Improvement in technology The ability to produce microelectronics relatively cheaply has enabled the manufacture of relatively small devices that store large amounts of data. These are now routinely integrated with computerised management systems. The last few years have seen an enormous advance in computer and communications technology. Now satellite tracking systems can follow a vehicle’s position and give total information about the refrigeration and engine systems to its depot. Retail display cases can also have integrated temperature and humidity control to ensure full shelf-life of non-pre-packed foods. Thus where temperature measurement is part of the integrated safety and quality, new technology lends itself to the storage and processing of the data. 5.2 Importance of temperature monitoring Temperature control requirements for England and Wales apply to food which is likely to support the growth of micro-organisms or the formation of toxins. Temperature monitoring and measurement 101
102 Chilled foods These foods need to be kept at 8C or below. However, this requirement has to be implemented in combination with the others laid down in the general hygie regulations(The Food Safety(General Food Hygiene) Regulations 1995) Obviously, if pathogenic organisms can be prevented from entering the food then temperature control is necessary only for extending the shelf-life of the product. However, this is rarely the case and the approach taken by HACCP is to identify at each stage of the preparation of a food where the hazards occur and how they can be controlled. Reducing the temperature does not kill micro- organisms, but it retards their growth. Hence keeping raw materials intermediate and finished products at chill temperatures will play its part in ensuring the food is safe. The other important areas are proper hygiene training of operatives, prevention of physical contaminants, suitable fittings and equipment, and good cleaning regimes and pest control Refrigeration equipment is built to fur nction I on attention, however there are many events apart from breakdown which can affect temperature control. The defrost cycles need attention to ensure they are at he correct frequency, and loading of food into refrigerated systems is often crucial to its operation and proper air flow. Air temperature monitoring can indicate whether refrigerated equipment is functioning correctly and is being operated correctly, even though it may be more difficult to extrapolate food temperatures. In some circumstances air temperature monitoring is not possible and product temperature or product simulant temperature is required 5.3 Principles of temperature monitoring 5.3.1 Choice of system There are an enormous number of different temperature monitoring systems available commercially, from a simple thermometer to a fully computerised system linked to a local refrigeration system or even central control system. The choice of system will depend on exactly the amount of detail the operator requires and the cost at which this information is provided If the monitoring stem is to provide detailed information on the operation of a system linked ith other reactive management systems, then obviously a more elaborate and complex system is required. This may include a large number of sensors nable a very complete picture of the temperature distribution within a efrigerated system to be obtained. It may also include other information such defrost cycles, compressor and expansion valve pressures, door openings, and nergy consumption, and may be linked to an alarm system(and even telephone) being G ing and batch codes of product. On the other hand, if monitoring Is rried out only to ensure that food is being kept within certain temperatures as a critical control point, then the amount of information which is collected may be reduced temperature monitoring (IIR 11 SRCRA 2 BRA, RFCA lie Very little formal advice has been given in the previous literature on Guidelines
These foods need to be kept at 8ºC or below. However, this requirement has to be implemented in combination with the others laid down in the general hygiene regulations (The Food Safety (General Food Hygiene) Regulations 19955 ). Obviously, if pathogenic organisms can be prevented from entering the food then temperature control is necessary only for extending the shelf-life of the product. However, this is rarely the case and the approach taken by HACCP is to identify at each stage of the preparation of a food where the hazards occur and how they can be controlled. Reducing the temperature does not kill microorganisms, but it retards their growth. Hence keeping raw materials, intermediate and finished products at chill temperatures will play its part in ensuring the food is safe. The other important areas are proper hygiene training of operatives, prevention of physical contaminants, suitable fittings and equipment, and good cleaning regimes and pest control. Refrigeration equipment is built to function for long periods without attention, however there are many events apart from breakdown which can affect temperature control. The defrost cycles need attention to ensure they are at the correct frequency, and loading of food into refrigerated systems is often crucial to its operation and proper air flow. Air temperature monitoring can indicate whether refrigerated equipment is functioning correctly and is being operated correctly, even though it may be more difficult to extrapolate food temperatures. In some circumstances air temperature monitoring is not possible and product temperature or product simulant temperature is required. 5.3 Principles of temperature monitoring 5.3.1 Choice of system There are an enormous number of different temperature monitoring systems available commercially, from a simple thermometer to a fully computerised system linked to a local refrigeration system or even central control system. The choice of system will depend on exactly the amount of detail the operator requires and the cost at which this information is provided. If the monitoring system is to provide detailed information on the operation of a system linked with other reactive management systems, then obviously a more elaborate and complex system is required. This may include a large number of sensors to enable a very complete picture of the temperature distribution within a refrigerated system to be obtained. It may also include other information such as defrost cycles, compressor and expansion valve pressures, door openings, and energy consumption, and may be linked to an alarm system (and even telephone) stock keeping and batch codes of product. On the other hand, if monitoring is being carried out only to ensure that food is being kept within certain temperatures as a critical control point, then the amount of information which is collected may be reduced. Very little formal advice has been given in the previous literature on temperature monitoring (IIR,11 SRCRA,12 BRA,13 RFIC14). Guidelines 102 Chilled foods
Temperature monitoring and measurement 103 published by the ifST give details about air temperature monitoring, and these were further amplified in the Department of Healths Guidelines. These Guidelines have been superseded by Industry Codes of Practice. Practical advice on temperature monitoring has been included as an advisory Annex in some of the Codes(retail and Catering Codes in particular), but these do not form part of the Codes 5.3.2 Which temperature to monitor? When designing a monitoring system, there are certain considerations in the choice of temperatures to be measured in the refrigerated system. These are The choice of whether to monitor air temperatures, product temperatures or simulated product temperatures will depend on the individual system and the The sensors should preferably be fixed in a position where they will not be maged during commercial activity. If manual readings are used, these should be taken from accessible positio The temperatures chosen should be representative of the refrigerated system and give a picture of its functioning, and therefore be linked indirectly with 5.3.3 Air temperature monitoring In terms of regulatory compliance and as part of HACCP, the temperature of the food should be monitored. However, the storage or holding times of chilled food re relatively short, making product temperature monitoring difficult without disruption to normal commercial activity and requiring the intervention of trained operators. It is easier to fix sensors separate from food loads, which are connected to read-out systems, where temperatures can be recorded auto- matically or manually Most refrigerated systems function by circulating cold air over the systems vaporator, and then passing this cold air over the food load to remove heat from the food Movement of air is by mechanical fans or in some cases gravity, which relies on density being greater for cold air than for warm air. In the case of mechanical circulation, the air returns to the evaporator after passing over the food, making the returning air the same temperature or warmer than the food it is cooling. Localised heating effects from lighting or other effects may give rise to hot spots or uneven temperature distribution, and make a small part of the food load warmer than the return air. In general, the relationship between air temperature and product temperature is best established by examining the difference between the cold air leaving the evaporator and warmer air returning to the evaporator. This gives a measure of the performance of the refrigerated system and its effectiveness in keeping the food cold (Bra). This differential is also used as the basis of air temperature monitoring. However, in order to
published by the IFST15 give details about air temperature monitoring, and these were further amplified in the Department of Health’s Guidelines.16 These Guidelines have been superseded by Industry Codes of Practice.9 Practical advice on temperature monitoring has been included as an advisory Annex in some of the Codes (Retail and Catering Codes in particular), but these do not form part of the Codes. 5.3.2 Which temperature to monitor? When designing a monitoring system, there are certain considerations in the choice of temperatures to be measured in the refrigerated system. These are: • The choice of whether to monitor air temperatures, product temperatures or simulated product temperatures will depend on the individual system and the way it operates. • The sensors should preferably be fixed in a position where they will not be damaged during commercial activity. If manual readings are used, these should be taken from accessible positions. • The temperatures chosen should be representative of the refrigerated system and give a picture of its functioning, and therefore be linked indirectly with the product temperature. 5.3.3 Air temperature monitoring In terms of regulatory compliance and as part of HACCP, the temperature of the food should be monitored. However, the storage or holding times of chilled food are relatively short, making product temperature monitoring difficult without disruption to normal commercial activity and requiring the intervention of trained operators. It is easier to fix sensors separate from food loads, which are connected to read-out systems, where temperatures can be recorded automatically or manually. Most refrigerated systems function by circulating cold air over the system’s evaporator, and then passing this cold air over the food load to remove heat from the food. Movement of air is by mechanical fans or in some cases gravity, which relies on density being greater for cold air than for warm air. In the case of mechanical circulation, the air returns to the evaporator after passing over the food, making the returning air the same temperature or warmer than the food it is cooling. Localised heating effects from lighting or other effects may give rise to ‘hot spots’ or uneven temperature distribution, and make a small part of the food load warmer than the return air. In general, the relationship between air temperature and product temperature is best established by examining the difference between the cold air leaving the evaporator and warmer air returning to the evaporator. This gives a measure of the performance of the refrigerated system and its effectiveness in keeping the food cold (BRA13). This differential is also used as the basis of air temperature monitoring. However, in order to Temperature monitoring and measurement 103