FIRST REPORT .sx MICROWAVE OVENS .sx The Agriculture Committee has agreed to the following Report :sx I. INTRODUCTION .sx 1 .sx We announced our inquiry into the safety of microwave ovens on 16 March 1990 .sx We were concerned at the disclosure by the Ministry of Agriculture , Fisheries and Food ( MAFF ) , on 4 December 1989 , that a sizeable proportion of microwave ovens had 'failed' a standard test ; we were also concerned at the manner in which that disclosure was handled .sx 2 .sx As this was clearly not a food safety problem of the greatest seriousness , we thought it was appropriate to allow MAFF and the oven manufacturers time to respond to the events of December 1989 , and then to examine what steps they had taken to protect the consumer interest .sx 3 .sx We have taken evidence from the Government , from the manufacturers' trade association and from bodies representing consumers and food retailers and manufacturers .sx A full list of the oral and written evidence can be found between pages iv and vi above .sx 4 .sx We acknowledge our debt to our specialist adviser , Mr Harry Barber , Senior Lecturer in Electronics and Electrical Engineering at Loughborough University of Technology , in helping us to understand a sometimes complex subject .sx II .sx THE NATURE OF THE PROBLEM .sx 5 .sx In themselves , microwave ovens are a safe , convenient and increasingly popular feature of the modern kitchen .sx There are about 11 million ovens in domestic use in the United Kingdom and no food poisoning cases have been specifically associated with them .sx It is well known , however , that there is a relationship between food safety and good kitchen practice and that pathogenic micro-organisms present in food can be destroyed if the food is properly cooked - or not destroyed if it is not .sx The correct use of microwave ovens therefore stands on a par with the correct use of conventional ovens , with one or two significant differences .sx 6 .sx With conventional cooking , the heat is transferred through the surface of the food and is then conducted through the bulk of the material .sx the surface temperature cannot be too high , otherwise the food is burnt , and the whole process takes a considerable time .sx long enough for temperature equalisation to take place within the product .sx The emphasis is on warming the food to an acceptable eating temperature and the bacteria are eliminated as an incidental part of the process .sx In microwave heating , the electromagnetic energy is transferred into the body of the product .sx This rate is also affected by the position of the product within the oven cavity , by the characteristics of the oven and by the geometry and layout of different food items in the package .sx The inevitable result is selective heating .sx The temperature will again equalise over a period of time but the heating process is much more rapid and the margin of error between satisfactory heating and overcooking is therefore much narrower .sx Hence it is important that the process be carried out accurately .sx 7 .sx A particular fear relating to microwave ovens was raises by the Chief Medical Officer when he described as " plausible , but unproven " the theory that the recent growth in listeriosis figures was related to the proliferation of " cook-chill meals " Cook-chill meals themselves are prepared in rigorously hygienic conditions , but special problems might arise if they were stored for too long or at the wrong temperature .sx Poor kitchen hygiene might also lead to micro-organisms being present in some of the 'do-it-yourself' dishes people put in microwaves .sx We should emphasise that these are largely hypothetical problems and that efforts to improve the performance of microwave ovens should be regarded as sensible precautionary measures rather than a direct response to actual lapses in food safety standards .sx .sx 8 .sx In this precautionary spirit , MAFF set up a Microwave Working Party in June 1989 , bringing together key bodies ( oven manufacturers , food manufacturers and retailers and consumer organisations ) in " a forum for sharing expertise and developing co-ordinated responses to emerging scientific data on the performances of microwave ovens " .sx It was , in some respects , an uneasy coalition of interests and it came unstuck in acrimonious circumstances a few months later ; but we believe that MAFF's efforts to approach the problems on a collaborative basis were well founded and we are satisfied that the Working Party is continuing to play a useful role .sx III .sx COOKING FOOD TO A SAFE TEMPERATURE .sx 9 .sx To cook food properly calls for different techniques depending on what food is involved , but DHSS guidelines stipulate that , for pathogenic organisms to be destroyed , food should be heated to a minimum of 70 degree C for two minutes .sx These figures should not be set in tablets of stone .sx A higher temperature for a shorter time or a lower temperature for a longer time would yield the same result .sx Nor should the practical realities of kitchen life be forgotten .sx How many cooks work with a thermometer in one hand and a stop-watch in the other ?sx But this time-temperature profile provides a valuable bench-mark against which the performance of microwave ovens can be judged .sx 10 .sx In the tests undertaken by the Institute of Food Research of the Agricultural and Food Research Council ( AFRC ) which sparked the controversy of December 1989 , a standard amount of energy was applied to a standard amount of mashed potato in 70 different models of microwave oven sic !sx . In 24 of the models , the lowest temperature found in the mashed potato after heating was below the critical temperature of 70 degree C. 11 .sx MAFF has been at pains to point out that the object of the research was " to determine the extent of variability of performance in a wide range of ovens , not to test the adequacy of any particular model " .sx The mashed potato was not stirred or specially positioned as it would have been by a cook in the kitchen working to the manufacturer's instructions ; and it is very likely that , if some different test had been selected , different ovens would have performed differently .sx In MAFF's words :sx " Ovens were not judged to have 'passed' or 'failed' and attempts to use the results in this way are based on a misunderstanding of the nature of the " .sx .sx 12 .sx We accept this statement - although we would add that MAFF greatly contributed to the public misunderstanding of the situation by the clumsy way in which they published the research .sx We return to this point later .sx 13 .sx The research , then , did not demonstrate the existence of millions of unsafe microwave ovens .sx Every functioning microwave oven is capable of cooking food to a safe temperature , just as every functioning car is capable of getting from London to Birmingham .sx What it did highlight is the fact that these aids to fast , convenient food are not quite as trustworthy or as simple to operate as is popularly supposed .sx They vary slightly from model to model .sx They need to be accompanied by accurate manufacturer's instructions and similarly accurate instructions must accompany any prepackaged convenience foods which they are used to heat .sx How far these two conditions can be satisfied was one of the issues we had to address .sx IV .sx STANDARDISATION .sx 14 .sx There are currently some 799 models of microwave oven in use in the UK , some old , some new , some incorporating a turntable , some not , each configured slightly differently and each competing in a fast growing market .sx The difficulties of achieving uniform standards from such a diverse range of equipment will be self-evident .sx 15 .sx Until 1 September 1990 , there was no standardisation of the declared power output of these ovens .sx This meant that two different 650-watt ovens might heat food to different temperatures , which made meaningful food labelling instructions extremely difficult .sx Since 1 September 1990 - in response , in part , to the furore of December 1989 - new models of microwave oven will be rated for power output according to a single method , the International Standard IEC 705 .sx Both the Association of Manufacturers of Domestic Electrical Appliances ( AMDEA ) and non-AMDEA oven manufacturers have been persuaded to join the IEC 705 power rating system .sx We welcome these developments .sx they represent a positive step in the right direction , if not a definitive solution to the problem .sx 16 .sx As witnesses were quick to point out , the IEC 705 standard is anything but perfect .sx It is based on heating a one-litre water load , which is practically the last thing anyone would put in a microwave oven , and calibrates power output rather than testing temperature measurements in food and their conformity with safety standards .sx The methodology behind it is therefore fundamentally different from the methodology used in the AFRC tests referred to in the previous section , which was based on re-heating rather than heating and was a closer simulation of the tasks microwave ovens are most frequently used to perform .sx 17 .sx Other difficulties to which IEC 705 gives rise are :sx ( i ) it includes no pass or fail criteria ; .sx ( ii ) it is an international standard and can only be modified after extensive international consultations ; .sx ( iii ) there are fundamental problems in applying it to models sold before 1 September 1990 .sx 18 .sx The IEC 705 standard does , nevertheless , enable important progress to be made .sx The declared power output of new domestic microwave ovens can be measured against that standard and the ovens 'banded' accordingly .sx MAFF proposed , when announcing the adoption of the IEC 705 standard on 7 August , that the spectrum of IEC wattages between 425 and 875 watts should be divided into five numbered categories - all bands but the first being 75 watts wide .sx Research carried out by the industry indicates that these bands may be too wide , while the Retail Consortium and others wanted to see fewer bands ; discussions are still in progress to determine what is the optimum number .sx But the existence of agreed and standardised bands should make the next hurdle easier , which is labelling food properly .sx 19 .sx In theory , once a microwave oven had been banded 2 , say , it would then be possible for cook-chill meals to carry instructions indicating how long to cook them in an oven of that type .sx Simple numbering systems work well in the case of other domestic appliances like washing-machines and we believe they would prove attractive to the consumer in this instance .sx The National Consumer Council maintained that " microwave labelling instructions to consumers have improved since December 1989 , but there is still considerable confusion " .sx We agree with this assessment .sx VII .sx MAFF'S PERFORMANCE .sx 35 .sx We referred earlier to MAFF's clumsy handling of the publicity given to the AFRC's research in December 1989 .sx Although we do not wish to dwell on mistakes made so long ago , there are clear lessons to be learnt from that experience .sx 36 .sx Details of what took place can be found in our evidence .sx The AFRC research was undertaken at the behest of a MAFF working party which contained both oven manufacturers and consumer groups .sx As the research entailed testing a large number of microwave ovens , the AFRC borrowed these from manufacturers , rather than purchasing them , and MAFF agreed not to name the models used in its eventual report .sx It was felt that such an arrangement would save money without giving unnecessary hostages to fortune .sx As far as the AFRC was concerned , the object of the tests was to measure variability and not assess the efficiency of individual models .sx 37 .sx The best laid plans can come unstuck , and this was not a best laid plan .sx When the Minister of Agriculture received the AFRC report , with its apparently damning evidence of erratic performance by microwave ovens , he was placed under immediate pressure from the Consumers' Association , who threatened to disclose the report's findings unless MAFF did so itself .sx The Minister accordingly published the report on the day he received it without , for the contractual reasons referred to in the last paragraph , naming the ovens used in the study .sx There followed an undignified 48-hour hiatus while the Minister withheld the names of the models which had 'failed' the AFRC test until the manufacturers concerned had prepared supplementary instructions for those using their ovens .sx In the resulting confusion , the seriousness of the threat to food safety was greatly exaggerated by the media , as could have been expected .sx