Domestic and catering storage and handling
Domestic and catering storage and handling
Friday, 10 April 2009
The past decades have seen a considerable increase in legislation defining maximum temperatures during the production, distribution and retailing of chilled food. However, as soon as the food is purchased by the consumer, it is no longer covered by any of these legislative requirements.
After a chilled product is removed from a retail display cabinet it is outside a refrigerated environment whilst carried around the store and transported home for further storage. In the home, it may be left in ambient conditions or stored in the refrigerator until required. In the late 1980s, there were few published data on consumers’ attitudes to chilled food and their handling procedures in the home. We therefore set out to obtain data on consumers attitudes and domestic temperature control. As part of the survey, participants were asked questions to assess their attitude to food poisoning, shopping habits and the length of time they stored chilled foods in the home (Evans et al., 1991; Evans, 1992; James & Evans, 1992a). Monitoring was then carried out to determine the length of time and temperature at which foods were stored in the home.
To evaluate temperatures within each refrigerator a miniature data logger with three air and two product sensors recorded data every 8 seconds. Results showed that the mean temperature over 7 days (evaluated from top, middle and bottom sensors) ranged from -1°C to 11°C. The overall mean air temperature for all the refrigerators in the survey was 6°C, with 70% of refrigerators operating at average temperatures above 5°C.
These data were augmented with experimental data from laboratory studies on the performance of refrigerators and measurements of temperature changes during transportation to the home (James & Evans, 1990; 1992b). Domestic refrigerators are tested empty with the doors always closed. Our studies showed poor temperature control within domestic refrigerators, large (>10°C) temperature differences within the working space, very slow cooling of warm foods and poor temperature recovery from door openings.
Design studies were carried out by FRPERC in the early 1990s and a prototype refrigerator designed, constructed and demonstrated that overcame all these deficiencies (Gigiel et al., 1993). The refrigerator had two food storage compartments that could be operated at any temperature between -1 and 10°C. Maximum temperature differences within a compartment and fluctuations in temperature at a position were <1°C and ±0.5°C respectively. In a third compartment eutectic plates were cooled overnight using a small refrigeration system. When cooling was required in either of the food compartments air was recirculated over the plates and into the compartment. This system resulted in a much quicker response to door openings and other heat loads that conventional refrigerators. This work won the students involved the UK Institute of Refrigeration’s Ted Perry Award.
A further project by Ed Hammond at FRPERC looking at the energy efficiency of domestic refrigerators also won the Ted Perry Award. This work showed the interaction between the compressor, thermostat and the cooling load of domestic refrigerator on its energy efficiency (Gigiel, Evans & Hammond, 2002; Hammond & Gigiel, 2004). One simple improvement was clearly identified. Improving the quality of the insulation was shown to improve energy saving in a domestic refrigerator by as much as 40%.
FRPERCs expertise in domestic refrigeration and retail display has also been extended to catering storage. As part of a Knowledge Transfer Partnership (KTP) with Adande Refrigeration Ltd a novel multi-drawer commercial refrigerator has been developed that is capable of controlling the temperature in each draw at temperatures between -20°C and 15°C (Gigiel, Hammond & Evans, 2006; Evans, Hammond & Gigiel, 2006; Evans, Hammond & Gigiel, 2008).
FRPERC remain interested in the performance and use of domestic refrigerators and a comprehensive review by FRPERC of published data over the last 20 years was recently published in the Journal of Food Engineering (James, Evans & James, 2008). This review concluded that despite all these surveys, how fridge temperatures and cleanliness impacts on consumer health remains to be fully assessed. What is clear is that many refrigerators throughout the world are running at higher than recommended temperatures. Since even these recommended temperatures are higher than the 0 to 1°C that is usually the recommended temperature range for storing fish and seafood, meat and many chilled products the current situation is even more detrimental to maintaining the high quality life of chilled foods. At present domestic storage of chilled foods would appear to be the weakest link in the entire chill-chain.