Retail display
Retail display
Friday, 10 April 2009
The retail display of refrigerated food has long been considered one of the weakest links in the cold chain (Malton, 1972). Controlling the temperature of an individual retail pack is far more difficult than that of a bulk pack or pallet load of product. In addition, the display cabinet has to cater for the marketing requirement for a minimal barrier between the customer and the product.
Retail display has always been one of the major areas of research at Langford. Initial studies in the early 1970s surveyed the temperature performance of commercial chilled cabinets (Malton, 1972), both for wrapped (Malton, 1971) and unwrapped (Bailey, 1972) meats. Other investigations looked at temperatures and weight loss (Cutting & Malton, 1973; 1974) and colour changes (MacDougall, 1974) in frozen meat on display. In the 1980s, studies concentrated on drip loss (Malton & James, 1983) and packaging developments (Taylor, 1985; Taylor, 1985).
The required retail display life and related environmental conditions for wrapped chilled products differ from those for unwrapped products. The chilled display life of wrapped meat, fish, vegetables and processed foods ranges from a few days to many weeks. It is primarily limited by microbiological considerations. Retailers of unwrapped fish, meat and delicatessen products, e.g. sliced meats, pate, cheese and prepared salads, normally require a display life of one working day. In the 1980s, a working day, in display life terms, was 6 h: now it is closer to 24 h.
The display life of unwrapped meat was shown clearly, in the mid 1980s, to be determined by colour changes caused by evaporation of water from the surface of the meat (James, 1986). Experimental investigations have clearly demonstrated the substantial effect of relative humidity on weight losses from chilled meat under retail display conditions (Swain & James, 1986). The same investigations resulted in recommended combinations of conditions that would produce a 6 h display life (James & Swain, 1986).
Before these investigations, it had been thought that poor control of temperature and relative humidity in retail display cabinets produced increased weight loss and reduced display life. However, the Langford studies indicated that mean conditions around the product were more important than their degree of control. Computer predictions have since substantiated this view (Fulton et al., 1987; James et al., 1988). However, substantial problems were encountered in the latter work in obtaining a relationship between heat (h) and mass (k) transfer coefficients that would allow predictions to be made of heat and mass transfer from the meat. A series of experimental investigations have since been carried out to measure h and k simultaneously (James, Swain & Daudin, 1988; Daudin & Swain, 1990).
Investigations (Swain, 1997) have also shown that relative humidity is the main factor controlling weight loss and the display life of delicatessen products. At a relative humidity of 40% the effect of surface drying became apparent after approximately 100 minutes. At 85% relative humidity the products could be displayed for between 4 to 6 h before surface drying could be noted. The overall weight loss at 40% relative humidity was approximately 3 times that at a relative humidity of 85%. In the same work it was also found that changing the lighting combination of 50 W sons and 100 W halogen spot lights to the 100 W sons and a colour 83 fluorescent tube increased the average weight loss by a factor of 1:4. The increase was similar in magnitude to that produced by a 20% reduction in relative humidity. Recent work has evaluated the effects of ultrasonic humidification in such cabinets for the retail display of fruits and vegetables (Brown, Corry & James, 2004) and meats (Brown, Corry & Evans, 2007). Humidification has been shown to significantly reduce weight loss and slow the rate of deterioration in the appearance of products during display. No adverse effects on the microbial quality of products stored in these humidified cabinets have been found.
Retail display cabinets are major users of energy with approximately 8,000 GWh being consumed annually by the UK retail food trade. However, until recently it was difficult for users to gain comparable information of the energy efficiency of cabinets. FRPERC were one of the major players, together with TNO (the Netherlands) and the Danish Technological Institute, in an EU project that developed an energy labelling scheme covering all types of cabinets for chilled and frozen foods (Evans, 1997; Evans, van der Sluis & Gigiel, 1998).
The control of air movement within retail display cabinets and the interaction between refrigerated and ambient air within the store has always been a critical factor in cabinet performance. CFD modelling expertise has been used by Alan Foster at FRPERC to study flow within and around cabinets. The design and position of shelves, for instance, has been shown to have a large affect on spillage of refrigerated air into a retail store (Foster, Phillips & Quarini, 1997). Research studies have been combined CFD with in store investigations to reduce both air spillage and the resulting ‘cold feet’ phenomena commonly found in the isles between refrigerated cabinets in supermarkets.
CFD modelling has also been used to improve the performance of chilled multi-deck retail display cabinets (Foster, Madge & Evans, 2005). Studies have been carried out to see if CFD modelling can be used to rapidly identify the changes that would be required to an existing multi-deck display cabinet so that it would meet a higher test specification. Implementing the changes on a Pastorfrigor MV 200TP display cabinet reduced the average power consumption from 1.37 to 1.29 kW as well as significantly reducing the number of test packs which spent any time above 4°C, from 12 to 1.
Projects have also looked into the use of environmentally friendly refrigeration systems, especially the use of the air cycle, for retail display. The application of air cycle to retail display resulted in prototype chilled and frozen display cabinets with temperature control, noise and energy levels that were as good as, if not better than, conventional cabinets (Russell, Gigiel & James, 1998; Russell & Fit, 1998).