Effectiveness of Cold-serving Units Using Two Cold-holding Methods in Foodservice Operations ¹

Effectiveness of two cold-holding methods commonly used to maintain temperatures of products held on cold-serving units (CSU) was determined by time-temperature and bacterial growth patterns of three products. Products used were bulk (2.27 kg) and portioned (100 g) cottage cheese, portioned (100 g) tuna salad, and deviled eggs halves (100 ± 10 g). All products were held on a cold-serving unit using the mechanical/ice cold-holding method (mechanical cooling used in combination with 3 to 10 cm ice) for 24 h (control; laboratory setting), as well as on three separate cold-serving units using the mechanical cold-holding method (at three university residence hall field sites under actual operating conditions) for 4 h (maximum length of service). Temperatures of all bulk and portioned products held on CSUs using the mechanical/ice cold-holding method (initial temperatures of food were 4 to 8.2°C) were >7.2°C after 2 h with a 50% load factor. When the mechanical cold-holding method was used, all portioned products (initial temperatures were 8.2 to 11°C) were <7.2°C after 2 h with a 75% load factor. Temperature differences between the mechanical and mechanical/ice cold-holding methods were attributed to ice on the cold-serving unit. The ice insulated the products from the mechanically cooled basin and allowed internal temperatures of the products to increase. Statistical significance for bacterial growth patterns was reported only for products held on cold-serving units using the mechanical/ice cold-holding method: mesophilic growth in deviled eggs (p<0.05) and psychrotrophic growth in tuna salad (p<0.001). As expected, bulk cottage cheese had a significantly higher temperature over time (p<0.05) than did portioned cottage cheese for both methods of cold-holding. Based on results of this study, portioned foods on cold-serving units should be held less than 2 h when the mechanical/ice cold-holding method is used, or up to 4 h when the mechanical cold-holding method is available.