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

Abstract

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.

Safety Issues Related to Use of Take-Out Food

“…Such foods may be kept cold in two ways: mechanical or mechanicaliice methods. Fraser and Sawyer (1990) reported on the effectiveness of these two cold-holding methods.…”

“…Cold-serving unit (CSU) was defined as a piece of foodservice equipment, open on top, and designed to maintain internal temperatures of 0-7.2"C for perishable food items displayed for convenient self-service by ice and/or mechanical means (Fraser and Sawyer 1990). In contrast to enclosed refrigerated storage methods, CSUs present special food safety problems for consideration: (a) CSUs are an open system and expose product to room temperature which may, given appropriate time, increase product temperature; and (b) CSUs use a variety of cold-holding methods, such as mechanical and mechanical/ice, unlike refrigerated storage, which only uses mechanical means to maintain temperatures of equal to or less than 7.2"C in a closed system (USDHEW 1978).…”

“…Recommendations for use of CSUs by Fraser and Sawyer (1990) were: (1) When ice is used between the container of food and the mechanically cooked basin of a CSU, foods should be held on the CSU for equal or less than 2 h.…”