Research note Effect of combined vacuum cooling and air blast cooling on processing time and cooling loss of large cooked beef joints Patrick Jackman, Da-Wen Sun * , Liyun Zheng FRCFT Group, Biosystems Engineering Department, University College Dublin, National University of Ireland, Earlsfort Terrace, Dublin 2, Ireland Received 10 July 2006; received in revised form 30 October 2006; accepted 31 October 2006 Available online 15 December 2006 Abstract Experiments were carried out to test two combined cooling methods for their suitability in minimising the cooling loss and cooling time to 10 and 4 °C of large cooked beef joints. The combined cooling methods were: vacuum cooling of the cooked joint to an inter- mediate temperature of 35, 30, 25, or 20 °C and then air blast cooling to the final temperature of 4 °C; and air blast cooling to an inter- mediate temperature of 35, 30, 25 or 20 °C and then vacuum cooling to the final temperature of 4 °C. It was found that the latter method was more effective at minimising the cooling loss with similar cooling loss to air blast cooling. Both methods were similar in optimising the cooling time to 10 °C and could produce cooling times similar to the Irish and British recommended cooling times. Neither method could give a cooling time similar to vacuum cooling. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Vacuum cooling; Air blast cooling; Beef; Meat; Food safety; Refrigeration; Combined cooling 1. Introduction Cooked beef is a significant sector of the food industry. Pre-cooked beef appears commonly in fast food outlets, sandwich bars and convenience food for domestic use. In order to ensure microbial safety of pre-cooked beef, rapid cooling is essential to stop microbial spores germinating, growing and forming toxins. Microbial safety is ensured by first heating all regions of the joint to at least 72 °C for at least 15 s and then cooling it to below 10 °C within 150 min (Desmond, Kenny, Ward, & Sun, 2000; McDon- ald & Sun, 2001a). There are a wide variety of recommen- dations throughout Europe on appropriate cooling times required to a specified low temperature for beef as reported by McDonald (2001). Cooling is normally continued to 4 °C when transfer to a slow chiller for storage. There are a number of commercial cooling methods available in practice, which includes air blast cooling, water immersion and slow chilling. Each is a variation of the same concept whereby the food is exposed to a cold med- ium, heat conducts through to the outer surface and heat leaves the food by surface convection. Air blast cooling is a rapid conventional method due to forced convection at the surface. An alternative method is vacuum cooling, in which heat leaves the food by means of latent heat of evap- oration of water. Vacuum cooling is currently the only technology available to cool large cooked meat joints within recommended times. However, vacuum cooling causes high weight loss due to the nature of water evapora- tion. A number of proposals have been put forward to mit- igate the high cooling loss but each with some disadvantages. For example, increasing brine injection can offset the cooling loss but it also increases the salty taste so brine injection cannot be increased indefinitely; reducing the evacuation rate can reduce cooling loss but it also slows down the vacuum cooling process; prewetting or water spraying in chamber can lower cooling loss but it may impose a cross contamination risk (Sun & Zheng, 2006). Vacuum cooling is able to generate very fast rates of heat transfer due to the vaporisation mechanism. 0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.10.026 * Corresponding author. Tel.: +353 1 716 5528; fax: +353 1 475 2119. E-mail address: dawen.sun@ucd.ie (D.-W. Sun). URLs: www.ucd.ie/refrig, www.ucd.ie/sun (D.-W. Sun). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 81 (2007) 266–271