food and bioproducts processing 89 (2011) 128–134 Contents lists available at ScienceDirect Food and Bioproducts Processing journal homepage: www.elsevier.com/locate/fbp Minimising heat losses during batch ohmic heating of solid food M. Zell, J.G. Lyng * , D.J. Morgan, D.A. Cronin School of Agriculture, Food Science and Veterinary Medicine, Agriculture and Food Science Centre, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland abstract The influence of cell design on the uniformity of batch ohmic heating of a solid foodstuff was examined. Various ways of minimising heat loss from the cell surface including insulation or providing supplementary heat via a heating belt or panel were assessed but discarded in favour of housing the cell in a hot air cabinet maintained at 80 ◦ C and eliminating the surrounding cell body. Various electrode materials and designs were evaluated prior to opting in favour of platinised titanium electrodes of minimal practicable thickness (1 mm). The final system developed involved the use of a combined ohmic/convection heating with the food stuff contained in a plastic casing pressurised between two spring-loaded electrodes. Under optimised conditions a maximum overall temperature variation of 12.1 ◦ C within the product was achieved after 150s which was reduced to 8.6 ◦ C after 3 min standing time. © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Ohmic heating; Cell design; Electrode design 1. Introduction Ohmic heating, also called electrical resistance heating, is a heating process where an alternating current is passed through food materials thereby leading to heat generation. It is a rapid heating method and has been suggested to be more uniform than other electroheating techniques (Morrissey and Almonacid, 2005). The main difference between ohmic heat- ing and other electrical heating methods is that electrical energy is directly dissipated into the product. Ohmic heating technology dates back to the end of the 19th century (Fowler, 1882) and the most successful commer- cial applications have been in the area of heat processing pumpable particulate foods (Biss et al., 1989; De Alwis and Fryer, 1990). In contrast ohmic heating of solid food materials is at a less advanced state of development. Lyng and McKenna (2007) comprehensively reviewed the use of ohmic heating for meat and meat products. These investigations focused mainly on the cooking of meat emulsions and batters (such as hams, luncheon rolls, liver pate) in static ohmic heating cells. More recent papers (Shirsat et al., 2004; Piette et al., 2004) concluded that ohmic heating has the potential to cook meat products ∗ Corresponding author. Tel.: +353 1 7167710; fax: +353 1 7161149. E-mail address: james.lyng@ucd.ie (J.G. Lyng). Received 5 August 2009; Received in revised form 23 February 2010; Accepted 14 April 2010 to a level of quality comparable to conventionally processed samples. Key requirements for an ohmic heating system for solid (i.e. meat) products include: (a) ensuring that the heating cell is uniformly filled, with a good contact between the product and the electrodes (Castro et al., 2004), (b) uniform electrical con- ductivity within the product (Halden et al., 1990; Sastry, 1992) and (c) minimising heat losses from the system (Marcotte et al., 1998; Marra et al., 2009). While the preparation of product with uniform electrolyte distribution is relatively straightfor- ward for highly comminuted emulsion type systems, it is less easy to achieve the same effect with injected whole muscle meats so as to ensure they are in an optimised state for ohmic cooking. Recent work by the present research group has led to the development of meat preparation protocols which largely satisfy the latter requirement (Zell et al., 2009b) and to a math- ematical model predicting cold regions and heat losses to the electrode and cell surfaces (Marra et al., 2009). Based on these preliminary studies it was apparent that a design modifica- tion was essential in order to reduce heat losses to the cell and electrode surfaces. In particular, depending on the type of product containment cell and electrodes used, heat losses 0960-3085/$ – see front matter © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fbp.2010.04.003