ABSTRACT
The concept of ohmic heating technology is not new and dates back to 1897 (Jones 1897). Ohmic heating, also known as Joule heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. This was rst studied by James Prescott Joule in 1841. Joule immersed a length of wire in a xed mass of water and measured the temperature rise due to a known current owing through the wire for a 30-min period. By varying the current and the length of the wire he deduced that the heat produced was proportional to the electrical resistance of the wire multiplied by the square of the current. This relationship is Joule’s First Law (https:// en.wikipedia.org/wiki/Joule_heating):
Q = RI 2. (3.1)
George Simon Ohm (1789-1854) determined that there is a direct proportionality between the potential difference (voltage, V in volts) applied across a conductor and the resultant electric current (I in amperes) (Ohm’s law):
V = RI, (3.2)
where R is the electrical resistance measured in ohm. Since the heat results from the electrical resistance, it is referred to as “ohmic” heating. Other synonyms are used in the literature to describe this principle of heating: direct resistance heating, electroconductive heating, and electroresistive heating. Ohmic heating has attracted considerable attention in the last two decades for the thermal processing of foods due to its rapid and uniform treatment coupled with its high-energy efciency and technical simplicity. Ohmic heating has been used for many food processes such as pasteurization, dehydration, extraction, microbial inactivation, blanching, and thawing (Sastry 1991; Palaniappan and Sastry 1990; de Alwis and Fryer 1990).
