OHMIC Heating

INTRODUCTION

  • Ohmic heating is a thermal electrical heating method. It is also called resistance heating.
  • Ohmic heating is a direct heating method where food is in contact with the electrodes [1].
  • The idea behind ohmic heating is straightforward. When an electrically conductive food substance is subjected to an electric current, Ohm’s law (V=IR) is followed, and heat is produced as a result of the electrical resistance of the food. 
  • The product may be heated to a sterilizing temperature of up to 140 °C in less than 90 seconds even though it contains big particles up to 2.5 cm in size that would be damaged in traditional equipment. [2].
  • It is regarded as a sustainable food processing method.

WORKING PRINCIPLE​

Ohmic heating operates on the basis of Ohm’s Law. [3].

That is V= I*R

Where V is voltage(Volts), I is the amperage(amperes), R is the resistance(ohms)

It contains three parts:

  1. Power supply
  2. Heater assembly
  3. Control panel

MECHANISM

  • Electrical conductivity influences Ohmic Heating.
  • Food is heated by electric current when it flows through it.
  • Substances like acids and bases facilitate conductivity, which may not occur in fats.
  • As a result, the material’s conductivity varies with the type of food.

Ohmic heating process diagram[3]

APPLICATIONS​ OF OHMIC HEATING

  • The Ohmic heating technology enables the manufacture of new, high-value, shelf-stable goods with a quality previously unachievable with alternative sterilization processes[3].​
  • Ohmic Methods offer a shorter drying time and a reduction in solute loss.​
  • It is also applicable for specific food products like meat(uniform heating), fish(no change in water-soluble protein), milk(effective pasteurization with no additional protein destruction), fruits (Juice extraction, Juice preservation), vegetables (Blanching), egg(pasteurize egg, Reduce fouling)[4].​

ADVANTAGES​ OF OHMIC HEATING

  • The temperature required for UHT processing can be achieved.
  • No problem of surface fouling or overheating of the product.
  • Useful in pre-heating products before canning.
  • Energy conversion efficiencies are very high.
  • Suitable for continuous processing.
  • Ohmic heating is more economical than microwave heating and conventional heating.
  • Large-scale processes can be carried out in heavy–duty ohmic cookers or batch ohmic heaters.
  • It has a high solid–loading capacity.
  • Ohmic heating causes less nutrient loss.
  • It provides a rapid, uniform treatment of liquid and solid phases with minimal heat damage.
  • Less maintenance cost.
  • Eco-friendly.

DISADVANTAGES​ OF OHMIC HEATING

  • Lack of generalized information.​
  • Fat-rich food may not be heated with Ohmic heating since it is a poor conductor of electricity.
  • Narrow frequency band.​
  • Difficult to monitor and control.​
  • Complex coupling between temperature and electric field distribution.​
  • It is limited to Direct Current [3].​​​