Ohmic heating is a method where alternating electric current passes through food, generating heat due to the food's electrical resistance, resulting in rapid and uniform heating. Initially used in the early 20th century for pasteurizing milk, its commercial applications have grown, particularly for high-value ready meals and sensitive liquid foods. The technology offers advantages such as reduced product damage, efficiency, and minimal nutrient loss, but faces challenges like complex conductivity relationships and regulatory approval for multi-phase food products.

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3. Introduction
Ohmic Heating is a process in which an alternating electric current is
passed through a food, and the electrical resistance of the food causes the
power to be translated directly into heat.
Electrical energy is dissipated into heat, which results in rapid and uniform
heating.
Unlike conventional heating where heat transfer occurs from a heated surface
to the product interior by means of convection and conduction,
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4. History Ohmic Heating
Its not a new technology , used as a commercial process in the early 20th century for
the “Pasteurization of Milk”.
The “Electro pure process” was discontinued between the late 1930s and 1960s,
because of the high cost of electricity and a lack of suitable electrode materials.
Interest in ohmic heating was rekindled in the 1980s, when investigators were
searching for viable methods for effective sterilization of large liquid particle.
In Conventional heating heat transfer occurs from a heated surface to the product
interior (means of convection and conduction) and is time consuming.
 Electro resistive or ohmic heating is volumetric in nature and thus has the
potential to reduce over processing by virtue of its inside–outside heat transfer
pattern.
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5. It is now in commercial use in Europe, the USA and Japan for:
• Aseptic processing of high added-value ready meals, stored at ambient
temperature
• Pasteurisation of particulate foods for hot filling
• Pre-heating products before canning
• High added-value prepared meals, distributed at chill temperatures
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6. How is Ohmic heating different from
conventional thermal processing..?
During conventional thermal processing, either in cans or aseptic
processing systems, significant quality damage may occur due to slow
conduction and convection heat transfer
Ohmic heating volumetrically heats the entire mass of the food
material, thus the resulting product is of far greater quality.
It is possible to process large particulate foods (up to 1 inch) that
would be difficult to process using conventional heat exchangers.
Ohmic heater cleaning requirements are comparatively less than
those of traditional heat exchangers due to reduced product fouling on
the food contact surface.
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7. Principle of Working
Based on the passage of alternating
electrical current (AC) through a body such
food system which serves as an electrical
resistance in which heat is generated.
➜ Foods contain water & ionic salts; capable
of conducting electricity, but also have a
resistance which generates heat when an
electric current is passed through. This
resistance produces heat.
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R = (1/σ)(L/A)

8. Working
 Electrode: Platinized titanium electrode to
prevent leaching (often coated with a high
temp inert plastic material) (if stainless
steel electrodes are used working at
frequencies of above 100KHz eliminates
this problem)
 Temperature : 40°C - 140°C, for <90 sec
followed by cooling for 15 minutes
 Pressure : Up to 4 bar for UHT to prevent
product from boiling
 Frequency : 50-60 Hz
 Voltage : upto 5000 V
 Uniform mass flow rate
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9. A viscous food product enters the
continuous-flow system via a feed pump
hopper.
 The product then flows past a series of
electrodes in the ohmic column, where it is
heated to process temperature.
Then the product enters the holding tubes
for a fixed time to achieve commercial
sterility.
Next, the product flows through tubular
coolers and into storage tanks, where it is
stored until filling and packaging
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10. Control Parameters
Electrical conductivity, temperature dependence of conductivity, design of
heating device, residence time, thermo physical properties of food, electric
field strength.
However, the most important factor is the electrical conductivity of the
product and its temperature dependence.
If the product has more than one phase such as in the case of a mixture of
liquid and solids, the electrical conductivity of all the phases has to be
considered.
The electrical conductivity increases with rising temperature.(resistance of
food falls by factor of 2 to 3 over temperature rise of 120 ·C)
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11. Factors affecting ohmic heating
Electrical conductivity of food and food mixture which in turn depends
on food components: ionic components (salt), acid, and moisture
mobility increase electrical conductivity, while fats, lipids, and alcohol
decrease it.
Fluid viscosity : higher viscosity fluids shows faster ohmic heating than
lower viscosity fluids
In case of liquid + solid mixture, the property of the two components
also affects ohmic heating, particulate size (up to 25mm ideally )
Density and specific heat of the food product
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12. Microorganisms inactivation by
ohmic heating
Like thermal processing, ohmic heating inactivates microorganisms by
heat
Also non-thermal electroporation type effects have been reported at
low-frequency (50-60 Hz), when electrical charges can build up and
form pores across microbial cells, however, it is not necessary to claim
such effects since heating is the main mechanism.
Electroporation is a significant increase in the electrical conductivity
and permeability of the cell plasma membrane caused by an externally
applied electrical field
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13. Ohmically Processed Commercial Products
Available on the Market
A number of processing plants
currently produce sliced, diced, and
whole fruit within sauces in various
countries
In the United States, ohmic heating
has been used to produce a low-
acid products and pasteurized liquid
egg
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14. Application of ohmic heating
Ohmic heating can be used for heating liquid
foods containing large particulates, such as
soups, stews, syrups and sauces, and heat
sensitive liquids
The technology is useful for the treatment of
proteinaceous foods, which tend to denature
and coagulate when thermally processed.
Liquid egg can be ohmically heated for a
fraction of a second, without coagulating it.
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15. Cont…
Juices can be treated to inactivate
enzymes without affecting the flavour.
Other potential applications of ohmic
heating include blanching, thawing,
on-line detection of starch
gelatinization, fermentation, peeling,
dehydration, and extraction.
Currently used in a large number of
fruit processing plants in the US and
Europe
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16. Advantages
It can heat particulate foods and Liquid–particle mixtures. By ohmic
heating, high temperatures can be rapidly achieved(due to uniform
heating). For e.g., Temperatures for UHT processing
As there are no hot surfaces for heat transfer, there is low risk of product
damage due to burning
It has high energy conversion efficiency (90%)
It requires relatively low operative cost.
Very clean and hygienic systems
Minimal thermal deterioration of food resulting in minimal mechanical
damage and better nutrients and vitamin retention.
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17. Disadvantages
Complex relationship between conductivity and temperature
Leaching of electrode material into the food systems
Ohmically processed multi-phase food product is not yet approved by the
FDA (as of 2001)
Expensive in terms of installation and equipment manufacture
Low conductivity foods cannot be processed eg. foods having fat globules
Rapid increase of conductivity with temperature may lead to “runaway
heating”
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18. Shelf Life of an Ohmically Processed Product
The shelf life of ohmically processed foods is comparable to that of
canned and sterile, aseptically processed products
This process uses ordinary electricity. No emissions are produced at
the point of use
One emerging application of ohmic heating is fruit peeling, which
may greatly reduce the use of lye that is common to such operations,
and results in environmental benefits
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19. Reference
• (De Alwis and Fryer 1990)
De Alwis, A. and P. Fryer (1990). "The use of direct resistance heating in the food
industry." Journal of Food Engineering 11(1): 3-27.
• (Halden, De Alwis et al. 1990, Icier and Ilicali 2005)
Halden, K., et al. (1990). "Changes in the electrical conductivity of foods during ohmic
heating." International Journal of Food Science & Technology 25(1): 9-25.
• (Icier and Ilicali 2005)
Icier, F. and C. Ilicali (2005). "Temperature dependent electrical conductivities of fruit
purees during ohmic heating." Food Research International 38(10): 1135-1142.
• Gopu Raveendran Nair, V.R Divya, Liji Prasannan, V. Habeeba, M.V. Prince, G.S.V.
Raghavan, Ohmic heating as a pre treatment in solvent extraction of rice bran, June
2012
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