Macrowave Radio Frequency Co.

Macrowave™ HydraTherm™ Pasteurization Technology for Controlling Salmonella Enteritidis PT30 in Harvested Almonds

Confirmed by Independent Laboratories, the Macrowave™ HydraTherm™ Treatment is Proven Capable of Achieving a >6 log Reduction


Studies funded by the Almond Board of California concluded that SE PT30 is particularly resistant to dry heat treatments. The thermal death time curves of this pathogen posed practical challenges when trying to identify a combination of temperatures and dwell times that would yield the desired 4-log reduction without adversely impacting the quality of the raw nuts.

Radio Frequency Co., Inc. provided the solution with its Macrowave™ HydraTherm™ Pasteurization system!

RFC's Macrowave™ Treatment system readily achieved a >6 log reduction as confirmed by an independent testing laboratory, and did so without any detrimental sensory impact to the natural raw almond flavor or texture in the treated almonds.

Benefits of Macrowave™ HydraTherm™ Treatment:
  • Rapid and Preferential Heating of the Exterior of the Almond Only
  • The Internal Almond Kernel is Virtually "Unaffected" According to Sensory Panel Experts
  • Minimizes the temperature/time necessary to achieve the desired log reduction as compared to alternative Pasteurization methods
  • Post Treatment Water Activity is Minimized
Advanced Features of HydraTherm™ Systems:
  • Automated Controls for Ease of Operation
  • Energy Efficient Design Minimizes Operating Cost
  • Heating is completely uniform and Controllable
  • Requires No Special Building or Boiler to Operate and Maintain.
  • Automatic Data Logging for Batch Validation
  • Non-Abrasive Conveyance Minimizes Fines

Founded in 1946, Radio Frequency Company specializes in developing and manufacturing high frequency heating systems for the food industry. RFC is the technological leader in RF processing technology and is widely known for maintaining the highest standards in quality equipment and service. With over 3,000 systems installed worldwide, Radio Frequency Company offers a full line of systems for the bulk pasteurization and/or insect deinfestation of nut meats, various types of flour, tobacco, fishmeal, xanthan gum, and other food ingredients as well as finished products.

Photo of Radio Frequency Co. Offices and Manufacturing Plant in Millis, MA Photo of Cracker Products

Recognizing the particular challenges posed by the exceptionally dry heat tolerant Salmonella strain, SE PT30, Radio Frequency Company (RFC) developed our Macrowave™ HydraTherm™ Treatment for almond pasteurization. Five key factors contribute to the efficacy of the system in achieving the required minimum 4-log reduction of SE PT30 while maintaining the desirable raw characteristics of the almond:

  • Reduction of SE PT30's heat tolerance through hydration;
  • Focusing the RF energy field on the surface of the almond where the Salmonella are present;
  • Providing rapid temperature rise on the almond surface to kill the SE PT30 before it can retreat to a defensive posture;
  • Minimizing unnecessary heating of the almond kernel; and
  • Minimizing the post-treatment water activity of the almonds by evaporating the water applied during hydration to prevent potential microbial, mold, and yeast growth.

In a radio frequency heating system the RF generator creates an alternating electric field between two electrodes. The material to be heated is conveyed between the electrodes where an alternating energy field causes polar molecules in the material to continuously reorient to face opposite poles much like the way bar magnets behave in an alternating magnetic field. Because the almonds are hydrated only on the exterior surfaces, they will be preferentially heated, killing the pathogens, while the internal kernel is virtually treatment free.

For additional information or a system proposal, please contact:

Tim Clark
President & General Manager
(508) 376-9555

Process and Instrumentation Diagram

Process and Instrumentation Diagram
  1. Product Feed Hopper with Vibratory Feed Tray - The Feed Hopper is a stainless steel product holding vessel that dispenses the almonds onto a vibratory feed tray and into the hydration system coating drum.
  2. Pre-Hydration Moisture Sensor - Moisture is measured prior to entering the hydration system. The moisture content is then transmitted to the system programmable logic controller (PLC) and is utilized in the calculation of the desired hydration rate.
  3. Hydration System - The Hydration System applies water to the surface of the almonds at a rate automatically controlled, based on the initial product moisture, temperature and operator inputs for the desired log reduction and final product moisture content.
  4. Post-Hydration Moisture Sensor - The moisture content of the post-hydrated product is measured and transmitted to the system PLC prior to entering the Macrowave™ System
  5. Conveyor - The Conveyor System transports the almonds through the RF Applicator on a food grade Kevlar coated open-weave "troughed" belt to prevent product spillage.
  6. Entrance Temperature Sensor - The temperature of the almonds is continuously measured and transmitted to the PLC and is utilized by the system algorithm that controls the process speed.
  7. High Frequency RF Generator and Applicator - The two major components of the Macrowave™ Heating System work together to apply radio waves, which will preferentially heat the moist surface and interstices of the almonds appropriately to achieve the desired log reduction of SE PT30.
  8. Exit Temperature Sensor - The temperature of the almonds is continuously measured and transmitted to the system PLC. Product that does not reach the appropriate temperature is diverted for re-treatment.
  9. Exit Moisture Sensor - The moisture content of the almonds is continuously measured to determine the average moisture content of the almonds as they leave the heating chamber and is transmitted to the system PLC.
  10. Integrated Operator Interface and Programmable Logic Controller (PLC) - The High Frequency System is controlled by an Allen-Bradley ControlLogix™ PLC. Process parameters are continuously recorded and stored locally or remotely in accordance with customer/industry requirements.
  11. Automatic Conveyor Diverter - The diverter logic is derived from the temperature and moisture content feed-back at the exit locations of the Macrowave™ Heating System.

Radio Frequency Co. 150 DOVER ROAD, MILLIS, MA 02054-0158 USA
TEL 508-376-9555 e-mail:
FAX 508-376-9944

Macrowave™ is a registered trademark of Radio Frequency Company, Inc. 2006 Radio Frequency Co., Inc.

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