Infrared vs hot-air roasting for nuts, seeds and spices

How a hot-air roaster works

A conventional roaster or dryer works by convection. A burner or heater raises the temperature of a large volume of air, a fan moves that air through the product, and the air gives up its heat on the way past. The air is the carrier, and the carrier has to be heated first.

How infrared differs

Infrared is radiant. Energy travels from the emitter to the material directly, with no medium in between. Four things follow.

• No medium to heat. Energy goes straight into the product, with no volume of air to heat and blow through it.
• No loss through the carrier. Convective systems lose heat through ducting, leakage and exhaust, because the air must be moved and moved air escapes.
• Instant heat. Emitters reach working output immediately, so there is no warm-up period.
• Quick start, stop and changeover. Switch off and the heat stops. A convective system holds its heat in the air and the ductwork, so the plant must cool before the next product goes through.

For a processor running several products in a shift, the last of those is often worth more than the energy saving.

Why shortwave infrared

Shortwave infrared penetrates further into the material than medium or long wave, so the heat is developed within the piece as well as at its surface. That is what allows the drum to run without scorching the outside to dry the inside.

Why a rotary drum

On a flat bed or belt the product lies still: the face towards the heaters takes the energy, and the top scorches before the bottom is done, so belts run long and slow. In a rotary drum every particle is lifted, carried and dropped, so the whole charge is presented to the heat. Roast-O-Dry^™ runs as a continuous, first-in first-out drum.

Adding UV-C

UV-C travels in straight lines and does not turn corners. Nuts, seeds and spices are irregular and opaque, so a static bed shades itself. In the drum each face comes round to the UV-C field again and again. This describes exposure, which is mechanical and can be observed. SpectraCure IR-UV^™ adds the UV-C stage to the Roast-O-Dry drum.

We do not publish log-reduction figures, shelf-life claims or microbial data for this machine. Process validation belongs to the food business operator, under its HACCP plan. Our part is to supply the machine, its parameters and its records.

Where to go next

See Roast-O-Dry^™ for sizes and throughput, SpectraCure IR-UV^™ for the UV-C version, or Solutions to start from the job you need to do.