Economical roasting thanks to a sensor inside a coffee bean
PTB develops a new technique for measuring the thermal conductivity and thermal diffusivity of small bodies and hereby helps industry save energy
Up to now, it has been impossible to measure a single bean. Instead, pressed coffee grounds are investigated, a procedure which unfortunately furnishes only rough estimates for the structure-dependent transport properties of beans. Not only the coffee bean is considered to be "too small to be measured", but the same applies also to other foods and luxury food, as, for example, to nuts.
The novel technique from PTB solves the above problem. As a sensor, a commercially available surface temperature detector of 50 m in thickness and a surface area of only 3.1 mm x 3.0 mm, is sufficient. For analysis, the sensor is sandwiched between the two halves of a bean and already after two or three minutes, the result is obtained. As the thermal conductivity of a bean also depends considerably on its humidity, this property can also be determined. The sensor tolerates temperatures of up to 180 °C. This enables it to constantly measure current values for the transport quantities mentioned - even during the drying or roasting process. Thus, the energy-relevant parameters of the two processing steps are at any time available for control and optimization of the entire process.
With the new procedure, the thermal conductivity of a sample having a volume of only 100 mm3 and, if required, also its moisture content, can be determined within a few minutes and with only one single measurement. In addition, the procedure allows the temperature diffusivity and the volumetric specific heat to be measured. A conventional - commercially available - sensor is sufficient for such measurements, which can then be performed at temperatures between -50 °C and 180 °C.
Contact person:
Dr. Ulf Hammerschmidt, Working Group 1.74 Thermal Conductivity, Heat Transport Department
Phone: +49(0) 531 592-3211,
e-mail: ulf.hammerschmidt(at)ptb.de