화학공학소재연구정보센터
Journal of Food Engineering, Vol.39, No.4, 359-368, 1999
Design of a cryogenic grinding system for spices
The fat content of spices poses problems of temperature rise and sieve clogging during grinding. Due to this temperature rise, spices lose a significant fraction of their volatile oil or flavouring components. Therefore, a cryogenic grinding system was designed and developed to cool the spices before feeding to the grinder and also maintain the cryogenic temperature in the grinding zone. The main components of the cryogenic grinding system are a precooler and grinder. The precooler consists of a screw conveyor assembly, a compressor, a liquid nitrogen dewar and power transmission unit. The design considerations, calculations and development of the precooler have been discussed in the paper. A commercially available grinder was adopted for this purpose. The tests conducted on grinding of cumin seed revealed that it could be successfully ground below the temperature of -70 degrees C. Above this temperature, sieve clogging took place. The increase in grinding temperature from-160 degrees C to -70 degrees C resulted in a significant increase in particle size of the product and specific energy consumption in grinding. A variation in volatile oil content was obtained in the range of 3.30-3.26 ml/100 g with increasing temperature from -160 degrees C to -70 degrees C, but this variation was found to be non-significant at 5% level.