Cryogenic Grinding Essay

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Design of a cryogenic grinding system for spices Abstract 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 favouring 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 ÿ70°C. Above this temperature, sieve clogging took place. The increase in grinding temperature from-160°C to-70°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°C to -70°C, but this variation was found to be non-significant at 5% level. process Grinding of spices is an age-old technique like grinding of other food materials. The main aim of spice grinding is to obtain smaller particle size with good product quality in terms of favour and colour. In the normal grinding process, heat is generated when energy is used to fracture a particle into a smaller size. This generated heat usually is detrimental to the product and in some loss of favour and quality. The fat in spices generally poses extra problems and is an important consideration in grinding. During

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