Spices play a major role in Indian cooking as ingredient that adds flavor and character to the
food. The spices are blend to make spice blends or masalas for different food preparations. The
masala making process has three major steps a) roasting, b) blending in proportion (recipe) and
c) grinding. The roasting process requires precision heating for imbedding aroma and color. LPG
(Liquefied Petroleum Gas) stove is used for precision heating like roasting. The roasting operator
uses hand eye coordination to observe color change and rate of stirring to achieve desired degree
of roasting along with smell of aroma.
India is blessed with average solar radiation of 5.5 kWh/m2
/day in the most of the parts of the
country, the use of solar energy for roasting could be one of the ways to reduce fossil fuel
consumption. The solar thermal energy has fully been used for boiling type cooking process
through generation of steam or hot water. Present research work looks at the possibility of using
the solar thermal energy for a roasting in spice industry. Pleasant aroma, attractive color and
texture are characteristics of good masala. Presently this is achieved by experienced (skilled)
roaster on LPG stove by precision stirring and heat control. The solar roaster wit heat control and
automated stirring could be useful product for spice industry. The present research is focused on
study of small scale spice industry, study their roasting process and develop a solar based roaster
for their roasting needs.
The small-scale spice industry field visit revels importance and critically of roasting operation in
spice making, the roasting is skilled job and requires a hand eye coordination along with sense of
smell to decide with roasting completion criteria. LPG cost in overall product costing is in the
range of 5-10%. The critically of roasting process blocks the skilled person (generally owner of
small business) and hampers his time spending on other business activity.
Concentrated Solar Thermal (CST) technology is used to deliver the desired heat rate at roasting
temperature. CST parabolic trough of 2m2
aperture along with evacuated glass tube collector
(ETC) is used for configuring the solar roaster. The parabolic trough is mounted with segmented
(long strips) glass mirror reflectors to reflect solar radiation at a focal point, at focal point ETC
tubes are used to intercept the solar radiation. The ETC tubes wee half filled with roasting
material and rotated using a 5W DC electric motor.
The research work was focused on proving the concept of using configuration of CST parabolic
trough with ETC tube for generation temperatures and heat rate for roasting process. First,
prototype is developed using various engineering and optics concepts like sizing of parabolas,
mirror mounting arrangement etc. the prototype is used for experimenting roasting of various
The amount of material varied from 300gm to 900 gm depending on bulk density of material.
The experimental investigation for roasting various ingredients suggest strong relation of solar
radiation and initial moisture content on roasting time, this varies from 10 minutes to 60 minutes.
The thermal efficiency of solar roasting process was in the range of 25-57%. The roasting
process is also demonstrated to spice roaster.