Background:
Nagauri methi (Trigonella corniculata L.) is a semi-arid crop belonging to the family Fabaceae. It is commonly known as Paan methi or Champa methi’ and ‘marwari methi’, is diffused sub erect and strongly scented annual herb. It remains rosette condition during most of the vegetative growth period. The dried leaves are the economic part of this plant. In India, it is mainly grown in northern states like Rajasthan, Maharashtra, Gujarat, Uttar Pradesh, Madhya Pradesh, Haryana and Punjab. Rajasthan occupies 80 per cent area and production of Nagauri methi in the country. The fresh green leaves are used as condiment for giving delicious flavour. The dried leaves have an aromatic odour and agreeable spicy taste. Being odoriferous, the dried leaves and their powder are used as condiment flavouring agent and for medicinal purposes in different vegetable and prantha preparations. Likewise fennel seed for Lukhnowi Saunf is dried under the thatched structures and leads to deterioration of quality:
Traditional drying of Nagauri methi and fennel seed: Open sun drying is one of the oldest and common techniques employed for drying Nagauri methi or paan methi. Considerable savings can be made with this type of drying since the source of energy is free and sustainable. However, this method of drying is extremely weather dependent and has the problems of contamination, infestation, microbial attacks and so forth, thus affecting the product quality. Additionally, the drying time required for a given commodity can be quite long and results in postharvest losses. Technology details:
Solar dryer is an improved form of sun drying in which drying is accomplished in a closed structure under relatively controlled conditions utilizing the thermal energy of sun. Various types of solar dryers have been developed as an alternative to open air sun drying and other conventional drying methods. In the plastic sheet covered walk in tunnel solar dryer, air is heated inside the dryer due to greenhouse effect by natural means. Increased drying process takes place by hot air flow, and the passage of an air mass around a product represents a complex thermal process where unsteady heat and moisture transfers occur simultaneously. Heat and moisture transfer removal rate depends on air velocity and temperature of the circulating drying air. The total cost of a tunnel (5x25 m =125 m2 area) is Rs 50000 and actual working/ annual cost is Rs 8500/- which can be recovered in first year itself as it can be used in cyclic mode (20-25 cycles) for drying leaves in a growing season of 135-150 days.