2.5.3 Drying Flowers and Buds

Clove buds are spread onto matting and dried in the sun. Occasional gentle raking will aid even drying and it is important to overcome heating and mould formation. Damaged and spoiled buds are removed during this phase. Drying is completed in 4-6 days with buds losing about two-thirds of their weight.

Saffron stigma should be dried the same day as picked from the field, following separation from the floral parts. The stigma is about 85% moisture at field picking and to enable long-term storage of the filaments, a dry matter level close to 1 0 2% is required after the drying. Drying temperatures above 30°C but below 70°C will provide good quality saffron, and irrespective of the drying method, it is important not to over-dry to a brittle stigma. The duration of drying is dependent on the drying temperature used and the higher the temperature used, the shorter is the drying time.

2.5.4 Drying Roots and Rhizomes

Turmeric rhizomes have to be cured after harvest for both colour and aroma. The traditional method of curing rhizomes is to steam or boil fresh rhizomes in lime or a 0.1% sodium bicarbonate solution. The ‘curing’ is to remove the raw odour, reduce the drying time, gelatinise the starch and produce a more uniformly-coloured final product.Traditionally the cooked rhizomes were spread in the sun to dry and this process takes 10-15 days. The final moisture level should be close to 6% moisture content. Today the majority of internationally-traded turmeric rhizomes are artificially dried with hot-air drums, tray and continuous tunnel driers and in India a maximum temperature of 60°C is advised. An important factor in drying time is the preparation of the rhizome. Rhizomes to be dried can be sliced or whole, with slicing generally producing a more uniform and brightly coloured powder. The yield of the dried product varies from 10-30% depending on the variety and the crop-growing environment.

Ginger curing of the rhizome prior to drying directly affects the fibre and volatile oil content. Removal of the skin reduces the fibre content and also increases the oil loss. Peeling also affects the pungency as these compounds (gingerols) are in the skin. When sun drying is not an option wood-fired or solar driers can be used while in Australia gas-heated dehydrators are used. The final dry matter should be in the 7-12% range with a weight loss during drying of 60-70%. Artificial drying minimises the loss of quality and can also eliminate microbial contamination. Drying temperature, airflow and the length of drying all affect the flavour compounds in ginger.

Subsequent to the field harvest, the garlic bulb is broken into individual cloves and the loose paper shell removed by screening and airflow. The cloves are then washed and sliced. The sliced garlic cloves are dried down to about 10% moisture, with a drying temperature below 60°C. In the final drying procedures care is needed to ensure there is no heat damage to the slices and the garlic is dried to 6.5% moisture. Onions are dehydrated in the form of flakes, rings, kibbles and powder. Small-scale onion drying has been achieved by solar drying, but cabinet drying at 55-60°C for 10-15 hours gives a better product than sun drying or drying in solar huts. Commercial dehydration is achieved by forced hot air with an initial temperature of 75°C reducing to 55-60°C as the moisture content falls. Final storage moisture content close to 4% is sought.

Horseradish are very sensitive to wilting and immediately after harvest the roots should be pre-cooled to <5°C using forced air cooling or placed at 0°C with 90-98% RH. Roots can be stored for 12 months under those conditions but pungency is rapidly lost at higher temperatures and roots dry out at lower RH. Perforated polyethylene bags and lined crates can maintain high RH during storage.