2.5.1 Drying Seeds and Fruits
(i ) Immediate drying. After threshing and blanching, pepper fruits are dried in the sun for 7-10 days till the moisture is about 10% and the seeds have the characteristic wrinkled appearance of black pepper. Pepper drying in the sun has to be turned over periodically to aid uniform drying and discourage mould infestation. The main disadvantage of sun drying is the lack of uniformity and potential contamination by microorganisms. Improvements in black pepper need to focus on the drying process. In areas where there is rainfall all year round and a high humidity, the quality of black pepper produced is dependent on drying. Mechanical driers have only had limited success at farm level and the cost of drying using fossil fuels is relatively high but other forms of drying such as solar-driers or solid fuel driers have not been found as effective.
Nutmeg & Mace fruit are dried in their shells in the sun and turned each day to prevent fermentation. The nuts are sufficiently dry when they rattle and drying takes about one week. Artificial dryers are sometimes used. Once dried the nuts can be stored for a considerable time. The separated mace is flattened by hand and dried on mats in the sun. This takes between 2-4 hours. In Grenada mace is cured in dark storage for 4 months. This produces a brittle pale yellow mace that has a premium price.
Chillis ( Capsicums, Chilli peppers and Paprika) have a thick waxy skin, which prevents rapid drying. Sun drying of fruit is the most common method and is undertaken by spreading the crop in a dry area exposed to the sun or under cover. Weather exposure can bring high losses and contamination is also a problem. Fruit are spread in thin layers on a hard dry surface. The use of black plastic under the fruit speeds the drying time. The fruit is regularly stirred to ensure uniform drying and to reduce discolouration and fungal growth. At night or in wet conditions the fruits are heaped and covered. Drying will take up to 15 days dependent on the sunshine hours and weather conditions. A 100kg of fruit produces about 25-35kg of dried spice. Large traders use racks that can be moved in or out of the sun until the fruits are dried below 10% whilst retaining colour and pungency. This system reduces the drying time by half and produces a more uniform product. A chemical emulsion ‘Dipsol’ can be sprayed on fresh fruit to accelerate sun drying. Artificial driers such as energy-efficient heat pump dryers are well suited for drying chillies as they operate at low temperatures. This can be essential for chilli drying under changeable weather conditions as the spice quality becomes less desirable when it becomes brown instead of bright red. The drying temperatures should be below 60°C.
(ii) Programmed drying – the enzymatic development of flavour compounds. Vanilla pods, d uring the curing process, develop flavour as a result of naturally-induced enzymatic action. The final vanilla quality depends mostly on the glucovanillin content in the green bean. This means that the quality of cured beans will be higher if the curing starts with mature beans that have the highest glucovanillin concentration. A number of procedures have been developed for curing vanilla, and they can be characterised into four stages. The first operation is to halt the plant’s physiological functions by stopping vegetative development so that various enzymes can come into contact with cell substrates. The most practical methods are sun- or oven-wilting or hot water scalding. The second operation that is the most crucial step is sweating. Bean moisture is initially allowed to escape rapidly to get to a level that will reduce the risk of microbial spoilage during the subsequent processing. The curing enzymes are most active during this stage and vanillin and related compounds are released during this step that takes 7-10 days. At the end of the sweating process, the cured beans are still 60-70% moisture: too high for safe storage. The third operation is drying to protect the beans from microbial spoilage and also to inhibit further enzyme activity and biochemical changes. At the end of drying the beans should be at 25-30% moisture. The fourth step is storage in closed boxes for several months while chemical reactions take place. There are two main methods of curing, the Mexican process (sun method) or the Madagascar process (Bourbon method). The Mexican method begins with shed storage for some days until the beans start to shrink. The beans are then placed in sweating boxes, for at least 24 hours, where the temperature is maintained to encourage the slight fermentation and flavour-developing enzymatic reactions. This process of wilting and sweating may be repeated a number of times during the early part of curing and extend over a 2-3 week period. The moisture is reduced to the desired level of 25% by frequent exposure to sunlight and sweating. The final curing occurs when the beans are matured in boxes for 2-3 months. The Mexican process of curing takes 5-6 months. The Madagascar process is faster and begins when the pods are dipped in hot water at 80°C for 7-15 min. The beans are then spread out on blankets in the sun, and when well heated are rolled in blankets to stand and ferment overnight. This procedure is repeated over 10 days. At the end of this period the beans are placed on trays and allowed to further cure and dehydrate. The Madagascar process takes 35-40 days.
Allspice – Pimenta berry clusters are taken to a drying shed and left in heaps or sacks for up to 5 days to ferment. Berries are then spread on outdoor drying floors, and turned daily to ensure even drying. The length of drying is dependent on the weather conditions (5-10 days) and the berries are covered at night and during rain. Moisture content close to 12% is the target and the yield from 100kg of green berries is about 55-65kg. Microbial contamination often occurs during the fermenting and drying phase, especially during wet and humid weather. This contamination is almost impossible to counteract and a high microbial count results in berries unsuitable for human consumption. These berries can be distilled. Correctly dried spice should have a pleasant characteristic odour and low microbial counts. These objectives are most easily met by artificial drying, under controlled conditions. Artificial driers (wood fired) are more common in areas where berries ripen in the wet season. Solar driers are more efficient but require a higher standard of post-harvest berry management. Permanently-placed large forced air driers, owned and operated by grower cooperatives or local government, are becoming more common. A maximum drying temperature up to 75°C can be used without loss of essential oil. The problems of microbial contamination can be kept to low levels with good drying and storage management. The dry berries are cleaned and bagged, and kept in a clean dry store.
(iii) Drying to retain colour. Cardamom capsule colour and the retention of greenness are important for highest quality. Capsules cured immediately after picking retained greener colour and the loss of greenness was more significant if the capsules were stored for more than 12 hours. Bagging of the capsules in jute bags, and cool storage, aids the retention of greenness. Cardamom capsules at picking contain 70-80% moisture and to enable storage the moisture has to be taken down to 8-10% by curing. Sun-drying is generally undesirable for cardamom because of bleaching and capsule splitting. The most widely-adopted drying system is a slow dry over 18-30 hours using a number of methods of artificial drying (electric, kiln, bin) with various methods of hot air flow. A temperature between 40-50°C helps retain the green colour and an increase in temperature significantly increases the percentage of yellow capsules, split capsules, and heat injury.
Drying is the transformation of the harvested leaf and stem, containing 80-90% water, to a stable state containing 5-10% water. It is important to minimise the holding time between harvest and drying, and these activities should be co-ordinated to prevent delays in drying and the chance of spoilage. The temperature during drying is critical and if the drying temperatures are too hot the volatile components in the essential oils will be depleted and lost. In general terms drying temperatures should be below 40°C with forced air movement.
