Organisation: Food and Agriculture
Organization of the United Nations (FAO), AGST
Prepared by Anne Plotto.
Edited by François
Mazaud, Alexandra Röttger, Katja Steffel, Larissa D'Aquilio (HTML transfer)
CHAPTER XXVIII HIBISCUS: Post-Production
Management for Improved Market Access for Herbs and Spices - Hibiscus
2 Post-production operations
2.1 Pre-harvest operations
2.1.1 Planting
2.1.2 Growth
2.2 Harvesting
2.3 Drying
2.4 Packaging and processing
Roselle is an annual bushy shrub that grows to approximately 2.4 meters in one growing season. While it is relatively easy to grow, it is more difficult to produce consistently high quality. This is a function of seed stock, local growing conditions, harvest time, and post-harvest handling, in particular the drying process.
Roselle is quite hardy and grows in most well drained soils. It can tolerate poor soil, and is often grown as a supplemental rather than a primary crop. It requires 4-8 months with nighttime temperatures not below 21oC. In addition, it requires 13 hours of sunlight during the first 4-5 months of growth to prevent premature flowering.
Roselle requires a monthly rainfall ranging from 5-10" (130-250 mm) in the first 3-4 months of growth. Dry periods can be withstood and are desirable in the last months of growth. Rain or high humidity during the harvest time and drying can downgrade the quality of the calyces and reduce the yield.
Hibiscus sabdariffa is very sensitive to changes in the length of day. This photoperiodic quality of blooming, when the days become shorter, require the planting time to be set according to the day length and not according to the rainfall requirements. It is a deep-rooted crop, therefore deep plowing is recommended in preparing the seedbed. To produce a large calyx 1,000-2,000 pounds of manure are added per acre (1-2 tonnes/ha).
Seeds are planted at a rate of 6-8 pounds or less per acre (6-8 kg/ha) and approximately one inch (2.5 cm) deep. Seeds are usually planted in the spring at the beginning of the rainy season, 2-3 feet (0.60-1 m) between rows and 18-24 inches (45-60 cm) within the rows. The reduced planting rate produces a larger calyx. Sowing can be done by hand, or with a modern grain drill. A good alternative tool would be a corn planter small enough to accommodate the hibiscus seeds. Thinning is done by hand as well.
There are over 100 cultivars or seed varieties of Hibiscus sabdariffa. The major commercial varieties are those grown in China, Thailand, Mexico and Africa, principally Sudan, Senegal and Mali. In most other countries, small farmers carry out the bulk of production, but in the Sudan, nomadic goat herders are known to pick the product from semi-wild sources.
Flowering of the hibiscus is induced as the days become shorter and light intensity reduces. Flowering begins in September or later depending on the country in question, and continues through October or later when the entire field is in bloom. Flowers begin to drop at the end of October or later. Flowers are diurnal and last only a day. The seedpods begin ripening towards the bottom and proceed to the top. In Sudan, growers will sometimes allow the seed to completely ripen and the leaves drop prior to harvest.
Hibiscus sabdariffa is harvested from late December onwards. The harvest is timed according to the ripeness of the seed. The fleshy calyces are harvested after the flower has dropped but before the seedpod has dried and opened. The more time the capsule remains on the plant after the seeds begin to ripen, the more susceptible the calyx is to sores, sun cracking, and general deterioration in quality. All harvesting is done by hand. Total yield is about half a ton per hectare.
Special care must be taken during harvesting operation to avoid contamination by extraneous material. At no time should the calyx come in contact with the ground or other dirt surfaces. Clean bags or containers should be used to transport from the field to the drying location.
Different harvesting methods are in use today. In Mexico the entire plant is cut down and taken to a nearby location to be stripped of the calyces. In China only ripe calyces are harvested with clippers leaving the stalks and immature calyces to ripen in the field. The field is harvested approximately every ten days until the end of the growing season. The calyx is separated from the seedpod by hand, or by pushing a sharp edged metal tool through the fleshy tissue of the calyx separating it from the seedpod.
Thailand has perhaps the most sophisticated production system. Growers and collectors are more organized, and during the growing season collectors monitor the crop and estimate the yield for the whole country.
The time between harvest and drying should always be kept at a minimum. Drying can be accomplished by different methods. Drying with adequate ventilation, using woven nylon mats for example, prevents sun baking, which can reduce quality. A clean sheet of plastic placed on the ground can also be used with the hibiscus spread thinly on top. This method is still prone to insect infestation and mold. Spreading the calyces on screens or frames would improve ventilation further and reduce drying time. Such frames could also be stacked or hung in a well-ventilated building. The drying ratio is 10:1.1. That is, for every 100 pounds of fresh calyx, 11 pounds of dry calyx is produced.
But often color, texture and flavor of these calyces are not up to standard, neither of the internal consumers nor of the international market. An improvement of product quality can be achieved by using more adequate methods. Hot air dryers as used in developed countries are rather expensive but for instance the "Solar drying tunnel" provides a cost-efficient alternative.
Figure 6: Solar drying tunnel 15
This dryer basically consists of an air collector, solar cells, a drying tunnel and several axial fans. Inside the drying tunnel the product is spread and passed by the hot air. For efficient conversion of solar irradiation into heat, the bottom of the collector as well as the dryer is painted with black lacquer. To prevent the product from rain, the machine is spanned by a plastic foil.
To permit using the machine all-the-year even during long periods of rain, it is possible to install an additional heater between the collector and the dryer. Experiences in the field show that generally the time to dry spices is only half as long using the solar dryer then using conventional methods. Advantageously concerning storage is the permanent drying achieved by using the solar dryer. Possible differences in moisture can be cleared by storing all products together in one box for a few days after the drying process.
While drying the product is protected against climatic influence, insects, birds, rodents and dust. Insects that get together with the product into the dryer while filling the machine, are killed during the drying process.5
Roselle is mainly sold whole and dried, packaged in bales. As mentioned earlier, Thailand is the only country that has been able to carry out value-added processing (cutting and sifting) because of its superior reputation for cleanliness.
Each buyer typically has his/her own product specifications. Table 6 contains common guidelines and specifications for dried roselle and Appendix 1 contains a sample technical specification sheet used by the leading specialty tea company in the US, Celestial Seasonings. Cleanliness is key and in general, no pesticides should be used.