The Process for Dried Ginger
- The fresh rhizome is harvested at between 8 to 9 months of age.
- The roots and leaves are removed and the rhizomes are washed.
- The rhizomes have to be “killed” or inactivated. This is done by peeling, rough scraping or chopping the rhizome into slices (either lengthwise or across the rhizome). The skin should be peeled off using a wooden scraper made from bamboo to prevent staining the rhizome. Whole unpeeled rhizomes can be killed by boiling in water for 10 minutes.
- After peeling and washing, the rhizomes are soaked for 2-3 hours in clean water then soaked in a solution of 1.5-2.0% lime (calcium oxide) for 6 hours. This produces a lighter colored (bleached) rhizome. After soaking, the rhizomes are drained.
- The rhizomes are dried. The traditional method is to lay the pieces on clean bamboo mats or on a concrete floor and sun-dry until a final moisture content of 10%. Drying may take anything from 7 to 14 days depending upon the weather conditions. During drying, the rhizomes lose between 60 and 70% in weight.
- In rainy conditions, a mechanical drier such as a tray drier should be used to accelerate the drying process. Sliced ginger pieces take only 5-6 hours to dry when a hot air drier is used. Whole peeled ginger rhizomes take about 16-18 hours to dry in a mechanical drier. It is important to monitor the air flow and temperature during drying. The drying temperature should not exceed 60°C as this causes the rhizome flesh to darken. See the Practical Action Technical Brief on drying for further information on the different types of drier available.
- After drying, the rhizomes are cleaned to remove any dirt, pieces of dried peel and insects. An air separator can be used for large quantities, but at the small scale it is probably not cost effective.
- The dried rhizomes should be packaged into air-tight, moisture proof packaging for storage or export.
Quality Assurance of Dried Ginger
Quality of the dried ginger is assessed by the appearance of the final product (color, lack of mould or aflatoxin) and the aroma and flavor. These qualities are influenced by a combination of pre- and post-harvest factors:
- The most important factor is the cultivar of ginger used as this determines the flavor, aroma, pungency and levels of essential oil and fibre.
- The stage or maturity of the rhizome at harvest determines its suitability for end use. Rhizomes that are 8-9 months old produce the best quality dried ginger as they have a good combination of aroma and pungency and not too much fibre.
- After harvest the rhizomes should be handled with care to prevent injury. They should be washed immediately after harvest to ensure a pale color. The wet rhizomes should not be allowed to lie in heaps for too long as they will begin to ferment.
- Care should be taken when removing the outer cork skin. It is essential to remove the skin to reduce the fibre content, but if the peeling is too thick, it may reduce the content of volatile oil which is contained near the surface of the rhizome.
- During drying the rhizomes should lose about 60-70% of their weight and achieve a final moisture content of 7-12%. Care should be taken to prevent the growth of mould during drying.
- The use of a mechanical drier produces a higher quality, cleaner product. The drying conditions can be carefully controlled and monitored and the time taken to dry is considerably reduced.
- After harvest, the cleaning, peeling and drying processes should be carried out as quickly as possible to prevent the growth of bacteria and mould and to prevent fermentation. If the drying process takes too long there is a risk of the ginger becoming infected by aflatoxin or other fungus.
- Dried ginger should be stored in a dry place to prevent the growth of mould. Storage for a long time results in the loss of flavor and pungency.
Quality specifications are imposed by the importing country and refer to the cleanliness specifications of the ginger rather than the quality. It is important to meet the minimum standards or the ginger will be rejected by the importers.
There are several forms of dried rhizome, which are described below:
Grinding can be a method of adding value to a product. However, it is not advisable to grind spices as they are more vulnerable to spoilage after grinding. The flavor and aroma compounds are not stable and will quickly disappear from ground products. The storage life of ground spices is much less than for the whole spices. It is very difficult for the consumer to judge the quality of a ground spice. It is also very easy for unscrupulous processors to contaminate the ground spice by adding other material. Therefore most consumers, from wholesalers to individual customers, prefer to buy whole spices.
Dried ginger is usually exported whole and ground in the country of import.
Bulk rhizomes can be packed in jute sacks, wooden boxes or lined corrugated cardboard boxes for shipping. Dry slices or powder are packaged in multi-wall laminated bags. Some laminates are better than others due to film permeability. The packaging material should be impermeable to moisture and air. Sealing machines can be used to seal the bags. Attractive labels should be applied to the products.
The label needs to contain all relevant product and legal information – the name of the product, brand name (if appropriate), details of the manufacturer (name and address), date of manufacture, expiry date, weight of the contents, added ingredients (if relevant) plus any other information that the country of origin and of import may require (a barcode, producer code and packer code are all extra information that is required in some countries to help trace the product back to its origin).
Dried rhizomes, slices and splits should be stored in a cool place (10-15°C). At higher temperatures (23-26°C) the flavor compounds start to deteriorate and ginger loses some of its taste and aroma. The storage room should be dry and away from the direct sunlight. During storage the rhizomes should be protected from attack by insects and other pests. Natural pesticides such as the leaves of Glycosmis pentaphylla or Azadirachta indica can be added to the rhizomes to prevent damage from the cigarette beetle (Lasioderma serricome).
The storage room should be clean, dry, cool and free from pests. Mosquito netting should be fitted on the windows to prevent pests and insects from entering the room. Strong smelling foods, detergents and paints should not be stored in the same room.
Ginger Oil Distillation
Ginger oil can be produced from fresh or dried rhizomes. Oil from the dried rhizomes will contain fewer of the low boiling point volatile compounds (the compounds that give ginger its flavor and aroma) as these will have evaporated during the drying process. The best ginger oil is obtained from whole rhizomes that are unpeeled.
Ginger oil is obtained using a process of steam distillation. The dried rhizomes are ground to a coarse powder and loaded into a still. Steam is passed through the powder, which extracts the volatile oil components. The steam is then condensed with cold water. As the steam condenses, the oils separate out of the steam water and can be collected. In India the material is re-distilled to get the maximum yield of oil. The yield of oil from dried ginger rhizomes is between 1.5 to 3.0%. The remaining rhizome powder contains about 50% starch and can be used for animal feed. It is sometimes dried and ground to make an inferior spice.