Processing of cereals

Processing of cereals

1. Primary processing of cereals

The main purpose of primary processing of whole cereal grains is to separate the outer layers of the grain from the inner section. When the grain is milled to produce white flour, the germ and the bran are discarded. The milling process grinds and pounds the grains. The process used for milling each grain type is slightly different.

After milling of the grain, the products can be described in the following ways:

·         Wholegrain or wholemeal products means the whole of the grain has been used that is the bran germ and endosperm. Because the oil component in the germ can go rancid after a time, wholemeal products can develop off flavours.

·         Refined products refer to products made only from the endosperm (starch). The bran and germ are removed. Refined products have a longer shelf life but are nutritionally poor because they contain mostly carbohydrate.

·         Enriched products have vitamins and minerals added, usually to give them similar nutritive properties to wholemeal products, but without the fibre content.

·         Flour is the powdered form of the grain after grinding or milling.

·         Meal is a more coarsely ground product than flour.

·         Instant or quick-cook products have beencooked, orpartiallycooked, then dehydrated. When reconstituted they require very little preparation time. Examples include instant porridge, quick-cook rice and instant Asian style noodles.

2. Secondary processing of cereals

Secondary processing of cereals results in a variety of products. The main products are as follows:

·         Breakfast cereal production may involve other processes such as rolling and baking to make flakes. Eg. Wheat flakes.

·         Bread and other bakery items such as savoury crispbreads, sweet biscuits, cakes and pastries require the additional processes of sifting, mixing, kneading, proving and baking. Some breads and cakes are leavened with raising agents such as yeast and baking powder.

·         Extruded snack foods— commercially produced using a dough or batter that is extruded and cooked into novelty shapes. Eg. macaroni.

·         Pasta is formed from flour-based dough and formed into shapes by hand or machine.

·         Noodles and dumplings are manufactured from flour-based doughs and shaped, then simmered or poached in liquid.

1. Milling

Cereal processing is complex. The principal procedure is milling, i.e., the grinding of the grain so that it can be easily cooked and rendered into attractive foodstuff. The steps involved in the process of milling are:

·         Rice is passed through two stone rubber discs rotating at different speeds and by shearing action on the grain, the hull is pulled away.

·         This is then milled in a machine called pearlor to remove coarse outer layers of bran and germ by the process of rubbing, resulting in unpolished milled rice.

·         Unpolished rice is liable to develop rancidity and so it is next polished in a brush machine which removes the aleurone layer and yields polished rice.

·         Sometimes the polished rice is further treated in a device known as trumbol to give a coating of sugar and talc to produce a brighter shine on the rice.

The percentage of losses of different nutrients during milling are: protein 15 percent, fat 82 percent, thiamine 85 percent, riboflavin 70 percent and pyridoxine 50 percent. The degree of milling determines the amount of nutrients removed.

2. Parboiling

Parboiling is a process in which rice has been partially boiled in the husk.

This makes rice easier to process by hand, boost its nutritional profile and change its texture.

1. Conventional process: This consists of the following steps:

·         Steeping paddy in cold for 2 or 3 days

·         in large cement tanks.

·         Steaming of the soaked paddy for 5-10 minutes, and

·         Drying in the sun.

2. Hot soaking process: This consists of the following steps:

·         Soaking of paddy in water at 65-70^o C

·         for 3-4 hours.

·         Draining of water and steaming of soaked paddy in the same vessel for 5-10 minutes, and

·         Drying of the paddy in the sun or in mechanical driers.

Advantages of parboiling

·         Dehusking of parboiled rice is easy.

·         Milled parboiled rice has greater resistance to insects and fungus.

·         Loss of nutrients due to the removal of husk and bran in milling are decreased.

·         Loss of water soluble nutrients due to washing of rice is less in parboiled rice compared to raw rice.

·         Parboiling improves digestability.

3. Malting of cereals

Malting is a controlled germination process, which activates the enzymes of the resting grain resulting in the conversion of cereal proteins and other macromolecules.

Generally barley is used in the production of malt. Other grains used in the preparation of malt includes wheat, jowar and ragi.

The process of malting of cereal grains consists of the following steps:

a.       Selection of grain and cleaning.

b.      Steeping in cold water for 36 hours with 2 to 3 changes in water.

c.       Germination: The grains are spread on wire mesh trays and kept for 3 days. Water is sprinkled over each of these trays.

d.      Kilning: The germinated grains are dried at slow rate on kilns.

Amylase rich food (ARF) is germinated cereal flours which are extremely rich in the enzyme alpha-amylase. ARF are excellent weaning foods because they reduce the bulk of weaning foods and are energy dense. Malt is used in commercial proprietary foods, breakfast cereals, malted milk confectionaries, infant foods, bakery products and in brewing.