PROCESSING OF RICE - FOOD TECH
- 2. TOPIC : PROCESSING OF RICE Presented by: Chethan N DGK1303 3rd year 2nd sem DSCK
- 3. INTRODUCTION: Rice (Oryza sativa,Linn.)is one of the oldest and most important food crops of the world. It is staple food for more than half of the world population.Rice belongs to the gramineae or grass family and the tribe Oryzeae. The total area of rice cultivation varied between 350 to 360 million acres globally during the last few years. About 92% of the world rice crop is produced in the asian continent.
- 4. RICE MILLING : The objective of the rice milling is to remove the husk and bran with minimum possible breakage of endosperm. Paddy is generally harvested at 18-25% moisture and then dried to 12-13% moisture either on farm or at the mill before processing. Milling Procedure: Combine-harvested rice generally has a moisture content of about 20% (wet basis) and the grain must be dried immediately to about 12% for storage. Rice is consumed mostly in the form of whole kernels, and accordingly the processing of paddy is designed to give a high yield of unbroken kernel.
- 5. Cleaning The paddy is first passed over a screen to remove larger particles, straws and string. After that it is passed through second screen, which is having smaller perforations than first screen, to remove weed seeds and sand. The paddy then flows in the form of a thin layer into a channel where an air current removes dead grains and other lighter impurities. At the last, paddy are passed through magnetic separator to remove metal particles.
- 6. Hulling/Shelling: Cleaned paddy is then passed through machine (disc huller/ sheller) comprising emery/ rubber rolls running in opposite directions; aspirated to remove husk and then sieved to separate from the unhusked and broken rice. The rice with the hull removed is commonly known as “brown rice”/“rough rice”. Scouring/Pearling/Whitening: Gradual removal of germ and bran from the rough rice is known as scouring/pearling/whitening process. The hulled rice is passed through a series of “pearling cones”. As it passes down, the bran is pushed through the interstices of the wire cloth. By-product of scouring process is known as “rice-bran” which is used as animal feed. It is also used to extract rice bran oil.
- 7. Polishing The rice grain consisting inner layers of bran is passed through polishing machine often referred to as “brush”. In this machine last bran fraction is removed. The grain is now called “polished rice”. Parboiling of Rice: In this technique paddy is soaked in excess water and later on cooked in its husk, the objective being pregelatinizing the starch. Any hairline cracks are sealed due to homogeneous mass of gelatinized starch and thus prevent breakage during milling. The paddy is then drained and dried. The general scheme is to hydrate (steeping) paddy to 32 – 38% moisture and partially gelatinize the starch by steam heating at 15 lb. pressure for 10 – 20 min. Parboiling causes certain physico-chemical changes such as improved milling yields (66 – 70%), increased resistance to insects and firmer cooked rice texture accompanied by a darker and more yellow endosperm.
- 8. Parboiling has further advantages like: During soaking and cooking the water soluble vitamins (niacin, riboflavin, and thiamine) which are present in germ and pericarp gets migrated into endosperm and thus improves the nutritional value of parboiled rice. Even proteins present on the grain surface are denatured, become insoluble, and therefore are not removed during washing and cooking. CFTRI parboiling process (Central Food Technology Research Institute, Mysore) This was developed to avoid bad smell. The paddy is soaked in hot water (65-70°C). Germ action does not occur in hot water, thus the smell is avoided. Soaking time is reduced to 3-4 hrs.
- 9. The CFTRI also developed the pressure parboiling method. Soaking time is only 30-60 minutes and steam is passed through the grain to raise the pressure slowly from an initial 0.28-0.70 kg/cm2 to 1.41-2.11 kg/cm2 and this is maintained for 20-30 min. In this method, the processing time is reduced. PPRC parboiling process (Paddy Processing Research Centre, Thanjavur) It is also known as chromate soaking process. Chromate at the rate of 50g/100 kg paddy is added to the soaking water which stops germ action and eliminates bad smell. A high temperature short time process was also developed at the PPRC. Steeped paddy is parboiled and dried concurrently by applying high temperature for a short time. Steeped paddy is fed into sand roaster. The paddy gets completely and uniformly parboiled and its subsequent cooking time is less.
- 10. Rice Quality and Grading Standards: The grain quality has many connotations and is perceived differnently depending upon the end use, field of interest, specialization, ethnic background, etc. Grain quality indicators 1.Grain dimension – size and shape: Short grain varieties vary in their length from 3 -6 mm (length-to-breadth ratio, 2.5-3.0) whereas long grain varieties have a length of 6mm and above (length-to-breadth ratio, more than 3.0). 2.Grain colour and translucency: The colour of the duhusked, unpolished rice is usually pale white, creamy white, brown or red. On polishing, the kernel becomes white, translucent or opaque according to the nature of the pericarp and endosperm colour of the brown rice.
- 11. 3. Cooking/eating quality indicators: Milling, cooking and processing qualities are the fundamental components of quality that determine and establish economic value of rice. Upon cooking, long grain rice is dry and fluffy with individual grains, whereas medium and short grain types are moist and chewy with grains that tend to stick or clump together. Nutritional quality Brown rice contains more nutrients (minerals and vitamins) than milled rice. However, status of nutrients is dependent on genetic variability of rice throughout the world.
- 12. Specific quality designations regarding cleanliness, soundness and purity. Special grades are provided for the specific qualities or conditions of rice that affect marketability. These special grades: 1.Rough rice: Parboiled rough rice, Smutty rough rice, Weevily rough rice 2.Brown rice: Parboiled brown rice and Smutty brown rice for processing 3.Milled rice: Parboiled milled rice, Undermilled milled rice
- 13. Reference: E course (ndri) Food technology-2 course developer: Amit patel, Devraj H.C