Embed Size (px)
Transcript of Milling kvg
WELCOMEINTRODUCTION TO MILLING AND PARBOILING presentation on :- - :Subject: - AGRICULTURAL PROCESSINGPRESENTED BY:- Kaushal. V. Gadariya (PAGEN-097-2012) Baria Dipak (PAGEN-091-2012) Dave Dhruv (PAGEN-094-2012) Chovatiya Chintan(PAGEN-093-2012)MILLINGMilling refers to the size reduction and separation operations used for processing of food grains into edible form.
PRINCIPLES OF SIZE REDUCTIONSFollowings are some laws of energy required to size reduction : - - Rittinger's law - Kick's law - Bond's law
RITTINGERS LAWIt is states that the work required in crushing is proportional to the new surface created.Rittingers assumed that size reduction is essentially a shearing procedure.Therefore, energy requirement is proportional to the square of the common linear dimension .The value of n = 2
Where, E is energy requirement for size reduction Xp is length of product Xf is length of feedSIZE REDUCTION METHODSThe size of agriculture products may be reduced by several ways, but mainly the following four methods are used in size reduction machines. 1.Compression or crushing. 2.Impact. 3.Shearing. 4.Cutting.
SIZE REDUCTION PROCEDURESCrushing :-
In crushing the particle produced after crushing are irregular in shape & size. The type of material and method of force application affects the characteristics of new surfaces and particles. Food grain flour, grits and meal, ground feed for livestock are made by crushing process. Crushing is also used to extract oil from oilseeds and juice from sugarcane.
CRUSHING ULTRAFINE MILLImpact:- When a material is subjected to sudden blow of force in excess of its strength, it fails, like a cracking of nut with the help of a hammer. For example Hammer mill. Shearing:- -It is a process of size reduction which combines cutting and crushing. The shearing units consist of a knife and a bar. Cutting:- In this method size reduction is accomplished by forcing a sharp and thin knife though the material. The size of vegetables and fruits are reduced by cutting. SIZE REDUCTION MACHINARYSize reducing devices are grouped as follows:- WHEAT FLOUR MILL
Crushers : - - These type of reducing machines squeeze or press the material until it brakes. - Crushers are mostly used to break large pieces of solid materials into small lumps. - Crushers are used in industrial operations, like mines etc. - Use of crushers in agricultural operations is limited.The crushers in use are, 1.Jaw crushers. 2. Gyratory crushers. 3. Crushing rolls. Grinders:- - The grinders are used to mill the grains into powder. - The grinder comprises a variety of size reduction machines like attrition mills, hammer mills, impactors and rolling compression mills. Cutting machines: - - Size reduction of fruits and vegetables are mostly performed by cutting operation. - To make thin slices of fruits and vegetables knife cutter are used. - Few types of knife cutters have been developed for cutting slices / chips of potatoes, banana etc. SIZE REDUCTION MACHINES OPERATION AND PERFORMANCETo achieve good results from any size reducing machines the followings should be given due care,Feed should be of proper size and feeding rate should be uniform.Hard or unbreakable material is not allowed to enter the mill.After grinding the product is removed as soon as possible.There should be some arrangement to remove the heat generated during milling operation.
OIL EXPRESSION Expression is the process of mechanically pressing liquid out of liquid containing solids.Screw presses, roll presses and mill, collapsible plate and frame filler presses, disk mill are some of examples of a wide range of equipment used for expression of liquid.
FIG: OLIVE OIL PRESSMECHANICAL EXPRESSION DEVICESHydraulic press: - - It considered of a series of horizontal corrugated iron plates. - These plates are separated by 4 to 14 remolded oil seed cakes. - Pressing is completed in two stages. - In the first stage, the oil samples are pressed at approximately 5MPa for 15 to 20 minutes. - Afterward a pressure of 28MPa is applied for 5 to 10 minutes to complete the expression process. - The output of the press varied depending on the sizes seed being pressed.HYDRAULIC PRESS
Screw press: - - In screw press, the press has a horizontal main shaft. - The screw assembly is formed integrally with this shaft. - This screw rotates within a cage of barrel. - Barrel is made of case hardened, tool steel bars or this may be made out of assembly of rings. - Spacers are used between the lining bars or rings to allow drainage of the oil as the pressure on the feed material is increased.
FIG: SCHAMETIC VIEW OF HYDRAULIC PRESSOIL EXTRACTIONExtraction is the process of separating a liquid from a liquid-solid system with the use of solvent.Extraction may also be said as a process to extract oil from oil bearing material through process of diffusion with the help of low boiling point solvent.This process gives a higher recovery of oil and a drier cake then expression. OIL EXTRACTION METHODExtraction methods include: -
Traditional methods:- - Oil is extracted from, for example, fresh coconut, olive, palm fruit Shea nut by separating the flesh and boiling it in water. - Salt can be added to break any emulsion which is commonly formed and the oil is skimmed from the surface. In palm oil processing the fruit is first heated in a digester. Manual methods:- - Oil can be extracted by pressing softer oilseeds and nuts, such as ground nuts and Shea nuts, whereas harder, more fibrous materials such as copra and sunflower seed can be processed using ghanis. - Pulped or ground material is loaded into a manual or hydraulic press to squeeze out the oil-water emulsion. MECHANIZED EXTRACTIONGhani (kolhus):- - The Ghani consists of a large mortar and pestle, the mortar being fixed in the ground and the pestle being moved within the mortar by animal traction (donkey or mule) or a motor. - Oilseeds are placed in the mortar and the pestle grinds the material to remove the oil. - The oil runs out of a hole in the bottom of the mortar and the cake is scooped out by hand. - This method is slow and requires two animals, replacing the tired one with another after about 3-4 hours of work.
ANIMAL DRAWN KOLHUS Expeller :- - The basic steps involved in processing oilseeds by expeller are shown in the flow diagram below.
PARBOILINGIt is a pre milling treatment given to paddy prior to its milling to achieve maximum recovery of head rice and to minimize breakage.In this process paddy is soaked and the wet paddy is heated and dried.During soaking of paddy water penetrates into starch granules and result in swelling of grains.In heating, the energy weakens the granule structure and more surface becomes available water absorption and result in irreversible granule swelling.This phenomenon is called gelatinization of starch.The main objectives of parboiling are 1. to increase the total and head rice yield of paddy. 2. to prevent the loss of nutrients during milling. 3. to salvage wet or damaged paddy. 4. to mill the rice according to requirement of consumers.
ADVANTAGES OF PARBOILINGThe milling yield increases and the quality is improved.The milled rice becomes translucent and shining.Shelling of parboiled rice is easier.Bran of parboiled rice has more oil.Parboiled rice retains more proteins, vitamins and minerals.Parboiled rice is more digestible and less solids are left behind in the cooking water.
DISADVANTAGES OF PARBOILING Parboiling process needs extra capital investment.Parboiling adds to the cost of drying.More power is required for polishing of parboiled rice. The process becomes difficult and lowers the capacity of polisher.Parboiled rice takes more time to cook than raw rice and may have characteristics off flavor which may not be liked by raw rice eaters.The heat treatment during parboiling destroys some natural anti-oxidants.
Parboiling of paddy is carried out in three steps,PARBOILING OF PADDYSoaking of paddy is carried out by dipping in water. Dipping in water at ambient temperature takes long time (72 h) for soaking, making paddy susceptible to development of micotoxins.Hence, soaking at elevated temperature of water is considered better. The soaking duration varies with water temperature.
Soaking of paddy: -S. No.Temperature, CTime, h1Water heated to 50C and allowed to come to ambient temperature242Water heated to 75C and allowed to come to ambient temperature123Maintained at 60C84Maintained at 65C65Maintained at 70C46Maintained at 72C3.57Steam at 0.5 atm. pressure0.4 The following time-temperature combination is considered optimum for soaking:Time-temperature combination for soaking of paddy:2. Steaming of paddy: -PARBOILING OF PADDY Steaming is carried out to gelatinize starch. Generally, saturated steam at a pressure of 1-5 kg/cm2 is used for steaming of soaked paddy. Duration of steaming depends upon quantity of paddy. For small batch, 2-3 min whereas for large batch (6-8 tones), 25-30 min of steaming is required.
FIG: -Household parboiling unit
FIG: -Industrial parboiling units3. Drying of paddy: -Drying of parboiled paddy from 45-50% (db) to 14-16% (db) needs to be done for proper milling and storage.Sun drying of paddy is generally practiced.For un