EXam procesing anatomy of grainss

• ›Why rice kernels break so easily on mechanical impact during the physical operations

  adjustment of hulling machines
• Anatomy of the Paddy Grain HULL - Most visible part of a rough rice grain Formed from the two leaves: Palea -covering the ventral part of the seed  Lemma - covering the dorsal portion
• ›Caloric Value - 3000 to 3500 kcal/kg › Has  a high proportion of silica
• 2. pericarp - A thin fibrous layer frequently known as the “silver skin” . The layer is usually translucent or grayish in color.

  Consists of three layers -  epicarp, mesocarp and cross layer
• 3. bran - removed whitening stage during milling.
• 4. endosperm - one of the most important parts of grain. it consist of starch.
• Physical properties/characteristics of rice:

  1. Length

  2. Husk-Surface

  3. Free Space between the Husk and the Brown Rice Kernel

  4. Tight Interlocking Fold of the Husk

  5. The Awn

  6. The pericarp
• length - determined by the brown rice kernel.
• 2. husk-surface - Rough and abrasive because of its high silica content. Rough and abrasive because of its high silica content.
• 3. Free space between the husk and the brown rice kernel - When the grains are dried, there is a distinct space between the rice hull and the kernel inside.
• 4. Tight Interlocking Fold of the Husk - husk sections consisting of the lemma and the palea, are tightly seamed. A force is required to open these folds in the process of dehusking.
• 5. awn - awn is sometimes very long in certain varieties.
• 6. pericarp - mainly the abrasive disc huller that damages the pericarp. free fatty acid (FFA)
• Other physical properties that are related to physical composition of the grain are: 1. Angle of repose 2. Angle of friction 3. Bulk density 4. Grain dimensions
• 1. angle of repose - The angle of the sides of cone-shaped mass of grain with respect to the horizontal, measured after the flow of the grain has completely stopped.
• 2. angle of friction - friction refers to the angle measured from the horizontal at which paddy grain will start moving downwards.
• 3. bulk density - Refers to the ratio between weight and volume of grains. At 14% MC the bulk density of paddy is 576 kg per m3.
• Grain dimensions are crucial in determining grain standards and throughout the processing cycle
• The type of paddy is classified according to the length of the whole brown rice grain, which can be categorized as:

  • Extra long
  • Long
  • Medium
  • Short
• Extra long – paddy with 80%of the whole rice kernels having a length of 7.5mm or more. Long – paddy with 80% of whole brown rice kernels having a length between 6.5 mm or more but shorter than 7.5mm. Medium – paddy having 80% of the whole brown rice kernels with a length between 5.5 mm to 6.5 mm. Short – paddy with 80% of the whole brown rice kernels shorter than 5.5 mm.
• sub-type of paddy grain refers to the ratio of length and width of the whole brown rice kernels. Slender Bold Round Ratio = Length/Width
• Slender – paddy with brown rice grain having a length and width ratio of 3.0 or more. Bold – paddy with brown rice grain having a length and width ratio of 2.0 or more but smaller than 3.0. Round – paddy with brown rice grain having a length and width ratio smaller than 2.0
• types of milled rice is classified according to the length of the whole grain: Extra long long medium short
• Extra long – 7.0mm or more. Long – 6.0 mm or more but shorter than 7.0mm Medium – 5.0 mm to 6.0 mm. Short – 5.0 mm
• sub-type of milled rice refers to the length or width ratio of the whole milled rice grain.

  The three sub-types of milled rice are defined in the same manner as that of paddy, to wit:

    Slender, bold and round.
• Brokens in milled rice is generally based on the rice particle and is referred to in units 1/8th of the length of the whole unbroken milled rice grain.

  Head Rice Large Broken Small Broken
• Head Rice – milled rice particle with length of 6/8 or more of the length of the whole unbroken milled rice kernel

  Large Broken- milled rice particle with length of 3/8 or more but shorter than 6/8 of the length of the whole unbroken milled rice kernel

  Small Broken - milled rice particle which will not pass through a perforated sieve with a round perforation of 1.4 but the length of the grain is shorter than 3/8 of the whole unbroken milled rice kernel.
• moisture content - amount of water present in grains.