Roller Milling of Wheat Flashcards
roller milling main products
Flour, farina, semolina
Semolina
mostly the white flour (endosperm) with some remaining small pieces of bran. coarse, sandy texture. puddings.
Flour
flour is the white endosperm, ground up. silky texture. pastries, bread, cakes.
Wheatfeed
used for animals; ground up bran
Bran utilization
bran is sold as bran or used to make cereals
wholemeal/whole wheat flour
mix pure flour with bran that was separated initially in the same ratio it was initially.
dry milling
separation of anatomical parts of the grain as cleanly as possible. subsequently, some of the parts are reduced in particle size.
involves recovery of the main tissue (starchy endosperm) and the concomitant removal of the bran (pericarp, seed coat, nucellar epidermis, and aleurone)
germ is usually separated from the endosperm as it is high oil.
what does the ‘bran’ consist of
pericarp
seed coat
nucellar epidermis
aleurone layer.
benefits of roller milling
consumer preference for white flour.
improved baking performance
enhanced shelf-life of flours and products.
Roller Milling objectives
- separate bran, germ, and starchy endosperm.
- grind starchy endosperm into flour, farina, or semolina
Drawbacks of Milling
- Cost of milling
- Nutritional losses – fibre, protein, lysine, oil, vitamin E, phytochemical.
How does milling separate particles
by size and composition differences via sifting/sieving. differences in bulk density between flour and bran aid their separation.
Roller Milling of Wheat steps:
- Preparation for Milling (blending, cleaning, tempering)
- Milling (break roll, sifting, purification, reduction)
- Flour blending and finishing
- Prep for Milling – Blending
types of wheat are blended to make specific flours. ensures quality requirements are met at the lowest cost. generates the grist for the mill
- Prep for Milling – Cleaning
removes foreign materials. Machines, screens, aspirators, de-stoners, disc separators, indented cylinders, and scouring are all used.
- Prep for Milling – Tempering/Conditioning
Adjusts moisture content with hot water/steam to soften endosperm, toughens bran, and makes germ rubbery. Moisture/time determined by hardness of wheat, desired fineness of flour, and temperature.
Tempering adds water. Conditioning adds steam. Rate of water uptake increases with temperature. Temperatures exceeding 50ºC will damage gluten.
Soft wheat tempered to 15.5% moisture, hard wheat to 16.5%, durum even higher.
- Milling – Break Roll System
Consists of 3 or more pairs of closest set, counter-rotating, differing speed, spirally-corrugated, steel rolls.
Rolls crush and break open kernels and scrape/chop the endosperm from the bran.
Each successive pair of rolls is more finely corrugated and set closer together.
Ground material from each pair is sent to the sifting system.
- Milling - Sifting System
Stacks of sieves in shaker boxes that segregate ground material from the break rolls into a number of fractions according to particle size (composition).
Coarse material is sent back to the break system for further milling.
Intermediate and fine fractions are sent to either purification, reduction roll milling, or flour collection.
The germ is collected after the first break. Bran and shorts collected after the last break.
- Milling – Purification
separates the intermediate and fine fractions from the Sifting System into purified middlings, flour, and branny particles.
Separation based on particle size & bulk density.
Purified middlings & flour sent to reduction rolls or flour collection. Branny particles sent back to break roll system or to the millfeed stream
- Milling – Reduction Roll Milling
Gradual Reduction of purified middlings into flour.
Several pairs of closely set, counter-rotating, different speed, smooth, steel rolls. each successive pair is set closer together.
Material from each pair of reduction rolls is sent to the appropriate stage of the sifting system where flour is sifted from coarser material.
Coarser material is returned to the appropriate set of reduction rolls for further size reduction.
- Flour Blending & Finishing
A mill generally produces several flours and not just straight-grade flour.
Finished flours are combinations of the multiple streams produced during milling.
Streams are combined on the basis of composition and functionality to meet the needs of end-users.
Flour additives- vitamins, minerals, amino acids, protein, bleaching agents, maturing agents, enzymes.
Products of Milling
Flour – 70-75% yield
Bran & Shorts – 20-25%
Germ – 5-10%
Middlings – purified or unpurified
Millfeed – consists of bran and germ
Milling Yield
extraction rate (%)
What is dough?
Dough = flour + water + mechanical energy
Dough is used in the preparation of yeast-leavened products: pasta, noodles, perogies, tortillas, chapattis.
What is bran used for
feed, 60%/100% whole wheat bread, graham flour, pasta, baked goods, cereal, snacks.
what is the germ used for
feed, baked goods, cereal, snacks, wheat germ oil, germ meal.
Semolina
The coarse, purified wheat middlings (intermediate milling stage) of durum wheat mainly used in making pasta, couscous, and pudding.
High-gluten flour made from hard durum wheat. It is coarse in texture, yellow in colour, and high in gluten protein.
Farina
The coarse, purified middlings of hard common wheat.
typically made into a hot breakfast cereal.
