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Flour milling
Rice milling

Flour Milling

How is flour milled?

Most wheat is milled to produce flour. Rye and barley flour are produced in the same manner.

Roller milling is the most common method used to produce wheat flour:

• Steel rollers are used to crack open the grain and release the endosperm from the bran.
• A series of grinding and sifting steps follow resulting in the production of flour (derived from the endosperm), bran, semolina (from coarse endosperm chunks), wheat germ and pollard (a mixture of bran, wheatgerm and flour particles).
• Varying amounts of bran, pollard and germ are removed from the original grain, producing flour of different extraction rates.
• Australian food law requires that all flour used to make bread is fortified with thiamin (vitamin B1).

What is the Flour Extraction rate?

The extraction rate is defined as the number of parts by weight of flour that is produced from 100 parts of wheat. It is used as an index of the overall efficiency of a flour milling system and the milling quality of the grain.

Extraction rate describes the type of flour which is milled:

• Wholemeal flour has an extraction rate of 100% because it contains all the grain's components (i.e. the endosperm, bran and germ).
• The shape of the wheat grain, which has a crease down its length, prevents a perfect separation of bran and germ from the endosperm so a clean white flour of 85% extraction is not possible.
• Australian white flour is milled to an extraction rate of approximately 78-80% of the original grain, most of which is endosperm. Depending on the milling technique, up to 50% of the germ may be retained in white flour.
• In barley, the bran shatters during roller-milling resulting in grey flour containing a substantial amount of bran.
• In rye, it is difficult to separate the bran from the endosperm. Hence rye flour has a higher extraction rate and a higher dietary fibre content.

Products of flour milling

i. Flour

• Plain flour - unbleached white flour.
• Self-raising flour - a raising agent made from a mixture of bicarbonate of soda and cream of tartar is added to plain flour.
• Bakers' flour - is used to make bread. Protein content is usually between 11-12%. It must have added thiamin (6.4 mg/kg).
• Cake flour - generally milled from soft, lower protein wheats. A flour of small uniform particle size is important to produce cakes of fine, even crumb and tenderness.
• Continental flour for making cakes and biscuits of Continental European origin.

ii. Semolina

Semolina is the coarsely milled endosperm of wheat which is granular in appearance. Semolina made from wheat, which would normally be used to produce flour, is often a pale beige colour. The semolina milled from Durum wheat, which is only used to make pasta, has a bright golden yellow colour.

iii. Bran

Bran has a relatively high unsaturated fat content which rapidly becomes rancid unless the bran is stabilised by heating to inactivate the lipases. Wheat bran is used as an additive to increase dietary fibre content, particularly of breakfast cereals.

iv. Gluten

Gluten, the protein component of wheat, is manufactured from wheat flour by mixing dough with water then washing out the starch. Gluten is used tomake high protein breads or improve baked products, such as high fibre grain breads and fruit buns. The binding and water absorption properties of gluten are used to improve the taste, texture, keeping qualities and nutritional value of foods such as small goods.

Gluten is also used to produce textured vegetable protein products.

v. Starch

Starch is used as cornflour and also converted into glucose, dextrose and other sugars for use in confectionery and other foods.

vi. Wheat germ

Wheat germ is added to breakfast cereals and some breads, biscuits, cakes etc. It has a nutty taste and is high in unsaturated fatty acids and vitamin E.

Factors determining the end use of wheat flour

• The protein content and hardness of the wheat grain determines the flour's end use:
• The harder the grain usually indicates a higher level of protein.
• The flour's protein content reflects the properties of gluten (protein) and hence its likely performance in the food products made from that type of flour.
• Medium to low protein flour is used mainly for making most types of cakes, sweet biscuits, and for general household use such as scones and pancakes.
• Noodles are made from a wide variety of flour types depending on the style to be produced.

End use for different types of flour

Rice Milling

The 8 000 varieties of rice have been classified in various ways:

• The length of the grain
  - Short-grain rice, about 4-5mm long, contains a lot of starch and tends to stick together after cooking. It is used mainly in soups and puddings.
  - Medium-grain rice, slightly longer than short-grain rice, is used in the same way. It is a softer cooking rice which carries flavours and colours well. The fluffy grains clump together when cooked.
  - Long-grain rice, 6mm or more in length, is very slender and contains a different type of starch compared to round-grain rice. The grains remain separate when properly cooked. It is used in many dishes, particularly in savoury dishes.
  - Glutinous, sweet or waxy rice has a chalky endosperm and is widely used as a thickener in processed foods because it does not retrograde.
  
  
• The botanical variety e.g. Arborio (used for risotto), Basmati.
  
  
• The degree of stickiness of the rice depends on the proportion of amylose and amylopectin, the two types of starch in rice. Rice with a low amylose content will be more sticky. Sticky rice is used to make noodles and cakes.
  
  
• The aroma of the rice, e.g. Jasmine rice.
  
  
• The extent of processing, e.g. polished, enriched or parboiled rice.
  - Parboiled rice is steeped in hot water or steamed and then dried before removal of the husk and polishing.
  

Products of rice milling

Rice bran
Rice bran has recently been marketed as a by-product of rice processing. Previously, enzyme activity present in rice bran resulted in rancidity of the fat content (20% fat) relatively quickly. However, scientists have now developed a way to inactivate the enzyme.

Rice flour
Rice flour is used to produce expanded and extruded rice snacks, rice crackers and various health bars, breakfast cereals and noodles. The end use of rice is determined partly by the fact that it contains no gluten.