Friday, March 5, 2010
Flour is the principal raw material used in the manufacture of bread, cakes, cookies & pastries. It provides bulk & structure to these products.
Flour indicates any foodstuff which is finely powdered e.g. rice flour, soya flour; corn flour etc. when there is no specific indication of the type of flour then it refers to refined wheat flour.
Wheat grows in almost every part of the world, except in extreme climatic conditions. However wheat flourishes best in temperate regions & the best quality comes from the American & Canadian borders under the names Manitoba ,Minnesota hard winter etc. The other countries producing wheat are China, India, Australia, Iran, Turkey, U.K etc.
The commercially grown species of wheat are:
Triticum compactum -Suitable for bread.
-Suitable for spaghetti pasta, macaroni etc.
-Suitable for cake-making.
The wheat berry is made up of three parts- Bran, Germ & Endosperm.
Bran: it is the outer covering of the kernel & consists of 5 layers:
Epidperm or Testa
Aleurone or Ceralin layer.
The first 3 layers are protective layers. The 4th layer Testa contains the coloring matter that gives color to the wheat e.g. red, amber etc. the 5th layer of Aluerone cells contains the protrase enzyme & has a softening effect on the flour protein. Bran is rich in vitamin B & dietary fibre. The sharp edges of bran fragments have a cutting action on gluten strands, reducing the gas retention power of the dough.
Germ or Embryo:
The germ of wheat consists of 3 parts:
The germ is that part of the kernel that becomes the new wheat if the kernel is sprouted. In the early stages the berry is incapable of obtaining food needed for the growth of the new plant, so all the nourishment is packed in the germ.
The endosperm is the starchy part of the kernel after the bran & germ is the kernel after the bran & germ is removed. It contains numerous compartments of cellulose & these are tightly packed with starch cells which are round or slightly oval in shape. In the spaces between them are found many other substances like soluble & insoluble proteins, fat, sugar, moisture & minerals.
The characteristics of the flour depend on the variety of wheat from which it is milled, the location & growing conditions.
For the production of strong wheat a hard winter & a hot ripening period is ideal. Nitrogen is the most important element in the protein molecule & is obtained from soil. According to the availability & solubility of nitrogen, the quality & quantity of protein will vary in the wheat & flour.
Some of the principal types of wheat are- Northern spring, Manitoba, Hard winter, Red winter, Pacific, Durum etc.
Types of flour:-
Whole wheat flour: - has a dark color, it consists of all parts of the grain i.e. bran, germ & endosperm. This flour has a characteristic flavor. As this flour contains the germ (oil) it will have a storage life of only 6-8 weeks.
Straight flour: - is flour from the entire endosperm. Because it contains the part nearer the bran as well as the whiter interior, the color of straight flour is darker in color than patent.
Patent flour: - is milled from the inner part of the endosperm. Patent flour made from hard wheat is a strong flour of excellent quality & light cream color. Patent flour has 11% - 13% protein content.
Clear flour: - the portion of the endosperm from the outer part of the endosperm nearer the bran thus is darker in color.
Cake flour: - is weak or low gluten flour made from soft wheat it has a very soft, smooth texture and pure white color. Cake flour is used for cakes & other delicate baked goods that require low gluten content.
Pastry flour – is also weak or low gluten flour, but is slightly stronger than cake flour. It has a creamy white color. Pastry flour is used for pie-dough, cookies, and muffins.
All- purpose flour: - medium quality flour which can be used for any type of baked items.
Self- rising flour: - is white flour to which baking powder (2%) & salt has been added.
High-ratio flour: - this is highly bleached, finely milled flour, made from wheat having good quality proteins. The fine milling increases the absorption properties of flour while chlorination increases the acidity & renders the starch more soluble making it possible to have a faster set in the oven & thus minimizing the possibility of escape of leavening gas. Mostly used in cake- making.
Rye flour: - contains some proteins but these do not form gluten.
There are two distinct methods of milling wheat – stone milling and roller milling.
Stone mills are still in use. From them we get the best whole meal. It consists of two circular stones lying on one top of the other. The one at the bottom remains stationary while the other stone revolves upon it. The faces of the stone are roughened up so that the grooves in them grip and cut into the berries as two rough surfaces pas over it. Cleaned wheat enters the hole in the center called the runner, trickles down and finds its way between the stones. During this process the grain is crushed into flour.
Steps involved in milling:-
1. Cleaning –
Screening – The grain is passed through several sieving operations to remove items both larger and smaller than the grain. It is passed over conveyer belt where any piece of metal is magnetically removed, rodents, bay hair, etc. are removed by hair currents.
Sorting – At this stage, non-wheat grains are removed by passing through a range of separators which separate foreign grains.
Scrubbing – The grain is scrubbed with scrowers which removes any mud, dirt and the beard and the epidermis (beeswing)
Washing – This operation cleans the grain by removing any fine dust and hair, stones which might not have been removed previously. After washing the grain is centrifuged to remove excess water.
2. Conditioning –
The purpose of conditioning is to ensure that the grain is in such a physical condition that milling can be easily and efficiently performed. This is done by moistening the grain and allowing it to lie in the bin for some 24-72 hours depending on the temperature and by heating wheat to about 49oC. Conditioning will assist in the toughening of the bran so that it can be easily separated from the endosperm and germ. Roller milling of wheat into flour is accomplished by a fairly complexed and highly refined system that uses corrugated or grooved steel roller called break rollers followed by reduction rollers which are smooth rollers.
Break rollers are set at such distances that the space between them is slightly smaller than the width of the kernel and the rollers rotate at different speeds. When the blend od wheat called grist is fed between them the rollers flake off the bran and the germ and crack the endosperm into coarse particles. Approximately, 75% of the wheat can be separated as endosperm and called middling and is further milled into fine flour by reduction rollers.
The remaining 25% of the grain consists of bran, germ and outer parts of the endosperm is called shorts. Roller milling produces white flour or refined flour.
Air classification or fragmentation –
Air classification or fragmentation milling is an advanced technology whereby different grades of white flour can be obtained from the same wheat. The advantage of this method is that flour with varying protein content suitable for any bakery use can be obtained.
Composition of flour –
Composition of flour will vary depending upon the types of wheat used in the grist.
Starch - 71.5-74.5%
Moisture - 13.5-14.5%
Protein insoluble - 7-10%
Protein soluble - 1%
Sugar - 2-2.5%
Fat - 1%
Ash - 5%
Starch – 71.5 – 74.5%
Flour with starch content above normal produces a shapely bread. Starch is not soluble in water but absorbs moisture through its cells, therefore it is necessary to protect flour from too humid atmosphere.
When starch is heated to about 60oC with about 6 times its weight of water, starch cells swell and the cell wall bursts. Starch becomes soluble in water and in concentrated form will form a gel. This process is known as gelatinzation. In case of bread, the water available to starch is less and the inner temperature of bread does not reach gelatinzation point until the last stage of baking when it is time to take out the bread from the oven. Due to this reason the starch is partially gelatinized in bread.
The action of amylolytic enzymes - andamylase play an important role during the baking of bread. Their activity is known as diastatic activity.
Moisture – 13.5 – 14.5%
The next important constituent of flour is moisture. If moisture in flour is higher than 13-14%, the baker will be getting less of solid material and more of water for his money. If moisture content is high then it will reduce the water absorption power (WAP) of flour, resulting in less yield.
Flour contains soluble and insoluble proteins. Soluble proteins are useful in providing nourishment to yeast for its growth and reproduction during fermentation process. Two insoluble proteins glutenin and gliadin form gluten when hydrated.
Glutenin gives strength to the dough in order to enable it to hold gases during baking operation and gliadin gives elasticity or stretch ability.
Sugars in flour consist of maltose, sucrose and dextrose.
Ash content of flour is indicative of the degree of its purity with respect to bran fragments. Higher ash content means that flour contains too much bran fragments. Apart from darkening the colour of flour, the bran fragments have a cutting action on gluten strands which inturn will affect the volume of bread.