Flour

Articles and reference material related to flour

Flour - An introduction

 Most of us would describe 'flour' as fine powder, made from wheat, which we use in cooking. However, depending on the wheat and the blending processes used by millers, it is now possible to buy different types of flour, each with a different purpose. No longer must the home baker use just one type of flour for all baking needs. The intended use of the various types of flour on sale is usually listed on the packet.

To ensure that the best type of flour for a particular end use is provided, flour millers produce different types of flour for cake/biscuit making, for bread making, for household use, and pasta production. A lot of care is taken before the milling process begins to ensure that wheats have been tested to determine their best potential end use.

Some wheat is eaten in grain form and whole wheat can be flaked, shredded or treated in some other way to make breakfast cereals or muesli bars. Softened, malted or kibbled grain is often incorporated into baked products.

Flour can also be separated into its major components, gluten (protein) and starch. Wheat starch is used primarily as a thickening agent for soups, gravies, puddings, spreads and various other products. Gluten protein is often added to wheat flour to improve bread making quality, and it can also be used as a base for making various vegetarian foods.

 

Wholemeal/White Flour
All of the flours listed can be found as wholemeal and white. Wholemeal flour contains all parts of the wheat grain including the outer layers of bran and the germ. White flour contains only the inner portion of the grain called the endosperm. Often when using wholemeal flour more water needs to be added to the recipe because the bran absorbs more water than the white portion of the grain.

Flour for Bread making
Bread making flour is made from a semi-hard wheat with a medium to high protein content. This type of flour is referred to as a strong flour. When water is mixed into flour two of the flour proteins combine to form gluten. It is gluten which forms a network that will stretch as the dough ferments and carbon dioxide gas is released. On baking this stretched gluten network sets to give the structure and texture to bread. Strong flour is needed to ensure that sufficient gluten is formed to produce bread of good volume and appearance.

Flour for Pastry
Puff pastry should also be made from flour with a high protein content as it is the water absorbed by the gluten that, with the folded-in fat, forms the layers and makes the pastry puff up during baking. For pastry, use the same type of flour that you would use for making bread.

Flour for Cakes and Biscuits
The ideal flour for making most cakes and biscuits has a lower protein content than bread making flour and is milled from soft wheat varieties. The protein needed to form the structure of cakes and biscuits is not from the flour used but from other ingredients such as egg. Use of cake flour gives a tender soft product as the gluten in the flour does not contribute significantly to the cake structure. If flour that is too strong is used the resultant cakes will be tough and dry and biscuits will not spread out when baked.

Self-Raising/Self-Rising Flours
These are made by combining and biscuit flours with chemical aerating agents similar to baking powder. The aerating agents cause batters to rise when heated. The flour and raising agents are sifted together many times to ensure even distribution and consistent product quality. Self-raising flour is ideal for making scones and pikelets. Note: plain flour should be used on the bench to pat out scones to avoid a bitter after-taste.

Remember that there is a difference between flours and it is important to use the correct flour for each type of baking. When storing flours there are a few pointers that should be observed. To ensure the flour is always at its best for use store in a cool, dry cupboard, preferably in an airtight container.

Flour is always readily available so it should only be brought in quantities that will last a maximum of two to three months. This is particularly applicable to wholemeal flour which contains the germ part of the grain as this can go rancid with time. If it is necessary to store flour for extended periods of time we recommend that the flour is kept in the freezer. It is better not to mix new flour with old and if you are not using the flour regularly, make sure bags are secure to prevent infestation by the flour moth or beetle.

History of Flour

Undoubtedly the cereal grains would first have been eaten raw by the ancient man. As a food they were doubly valuable because in the dry state they could be stored from year to year. This storage aspect is still important as one of the reasons for the large international trade in grains. Raw wheat is not particularly palatable and man next discovered how to soak and boil the grains.

But the really important discovery was that the grain could be ground to make a meal. Some native tribes still make meal by pounding the grain. However, grinding is more efficiently carried out by rubbing wheat grains between two stones - a small stone held in the hand and a large "saddle" stone lying on the ground. Such a device requires a lot of hard work, but its' efficiency was improved by the cutting of grooves in the faces of the stones, and by fixing the upper stone to a lever that reduced the apparent effort required. Backwards and forwards motion is very wasteful and a real advance came with the rotary motion - the quern consisted of two round flat stones one above the other. The upper stone was turned by a wooden handle, wheat was trickled in through a hole in the centre and came out around the edge.

Up to now the grinding of meal had mostly been carried out in the home. During the Roman times the first milling "industry" probably arose, with an increase in the size of the mill stones and a change in their shape. With the increased size, animals as well as slaves were used to turn the stones. The "industrial" milling process was carried out in the bakery. It was during this era also that water power was used to drive the millstones by means of a paddle wheel. The use of wind power, in the form of a windmill, is a much more recent innovation, dating only from mediaeval times. The remains of many watermills and windmills are to be found around the country, for this was the normal method of driving mills in New Zealand up to around 1900.

Very clearly in history it must have been discovered that a more palatable product could be made by sieving the ground meal. The whiter flour thus obtained by the use of sieves made of horse hair was called "pollen" (meaning fine powder) by the Romans. The especially fine grade they called "flos" a word that meant the best part of anything. They used the same word for a flower - it being the best part of the plant. So our words flour and flower originally were the same. The Dutch word for flour is "bloem" - easily recognisable as our word "bloom".

Very little change took place in the actual milling process between Roman times and the 1700's, though considerable progress was made in the associated mechanics - the methods of driving the the stones and their setting and feeding. Many of today's mechanical devices were invented by the millwrights. Most impotant perhaps was the centrifugal governor, patented in 1797 and later very successfully adapted to the steam engine. The later versions of wind and water mills incorporated many automatic controls, together with alarm systems to call the miller when things were going wrong - the millers might said to be the originators of automation.

The next major developments came during the 1700's and 1800's. They were "high" milling processes and improved methods of separating the constituent parts of the ground stocks.

High milling is said to be a Hungarian invention; certainly it reached its highest state of development in Hungary, though when introduced to America it was called the "French" system. It involved the use of several pairs of millstones with coarse grooves and a wide gap on the first pair, hence the name "high". Finer grooves and narrower gaps were set on succeeding pairs of stones. The use of more stones meant more handling of stocks and this led to the development of the "automatic" mill, in which the hard work of transferring grain and stocks was done by machines rather than by hand. The vertical arrangement of the mill dates from this time, the grain being initially being raised to the top of the mill building, and then flowing downwards through successive machines.

Many more machines were introduced to separate the constituent parts of the stocks. From the early hand-shaken sieve the modern plansifter has been developed, whilst at the same time it was found convenient in mechanising sifting to use a cylindrical reel type of sieve, from which the centrifugal reel was developed. In the 1700's some millers had used air currents in wheat cleaning and in cooling stocks but in the early 1800's it was realised that stocks could be separated in this way. The Hungarians also discovered that bran could be floated to the surface of a tub of meal and so scraped off. This layering principle was combined with the use of air currents to give the modern purifier. Thus the modern stock separating devices were discovered before the great revolution in milling.

This revolution was the substitution of steel rollers in place of the flat mill stones. The first successful roller mill operated in Switzerland in 1834 and within five years such mills were operating in many parts of central Europe. However, because of considerable vibration the rolls were placed in the lower floors of the mill, thus accounting for their current position in modern mill layouts. The use of metal break rolls spread to Britain in the 1870's and to North America in the 1880's. The use of smooth rolls for the reduction part of high milling was a discovery of the 1870's that was very quickly put into wide use, replacing the the millstones that had hitherto been used for that purpose. Porcelain rolls were used for a time, but were eventually replaced by steel.

So by 1900 most of the common machines of the present day mill had been developed. The handling of materials in sacks and buckets had been replaced in the automatic mill by mechanical transfer with bucket elevators and worm conveyors. Since the Second World War another revolution in milling has taken place with the introduction of pneumatic conveying of stocks from one machine or place to another. Along with this has come better dust collection systems, with high efficiency filters and cleaning mechanisms.

Flour Quality Parameters

Flour Colour
A very simple way to determine colour differences in different batches of flour is to look at the colour of different types of flour under a sheet of glass. This can be done with more than one flour at a time. This method not only facilitates a comparison of the whiteness of different flours but also allows for an inspection for impurities. The flour should be of "perfectly regular consistency and not contain any specks”. This obviously does not pertain to mixed grain or to other than white flours. Several methods exist for the measurement of colour, all of which relate to the quantity of reflected or absorbed light.

Texture and Feel
The texture and size of granulation plays an important role in kneading and also determines the speed at which the dough rises. In general, bread flour is slightly coarse and falls apart when pressed into a lump. Pastry flour is smooth and fine and can be squeezed into a lump. Cake flour is smooth and fine, can be squeezed into a lump, and stays in a lump more solidly when pressed.

Absorption Ability
Absorption measures the amount of water that can be absorbed by a given quantity of flour. In bread making, it is usually preferable to have flour that can absorb a large amount of water. Measurements of absorption are done to determine the amount of water the dough can absorb, which in turn indicates dough yield and shelf life. Optimum absorption represents the maximum amount of water, as a percent of the flour weight that will produce a high yield of bread during the baking process.

Flour Protein

 
© Canadian Grain Commission

Traditionally flour protein has been the main parameter used to judge flour quality and strength. Today we know that not all wheat protein is created alike. Wheat "protein" or Albumen is composed of four types of protein: gliadin, glutenin, albumin and globulin. Gliadin and glutenin comprise roughly 85% of the Albumen, and are the gluten-forming components. Albumin and globulin are water soluble, and thus don’t add to the strength of the flour. The percentage of protein (Albumen) only tells us the amount of protein, and is only a hint as to the real character of the flour. This figure does not tell us anything about the type, or quality of protein. The farinograph test gives us more valuable information about the “quality” of the protein; and thus how it will perform in the bakery.

Flour Moisture
The level of moisture in flour is important mainly f or the issue of storage. When the moisture level exceeds 16 % the shelf life of the flour is greatly reduced. Generally, the moisture will be 14-15%, which when stored in appropriate conditions (relatively cool, dry and aerated) allows for plenty of shelf life. There is a correlation between moisture content and water absorption but can be counteracted by starch damage.

Flour Ash
The ash content of the flour is determined by incinerating a sample of flour. The minerals naturally present in the flour do not burn and remain as ash. The weight of the ash is then compared to the original sample. The ash content tells us something about the extraction of the flour. In the endosperm of the wheat kernel, the mineral content increases from the centre outwards. The area of the endosperm nearest the aleurone and bran layers has the highest mineral content. Higher ash contents indicate higher extraction. Most flours will have an ash content below 0.6%, patent flours can go as low as 0.35%

Falling Number
The falling number test determines the amylase activity of a flour sample. The amylase enzymes are used to break down the starch in flour to release sugar ready for fermentation. The test entails heating measured amounts of water and flour in a special test tube. The tube is placed in a boiling water bath and agitated with a plunger for 55 seconds to allow the sample to gelatinise. Then the plunger is released at the top of its cycle on the surface of the sample, the time that it takes the plunger to sink through the gelatinised starch to the bottom of the tube is recorded. The total time in seconds (including the original 55 seconds) is recorded as the "falling number". Therefore the minimum number is 55 and some flours can push into the high 400's and beyond.

Depending on the alpha-amylase activity, the degradation of the starch paste will vary. The higher the alpha-amylase activity, the lower the number, and vice versa. In Australian and Canadian wheats, typically the falling number has to be adjusted (reduced) in the flour through the addition of diastatic malt, or fungal amylase for use in the Bakery. Generally the baker will find that fermentation progresses more rapidly as falling numbers become lower.

Farinograph

The “Brabender Farinograph” is one of the most common flour testing machines in use today. The farinograph produces a graph that represents the force required to turn two mixing arms in a small mixing chamber with dough at an adjusted hydration. On the graph each vertical line represents thirty seconds. The horizontal axis spans 0-1,000 brabender units; each line marking 20 BU, (i.e. force/resistance). The key points of record on the graph are as follows:

Arrival Time ( A ) Indicates the time taken to achieve consistency from zero minutes to the point at which the graph touches the reference line (500 B.U)
Development Time ( B ) Indicates the interval between zero minutes and the peak (maximum height) of the curve ie., shows first signs of weakening
Stability ( C ) Indicates the time for which the dough maintains its consistency at 500 B.U
Elasticity ( D ) is measured by the breadth of the curve at its peak
Softening ( E ) is the drop from the reference line to the centre line of the curve 12 minutes after the peak. The greater the weakening the less abuse the flour can withstand

 
© Canadian Grain Commission

Absorption
Dough hydration is adjusted so that the peak of the graph is centered on 500 BU, resulting in a predetermined dough consistency. The absorption indicated is the adjusted hydration. When looking at farinograph absorption it is important to realize that this is not an absolute value. The greatest value can be had from comparing absorption values from lot to lot, and making adjustments proportionately.

MTI
Mixing tolerance index is the difference in BU, from the top of the curve at the peak to the top of the curve measured at five minutes after the peak. Higher MTI numbers indicate greater mixing tolerance.

Starch Damage
Inherent characteristics of the wheat, along with the physical effects of milling determine the level of starch damage. The process of wheat milling damages a portion of the starch granules. This tendency is amplified as the hardness of the wheat increases. Because of this, starch damage is of particular concern here in New Zealand. Starch damage increases the amount of fermentable carbohydrate as well as the absorption of the flour. Normally starch granules absorb one-third their weight in water, when damaged that increases to 2-3 times their weight. Damaged starch granules are very susceptible to attack by alpha-amylase enzymes.

The combination of high levels of fermentable carbohydrate, and water, (and thus rapid enzymatic activity) make conditions optimal for more active fermentation as the damaged starch levels increase. Also, though flour with high starch damage figures absorbs a lot of water, once the amylase enzymes do their work, the dough becomes slack. Balance, as always, is key. Too much starch damage, and the dough tends to be slack and over-fermented; too little and the fermentation stalls after the immediately available sugars are consumed.

One should expect to see starch damage at 6-9% for winter wheats, and 7-10% for spring. Damaged starch significantly affects both Farinograph water absorption, and dough extensibility and resistance (Alveograph).

 

Extensograph

 

Evaluating an Extensograph Chart
A cylinder shape dough ball is proved for 45, 90 and 135 minutes. After each stage the dough is installed into a cradle in which the dough is stretched to breaking point. The graph generated from this process conveys information about the properties of the flour from which the dough was made.

The area within the curve is measured is reported in cm2. This indicates the total energy required to stretch the dough. This indicates the efficiency of the dough during fermentation eg. The higher the area, the greater the tolerance and vice versa.
The resistance (R) is measured in BU as the peak force during the curve creation
The extensibility (E) is measured in mm along the base of the curve and indicates the stretchability of the dough
The ratio R:E is calculated as the resistance quotient of resistance to extensibility. When combined with the energy reading indicates the dough behaviour, stability and potential baking volume.

Typical results for bread flour: R:400 E:190 R:E 2.11
Trypical results for a biscuit flour: R:130 E:160 R:E 0.81

 Alveograph CH (Constant Hydration)

Produced by Chopin, the Alveograph is an instrument that gives valuable rheological information about a dough sample by measuring the pressures attained during the inflation of a dough sample into a bubble. Because the test expands a dough sample in a biaxial plane, similar to the way dough cells expand in actual bread dough, this test is highly regarded. This test is traditionally used as standard in countries that have historical or cultural links to France, but is used elsewhere in the world as a supplementary test for evaluation or verification purposes.

Evaluating results:

W

Also known as, “the deformation energy”, the W represents the force required to inflate the dough bubble until rupture. Literally the W is the area under the curve on the graph, multiplied by a factor of 6.54. This value generally indicates the overall baking strength of the sample. The water absorption is generally thought to increase as the W increases. Loaf volume is also thought to increase as the W value rises. Bread flour W values tend to be 200+, with number up to 400 being especially appropriate for dough undergoing long fermentation times. Along with the numerical figures, it is important to actually see the drawing of the curve. Using the drawing along with the other Alveograph values, gives the baker the greatest chance in predicting flour performance. There is great value in compiling drawings and data along with real-world impressions of flour over time. Only in this way can rheological testing data be put to its greatest use.

 

P

Also known as the overpressure, the P is the maximum height (h) in mm. on the alveogram multiplied by a factor of 1.1. This figure represents the viscosity, tenacity, or even strength of the sample. The AACC defines overpressure P as an indicator of dough resistance to deformation. As P rises, so does the resistance. Some also believe that P can be taken as a measure of the hydrating capacity of the sample. Because the maximum height is effected by the type and thickness of the dough, some researcher believe that the ratio of the height of the curve at the bubble volume of 100 ml (P100) to the height of the maximum (Pmax) provides a better correlation with potential loaf volume.

L

Hamed Faridi and Vladimir F. Rasper write in, "The Alveograph Handbook": "The average abscissa to rupture, L, is the average length, in millimeters, of the quintuplet curves from the point where the dough bubble starts to inflate to the point where the bubble bursts and the pressure drops suddenly. Unlike overpressure P, the meaning of this index seems to be unambiguous. L is commonly used as a measure of dough extensibility."

P/L

This ratio is thought to indicate general gluten performance; In other words, the balance between dough elasticity and plasticity. In general values of 0.40-0.70 are thought to be appropriate for bread baking. As the number rises, there will be a certain point where the dough will be too elastic/resistant, yielding a less developed loaf with compact crumb. Conversely, when very low P/L values indicate a dough that is too extensible. There is no absolute perfect value. Finding a balanced value that is appropriate for the application is key.

 

Types of Flour

We have seen, from the descriptions of wheat types available, that there are many characteristics of the grain which will determine the quality of the finished products. There is no such thing as one flour being any "better" than another. The priority for the flour miller is to provide the customer with a flour that is "fit for purpose". A clear understanding of the requirements of the customer will enable the miller to select which wheats, or which blend of wheats, will provide that functionality.

There are three main categories of flour: White, Brown and Wholemeal. White flour is made with only the starchy endosperm, wholemeal is made with the whole grain and brown flour is a varied mixture at differing levels of both endosperm and branny material.

Wholemeal bread has the least varieties due to its nature. The main differences between them is the granulation of the flour and the size of the bran particles. Wholemeal flour made in the traditional stoneground mill will be relatively coarse as the system is unable to grind the material fine enough without risking damage to the stones. The modern flour milling process is able to separate all the component parts of the grain, manipulate the granularity or size and mix them back together again.

This same process of separation and adjustment is used to create brown flours with the exception that extra flour may be added or some of the branny materials removed to produce the desired quality of brown flour.

Protein levels on wholemeal flours is generally higher than the white flour made from the same grain, and it is not uncommon to use lower protein wheats for wholemeal and for gluten to be added to improve its bread baking quality. The particle size of the bran will also affect the resultant loaf.

White flour is by far the biggest category, amongst which breadmaking is probably the biggest percentage. Breadmaking flour generally needs the following characteristics:

  • Sufficient quantity and quality of protein to give required stability, strength, extensibility and gas retention needed for the baking process
  • There should be sufficient enzyme activity to break down the starch to release sugar for fermentation to occur
  • The amount of damaged starch granules should be sufficient to allow the required water absorbtion, and to make accessible the sugars for the enzymes

Most breadmaking fours are produced as straight run flours ie. all flour streams from the process are combined to give an average quality. In some cases there is a requirement for "patent" flour which requires some streams of darker flour to be removed - this increases the brightness or colour of the flour.

Other grades of white flour, created by blending appropriate qualities of wheat for milling, are also produced to meet their specific purpose. This could include, but is not limited to, biscuit flour, cake flour, pizza flour (different types for deep pan or crispy !), soup flour, batter mix, cake mixes, rusks and coatings, burger buns, ethnic breads etc.

Milling - overview of the process


The milling process is outlined in the diagram below, with further details outlined in the following text.

 

Wheat arrives at a mill by truck after either being shipped or hauled from its point of origin. Once at the mill the incoming wheat is subjected to a series of quality control tests, then the wheat is unloaded and stored in silos. The diagram shows a simplified view of the milling process.

The Cleaning of Wheat


Before wheat can be milled the impurities that were gathered up with the wheat during harvesting must be removed.Different mills use various makes of machinery to remove the small stones, husks, weed seeds, etc gathered with the wheat during harvesting but they all use the differences in size, weight, shape and density to isolate and remove impurities.

The Conditioning of Wheat

Water is added to the wheat in small amounts to ensure easy separation of the bran (outer coating) from the endosperm (inner part of the wheat). The water helps to toughen the outer bran layers and softens the inner portion. This makes the soft inner portion easier to remove.

 

Rolls and Sifters

The whole milling process can be seen as a repetition of two processes - grinding and sifting. The wheat is first passed over a series of fluted break rolls. A pair of break rolls do not turn at the same speed, the higher roll usually turns about twice the speed of the lower roll.Wheat travelling between the break rolls is ripped apart and the white endosperm material is released. After passing through each set of break rolls the particles are sorted on a sifting machine. The flour is removed and the coarse branny material is returned to the break rolls in order to separate out any flour still attached to the bran. Semolina, which is chunks of endosperm, is also produced in the break system and this Semolina is passed onto a new series of rolls called reduction rolls.

Eventually all the wheat going through the break system is removed as either flour, semolina, pollard or bran. The reduction rolls are a series of smooth rolls which grind the semolina particles down into three products, flour, fine bran and wheatgerm. Each of these products can then be separated by repeated grinding and sifting. The flour obtained by the various rolls and sifters is of differing quality depending upon when it was removed from the system. Mills can blend flours from the various parts of the system to obtain a flour suitable for selling.

Finally the mill ends up with wheatgerm, pollard, which is fine bran and flour. Mills can then either bag these products or send them off via bulk supplies. Mills can also add value to their product by making flour into self-raising flours, pastry flours and premixes. All these are produced by using flours from different parts of the system and in some cases adding additional ingredients.