WO1989004723A1 - Method and apparatus for grain treatment - Google Patents

Abstract

A method for increasing the Hagberg number of wheat etc. comprises subjecting the grain to separation on the basis of specific gravity, e.g. by means of a reciprocating gravity table separator. The separator may be mounted on a mobile chassis fitted with jackable support legs. The degree of separation and/or quality of the grain can be estimated by flotation in a fluid of calibrated specific gravity.

Description

Method and Apparatus for Grain Treatment

This invention relates to the provision of wheat for bread making which is of a suitable quality when measured by the Hagberg test. In particular the invention relates to the separation of wheat having a low Hagberg number to provide an upgraded product having a much higher Hagberg number, and to apparatus for carrying out this and other grain separations.

The Hagberg test is described in some detail in two original papers by S. Hagberg in Cereal Chemistry 37, 218, 222 (I960) and 38 202-203 (1961). In the Hagberg test, the "falling number" is measured for a flour sample. In this process the wheat to be analysed is milled, conventionally in a high-speed hammer mill, and a standard amount of the flour is combined with a standard amount of water in a standard test tube. The mixture is heated for a standard time during which it is gently agitated and then the time is measured for a standard plunger to fall a standard distance through the paste which is formed. The time (in seconds) for the plunger to fall is added to the time during which the flour-water mixture is heated (60 seconds) to give the falling number or the Hagberg number for the wheat sample. The test is a measure of the degree of amylolysis which had taken place in the wheat. Adverse weather conditions, particularly cold and wet. activate the aroylase content of the grain leading to breakdown of the starch chains to produce di- and oligo-saccharides. Even a relatively small degree of hydrolysis has a drastic effect on the viscosity of the gelatinized starch and thus has a critical effect on the suitability of the wheat for the production of bread.

The Hagberg test is widely used in the cereal market as a measure of the suitability of wheat for bread production. Unless the dough has a sufficient viscosity, bread making is not possible. Good viscosity is provided primarily by a high starch content. As wheat ripens, the starch content increases to a maximum value. Ideally, wheat should be harvested at that point. However, if there is a period of wet weather at harvesting time, and the grain stays wet for a considerable period, the starch begins to degrade to release free sugars in a chemical process akin to that of malting. As this process proceeds, the Hagberg number of the wheat decreases. Conventionally for suitable bread production, the Hagberg number should be at least 250. Bad weather conditions can reduce the Hagberg number of a crop to a value of 80 to 100. Conventionally, such wheat is then considered to be of no use for bread making and, in particular, has not been considered to be susceptible to any treatment which would cause significant improvement. It thus serves only as much cheaper feed wheat.

It has now been discovered that weathered grains of low Hagberg number can be simply separated from good grains of higher Hagberg number by subjecting the grain to specific gravity separation in suitable apparatus. Although the weathered grains are only slightly lighter in weight than the good grains (typically about 1% lighter), it has been found that this slight difference in specific gravity coupled with an increased roughness of the outer coating, enables effective separation to take place.

According to the present invention, there is provided a method for increasing the Hagberg number of a sample of wheat or other grain comprising subjecting the wheat to separation on the basis of specific gravity to exclude low Hagberg number grains, and to recover grains of higher Hagberg number.

The effect of the method according to the invention (known as the Wilsdon method) is quite dramatic. With a loss of only 30% weight, wheat having an overall Hagberg number of less than 90 can be converted into a sample having a Hagberg number of 220, well above the minimum requirement for bread manufacture.

The proportion of lighter grains to discard can be simply judged by monitoring the Hagberg number of withdrawn samples. In one specific example of the method according to the invention, weathered wheat having a Hagberg number of 86 overall was fed to a specific gravity separator and a cut of about 30% of the lighter grains was removed. The remaining grains were found to have a Hagberg number of 280 and were completely suitable for milling.

The separation on the basis of specific gravity can be conveniently effected in a specific gravity separator, or gravity table, of the type commonly used for the removal of foreign bodies from cereal crops, for example weed seeds, ergot grains and soil particles. Such machines conventionally comprise an inclined table formed of an oscillating mesh screen over which the wheat grains move. Conventionally, compressed air is supplied under the screen to cause flotation. Typical machines of this type are supplied by Spiroll Kipp Kelly (1984) Incorporated of Winnipeg, Manitoba. Canada, although many other similar types of machine are available, eg HEID, Oliver and Kamas separators. Gravity separators comprise large, heavy machines including a reciprocatable perforated or slatted table and a source of compressed air which can be passed upwards through the table to fluidise grains placed thereon. The separators are used to clean up grain by removing weed seeds, grit etc. In the process of the invention separators of this type are used, surprisingly, to upgrade by a dramatic amount the Hagberg value of wheat and other grains by removal of partially weathered, low-starch grains.

A problem with these machines is that, because of the large reciprocating masses within the gravity separator, it was absolutely esential that these machines were mounted securely by being bolted or otherwise firmly fixed to a solid floor such as a concrete slab, which is completely resistant to vibrations. Indeed, all the literature provided by the suppliers insists on this. This means that the machines cannot be taken to the site for working, but instead all the seed to be treated must be carted to the machine and back again.

It has now been discovered that a gravity separator can be mounted on a suitably rigid and massive truck chassis or other wheeled or tracked vehicle provided with jackable stabiliser legs (after the manner of a mobile crane etc). Surprisingly, the combined weight of the gravity separator plus the chassis and wheels etc, together with the vibration-damping effect of the stabiliser legs, is sufficient to dampen and absorb the reciprocation energy so that the apparatus remains stationary and stable during use without the need for permanent ground fixings.

Typically, a gravity separator of say, 2 - 3 tonnes (e.g. an Oliver Hi-Cap Model 480) is rigidly bolted onto the chassis of a truck (e.g. a Ford Cargo) fitted with jackable or hydraulically operated stabiliser legs which can be lowered to contact the ground around the chassis. The total weight is about 7 tonnes.

The resulting equipment can be driven or towed to any required site, the legs lowered into place, and the machine is then ready for immediate use. The gravity separator can receive operating power from mains electricity on site, or as an option, electricity can be provided by an on-board generator, powered by the engine of the truck. It is most surprising that an arrangement as apparently simple as this is so effective, since the general view in the field has always been that permanent solid fixings were required, and that mounting a truck with a normal type of suspension and tyres would immediately result in a complete loss of useful reciprocating movement. However, we find that the table works well for all types of seed separation, provided that the stabiliser legs are firmly on the ground. Indeed, if the legs are lifted, the table immediately becomes useless.

The gravity separators used in this process can be of various designs, but in all types grain passes up the sloping table and spreads into a generally wedge-shaped flow, with good quality, heavy grains reaching one edge of the table and being removed in a trough running along the edge of the table. Inferior grains move across the table and are removed from outlets on an adjacent side.

One problem with apparatus of this type is that small stones and particles of earth tend to travel with the good grain and emerge from the top of the table into the exit trough. It is important that stones and earth are removed, partly to ensure that grain for milling is pure and uncontaminated, and also to ensure that seed grain does not contain foreign particles which would foul the seed drills. While it is possible for stationary systems to have separate sieving mechanisms for cleaning up the grain, the mobile system described above has very little room.

It has now been found that a simple modification of the apparatus can remove stones and grit from the good grains at the point of exit, while only removing a very small percentage of the grain itself.

According to a further feature of the present invention there is provided a specific gravity separating table having an outlet arranged for removal of good quality grain, this outlet being in the form of a channel or trough or other open receiver into which grain falls having left the reciprocating table and which also reciprocates; and a perforated or mesh screen placed across the top of the grain outlet and communicating with a separate outlet for stones and grit, the screen being arranged so as to intercept the flow of only the heaviest grains from the table into the outlet. In a prefered embodiment the screen is placed across the top of the grain outlet level with the top edge of the table or deck, effectively bridging the top edge of the table to an outlet for stones.

In use, the combination of heaviest grains (eg. about 5%) and stones passes off the table onto the screen. The apertures in the screen are chosen so as to pass the grain while stones and pieces of earth remain on the screen and pass to the stone outlet under the influence of the reciprocating motion. The size of aperture in the screen can be varied, depending on the grain to be treated. For English soft wheat a pass range of up to 5mm is desirable, for example, while for barley wheat a size range of up to 5.5mm is preferred; for peas a pass of up to 12mm is satisfactory. Since only about 5% of the grain is being sieved at all it is acceptable to have a very "tight" specification.

The screen can be made of perforated mild steel sheet, woven wire or any other suitable material. The stone outlet can conveniently comprise a simple sheet metal shute, which can be arranged to lead to a receptacle.

It will be seen that the modification according to the present invention enables only a small fraction of the good grain to be required to be sieved, and that can be achieved with apparatus which adds very little to the bulk or weight of the separator. The invention is thus ideally suited to the mobile separator table of the invention in particular and to all separators in general.

A further modification to reciprocating gravity tables we have found of considerable advantage is to replace the usual large centrifugal fan or fans in the plenum chamber by a smaller axial fan of variable pitch mounted at the air inlet. Such an arrangement provides much better control and considerable energy saving and noise reduction. Typically a fan and table drive of 13 amp rating gives rise to electricity costs (UK) of about 5p per tonne. In contrast, conventional machines can only limit air flow by blanking off part of the fan surface and continuing to run at full power.

In the principal feature of the invention, the Hagberg number of wheat etc is upgraded and so it is necessary to be able to measure the Hagberg number of different fractions of grain being separated in order that the correct "cut" is made and the minimum amount of poor grade wheat is discarded.

There is thus a need for a simple Hagberg test which can be carried out on the farm with the minimum of equipment, but with reliable results. Standard Hagberg equipment tends to be very expensive and involves a precision mill. It has now been discovered that flour of a suitable type and quality for the test can be simply prepared, provided the right particle sizes are chosen.

According to a further feature of the present invention, there is provided a method of obtaining the Hagberg number of cereal samples, especially of wheat or rye, by measuring the time taken for a plunger to fall a standard distance through a cooked flour-water paste, characterised in that the flour is obtained by grinding the wheat in a rotary blade (flail) grinder until substantially all will pass a 500 micron screen and discarding the material which does not pass through. The size of the screen, and the size to which the substantial proportion of the wheat should be ground, is preferably between 250 and 500 microns; greater than 500 microns and smaller than 250 microns does not produce reproducible results.

The term "rotary blade grinder" is used to refer to the electrically powered intermittent flail type of grinder typified by the domestic coffee grinder, where two or more opposed blades rotate rapidly to chop the material into small fragments. A typical machine has a power of 150 watts. It has been found that using this combination of a simple electric grinder and an appropriately sized screen, a flour sample can be produced which is suitable for the falling number test.

The test itself can then be effected by measuring out a predetermined standard weight of the flour and mixing it thoroughly with a predetermined standard amount of water in a standard tube. As in the conventional Hagberg test, the flour-water mixture is then heated, for example in a boiling water bath, for a standard time while be gently agitated. A calibrated plunger is then positioned at the top of the paste and is allowed to fall a standard distance through the tube. The time taken for the fall is measured, and is added to the above-mentioned standard time of heating to obtain a Hagberg number. Naturally, the amounts of flour and water used, the standard heating time and the dimensions of the tube and the plunger are all subject to variation; any particularly combination can be simply calibrated to provide a correct Hagberg value by using samples of known Hagberg value. In practice, we find it particularly convenient to use a tube of dimensions similar to those used in the original Hagberg paper, typically a test tube of interior diameter 21mm and length 220mm containing 25g of water to which 7g of the flour is added.

According to a further feature of the present invention there is provided apparatus for carrying out the Hagberg test on a grain sample comprising milling means, means for gelatinising a flour sample under controlled conditions and callibrated means for measuring the falling number, characterised in that the milling means comprises rotary blade grinder in combination with sieving means capable of passing particles of up to 500 microns.

The conventional Hagberg test is conducted in a glass (or borosilicate) test tube. According to Hagberg (Cereal Chem. 37: 218-222 (1960)) the tube should have an internal diameter of 21 mm and a length of 220 mirt. The tubes are generally formed of relatively thick glass for strength. At the end of the test, the gelatinised, glutinous starch paste must be washed out so that the tube can be re-used. This can be difficult and time-consuming, especially if the contents of the tube are allowed to cool and/or dry.

We have attempted to use an open-ended cylinder in place of a test tube, sealed at the bottom with a stopper. However, we have found that most conventional stoppers (e.g. corks and rubber bungs) do not conduct the heat from the heating bath as rapidly as the glass, causing erroneous results in the Hagberg readings. It has now been found that a particular type of stopper can be used and good readings can be achieved using an open-ended cylinder which can be washed in seconds. The stopper must be a hollow silicone rubber bung or cap. for example a bung of the type known as the Suba Seal 51 (UK Registered Design No.929478). At the completion of each test, the tube can be easily cleaned with a resilient plunger.

It is also useful to be able to do a rapid estimation of the quality of seed in any fraction, even when separation is being effected for other purposes. In particular, it is particularly desirable to be able to estimate the bushel weight, or hectolitre weight, of a grain sample. There is thus a need for a simple test which can be carried out on the farm with the minimum of equipment, but with reliable results, so that the degree of separation and the nature of the yield can be estimated. With such information the separator may be adjusted and the desired degree of separation effected.

According to another feature of the present invention there is provided a method of estimating the quality, eg. the homogeneity, of a cereal sample, comprising immersion of a sample of the grain in a fluid with a specific gravity chosen such that, for the required quality, substantially all the grains sink to the bottom of the fluid. In other words, the method utilises the specific gravity of the grain as a means of indicating its quality. In a modification of the method, the proportion of grains in a sample having a suitable quality can be obtained by doing a flotation/sinking test in a given fluid and determining the proportion of grains which sink.

It will be seen that the method of the present invention is exceptionally simple and easy to carry out. A result is obtained almost instantaneously, thus providing an estimate useful in determining the adjustment needed to the separator when setting it up for use. for "fine tuning" during use. etc. In addition it offers the grain trader a rapid estimate of the quality and homogeneity of a grain sample: a separation of grains into floating, sinking and in-between, would indicated an undesirable degree of heterogeneity.

The test requires the use of a relatively inert medium which does not deteriorate at ambient temperature, which is easily re-usable and which is not unpleasent (ie, is not noxious). For preference, the medium should be cheap. It must also be relativly low viscosity, in order that clear separations of floating and sinking grains can be rapidily achieved. We find that a prefered fluid medium comprises an aqueous solution of a suitable solute, eg. a sugar such as sucrose or an inorganic salt such as magnesium sulphate. When dealing with wheat samples, a range of specific gravities of 1.15 - 1.30 at 20ºC. is suitable and specific gravities within this range can be easily achieved with a wide varity of solutes in water, e.g. other inorganic salts such as sodium chloride, sodium sulphate etc. In practice, suitable solutions can be pre-packed or suitable solutes can be pre-packed or tabletted so as to provide the required specific gravity solution in a standard volume of water at a standard temperature such as 20°C. Simple tables can be provided for calibration if the ambient water temperature is lower (or higher) and means are not available for altering the temperature. It can be envisaged that pre-packed solutions or solutes could be simply labelled with Hagberg numbers or other indications of quality. It will be seen that in the method of the invention, the homogeneity or the bushel or hectolitre weight of grain can be estimated in an extremely short time without the need for a more elaborate test. The flotation test can thus be used to assist in calibrating a specific gravity separating machine for use in the Wilsdon process. The method can also be used as a spot check during gravity separation to ensure that the product is of a constant standard.

Claims

1. A method for increasing the Hagberg number of a sample of wheat or other grain comprising subjecting the wheat to separation on the basis of specific gravity to exclude low Hagberg number grains, and to recover grains of higher Hagberg number.

2. A method according to Claim 1 effected using a reciprocating gravity table separator.

3. A reciprocating gravity table separator mounted for use on a heavy tracked or wheeled vehicle fitted with jackable stabiliser legs arranged such that, in use, the stabiliser legs are firmly in contact with the ground.

4. A reciprocating gravity table separator having an outlet arranged for removal of good quality grain, this outlet being in the form of a channel or trough or other open receiver into which grain falls having left the reciprocating table and which also reciprocates; and a perforated or mesh screen placed across the top of the grain outlet and communicating with a separate outlet for stones and grit, the screen being arranged so as to intercept the flow of only the heaviest grains from the table into the outlet.

5. A reciprocating gravity table separator provided with an electric fan. characterised in that the fan is an axial, variable pitch fan mounted at the air inlet to the separator.

6. A method of obtaining the Hagberg number of cereal samples by measuring the time taken for a plunger to fall a standard distance through a cooked flour-water paste, characterised in that the flour is obtained by grinding the wheat in a rotary blade (flail) grinder until a substantially all will pass a 500 micron screen.

7. A method according to Claim 6, using an open ended test tube of interior diameter about 21 mm and length 220 mm, fitted with a hollow silicone rubber stopper, containing 25 g water to which 7 g of flour is added.

8. Apparatus for carrying out the Hagberg test on a grain sample comprising milling means, means for gelatinising a flour sample under controlled conditions and callibrated means for measuring the falling number, characterised in that the milling means comprises rotary blade grinder in combination with sieving means capable of passing particles of up to 500 microns.

9 . A method of estimating the quality and/or homogeneity of a cereal sample obtained from a reciprocating gravity table, comprising immersion of a sample of the grain in a fluid of specific gravity chosen such that substantially all grains of a specified quality sink but grains of lesser quality do not, and observing the proportion of grains that sink.