GB2268386A

GB2268386A - A process for treating cereal grain prior to milling

Info

Publication number: GB2268386A
Application number: GB9314180A
Authority: GB
Inventors: Dennis Edward Forder; Ian Cameron Shand
Original assignee: Satake Corp
Current assignee: Satake Corp
Priority date: 1992-07-11
Filing date: 1993-07-09
Publication date: 1994-01-12
Anticipated expiration: 2013-07-09
Also published as: GB9314180D0; GB9214771D0; GB2268386B

Abstract

A process for treating cereal grain prior to milling in which the stock is initially wetted to soften and loosen an outer portion of the bran coat. It then passes through a debranning stage in which the first portion of the bran coat is removed by a mechanical treatment after which the grains are cleaned and then tempered by the addition of water to penetrate into the grains. After tempering further wetting is effected to soften and loosen the remaining bran coat which is subsequently removed in a final debranning stage, again by mechanical treatment, thus rendering the stock easy to handle for transfer to a milling machine without the risk of agglomeration of the grains which might otherwise occur if the entire bran coat were removed prior to tempering. At the separate debranning stages the bran is collected for further treatment and use.

Description

A PROCESS FOR TREATING CEREAL GRAIN PRIOR TO MILLING THIS INVENTION concerns a process for treating cereal grain such as wheat kernels, prior to milling in the manufacture of flour and other wheat byproducts.

Cereal grains, particularly wheat, are enclosed in a series of discrete bran layers, and it is known that substantial improvements to the milling of wheat kernels may be realised by sequentially removing the bran layers before they are subjected to milling.

In a known process the grain is fed through a series of mechanical operations including friction and abrasion which progressively remove the bran layers in such a manner that the bran layers may be extracted as byproducts and the grain may proceed onwards for milling.

Another essential step in the pre-treatment of grain is known as tempering or conditioning in which water is added and sufficient time is allowed for the water to penetrate to a substantial depth into the grain so as to improve the milling performance and to ensure that the flour produced is at a consistent target moisture content.

In a known process for pre-treating grain in this way the mechanical bran removal is completed prior to tempering of the grain, but the process suffers from the disadvantage that freshly tempered grain with little or no residual bran coat tends to agglomerate rendering it difficult to hold in a bin for the period of penetration of moisture or to handle in the subsequent passage to and through the milling machines.

It is an object of the present invention to provide an improved process for treating cereal grains prior to milling, including a tempering step and including bran removal, but where the aforementioned disadvantage is substantially avoided.

According to the present invention there is provided a process for treating cereal grains prior to milling, thus to remove the bran coat from the endosperm, the process comprising, in the following sequence, the steps of: a) adding water to the grains which may be untempered or partially pre-tempered and holding same for a sufficient time to soften and loosen an outer portion of the bran coat; b) mechanically treating the surface of the grains to remove a first portion of the bran coat; c) tempering, the grains by the addition of water and allowing sufficient time for the water to penetrate into the grain; and d) mechanically treating the surface of the grains to remove final portions of the bran coat thus to render a product grain which is immediately available for milling.

Preferably, the process includes the step of treating the grains to remove loose particles adhering thereto prior to the tempering.

The final mechanical treatment is preferably carried out in two separate machine stages whereby the operating conditions may be selected to maximise removal of the final portions of the bran coat.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing which is a flow chart indicating the various steps in the process.

The process is applicable to cereals which have been partially tempered as well as those which are at their "natural" moisture content i.e. in the condition in which wheat is normally traded.

Tempering is a term used throughout this specification to refer to a process of conditioning wheat by the addition of water at the natural moisture content of the wheat and allowing several hours, usually 6 to 12 hours, for the water to penetrate to a substantial depth into the grain. The tempering process is required so as to improve the subsequent milling performance.

Initially therefore, the stock is fed to a vessel 10 in which water is added in an amount of 1 to 3 per cent by weight, and the stock is held for a period of 1 to 10 minutes as considered sufficient to soften and loosen an outer portion of the bran coat of the kernels.

The stock is then fed to a first debranning stage 11 in which it is subjected to a mechanical surface treatment which may be by friction or abrasion or a combination thereof, to remove an outer portion of the bran coat.

Thereafter, if required, the stock is passed to a second debranning stage 12 in which a further portion of the bran coat is removed by a similar mechanical surface treatment.

The bran which is removed during the first and, if used, the second debranning stage is collected as a byproduct for further treatment and use.

After initial debranning the stock is preferably subjected to a brushing or similar mechanical treatment such as scouring or aspirating at 13 in order to remove loosely adhering dusty particles which have become lodged particularly in the creases of the kernels.

The dusty deposits removed in this treatment stage could, if allowed to remain on the surface of the grain, give problems in the subsequent water addition stage and produce a discolouration or contamination of the final milled product.

After the cleaning stage the stock is passed to a vessel 14 in which it is subjected to tempering, or conditioning, for several hours.

After tempering further water is added at 15 to the surface of the grain in an amount of 0.5 to 2 per cent by weight and allowed to penetrate the remaining bran layers for a period of up to 5 minutes before the stock is fed to a further debranning stage 16 in which a further portion of the bran coat is removed by a mechanical surface treatment, and then to a final debranning stage 17 in which a final portion of the bran coat is removed by a further mechanical surface treatment.

From these further and final debranning stages the bran is collected for further treatment and use. The grain is immediately available for milling without the need for any further tempering or pre-conditioning. Thus, the grain has a substantially clean and dry surface rendering it easy to handle for transfer to a milling machine.

Thus, it can be seen that a final part of the debranning process is carried out immediately in advance of the flour milling process whereby all of the equipment involved after the tempering step operates simultaneously as a single operating unit. In this way, recovery of flour from the by-products from the further and final debranning stages can be incorporated into the mill so as to extract usable flour from this normally byproduct material. This feature substantially enhances the economic viability of the process for the following reasons: 1) Significant storage capacity must otherwise be provided for these materials which are produced at a prior stage when the mill may not necessarily be operating. In addition, conveying and metering systems must otherwise be installed to transfer the materials from storage back into the milling process.

2) Usable flour extracted from the byproduct is an additional financial benefit of the process since flour usually has a higher commercial value than the byproduct.

3) The ability to recover flour from the byproducts renders control of the debranning process less critical.

It is a feature of such systems conventionally that the amount of bran which can be economically removed is restricted by the need to reduce any potential loss of flour. By processing the grain to a greater degree it carries less bran into the milling process and hence potentially will yield a brighter flour or semolina.

4) Quality variations in the flour or semolina after milling can be rectified more readily when compared with conventional debranning systems in which there is a substantial delay during which the grain is tempered between debranning and milling.

Enhanced byproduct recovery is ensured by this process which will include sifting to separate the material into flour, also into fine flour-bearing particles which can be further processed to produce more flour and into coarse flour-bearing particles such as semolina from which flour can be produced by known methods, and into particles which are too contaminated by coloured bran elements to yield usable white flour. The system therefore ensures more positive classification of the byproducts.

The process as described herein is applicable equally to the preparation for milling of vulgare and durum varieties of wheat for flour or semolina production.

Claims

1. A process for treating cereal grains prior to milling, thus to remove the bran coat from the endosperm, the process comprising, mechanical surface treatment and tempering; characterised by, in the following sequence, the steps of: a) adding water to the grains which may be untempered or partially pre-tempered and holding same for a sufficient time to soften and loosen an outer portion of the bran coat; b) subjecting the surface of the grains to a first mechanical treatment to remove a first portion of the bran coat; c) tempering, the grains by the addition of water and allowing sufficient time for the water to penetrate into the grain; d) subjecting the surface of the grains to a second mechanical treatment to remove a final portion of the bran coat thus to render a product grain which is immediately available for milling.

2. A process according to Claim 1, including the step of cleaning the grains to remove loose particles adhering thereto, prior to tempering.

3. A process according to Claim 1 or Claim 2, wherein said second mechanical treatment is carried out in two separate machine stages.

4. A process according to any one of Claims 1 to 3, wherein said first mechanical treatment is carried out in two separate machine stages.

5. A process according to any preceding claim, in which the addition of water to the grains prior to said first mechanical treatment thereof, is in an amount of 1 to 3% by weight, and the grains are held for a period of from 1 to 10 minutes or at least sufficient time to soften and loosen an outer portion of the bran coat.

6. A process according to any preceding claim, in which the mechanical surface treatment of the grains is by friction or abrasion and/or a combination thereof.

7. A process according to any preceding claim, in which the bran removed prior to tempering, or conditioning, is collected for further treatment and use.

8. A process according to Claim 2, wherein cleaning of the grains to remove loose particles, is by brushing, scouring or aspirating.

9. A process according to any preceding claim, wherein said tempering, or conditioning, of the grains is carried out for a period of several hours.

10. A process according to any preceding claim, wherein, after tempering, or conditioning, of the grains further water is added in an amount of 0.5 to 2% by weight and allowed to penetrate the remaining bran layers for a period of up to 5 minutes before said second mechanical treatment.

11. A process according to any preceding claim, wherein the final portions of the bran coat, after removal, is collected for further treatment and use.