GB2029193A - Polishing brown rice - Google Patents

Abstract

Brown rice is polished in apparatus comprising an endless enclosed moving belt, the upper part of which runs within a channel to which is attached a series of weirs with clearance between the belt and the undersides of the weirs for carrying away bran, the weirs retaining brown rice fed on to the belt and causing abrasion of the bran layer from the rice by the movement of the grains piled up at the weirs. Polished rice overflows the weirs and is collected.

Description

SPECIFICATION Brown rice whitener and polisher This invention relates to methods of, and apparatus for, removal of coatings on seeds, including certain cereals, legumes and nuts for polishing small objects of wood, plastic, mineral or metal, without using mechanical pressure.

More particularly, the invention relates to methods and apparatus for removing the soft bran coating of brown rice which has already had the hulls (husks) removed. The products are white rice ready for cooking; also bran for stock-feeding, before or after a heat stabilising process and, on occasion, for edible oil extraction which leaves a residual meal for stockfeeding.

It will be understood that adjustments may be necessary to the settings of the apparatus used for brown rice polishing if the material to be polished is other than brown rice. The description that follows is applicable to brown rice.

Brown rice is wholly edible by man after cooking; the soft bran coating contains 20-30 per cent of proteins and fats. The (seed) embryo contains vitamins.

Whitening, and then full polishing, remove these nutrients leaving modules of an almost pure carbohydrate, starch, which is the white rice of commerce.

Rice-eating peoples will not willingly eat brown rice and the higher the degree of polishing to remove all the bran and the minute embryos, the more the white rice is esteemed. The texture and the flavour of cooked brown rice are both unpopular.

A grain of paddy contains a grain of brown rice weighing 80 per cent of the paddy grain, the hull (or husk) weighing the remaining 20 per cent.

The brown rice grain comprises about 70 percentage points of white rice and 10 percentage points of bran and embryo. Therefore the full whitening and polishing process for brown rice involves removing up to about 12.5 per cent of the weight of the brown rice and recovering it separately as bran. Full polishing also tends to remove some of the white rice, transferring it to the bran, as flour.

About 325 million tons a year of paddy, over 90 per cent of the world crop, is grown in Asia. It is probable that not more than 33 million tons, 10 per cent of the Asian crop, in processed in multi-staged mills which first hull the paddy, then remove and recover the bran and the white rice separately.

The apparatus used in most ofthe multi-stage mills for removing bran from brown rice is a rotating cone on a vertical shaft, the conical surface being covered with sharp abrasive grit. The cone operates inside a perforated stationary steel cage. The brown rice gravitates into the narrower annular space between the cone and the cage. Grain breakage is considerable due to pressure, friction and the resultant overheating of the grain. Broken grains fetch lower prices than whole grains.

The remaining 90 per cent of the Asian crop of paddy, about 290 million tons, is either hand pounded or single-stage milled in a power-driven machine designed for coffee-grinding in the late 19th century. It is known as an Engleberg or a Kiskesan. Its optimum yield on paddy is 50 per cent of well-polished rice, but containing up to 55 per cent of broken grains.

The residual 50 per cent is an inseparable mixture of shredded hulls, powdered rice and bran for which an economic use has yet to be found. The silica content of the hulls is far too high forthe mixture to be used as stock-feed, even for poultry. All evidence points to hand-pounding being similarly destructive as single-stage milling. The discarded residual mixture creates a pollution problem. It is sometimes piled in heaps and, when ignited, it smoulders very slowly to ash; or, it is dumped in marshes to rot.

The annual Asian losses due to single-stage milling and hand-pounding could now be about 146 million tons, made up of 59, 58 and 29 million tons of white rice, hulls and bran; potential food, or fuel or stock-feed. An unknown but relatively not large amount of paddy is parboiled before processing, mostly at village level. The effect is to reduce the loss of rice which is less liable to shatter to powder after parboiling. The rice also absorbs some of the bran, beneficially for nutrition, but the flavour is generally disliked and often not tolerated.

The novel aspect of the invention is the use of an endless boxed-in flexible belt, running over rollers or pulleys driven by mechanical power to whiten or polish brown rice without putting it under pressure.

Optionally, small belts can be driven by musclepower, human or animal.

The brown rice from the huller is fed, preferably by gravity, on to one end of the top of the belt and white rice and bran are discharged separately at the other top end. Any stray hulls are also discharged separately.

The upper part of the belt runs through a closefitting channel, part of the box, any gaps being too small to allow the leakage of rice grains which are at least 1.5 mm in diameter.

The whitening and polishing is effected by a series of weirs slotted into, or otherwise attached to, the channel or lid.

The weirs have small gaps under them so that they do not rest on the moving belt. These gaps allow the stray hulls and powdery bran to pass but retain the rice.

The weirs divide the channel into a series of chambers, successively whitening and then polishing the rice. There is a larger gap above each weir through which rice overflows. The gaps are created optionally by a lid on the channel or by baffles above the weirs. The purpose of the baffles is to minimise the escape of rice bouncing off the belt and over the weirs.

The movement of the belt under the rice in the successive chambers causes the grains to pile up againsttheweirs. The cross-section of a pile is roughly a right-angled triangle, in elevation, with a height to width ratio of about one to one or one to two.

With a continuous flow of brown rice into the first chamber, the surplus overflows the weir into the second chamber, piles up again and overflows into all the chambers in succession. At the top of the last weir, the polished rice is caught by a chute and gravi tates away for disposal.

The rice piled up against each weir is in constant rotary motion, rising up the face of the weir, some of it rolling back down the angle of lie and the rest over-flowing the weir. This is a rumbling action which cleans the grains of loosened bran.

The bran and stray paddy hulls fall onto the belt and pass under the weirs until the discharge pulley is reached. There the bran gravitates off the belt into a tray or other form of catcher.

The stray hulls fall further out and are caught separately. They represent only a few percent of the hulls removed in the paddy huller which are entrained with the brown rice.

The accumulation of bran and some hulls on the belt passes easily under the weirs. There is no build-up of bran or hullers on the belt which is virtually self-cleaning at the discharge pulley.

The amount of polishing required by customers varies from zone to zone. In view of the shortages of rice in Asia, and elsewhere, some governments insist on a minimum whitening and polishing to increase the yield of edible rice and increase its nutritional value, at the expense of less yield of bran mixed with powdered rice.

The weirs in the channel are easily removed and replaced. The greater the number in use, the greater the amount of whitening and polishing.

The upstream faces of the weirs can be covered optionally with abrasive. The weirs, while normally vertical, can optionally be set at an angle to the vertical. Likewise, the weirs can optionally have straight, convex, concave or otherwise shaped faces across the channel.

The machine, normally horizontal, can optionally be raised at either end to change the abrasive action.

The aspect ratios of grains of rice, maximum lengths to maximum diameters, generally range between 6 to 1 and 1.5 to 1, depending on variety.

The milling characteristics differ so that a considerable degree of flexibility of polishing is needed in the apparatus to allow for the characteristics of the brown rice as well as for the degree of polishing required.

Claims (1)

1. i) Very much lower breakage of rice grains than that of apparatus now widely in use.

   ii) Low heating of the grains and consequential low power requirements.

   iii) An abrasive surface with a long life and which can be replaced quickly and cheaply on site.

   iv) Low inertial starting load.

   v) Power supply optionally taken from an associated paddy huller.

   vi) Option of gravity feed of brown rice from the associated paddy huller.

   vii) Ease of adjustment of the amount of polishing by removal or replacement of weirs.

   viii) Automatic rumbling action at the weirs to remove polishings (fine bran or rice flour) and stray paddy hull from the grains of rice which then emerge clean and smooth.

   ix) Stray paddy hulls and bran are each ejected separately from the white rice.

   x) Simplicity and cheapness of construction, operation and maintenance.

   xi) Flow over the weirs is self-adjusting to the input of rice, subjectto no overloading of the first polishing chamber.

   31. The attached sketch is a diagrammatic elevation and plan of the polisher.

   32. A- is the belt on its two pulleys.

   33. B - is the belt pulley driven by surplus power of the huller engine, or otherwise.

   34. C - is the channel and its weirs and baffles to control the flow of rice on the belt.

   35. D - is the hopper fed with brown rice by the paddy huller.

   36. E, F and G - are the receptacles to catch the white rice, the stray hulls and the bran, each separately.

   37. H - represents three rollers of the paddy huller built to Patent Application No. 27002/78 of 15/6us, or any other paddy huller.

   38. This design is an alternative and improvement on Patent Application No.33045178 of 11/8/78 and it eliminates some of the side-effects of using an abrasive linisher belt. It does not necessarily replace the linisher belt machine which is still in an advanced stage of development.

   39. My colleague, Mr. E. C. Bursey, is abroad for some weeks, but we have a written agreement to share equally in a series of inventions on which we have been engaged for four years. On his return, he will undertake some follow-up work on the invention, in collaboration with me, on this Application in my name.

   40. The exploitation of this and our other inventions on paddy and rice machinery may be assisted by UNIDO and EEC with whom lam working as a Consultant or Engineer on post-harvest processing of paddy-rice in Asia and Africa.