The pour table

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In large factories of medium size a great step forward in the settling operation has been taken through the replacement of the settling tanks by flour tables or basins. Because of the space it occupies, a table is generally practical only in medium-size and larger factories.

The flour table is a shallow channel, some 50 m long, about 30 cm deep and of a width varying with the amount of starch to be worked up daily. The bottom is covered with wood or tiles, as described in the previous section, and in principle should be horizontal, though it is sometimes given a slight inclination, say of 1 cm per metre.

The flour milk enters at one end, preferably from a compartment of the table itself, occupying over one half metre of its length and separated by a silt about 20 cm high, which ensures a uniform overflow over the whole width of the table. The liquid drawn off at the end of the table should be substantially free of starch and is thus rejected.

In settling on a table, the sedimentation path of the starch granules, which is vertical in the case of settling in tanks, will be drawn out into oblique lines on account of the horizontal movement of the slurry. The longer the time needed by any particle to pass from its position in the suspension down to the bottom, the further its ultimate place in the sediment will be from the head of the table. The stratification obtained in settling tanks is therefore in the present case partly converted into a differentiation as to granule size over the length of the table. Hence, floating or very slowly deposited fibre and dirt particles, including protein, will be removed at the end of the table, and the flour settling on the higher parts will contain a larger proportion of the larger starch granules and very little of the protein and other contaminants. Thus, the sediment on these parts of the table constitutes, generally, a better grade of flour, the rest being worked up as a lower grade. As the time of settling for all particles is much shorter than in settling tanks, the contact of the starch with the fruit-water is likewise considerably reduced.

As settling is most copious at the upper end of the table and slowly falls off toward the far end, the sediment soon shows the effect of an inclination of the table itself. As the working proceeds, the movement of the slurry is therefore accelerated on the upper end, tending to accentuate the difference in quality.

The flour table acts most efficiently if filled to maximum capacity. Some factories which must work up different quantities from day to day have flour tables of varying width - say, 2, 3 and 4 m.

The advantages of the flour table over the settling tank may be summed up as follows:

1. The time of contact of the flour with the fruit-water is shortened.

2. The starch settled on different parts of the table is differentiated according to purity and granule size, thus enabling the manufacturer to produce simultaneously and without extra cost at least two brands of different quality.

3. Losses of fine starch are far less because the sedimentation path is much shorter and drainage proceeds at a minimum rate.

Influence of chemicals on settling and the proprieters of the product

It may therefore be surmised that' apart from the rate of settling, the right consistency of sediment is important in achieving an efficient separation of the starch from the fruit-water. The starch losses incurred with draining in settling tanks will decrease as the starch settles to a firm cake, and even the efficiency of tabling will depend partly on the compactness of the sediment.

Pure starch settles in clean water to a compact mass of peculiar mechanical properties. If suddenly broken up (e.g., with a scoop). it crumbles like a brittle substance: but as soon as the forces causing deformation relax' it loses all form and spreads out like a thick syrup (melting. as it were, on the scoop). This phenomenon. termed dilatancy is explained by imagining the granules in the sediment, when at rest piled up on one another in the most space-saving manner' whereas any disturbance of this array by external forces results in an increase of the interstitial volume accompanied by a " drying up" of the cake. The same factors may give the dry flour its "crunchy" property.

The volume of the sediment and its compactness depend very much on the presence of impurities, such as fibre, which tend to result in a softer sediment. Apart from this, it has been found that the composition and the reaction of the ambient solution have an important influence on settling. An acid reaction promotes rapid settling and a compact sediment; an alkaline reaction has the opposite effect.

As in many medium-size factories chemicals are added for various purposes before settling, it seems worth while to review in some detail the effect of the substances most often applied, both on the consistency of the sediment and on the properties of the product.

It should, however' be emphasized that there is little sense in adding chemical aids where the basic conditions for the production of a high-quality flour are not fulfilled. in particular if clean working is not put first and foremost. On this condition there is no doubt that a flour of prime quality can be produced without the use of any chemicals. Moreover. because of the danger of misapplication. these additions are not to be recommended without the expert supervision as a rule available only in large factories.

Sulfuric acid In many instances this acid, which is added as an aid to sedimentation. results in a product of enhanced whiteness. The effect on sedimentation is noticeable at concentrations above 0.001 ml of the concentrated acid (specific gravity 1.84) per litre of starch of 2" Brix. (Degrees Brix are about proportional to the grams of flour per litre.) Addition of ten times the quantity causes very rapid sedimentation, but a rather soft sediment is obtained. The effect of this chemical in lowering the viscosity of the product is already appreciable at very small concentrations. Up to about 0.001 ml per litre of starch milk there is a slight increase in viscosity; at higher concentrations a marked decrease. The latter effect is a disadvantage in most applications of the flour; however, it is less so in the manufacture of baked products as whiteness is all-important.

Great care should be taken in adding this chemical, which should only be used in diluted form, prepared beforehand, and thereafter removed by one or more subsequent settlings in pure water.

Alum (aluminium sulfate). The presence of alum in the starch milk may be the consequence of the addition of a surplus of this chemical in the purifcation of the water used. It has a favourable effect on sedimentation, and also enhances the viscosity of the flour, an addition of 0.1 g per lire of starch milk of 2" Brix resulting in an increase of about 50 percent in viscosity.

Sulfur dioxide (sulfurous acid). The addition of sulfur dioxide is a common practice in the manufacture of most grain starches (e.g.' maize starch). It probably helps to separate the starch from the other substances to which it is more or less firmly bound in its protoplasmic state. Furthermore, it keeps bacterial and enzymatic action within bounds. Sulfur dioxide also acts as a bleaching agent, although the white colour thus obtained soon deteriorates. The acid produces a lowering of the viscosity of the product, especially after prolonged action, but e single settling from water containing the usual concentration of 0.3 to 0.4 g per litre followed by settling in pure water has no serious effect.

It is questionable whether the use of sulfur dioxide is advantageous in the processing of root starches and in particular of cassava. In any case, the acid should be applied with great caution and thereafter carefully washed out by subsequent settlings in pure water.

Chlorine. The addition of active chlorine in its different forms (the element itself, chloride of lime or one of the various commercial hypochlorites) considerably augments the viscosity of the product' provided the concentration is kept low - about I mg per hire of starch milk. At that concentration it acts favourably on sedimentation, while its disinfecting and bleaching properties are also very marked, the sediment obtained being compact and white. Higher concentrations of about 50 mg per litre result in a very soft and discoloured sediment and a product of very low viscosity. These properties of active chlorine preparations make them the very best means of obtaining an end product of better quality.

Sedimentation processes

Up to the Second World War, the sedimentation processes used in large cassava factories usually consisted of refinement in tanks and on tables. Separation by centrifuging, though practiced in the starch industries using potato and maize as raw material, does not seem to have found wide application with cassava during this period. Since then, more efficient centrifugal processes for the separation and cleaning of starch in general have been devised. Although originally designed for the processing of potato and maize starch, both machines and centrifuges of a more conventional type are now beginning to be applied in the cassava industry, and it may be expected that at the higher production levels they will soon supersede other methods.

Sedimentation on one flour table is not usually sufficient to effect a complete separation of pure starch from slurry. One obvious defect of both tables and sedimentation tanks is that they do not separate contaminating particles heavier than starch (sand, clay). In the large factories, when producing a high-grade flour the product is collected, after a first tabling, in containers with conical bottoms, where it is stirred moderately with fresh water. Heavy particles settle in the lower part of these stirring tanks and can be discharged from time to time from a tap in the bottom. The flour milk obtained is then pumped to a second table or set of parallel tables, where settling takes place. To prevent any reaction between the flour milk and the wall material, these channels may be coated with a resistant material such as aluminium.

The action of this second tabling operation is different when the table is inclined. Apart from settling in the channels, the more rapid motion of the liquid subjects the underlying sediment of flour to silting - that is, the starch granules and other particles, even after settling, are carried along with the stream to be deposited farther on.

The drag exerted by the stream on a body at the bottom increases with its dimensions. Therefore, the more voluminous fibre particles, which on account of their specific gravity might settle on the higher parts of a table, will be swept down to the lower end by silting. Silting thus supplements the purification obtained by the flour table; in addition' it tends to homogenize the settled starch mass.

Concentration of flour milk in all sedimentation processes has definite limits. In particular, during tabling the suspension should contain no more than 25-30 g of starch per litre. Higher concentrations will result in an undesirable lengthening of the sedimentation time. In silting. higher concentrations, up to 250 g per litre, are allowed.

The supervision of the concentration is best carried out by measuring the density of the slurry with hydrometers. It is usually expressed in degrees Brix, a standard taken over from the sugar industry (grams of sucrose per litre at 17ºC The relation between the latter quantity. specific gravity, and hydrometer readings according to Brix and Baumé for different starch suspensions at room temperature is presented in Table 5.

TABLE 5. - DENSITY OF STARCH SLURRIES OK VARIOUS CONCENTRATIONS AT ROOM TEMPERATURE (20°C)

Lamellators

The principle of cutting down the settling distance of the starch granules, as achieved by the use of a flour table. is followed also in the construction of lamellators: oblique plates (lamellae) of glass or metal (for cassava only copper can he utilized) are fitted radially into the upper part of conical tanks, the lower part being provided with a stirring device and a tap. The flour milk enters the centre of the upper part and from there flows radially and at low velocity through the spaces between the lamellae and over the outer rim of the cone.

The path of free sedimentation of the starch granules is limited here to the vertical distance between two adjacent plates, which amounts to a few centimetres only, after which they roll down more rapidly along the surface of the plates into the lower part of the cone. The larger granules will thus sink in the central part of the apparatus and will collect at the bottom of the cone; the finer grains will settle at the periphery and collect on the conical wall. As small granules slip along an inclined surface faster than large ones, clogging on the walls is minimized. Clogging of the flour in the spaces between the lamellae is prevented by their radial arrangement, each interspace widening in the direction of flow of the suspension.

Centrifugal methods

A rapid separation of starch grains from fruit liquor and the elimination of the impurities in colloidal suspension are attained by centrifuging, with consequent improvement in quality of the finished product. Centrifuging cannot, however, replace entirely the gravity settling operation: after centrifuging? the starch still has to be freed from any remaining solid impurities by settling in tanks or on tables.

One of the current conventional types of centrifugal separator consists mainly of a horizontal imperforate drum or bowl (Figs. 13, 14) with a continuous spiral-ribbon starch remover or scraping device inside (A, D). The drum rotates in a frame with bearings at both ends. Over a gearbox, the drum and the scraper are driven at slightly different speeds by a direct-coupled motor. The starch milk enters the slightly conical drum at the narrow end (B) and passes to the other end. where the liquid outlet (E) is located. On its way through the howl. the milk throws off starch grains and other solid matter' which concentrate at the periphery. Here the concentrate is taken up by the scraper and brought counter-current to the narrow end. where it is discarged (c) with the addition of fresh watter The purest starch is made by using liberal amounts of soft water. Hard water (high in lime content) has been known to leave calcium oxalate in the finished product.

FIGURE 14. Longitudinal section of a centrifugal separator

The rapid displacement of fruit liquor by fresh water has been brought to a certain degree of perfection in machines known as concentrators.

The current type of concentrator illustrated in Figures 15 and 16 consists of a separator bow with a double wall which turns on a hollow spindle (i). The starch slurry is fed through the inlet (a and b) into the inner howl (C) where it is pressed by centrifugal force onto the inner wall. which is fitted with a number of nozzles of special design. At the same time. water is pumped by a centrifugal pump (K) along the hollow spindle into the water chamber between the inner shell anti the outer howl wall. This wall is provided with similar nozzles located just opposite those in the inner shell. The fresh water from the water chamber enters the nozzles in the inner shell. thus intensively washing the starch coming out of these openings. and the diluted truit-water leaves the apparatus through .1 after passing a set of separating disks and a paring device serving to quench excessive frothing.

FIGURE 15. Cross section of a starch concentrator

The starch' together with fresh water, is pressed through the outer nozzles and leaves the apparatus through e as a concentrated suspension in substantially clean water.

The capacity of the separator depends primarily on the size of the starch granules: the throughput capacity will be lower for fine-grained starches. In fact' some loss of starch with the separated fruit-water is inevitable' because very small starch granules will escape sedimentation under any circumstances. It is claimed that such losses are smaller than in other centrifugal processes. Moreover. the separator consumes less power and its operation is less sensitive to variations in the starch concentration of the treated starch milk' which otherwise often results in clogging. Separators of this type are easy to install and do not need foundations: in operation' however. they require expert supervision.

The action of the separators (concentrators) is completed by rapid batchwise settlings in bowl centrifuges or in purifiers where the purest starch is the first to settle in a thick layer on the bowl wall' followed by strata of starch mixed with FINE fibre ("grey starch"), the fruit-water forming the inner layer. In the older types of centrifuges the operation is discontinued after a few minutes' the water is let off, and the grey starch is removed by washing. The purified starch is then stirred up with fresh water and either drawn off for dewatering or subjected to a second centrifuging.

The newest purifiers have the advantage of performing the above operations while the bowl is in motion. As shown in Figure 17, the bowl or drum turns on a rigid axis and is furnished with a winged feeding chamber. The bowl is fed through a tube (1) The pivot arm (2) carries an agitator (3) and a knife (4) which skims off the fruit-water and scrapes off the grey starch, both of which are discharged through an opening in the bottom of the bowl. The skimmer (5) for purified starch milk is mounted on another pivot. These tools are operated hydraulically and make about a quarter turn from one extreme position to the other.

The operation of a purifier is usually linked directly with that of the above concentrators, the crude starch milk being first washed and concentrated to 16-18°Bé by two concentrators in series.

The starch dispersion is washed with large quantities of water in a series of wooden tubs, settling tanks or basins as described before or in refiners and separators. The crude starch is transferred by hand or in baskets from the settling tanks into the washing tubs or basins, where the starch is agitated vigorously with clear water and then allowed to settle for 6-12 hours. This process is repeated several times until the starch is thoroughly purified. During settling, the starch sediment is sometimes covered with cloth to absorb the excessive moisture. However, in modern factories, two types of equipment are used for the purification of starch:

1. The Merco centrifugal separator, which is based on the well-known cream-separation principle. The separator features an integral re turn-flow principle which ensures a continuous and uniform output of solid products by recycling a portion of the underflow back into the rotor. This creates a flushing action and permits the use of a rotor nozzle size sufficiently large to prevent clogging.

FIGURE 17 Horizontal section of a current type of purifier

2. The Starcosa channel separator, which involves the nonturbulent flow of starch dispersion over dividing plates for the purpose of separating the heavier fine fibres from the lighter starch water dispersion.

Preliminary drying by centrifugation

At higher production levels in larger factories, technical and economic reasons have led to the adoption of a system in which concentrated slurries of pure starch are concentrated or thickened by mechanical means to a moisture content of 35 40 percent before drying by evaporation. Mechanical dewatering is generally performed in dewatering centrifuges. although continuously working vacuum filters are also used. especially in combination with modern tunnel driers.

The centrifuges for this purpose are of the basket type, as shown in Figure 18, equipped with a perforated bowl lined with a filter of cloth, small-mesh wire netting or the like. The starch is fed by batches as a slurry of 23ºBé; during centrifuging, the water is removed through the filter and the starch settles on the bowl wall in the form of a cylindrical cake. Some fine fibre and dirt always cover the inner surface of the cake and are scraped off before discharging the batch. Cassava starch, like other fine-grained starches, has properties allowing it to form a very firm sediment in the bowl, which is difficult to clear by hand or even with a mechanical clearing device. The most useful form of centrifuge is thus equipped with an exchangeable set-in which permits removal of the whole batch of starch after centrifuging. Vertical positions on the ground plate of the set-in facilitate the discharge.

In general, centrifugal drying, which brings down the moisture content to about 40 percent, is linked up with some form of evaporation drying in a continuous process. While a great variety of such driers are available in commerce only a few which are especially suited to the drying of starch will be described here.

DRYING

The removal of free water from the starch sediment obtained in settling tanks and on flour tables or from the concentrated slurries produced by separators and purifiers can be partly accomplished by mechanical means (e.g., centrifugation). The final drying. however. must always be performed by evaporation, either in the open air (sun drying) or in ovens. In modern factories, oven drying is always combined with mechanical drying, the whole operation, as in all other phases of the process, being conducted so as to take the least possible time.

Sun drying

As the sun is the cheapest source of heat, all small mills and many medium-size factories resort to this kind of drying despite the problems and the risk of contamination involved. The flour cake left after draining in the sedimentation tank or on the flour table is scooped up and after crumbling (sometimes with the aid of coarse matting or a wire screen) is spread out on basketwork trays about I m in diameter. Each tray is covered with as much of the wet product as contains some 0.5 kg of dry starch. The trays may be placed on the ground itself, but preferably should be laid on racks 1 m above the ground (Fig. 19). In this way, besides direct radiation, the heat reflected from the ground aids drying while the circulation of air is ensured on both sides of the layer of flour.

It is preferable to begin the drying process soon after sunrise so that in fair weather and a dry atmosphere it can be completed in one day. Often, however, this does not suffice, and before sundown the trays are stacked up on the factory premises. During the night, evaporation continues slowly, aided by the retained sun warmth, and is completed the next day in the open air. In the course of drying, a number of workers continually crumble the lumps of starch on the trays to speed up the drying. The crude flour is considered sufficiently dry when the remaining lumps are too hard to be crumbled by hand. The moisture content is then between 15 and 20 percent.

An important advantage of sun drying is the bleaching action of the ultraviolet rays. At the same time, however, a certain chemical degradation sets in, ultimately having an unfavourable influence on the quality of the product. Besides, contamination by dust cannot be entirely avoided during sun drying, especially on windy days; a lowered whiteness and the occurrence of "specks" will result. Finally, the baskets have to be cleansed regularly with a solution of bleaching powder, in order to prevent contamination by microorganisms. Even then, the baskets are subject to rapid wear and have to be replaced frequently.

Given sufficient space and the necessary number of baskets (about 5 000), a daily output of 2 tons of dry flour may be realized with sun drying. Of course, in cases like this, the manufacture would gain very much in efficiency and stability if drying were accelerated and concentrated in a smaller space by the use of ovens. At medium production levels ovens are rarely used, however, because both the installation and use of ovens, apart from the initial expense and the cost of fuel, require some engineering knowledge. Until now a completely satisfactory solution of the drying problem for medium-size factories has not been found. Rather primitive oven driers are used here and there, whereas factories with a somewhat higher daily output employ chamber and drum driers. The latter two types, applied in the manufacture of baked tapioca products, are described below.

Drying ovens

The simplest type of oven consists of a firing tunnel of brickwork covered with galvanized iron or copper plates on which the moist flour is spread in a thin layer. Firing should be moderate, so as to keep the temperature of the plates well below the gelatinization point of the starch, and the flour should be frequently raked up. The space above the oven should be vigorously ventilated. In Malaysia and other parts of the Far East, ovens called "drying yards," about 30-40 m long and 3-5 m wide are used for the drying of cassava starch. Enough wood is burned in the tunnel to heat the cement surface to the required temperature (see Fig. 20). The number of drying yards ranges from two to five, depending on the size of the factory and the kinds of products.

FIGURE 21. Sectional view of a chamber drier

Chamber drier

The chamber drier consists of a number of adjoining compartments with insulated walls, each one equipped with heating, ventilating and control devices. The wet material is placed on the trays. which are either directly introduced into the chamber drier or loaded on a trolley that is pushed into the drier. The process can be rendered more economic in this kind of drier by a system of air circulation. In a model drier, the air current produced by the screw fan is warmed by a heating element and moves across the material to be dried, giving off heat while taking up water vapour from the moist flour (Fig. 21). Through the adjustable slot a small part of the circulated air is discharged from the chamber, and at the same time a corresponding quantity of fresh air is drawn in from the outside, whereas the main air current recommences the cycle as described above. A considerable reduction of the drying time can be obtained by the insertion of air-guiding surfaces which effect an equalization of the air speed over all the trays.

Although drying in this apparatus takes relatively much time and labour, it is easy to handle and for that reason suitable for medium-size factories producing limited quantities of flour.

Drum driers

Probably the simplest arrangement for the continuous drying of flour is a horizontal or inclined revolving drum, heated from the outside, into which the moist flour is fed at one end. During transport inside the drum, which may be accomplished by various mechanical means, the product gives off its moisture to a stream of ventilating air (Fig. 22). In applying direct fire or steam the usual precautions against overheating have to be taken.

Bell driers

These represent an efficient form of continuous drier, combining a high capacity with a simple construction, which does not necessitate supervision by skilled workers. Here the starch is carried along on a series of conveyor belts, one on top of the other, in a stream of hot air. Moist starch is shed onto the top belt and conveyed over the whole length of the construction; at the end it drops on to the belt below, which is driven in the opposite direction, and so on. With each drop from a belt to the one below, the starch is turned over and ventilated. Heaters such as steam pipes are fixed between the belts and effect a rapid evaporation, the water vapour being removed by the upward draft.

Tunnel driers

The manufacture of a uniform product of definite moisture content is best ensured with modern tunnel driers in which the moist starch is carried on a conveyor belt through a tunnel divided into compartments forming drying zones. The circulating air is kept at a definite temperature, and moisture content in each zone is automatically controlled by conditioning devices. The flour is sucked up by vacuum from a concentrated slurry on a revolving cloth sieve with a cake-scoring device and a spring discharge. The starch cake, containing 40 percent water on the wet basis, is discharged in small broken strips directly to the travelling bed of the drier, where it encounters gradually changing drying conditions. The flour is discharged at the other end of the tunnel with a moisture content of about 17 percent, in the form of very loose agglomerations which are easily crumbled and bolted. The drier, 2.5 m wide and 10 m long and divided into four zones, has a capacity of 15 tons of dry flour per 24 hours.

Pneumatic driers

Another type of drier is the pneumatic flash drier. The starch cake is led from the basket centrifuge by a warm conveyor to a pneumatic drier, where the final moisture content is reduced to 10-13 percent. Drying is effected by hot air produced by a set of oil burners working on the atomized burning principle and compressed air. The required quantities of fresh air are sucked into the hot air generator through an air filter and heated to about 150°C. During the drying process the starch is pneumatically conveyed from the bottom to the top of the drier and then deflected downward.

Starch particles which are not quite dry are returned to the drying unit located at the bottom, while the dry starch is separated in the cyclone from the conveying air and led through a rotary pocket seal into a starch powder sifter.

FINISHING AND PACKAGING

Bolting

Crude dry cassava flour consists for the greater part of hard lumps of starch. As it is useless for most purposes in this form, it has to be subjected to a pulverizing process followed by dry-screening. The latter operations are often referred to as bolting.

As a bolting installation is remunerative only where production is relatively high, smaller enterprises do not as a rule install their own equipment for the purpose. Often, however, a number of small mills deliver their crude flour to a central bolting factory, which at the same time may function as a trading concern for the finished product. In these central installations bolting is carried out as in medium-size and larger cassava factories, while at the same time definite "brands" are composed by mixing.

At the medium production levels it pays to have simple bolting machines, in which the flour is crushed between rolls. The apparatus, if necessary, can be driven by hand.

Roller bolting The crude flour is shed into a hopper placed above a pair of rollers turning in opposite directions at the same speed. The agglomerations of starch are broken up by the action of the rollers, but fibre and other tough particles are left intact. The crushed flour is subsequently received in a conical rotary screen of the same construction used for wet-screening and described previously. Here the small lumps which have escaped crushing, fibre and other foreign particles are separated from the starch by a screening gauze 100 to 200 mesh/inch. The dry pulp discharged is fed back into the hopper once more. The rolls and the revolving screen are coupled to the same motor, which in an emergency may be replaced by a hand-driven crank.

Roller bolting is a relatively slow process and has therefore been superseded by disintegrator bolting. Recently, however, the particular advantage of the roller process - its relatively mild crushing action - has been combined with a greater speed of working in new machinery with a system of grooved rollers.

Bolting by disintegrators At present. most medium and all larger factories are equipped with beater disintegrators for the bolting process. In the disintegration action not only the starch lumps hut also here and other foreign material are pulverized and forced through screen plates of 100 mesh/inch or finer. as desired. If the starting material was of questionable purity. the resulting flour may contain appreciable amounts of nonstarch material. which cannot be separated easily. The power consumption of these disintegrators is between 10 and 20 hp depending on the amount of flour that needs to be disintegrated per hour: the working speed is some 1 200 rev/mint

The arrangement of the equipment is similar to that for roller bolting. As much starch is strewn during the operation. the disintegrator and rotating screen are housed in wooden chambers provided with windows for the discharge of the bolted flour which can be closed by shutters or a thick cloth when in operation.

Storing and packaging

The finished starch should he stored in a dry place. preferably on a board floor or in bins. where it can he mixed in order to obtain a uniform lot.

Before storing, the starch is sifted to assure lump-free uniform particles. It is usually packaged in gunny sacks for shipment, but multiwall paper bags are becoming more popular. A modern sifting and bagging machine is shown in Figure 23.

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