The choice of maize milling technology represents a classical example of technological choice in food processing. It involves a large number of variables including those typically used in the evaluation of alternative technologies (e.g. wages, depreciation costs, socio-economic objectives) as well as additional factors such as product choice, transport costs and supply of raw materials. It is therefore important to describe the overall framework for technological choice in maize milling with a view to facilitating the evaluation of the technologies described in this memorandum.

This chapter should be of interest to both public planners and producers since it takes into consideration socio-economic objectives as well as factors which influence the private profitability of maize milling units.

The chapter is organised in the following manner. An analysis of the demand for various types and qualities of meal, together with a number of suggestions for influencing such demand, is followed by a section which looks into the supply of maize products in terms of available milling techniques and scales of production. A third section provides some information on the socio-economic implications of alternative technologies and suggests policy guidelines for the promotion of appropriate maize milling techniques and products.


Three main types of maize meal are marketed in developing countries: whole meal; partly de-germed meal (i.e. meal from which part of the bran and germ has been removed) which is designated under various names (e.g. partly sifted meal, bolted meal, roller meal (Zambia)); and fully de-germed meal from which most of the bran and germ have been removed and which is also designated as Â"super-sifted mealÂ". Quality differences exist within each type of meal, depending upon the milling technique adopted, the quality of the grain, and the addition of various vitamins.

A number of by-products may be produced through the milling process: limited amounts of poultry feed (coarse bran), cattle feed, and maize oil through the further processing of the germ that has been removed.

I.1 Nutritional elements[edit | edit source]

Maize is an important element in the diet of the population of developing countries, especially in Africa and Latin America. In some cases (e.g. Malawi), maize may account for 80 to 90 per cent of the total calorie intake of the rural population. Yet maize is deficient in a number of essential nutrients, and excessive reliance on maize diets could result in severe diseases such as pellagra. Consequently, a number of countries have implemented various measures for the enrichment of maize meal for human consumption (e.g. addition of various vitamins, soya bean meal, groundnut flour).

Given the deficiency of maize in a number of essential nutrients, it is paradoxical that a number of developing countries have allowed or even favoured the adoption of milling technologies which further reduce the amount of these nutrients per unit of output as well as the total amount of maize meal for human consumption per tonne of processed maize. Reasons for the increasing adoption of these technologies will be provided later, and suggestions will be made for the promotion of milling techniques consonant with desirable socio-economic objectives. It will first be useful to indicate the effect of alternative milling technologies on the nutritional value of the meal produced.

Table I.1 provides estimates of the main nutrients which constitute the three types of maize meal consumed in developing countries: whole meal, bolted meal (partly de-germed) and de-germed (super-sifted) meal. While the number of calories per 100 grams of flour are approximately equal for the three types of meal, the proportions of important nutrients per unit weight of flour are generally much larger for whole meal than for bolted and super-sifted meal. This is particularly true for calcium, iron, niacin, riboflavin and the fat content of the meal. The production of sifted meal by roller mills also removes two important types of proteins (globulins and glutelins), leaving zein which is a poorer source of protein.1 Furthermore, enriched sifted meal is in general nutritionally less adequate than whole meal.

1 Source: see Stewart (1977)

Nutrient composition of different types of maize meal


Whole meal

Bolted meal
(partly de-germed)

De-germed meal

Moisture (percentage)




Calories per 100 gr




Protein (percentage)

  1. 3-9.5
  1. 3
  1. 9-8.4

Fat (percentage)

  1. 8-4.5

Variable (>2)

  1. 2-2.0

Carbohydrates (percentage)


Variable (>74)


Fibre (percentage)

  1. 9-3.0
  1. 7-1.0
  1. 6-0.7

Ash (percentage)

  1. 3


  1. 5

Calcium (mg per 100 gr)




Iron (mg per 100 gr)

  1. 3-4.2
  1. 8
  1. 1-1.2

Thiamine (mg per 100 gr)

  1. 3-0.45
  1. 35
  1. 14-1.18

Niacin (mg per 100 gr)

  1. 8-2.0
  1. 3
  1. 6-1.0

Riboflavin (mg per 100 gr)

  1. 11
  1. 09
  1. 08

Note: Variations in data according to sources may be explained by variations in the raw materials analysed and/or variations in the quality of meal.

Sources: Schlage (1968); FAO (1968); FAO (1953); FAO (1954); Uhlig and Bhat (1979).

Table I.2 provides estimates of the minimum daily consumption of whole meal and sifted meal (de-germed) which will be required for an adult's daily needs of four essential nutrients: iron, thiamine, riboflavin and nicotinic acid. The table shows that, should adults rely exclusively on maize, they will need to consume two to seven times more de-germed meal than whole meal in order to satisfy their daily needs of these four nutrients. Obviously, few people will rely exclusively on maize for their diet, and the estimates provided in Table I.2 are of a purely theoretical nature. However, as to be shown later, the deficiency of de-germed meal in a number of essential nutrients could have serious repercussions on the diet of low-income groups in developing countries.

Table I.2

Minimum daily consumption of whole meal and super-sifted meal
(Amounts of meal required in grams to provide an adult's daily needs of one mineral and three vitamins)

Maize meal





Nicotinic acid

Whole meal





Sifted meal





Source: FAO (1968); Harper (1974).

Milling techniques also affect the availability of flour for human consumption. The extraction rates of bolted or sifted meal per tonne of processed maize are much lower than those of whole meal. Table I.3 shows that extraction rates for whole meal vary from 97 per cent to 99 per cent while those for bolted and sifted meal vary respectively from 80 per cent to 96 per cent and from 60 per cent to 75 per cent. On the other hand, the proportion of by-products may be as high as 40 per cent in the case of sifted meal whereas generally it does not exceed 3 per cent for whole meal. These by-products are used either as animal feed or for oil extraction. The production of bolted or sifted meal may thus have important repercussions on consumption by low-income groups for the following reasons.

First, from the purely quantitative point of view, and given the above extraction rates, approximately 20 to, 40 per cent of cultivated maize will not be available for direct human consumption if, for example, it is used to produce sifted meal instead of whole meal (the corresponding percentages for bolted meal will be 3 to 17 per cent). The lower extraction rates associated with the production of sifted and bolted meal should be of little consequence for countries producing a net surplus of maize (e.g. for export or further processing into oil or animal feed). On the other hand, countries which do not grow enough maize to fully satisfy the needs of their population may face larger shortages of maize meal if sifted rather than whole meal is produced. If these countries do not make up for these shortages by importing maize or other kinds of grain, in the absence of price controls the low-income groups will either have to pay higher prices for the available supply of maize or cut down consumption. In either case as shown in table I.3, they will suffer from the lower supply of maize flour due to the low extraction rates of sifted maize mills (i.e. roller mills).

Table I.3

Extraction rates per 100 kg of maize



Flour for human consumption

By-product used for animal feed or oil extraction

Whole meal



Bolted meal



Sifted meal



Source: Stewart (1977) and Uhlig and Bhat (1979).

Secondly, the use of by-products (bran and germ) as animal feed (e.g. for cattle or poultry) may not fully compensate for the low extraction rates associated with the production of sifted meal: if these by-products are used to increase the production of meat, their nutritional value will not generally exceed 10 per cent of that of bran and germ (i.e. the conversion of bran and germ into meat results in a 90 per cent loss of the nutritional value of these two by-products). Furthermore, it is very unlikely that low-income groups will be able to afford to improve their daily diet by buying the meat produced.

Thirdly, it may be noted that by-products are generally locally marketed or exported as animal feed and that few developing countries have maize oil extraction plants. In any event, however, the extraction of oil from the by-products may not justify the production of sifted meal. Two important factors should be considered before deciding to invest in a maize oil extraction plant. These are:

- whether a sufficiently large and regular supply of by-products will be available to ensure a continuous high capacity utilisation of the plant, and therefore competitive (non-subsidised) retail prices of oil; and

  • whether oil should not be obtained from some other raw material given the importance of maize for direct human consumption.

The previous analysis of the nutritional value of the three types of maize meal indicates that in terms both of quality and quantity, the production of whole meal is to be preferred to that of sifted or bolted meal if the satisfaction of the basic needs of low-income groups constitutes a major development objective. Other factors may, however, vitiate the above analysis, as indicated below.

I.2 Shelf-lives[edit | edit source]

An important consideration in the marketing of maize meal is its shelf-life. A reason often advanced for the production of sifted meal (and to a lesser extent bolted meal) is that its shelf-life is considerably longer than that of whole meal. Thus, in cases where the marketing chain requires long shelf-lives (e.g. when the meal must be transported over long distances or when wholesalers and retailers must keep stocks for an extended period), the only practical possibility is to produce sifted meal because whole meal tends to become quickly rancid as a result of its high fat content (approximately 3 to 4 per cent fat as against 1 to 2 per cent for sifted meal). This reason for justifying the production of sifted meal has not, however, met with the unanimous agreement of practising millers and retailers of maize meal in developing countries. Various aspects of this matter are briefly outlined below.

Estimated shelf-lives

The shelf-life of maize meal depends on the following; the fat content of the meal, the humidity of the maize grain, the presence of various contaminants in the maize and the meal storage conditions (e.g. choice of packaging material, air temperature and humidity level within the storage area). The effect of the above factors on the shelf-life of maize meal has not yet been investigated in a systematic manner. Differences in shelf-life between sifted meal and whole meal may not, therefore, be ascribed entirely to differences in fat content. The differences in shelf-life could well be explained to a certain extent by the conditions under which maize is processed in roller mills producing sifted meal and in hammer or stone mills producing whole meal (e.g. humidity level of the maize, presence of contaminants). The widely divergent estimates of shelf-lives found in publications on the subject may thus be explained by big differences in the above conditions from one country to another or among processing units within the same country. Estimates of these shelf-lives are provided below:

- 4-6 weeks for whole meal if stored at high temperatures and humidity levels, as compared to a maximum of two years for sifted meal if stored under carefully controlled conditions (Uhlig and Bhat, 1979);

  • 2-3 days for whole meal versus a considerably longer shelf-life for sifted meal (Stewart, 1977);
  • 4-8 weeks for whole meal versus 6 months for sifted meal, but humid or hot climates do not allow long storage of any type of flour (JASPA, 1981);

The JASPA (1981) study also includes estimates provided by individual millers in Kenya and Zambia:

- sifted flour may last up to 3 months if the moisture content can be kept at a low level, while a 5 per cent fat whole meal flour will last for only three weeks (a miller in Kenya);

  • storage characteristics are almost identical for all types of flour, with shelf-lives reduced to 2 weeks during the rainy season (manager of a large mill in Zambia);
  • there are few differences between the shelf-lives of sifted meal and whole meal (small-scale miller in Kenya).

The above views on the shelf-lives of sifted flour and whole meal indicate that this matter needs to be further investigated by food technologists in developing countries with a view to determining the extent to which differences in shelf-lives do exist, the reasons for such differences, and whether it will be possible to promote appropriate milling conditions (e.g. use of sufficiently dried maize, adequate storage conditions) with a view to narrowing down the difference between the shelf-lives of whole meal and sifted meal.

Need for extended shelf-life of maize meal

Although there is a consensus regarding the longer shelf-life of sifted flour, no such consensus seems to exist regarding the importance and significance of the difference in shelf-lives between the two types of meal. It is argued that consumers in rural areas - especially maize-growing areas - have their maize milled to order as the need arises, and do not generally stock whole meal for more than a week. It is further argued that long shelf-lives will be required mostly in large urban areas where flour must be stored over an extended period because large stocks are needed in order to ensure steady and regular supplies of flour to retailers. Sifted flour may also be required wherever there is a need to transport it over long distances to parts of the country where maize is not grown.

This line of reasoning, which assumes different shelf-lives for sifted flour and whole meal, may need to be modified for the following reasons. First, whole meal can be produced by small merchant mills in urban areas if the grain can be supplied to them on a regular basis by, for example, a national maize marketing board. Thus, whole meal can be produced and retailed in such a way as to reduce the storage period to a minimum and therefore avoid rancidity. In this case, it will be marketed as a perishable food product but with a shelf-life longer than that of meat or milk, for example. Secondly, custom or merchant mills can also be established in parts of the country where maize is not grown as long as the transport of shelled maize can be ensured on a regular basis. However, it must be emphasised that long storage of shelled maize for further processing by small custom or merchant mills will require that the maize be properly dried (i.e. moisture level not to exceed 12 to 13 per cent) and stored, and that adequate transport facilities be available.

I.3 Consumers' preference, retail prices and marketing channels[edit | edit source]

Demand for whole meal, bolted meal and sifted flour is function of three main factors: consumers' preference, retail prices of the different kinds of maize meal and marketing channels. These factors are briefly analysed in the light of available evidence from developing countries, especially in the African region.

Consumers' preference

It is argued that if they had a choice, consumers in developing countries would prefer to buy sifted (i.e. de-germed) flour rather than whole meal for a number of reasons, including the better appearance of sifted flour (it is whiter and finer than whole meal) and its easier utilisation in cooking (whole meal needs more energy than sifted flour, and thus takes more time to cook). On the other hand, consumers do not seem to be concerned - probably for lack of information - by the lower nutritional value of sifted flour. The above arguments do not, however, apply in all cases. In some countries (e.g. Somalia - see JASPA report, 1981), the urban population prefers whole meal whenever it is available. Large institutions such as hospitals also tend to prefer the more nutritious whole meal. Available evidence on this subject is generally limited, and it will be useful for developing countries to undertake individual surveys of consumers' preference for various types of maize meal.

For some urban areas (e.g. in Kenya) where preference for sifted flour is well established, a number of both objective and subjective reasons may explain that preference. The objective reasons include those already mentioned (i.e. attractive appearance of sifted flour, its better cooking characteristics) as well as the possibility of buying limited amounts of packaged flour at food stores close by. The apparently longer shelf-life of sifted flour does not seem to play a role in the urban consumers' choice, probably because the flour is used up in a relatively short time.

Among the subjective reasons adduced for the preference for sifted flour by urban consumers, advertising is by far the most important. Available evidence from a number of African countries (e.g. Kenya) shows that large milling firms (some of them of foreign origin) earmark large sums for major advertising campaigns in urban areas. For example, collected information from Kenya shows that in some cases marketing costs amount to as much as a third of production costs (Stewart, 1977). It is even suggested that the market for sifted flour might have been artificially created by the large roller mills (see Stewart, 1977).

Retail prices

Available evidence shows that the retail price of sifted meal is generally higher than that of whole meal, price differences varying from country to country as well as within the same country. This does not mean that the actual milling costs of sifted meal are necessarily higher than those of whole meal. Differences in retail prices may also be the result of the following factors:

1. Low extraction rates of roller mills which produce the sifted flour (i.e. less flour is produced per tonne of shelled maize than in the case of the production of whole meal). These low extraction rates, and therefore higher input of raw materials is not offset by the sale of by-products (germ and bran) since the unit prices of the by-products are generally much lower than that of whole meal;

  1. The high packaging cost of sifted flour (e.g. in 1 kg or 2 kg paper bags) whereas little if any packaging is used in the case of whole meal. Custom mills (generally located in rural areas) do not package their products (the customers bring their own containers) while small merchant mills use cheap packaging;
  2. Roller mills market their product through traders who must add their operating costs and profit margin to the ex-mill price.
  3. For sifted meal, there are high advertising costs whereas there is no costly advertising for whole meal;
  4. Transport costs associated with the production and marketing of sifted meal are generally higher than those associated with that of whole meal. Maize and sifted meal must generally be transported over long distances, whereas transport costs are cut to a minimum by the proximity of custom mills (which produce whole meal) to maize-growing areas and to the consumers.

The relatively high retail prices of sifted meal do, generally, limit consumption to the middle-income and high-income groups in urban areas. In a few exceptional cases, government subsidies and price controls have maintained retail prices of sifted meal low enough to allow consumption by low income groups.

In general, an increase in the retail price of sifted flour should not lead to an increased demand for whole meal on the part of middle-income and high-income groups. It may rather lead to an increase in demand for polished rice or other flours (e.g. wheat flour) of equivalent quality should these be locally available. On the other hand, an increase in the retail price of whole meal maize should generally increase demand for other meal of equivalent quality (e.g. sorgho meal, millet) by low-income groups. Although no firm evidence exists on the above shifts in demand, their possibility should be taken into consideration whenever government action may lead to an increase in the retail price of sifted maize flour or to a decrease in its availability for whatever reason.

Geographical distribution of demand for sifted flour and whole meal

As stated earlier, rural areas consume almost exclusively whole meal, especially in maize-growing areas. Furthermore, whole meal is either produced by households (e.g. by the use of mortar and pestle or of querns), or by custom mills for payment in cash or kind. Recourse to custom mills is not yet widespread. However, an increasing number of rural women are willing to give up the long and tedious milling of maize at home in order to be able to devote themselves to other more profitable activities.

It is doubtful whether demand for sifted flour will expand substantially in maize-growing areas for the foreseeable future. The retail price of sifted meal will generally not be competitive with that of whole meal whether the latter is produced at home or at a custom mill. On the other hand, sifted meal is in some cases marketed in rural areas which do not grow maize, especially if no other cereals are available. In some cases, the sifted meal is sold at subsidised prices because it could not be otherwise afforded by the poor in rural areas.

The situation in urban areas is different; both whole meal and sifted meal are consumed by the urban population. Whole meal is often produced by small merchant mills (e.g. hammer mills) which keep stocks of both the raw materials and the meal. These mills either retail their output directly or sell it to retailers. Some whole meal is also produced in neighbouring rural areas and sold in the urban markets. In general, the whole meal marketed in urban areas is consumed by low-income groups.

Sifted meal is in most cases marketed in urban centres. It is produced by large roller mills located in urban areas, or, if feasible, close to the maize-growing areas. Sifted meal is mostly consumed by the richer sections of the urban population and is marketed through traders. Consumption of sifted meal by the poor is rather limited since its higher price puts it in the luxury goods category.


The five distinct milling techniques used in developing countries are listed below:

(1) The mortar and pestle technique used in the household. Output per hour varies from one person to another, but does not generally exceed 5 kg per hour.

(2) Hand-operated grinders used by individual households or groups of households. Available equipment allows production rates ranging from 7 kg to 30 kg per hour. Figure I.1 shows one type of hand-operated mill produced in Kenya.

(3) Water-powered stone mills, mostly used in the rural areas of a number of African countries. Their production rates are relatively low, varying from 20 to 30 kg per hour, depending on the force of the water flow. These mills usually operate as custom mills.

(4) Engine-powered hammer mills and stone mills, equipped with diesel or electric engines, and used by custom mills and merchant mills for the production of whole meal. The rated outputs for these mills range from about 100 kg/hr to 1,100 kg/hr. These outputs cannot, however, be maintained over long periods, capacity utilisation ranging usually between 200 to 3,000 kg per 8-hour day.

(5) Roller mills of various sizes producing partly or fully de-germed meal, and generally located in urban centres. Their output varies on average from 1 tonne to 12 tonnes per hour, depending on the mill's size, the number of shifts worked and the fraction of time used for maintenance and repairs. In developing countries, roller mills generally operate at lower capacity levels than in industrialised countries where the economic size of roller mills ranges between 250 tonnes and 300 tonnes per three-shift day. By comparison, an output of 120-150 tonnes per three-shift day is relatively large for roller mills in developing countries.

Maize P013.GIF

Figure I.1 Duna hand-operated grinding mill

This small, hand-operated plate mill is of all-welded steel construction and has been designed in Africa for the grinding of maize and other food grain. The front cover can be removed for cleaning and inspection by unscreewing three wing nuts.

Source: ITDG (1976)

An increasing number of developing countries (e.g. India, Kenya, Tanzania) produce hand-operated grinders, water-powered stone mills and small hammer mills. Roller mills, on the other hand, are mostly produced in industrialised countries, India being one of the few developing countries which produce small roller mills.

Roller mill equipment does not differ much from one equipment manufacturer to another, the main differences relating to ancillary operations such as the feeding of maize and packaging. From economic comparisons undertaken in Kenya by Uhlig and Bhat (1979), it would seem that, given the relatively low wage rates prevailing in developing countries, manual or semi-automated feeding and packaging are more appropriate than fully automated ancillary operations.

Regarding hammer mills, a number of studies (Uhlig and Bhat (1979), Stewart (1977), JASPA (1981)), have shown that equipment used in developing countries can be improved with a view to increasing productivity and decreasing maintenance costs. For example, hammer mills can be fitted with magnets in order to remove pieces of metal in the grain which might break the sifting gauge. The hammers used in some of the mills can also be re-designed in order to improve the meal quality and the productivity of the equipment. For example, some hammer mills produced in a developing country make use of fixed hammers (within the grinding chamber) which are not as efficient as non-fixed hammers (see R. Kaplinsky in Baron, 1980).

The capacity utilisation of hammer mills and roller mills varies from country to country. In general, hammer mills are used at high capacity levels because they are fairly versatile and can be used, with few adjustments, for the grinding of a number of cereals in addition to maize. Thus, they can still operate outside the maize-growing season. Roller mills, on the other hand, are used exclusively for the processing of a single grain (e.g. maize) and must depend on large stocks of raw materials for continuous running. Thus the lack of sufficient stocks is often responsible for the low capacity utilisation of roller mills and has at times necessitated government action to ensure sufficient supplies. For example, it is reported in JASPA (1981) that the government of an African country has taken steps to ensure the priority supply of maize to a government roller mill to the detriment of small hammer mills.

While the capacity utilisation of rural hammer mills is relatively high, it is reported (see JASPA, 1981), that some small urban mills may be suffering from the competition of roller mills in areas where consumers' preference has shifted in favour of sifted meal. However, the effect of such a shift on the profitability of small urban mills is not precisely known.


The previous two sections provided an overall assessment of demand for and supply of different types of maize meal in developing countries. It was also suggested that existing demand and supply conditions could be improved for the benefit of both consumers and producers. In addition, like any other sector of production, maize milling can be organised in such a way as to contribute to the government's socio-economic objectives. The present section therefore puts forward some tentative guidelines for the identification and adoption of milling technologies consonant with adopted development objectives. Although these guidelines apply specifically to maize milling, they can also be applied, with suitable adjustments, to other food grains.

Development objectives may vary from country to country according to prevailing local socio-economic conditions. Consequently, the choice of maize milling techniques may also vary according to these conditions. However, existing development plans and available evidence tend to suggest that the following objectives - as they relate to the production and consumption of maize meal - are common to the majority of developing countries.

Self-sufficiency in food

Food is one of the most important basic needs, and a main objective of developing countries is to expand the local production of food products, especially in favour of low-income groups. Since the purchasing power of these groups is relatively limited, priority should be given to the production of low-priced food products with a high nutritional value while making due allowance for consumers' preferences. If some sections of the population (e.g. the better-off and the urban population in general) require other types of foods (e.g. sifted flour instead of whole meal), the government may satisfy such demand either through limited local production or by imports. In the case of maize, the production and marketing of whole meal seems to be more appropriate than that of sifted meal given the high nutritional value and relatively low prices of whole meal. Demand for sifted meal may be satisfied through limited production by local roller mills as long as such production does not jeopardise that of whole meal.

Technological self-reliance

Another development objective of a large number of developing countries is to promote technological self-reliance with a view to reducing the costly import of know-how and equipment, and promoting the production of consumer and capital goods consonant with the local needs, customs and culture. In the case of maize milling, the promotion of hammer mills or hand-operated mills constitutes, for the majority of developing countries, the right step towards the achievement of technological self-reliance. This is not the case for roller mills which must be imported by most developing countries, India being one of the few countries which have mastered the roller mill technology.

Employment generation

Employment generation is, by far, one of the most important development objectives. A number of developing countries have focussed their efforts and resources towards the achievement of this objective with special emphasis on the promotion of rural employment.

Regarding maize milling, the employment generation objective may take into consideration the following:

- the total direct employment generated per unit of output;

  • the investment cost per unit of employment generated; this criterion is of paramount importance for countries suffering from severe shortages of local capital and foreign exchange;
  • skill requirements per unit of output; this factor is also quite important, since the shortage of skilled labour requires the implementation of long and costly training programmes;
  • indirect employment effects, such as those generated by the transport of maize grain, of whole meal or sifted flour, the production and maintenance of milling equipment and the production of packaging material;
  • foreign exchange savings; and
  • rural industrialisation.

The above factors are analysed below in relation to the existing maize milling technologies.

Total direct employment per unit of output

The available evidence does not yield reliable estimates on the employment effect of alternative technologies. Table I.4 provides estimates of output per man-hour from Stewart (1977) and JASPA (1981).

Table I.4

Labour intensity of alternative milling techniques
(in tonnes per work-hour)



Stewart 1977

JASPA 1981

Water-powered stone mill

  1. 018

Hammer mill

  1. 198-0.225
  1. 041-0.062

Roller mill

  1. 153
  1. 040-0.093

Table I.4 shows that the labour intensity of hammer mills is either lower or higher than that of roller mills, depending on the source of information. Differences in scales of production, capacity utilisation, or levels of automation (e.g. fully or partially automated roller mills) may explain the different estimates obtained by Stewart and JASPA.

The fact that hammer mills may not be much more labour-intensive than roller mills is not altogether surprising for the following reasons. First, the roller mill technology includes a number of sub-processes which are not generally part of the hammer mill technology (e.g. grain cleaning, de-germing, packaging). Secondly, medium and large-scale roller mills require a much larger managerial and maintenance staff than do hammer mills, especially when the latter are custom mills. It may thus be concluded from available evidence, that the direct employment criterion does not favour any particular milling technology, the only exception being the water-operated stone mills which are particularly labour-intensive (0.018 tonnes/man-hour). However, as will be noted later, the indirect employment criterion does favour the establishment of hammer mills.

Investment cost per unit of employment

As is to be expected, this criterion favours hammer mills by a wide margin. Table I.5 provides estimates of investment costs per worker for hammer mills and roller mills.

Table I.5

Investment costs per worker



Stewart 19771
(Eastern Africa shillings)

JASPA 19812
(Tanzania shillings)

Hammer mills



Roller mills



a One-shift operation.
b Two-shift operation.
c Three-shift operation.

Table I.5 shows that, depending on the source of information, investment costs per worker for roller mills are three to seven times higher than those for hammer mills. These estimates do not take into consideration working capital which is considerably higher for roller mills than for hammer mills.

Thus, it may be concluded that the promotion of hammer mills should benefit developing countries that are short of investible funds but wish to expand employment.

Skill requirements

Skill requirements for hammer mills are substantially lower than those for roller mills. Two to three weeks of on-the-job training are usually sufficient for the operation of hammer mills, skilled labour being needed mostly for maintenance. On the other hand, 30 to 50 per cent of the workers of roller mills are in the skilled labour category (see, for example JASPA, 1981). The establishment of hammer mills should therefore require much less training of labour and will not require the recruitment of costly foreign manpower.

Transport of raw materials and flour

Whenever production takes place in large roller mills, the maize grain and meal produced must generally be transported over long distances, for the following reasons. First, roller mills are often located in urban centres where the necessary facilities (e.g. energy) are fairly well developed and where there is a sufficiently large pool of skilled labour. The raw materials must therefore be transported from generally distant maize-growing areas to the roller mills. Secondly, as the flour produced is marketed in the main towns of the country, it also must be transported over long distances. Whole meal, on the other hand, is often produced close to the maize-growing area and thus little transport is required. For example, maize processed by custom mills is often transported over short distances by foot or by animal-drawn carts. Long-distance transport of maize to hammer mills occurs whenever they are located in areas which do not grow maize or in urban centres where they are operated as merchant mills.

The foregoing assessment of transport needs shows that in general, employment generated by such transport should be substantially larger if maize were processed in large-scale roller mills than if it were processed in small-scale hammer mills. However, because of the high cost of petroleum and transport equipment, and the need for most developing countries to import them at the expense of other essential goods, it is not always in the national interest to rely on the transport of maize grain and flour as a means of generating employment.

Production of milling equipment

The large majority of developing countries do not produce roller mills and, for small to medium-sized countries the production of such mills may never be feasible because demand will not be sufficient to justify the establishment of a manufacturing unit. On the other hand an increasing number of developing countries are now producing various types of hammer mills, and there seems to be no technical or economic reasons to prevent most countries from producing such mills. The manufacture of hammer mills should generate substantial indirect employment through the production of the various mechanical components, whereas the manufacture of roller mills will have no such advantage. However, it may be noted in passing that hammer mills run on diesel or electric engines, which developing countries generally do not produce themselves and will therefore have to import.

Estimates of the employment generated by the production of hammer or stone mills are not generally available. A JASPA (1982) study indicates that in one year ten workers can produce up to 100 small mills with imported engines and that the repair and maintenance of 30 small hammer mills need one full-time worker. Considering that, on average, one small hammer or stone mill is needed for every 1,000 inhabitants, and that 10 per cent of the mills must be replaced every year, the employment generated by the production, maintenance and repair of mills could be significant.

Other backward and forward linkages may also generate indirect employment (e.g. production of packaging materials, marketing). These are, however, of minor importance and should not significantly affect the choice of milling technology.

Foreign exchange savings

The use of hammer or stone mills in place of roller mills should yield substantial foreign exchange savings and should therefore be of particular interest to countries suffering from balance of payments problems. Table VI.1 provides a price list for a large number of stone, plate, hammer and roller mills. It can be seen that while the f.o.b prices of stone, plate and hammer mills vary between £200 and £10,000 (1980 prices) depending on the mill's output, those of roller mills vary between £250,000 and £700,000. Foreign exchange savings may be illustrated by the following example based on the price list in Chapter VI. Let us assume that a country may choose between a roller mill with an output of 120 tonnes a day on three-shift working or eight hammer mills with an individual output of 15 tonnes per day on two-shift working. The f.o.b. price of the roller mill from the United Kingdom will be £400,000 while the cost of the eight hammer mills from Brazil will be £6,000 f.o.b. If the hammer mills were to be produced locally with imported engines and steel, foreign exchange costs might not exceed £3,000.

Other similar examples from the price list will indicate that substantial foreign exchange savings may be derived from the adoption of stone or hammer mills in place of roller mills.

Rural industrialisation

A large number of developing countries have launched programmes in favour of rural industrialisation with a view to improving the employment and incomes of the rural population and slowing down their migration to urban areas. Food processing, and in particular the milling of grain, constitutes a basic rural industry. It is therefore important to maintain this type of industry in rural areas, and to avoid measures which will put processors at a disadvantage in relation to processors established in urban areas. For example, subsidisation of large roller mills or government measures which may restrict the supply of maize to small rural mills (e.g. in cases where the limited supply of maize is assigned, in priority, to roller mills by government decree) could, in the long run, force the closing down of hammer mills in rural areas. In some countries, such as Tanzania and Kenya, some small mills have already closed down or are operating at low capacity partly as a result of the expansion of roller mills.


The previous section suggests that, from a socio-economic point of view, the production of whole meal by small merchant or custom mills might be more appropriate than that of sifted or bolted meal by large plants. However, as pointed out earlier, the choice of milling techniques may vary from one country to another depending on such factors as the level of development, consumers' tastes and the distribution of the population between rural and urban areas. The promotion of any particular milling technique should therefore follow a careful evaluation of the supply and demand of different kinds of maize meal, taking into consideration the country's development objectives. An overall study of the maize milling sector might include the following:

- a survey of consumers' demand for various types of meal, including the identification of the reasons which may explain demand for specific types of meal (e.g. availability, tastes, advertising, low prices, packaging, shelf-life);

  • a survey of maize meal production by households, custom mills, merchant mills and roller mills, including the location of production units, milling techniques, scales of production, quality of output, marketing channels and wholesale and retail prices; and
  • a socio-economic analysis of alternative maize milling techniques based on information obtained from the above surveys, taking into consideration the country's development objectives. The assessed techniques should include those currently used in the country as well as improved techniques which have been developed elsewhere.

Findings from the above study may then be translated into concrete action for the promotion of milling techniques consonant with the country's development objectives. Government action in this sector may include the following:

- formulation and application of measures to induce consumption of specific types of maize meal;

  • dissemination of information on improved milling techniques;
  • promotion of research and development directed to the improvement of the quality and shelf-life of whole meal, including the development of appropriate packaging required by some segments of the market; and
  • formulation and application of measures to promote the right balance among various types and scales of mills, taking into consideration the consumption pattern which the government wishes to encourage.

The technical information contained in the following chapters should be useful for the undertaking of the suggested study, as well as for the formulation of government measures for the promotion of suitable milling techniques. It is also particularly intended for practising and would-be millers who wish to improve their current milling techniques or set up a new production unit.

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Authors Eric Blazek
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Aliases Small Scale Maize Milling 4
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Created April 27, 2006 by Eric Blazek
Modified December 9, 2023 by StandardWikitext bot
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