The profit center

Steaming soy beans (Image source: 

allaboutsushiguide.com)

Different methods of steaming soy

beans (Image source: misorecipes.net)

Soy grits 

(Image source: shreekalkaglobal.com)

Whole beans and large fragments are 

returned to the cracking rollers. 

The soy fragments (cotyledon) contain 

about 20% oil while the hull has a 

negligible oil content. The removal of the 

hulls by aspiration is optional but has 

the advantage of producing a defatted 

soy meal with a higher protein content 

(48% as opposed to 44% protein of flour 

containing hulls). 

Grinding soy beans to produce grits 

The flakes are ground by a series of 

rollers into smaller particles (grits) or 

fine flour. After each pass through the 

grinding rollers, the grits are screened 

and classified according to particle size. 

The coarse particles pass through a no. 

10 – 20 screen, the medium particles 

pass through a no. 20 – 40 mesh screen 

and the fine particles pass through a no. 

40 – 80 mesh screen. Each size class 

finds specific application in food products. 

If the grits are too big for the intended 

use, they are simply transferred back to 

the grinding rollers. 

Further grinding of grits to produce 

soy flour 

Soy flour is produced by grinding the 

grits into a fine powder. The flour is 

screened to ensure that 97% of the flour 

particles pass through a very fine 100 

mesh screen. Because of the high lipid 

content, the product is difficult to screen. 

Packaging of soy grits and flour

Full-fat soy grits and flour require 

non-transparent and moisture proof 

packaging. All precautions should be 

taken to prevent lipid oxidation. 

Literature sources 

Lui, KeShun. 1999. Soybeans: chemistry, 

technology and utilisation. Gaithersburg: 

Aspen Publishers, Inc. 

The characteristics of soy grits and 

flour

The soy bean contains approximately 

40% protein and 20% oil on a moisture 

free basis. When soy beans were 

first processed commercially, the oil 

was considered as the most valuable 

component and the defatted soy bean 

flour as a by-product. But since 1960, the 

need for alternative protein sources has 

risen sharply across the globe. Today the 

flour is a highly sought after component 

that is mainly used in animal fodder.

One metric tonne of soy beans yield 

approximately 180 kg oil and 800 kg 

flour. Soy beans have long been a major 

source of protein to the people of the 

Orient where it is consumed in various 

forms. The world demand for food protein 

is increasing sharply along with the ever 

rising population.

Many types of soy protein products 

have been developed for human use from 

defatted soy flakes, including soy grits 

and flour, soy concentrate, soy isolates 

and textured soy proteins.

Apart from economic and health 

advantages over animal proteins, soy 

proteins have more functional properties 

and thus a wider range of applications. 

It is used in virtually every food system 

including meat products, dairy products, 

baking and confectionery, breakfast 

cereals, infant foods and beverages.

Soy grits and flour are produced from 

the defatted soy flakes that are separated 

from the miscella during oil extraction. It 

only requires desolventising, grinding and 

screening to produce a highly nutritional 

product with wide application possibilities 

in the food and feed industry.

Desolventising flakes for animal feed

The end use of the soy grits or flour 

determines the type of desolventising 

process. The method used for flakes 

intended for animal feed is required 

to remove the solvent and inactivate 

anti-nutritional factors such as trypsin 

inhibitors, thus rendering a product that 

is safe for animals. A steam treatment 

is used to remove the solvent, followed 

by toasting at 100°C to 105°C to 

ensure sufficient heat for inactivation 

of the toxicants. This high temperature 

treatment, however, also causes 

severe protein denaturation, which is 

unacceptable for products intended for 

human use. A different method is thus 

used for flakes intended for food. 

The hot flakes exiting from the 

desolventiser-toaster is dried with hot air 

to reduce the moisture content to 10%. 

Hot air is followed by cold air to cool the 

flakes prior to grinding. 

Desolventising flakes for food

The aim of this process is to minimise 

the heat denaturation inflicted on 

the soy proteins while effectively 

removing the solvent. The solubility of 

the proteins is very important to the 

functional properties and use of soy 

proteins in food. 

Two types of desolventising systems van 

be used: the vapour system or the flash 

system. In the vapour desolventising 

system, superheated hexane vapour 

is brought in contact with the flakes 

in agitated containers. This causes 

extraction of hexane from the flakes. 

In the flash desolventising system, 

superheated hexane vapour and flakes 

are brought in contact with each other 

in conveying tubes where the residence 

time of the flakes is kept relatively 

short. 

(► p27)

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The production flow process of soy grits and flour 

Final packaging of soy grits

(Image source: bobsredmill.com)

In both cases, desolventising is 

followed by deodorising. A steam unit 

with controlled pressure is used to 

deodorise the flakes. Residual solvent 

is also removed in the process. By 

controlling the conditions inside the 

deodorising unit, the flakes with varying 

protein dispersibility index (PDI) can be 

produced to suit the specific end use. 

The PDI can vary from 10 to 90%. The 

hot flakes exiting from the deodoriser is 

dried with hot air to reduce the moisture 

content to 10%. Hot air is followed 

by cold air to cool the flakes prior to 

grinding. 

Grinding soy flakes to produce grits

The flakes are ground by a series of 

rollers into smaller particles (grits) or 

fine flour. After each pass through the 

grinding rollers, the grits are screened 

and classified according to particle size. 

The coarse particles pass through a 10 

- 20 mesh screen, the medium particles 

pass through a 20 - 40 mesh screen and 

the fine particles pass through the 40 

- 80 mesh screen. Each size class finds 

specific application in food products. If 

the grits are too big for the intended use, 

they are simply transferred back to the 

grinding rollers. 

Further grinding of grits to produce 

soy flour 

Soy flour is produced by grinding the 

grits into a fine powder. The flour is 

screened to ensure that 97% of the 

flour particles pass through a 100-mesh 

screen. 

Packaging of soy grits and flour

Soy grits and flour require moisture proof 

packaging.

Uses of defatted soy grits and flour 

Defatted soy flour is mainly used for 

animal feed, pet food and for the 

preparation of protein concentrates. A 

small quantity is used as human food. 

Non-food uses include the preparation of 

antibiotics, vitamins and other medicines. 

Literature sources: 

1.  Lui, KeShun. 1999. Soy beans: 

Chemistry, Technology and Utilisation. 

Gaithersburg: Aspen Publishers, Inc. 

2.  Snyder, H.E. & Kwan, T.W. 1987. Soy 

bean Utilisation. 

3.  Tanteeratarm, K. 1992. Soy bean 

Processing for Food Uses.

Next month we shall focus on the 

processing of soy bean oil.

Published with the acknowledgement

to the ARC Institute for Agricultural

Engineering for the use of their 

manuals. Visit www.arc.agric.za for

more information.

T

he soil formation factors control, in 

turn, the soil formation processes 

that determine which horizontals 

(layers in the soil) form in the soil. It 

is these horizontals that eventually 

determine a soil’s unique properties 

and thus the land usage.

This article focuses on the soil 

formation factors and forms part of a 

series that highlights this resource.

Mother material

Mother material may be regarded as 

the matrix or the building block of 

soil, because soil develops out of the 

unconsolidated, weathering of rocks 

or sediments. Various mother materi-

als give rise to a variety of weather-

ing products and therefore a variety 

of (primary) mineral particles which 

develop into a specific type of soil.

The mother material therefore has a 

major impact on the soil characteris-

tics, especially when the soil is in early 

development. If the mother material 

is known, this information can then be 

used to deduce the probable char-

acteristics of a particular soil. (The 

various types of rocks, their mineral 

composition and the influence they 

have on the soil characteristics, were 

discussed in Part 2 of this series.)

Climate

Rainfall and temperature are the 

most important elements of climate 

influencing soil formation, as they 

determine the rate of weathering. In 

deserts (hot and dry) or the tundra 

(cold and wet), soil develops slowly, 

while it develops rapidly in the tropics 

(hot and wet). When it is hot and dry, 

the soil is shallow, not significantly 

alkaline and has a low organic mate-

rial content. When it is hot and wet, 

the soil is deeper, more alkaline and 

contains more organic material.

The effect of rainfall on the soil 

formation process is determined by 

the type and intensity of the rain, the 

distribution over seasons, the rate of 

evaporation, the aspect of the terrain 

(for example northern or southern 

slope) and the porosity of the mother 

material.

The water that is available for soil 

formation, is determined by the ratio 

between the average annual rainfall 

(P, mm) and evaporation (E, mm). 

The higher the P/E ratio, the greater 

the leaching  and removal of soluble 

salts and plant nutritional materials 

from the soil; the more intense the 

weathering of minerals will be and the 

greater the amount ofclay that will be 

leached to the deeper horizons and 

lower down in the landscape.

The rate of weathering and soil for-

mation reactions doubles with about 

every 10°C increase in soil tempera-

ture.

However, there is a strong relation-

ship between rainfall, temperature 

and soil formation. Dry, hot desert 

and cold, wet tundra conditions are 

not condusive to soil formation, while 

intense soil formation and weathering 

occurs under wet, tropical conditions.

Organic material will increase 

with increasing soil wetness, leach-

ing will increase, pH decreases, base 

saturation decreases, acid saturation 

increases, clay minerology changes 

from 2:1 to 1:1, CEC decreases, fertil-

ity decreases, underground saturation 

increases, and more water is available 

for plant growth.

With an increase in temperature, 

while the rainfall remains constant, 

the effective rainfall will decrease, 

organic material content decreases, 

and weathering of clay minerals will 

increase from 2:1 to 1:1.

Organisms

All the organisms living in or on the 

soil influence soil formation. Plant 

roots bind soil particles together and, 

in doing so, lower soil erosion. The 

same process also helps with the 

formation of crumbly and granular 

structure. The thick roots of trees 

Soil does not form by chance, but as a result of the influence of climate, organisms and topography on the mother mate-

rial over time. The result of these five soil formation factors is the formation of a unique soil type at a specific place.

PART 22: Soil formation

thicken and therefore mix the soil in 

this way. Plant roots can also contrib-

ute to physical weathering by break-

ing up the rock. When the roots die, 

organic material remains behind and 

when that weathers, it leaves chan-

nels which improve aeration and water 

movement in the soil.

Plants also provide the soil with 

organic material – on the surface 

through leaves and in the soil by 

roots. Although trees provide a lot of 

organic material when they die, it is 

the perennial plants such as grasses 

which provide the most organic mate-

rial per annum. The plant cover also 

protects the soil against raindrop 

impact and, in so doing, limits erosion. 

It also reduces the soil temperature, 

thus lowering evaporation.

In the natural ecosystem, plants 

absorb nutritional substances from 

the soil and replace them with organic 

material. This is a very delicate bal-

ance and may easily happen through 

the removal of plants via, for example, 

the exploitation of tropical rain forests, 

overgrazing or cultivation, where crops 

are removed from the land.

Mesofauna, such as earthworms, 

nematodes, mites, termites, ants, 

centipedes and other insects, are nor-

mally found in the upper soil, where 

organic material is concentrated and 

the soil is well aerated.

The majority of these animals can-

not survive in wet, water saturated 

soil. Mesofauna change the soil by se-

creting organic material and minerals 

in a digested form. These secretions 

are usually more stable than the rest 

of the soil. They therefore lead to an 

improved soil structure.

These animals mix the soil through 

their constant movement and tunnels 

that are excavated. The tunnels and 

structure improve the movement of air 

and water in the soil.

The majority of animals live above 

the soil, but a small number, such as 

rats, moles and rabbits remain in the 

Martiens du Plessis, Soil Scientist, NWK Limited & Prof Cornie van Huyssteen, Lecturer: Soil Science, University 

of the Free State

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                               ProAgri Zambia 25     

soil. These animals can tunnel deeply 

into the soil and thus mix the soil. 

They also take organic material into 

the soil, where they store it as food or 

nesting material. Animals are there-

fore responsible for the mixing of the 

soil, the addition of organic material 

and improved aeration through tun-

nels.

Uncontrolled utilisation of the plant 

cover through grazing can lead to the 

total exhaustion of the plant cover. 

This leads to reduced water infiltra-

tion, increased run-off and therefore 

increased erosion.

People can also influence soil forma-

tion through usage thereof, for ex-

ample through tillage, grazing, urban 

development, mining and forestry. 

Tillage mixes the soil, organic material 

is removed and the fertility changes 

drastically. People can therefore 

degrade the soil through overutilisa-

tion, but can also artificially create soil 

through, for example, the reclamation 

of mine dumps and the sea.

Topography

Topography refers to the shape of the 

earth’s outlines. In particular, it is the 

slope and aspect of the local relief that 

are important to soil formation.

Slope refers to the angle between the 

earth’s surface and an imaginary horizon-

tal line, while slope position refers to the 

specific position on the hillside (Figure 

1). Aspect is the compass direction of the 

slope (e.g. north or south), and slope is 

measured downwards against the vertical 

on the contour line.

Topography influences soil formation 

by the effect it has on the microcli-

mate, plant growth, mother material 

and time. The physical shape of the 

landscape determines how, and how 

much soil and water is redistributed. 

Flat areas are, for example, more 

susceptible for wind erosion, while 

water erosion has the greatest impact 

in steep areas.

Soil in crest positions usually forms 

in situ (right there from the mother 

material), is older and shows signs of 

advanced weathering and leaching. 

Escarpments are too steep for any 

soil to form as all the soil is lost to 

erosion.

Soils on the middle slopes are usually 

deep and well-drained. Soils on the foot-

hills are more poorly drained than those 

on the middle slopes and signs of wet-

ness are common. Poorly drained soils 

are common on the floors of the valley, 

where soil forms in alluvial deposits. This 

succession of soils in a slope is referred 

to as a catena or an hydrological topo 

series.

Time

Soil formation is a very slow process. 

It can take several thousands or mil-

lions of years. The longer a soil is 

exposed to a specific set of soil forma-

tion processes, the more prominently 

the soil properties develop.

The combination of soil formation 

processes that are dominant, will 

determine how long the soil takes to 

become “mature”. Because soil forma-

tion is such a slow process, it can 

take place under a variety of climatic 

conditions, as the climate has changed 

a number of times in the past.

When the climate changes, the 

soil will also change. A soil that has 

developed under a previous climatic 

cycle, is known as a palaeosol (palaeo 

= old; sol = soil) or primary soil. A soil 

reaches maturity when soil formation 

and soil destruction (erosion) take 

place at the same rate. The degree 

and depth of horizon differentiation 

Figure 1: Crest, escarpment, middle slope, foothills and valley floor.

is also an indication of the age of the 

soil.

Summary

The five soil formation factors – 

mother material, climate, organisms, 

topography and time – control the soil 

formation processes and thus deter-

mine which soil forms in a particular 

place. In many cases, the type of soil 

may be deduced from the specific set 

of soil formation factors. However, this 

takes experience and should be done 

with circumspection and should always 

be verified.

Crest

Escarpment

Middle slope

Bottom slope

Valley floor

For further information, please

contact the authors on:

Martiens du Plessis: 072 285 

5414 / [e-mail]

Prof Cornie van Huyssteen: 051 

401 9247 / [e-mail]

REFERENCES

Brady, N.C. 1990. The nature and 

properties of soils. 10th ed. Macmil-

lan Publishing Company, New York.

ProAgri Zambia 25   

 

 

 

 

 

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