Wheat
The
wheat plant
The wheat plant is a type of grass which develops
over the course of a year, maturing in the summer ready for grain
harvesting in late January and February. Some wheats are planted
in the autumn and require a period of cold before they will form
grain in late spring. Others are planted in the spring and require
no cold for normal growth and grain development. In New Zealand
about half the total wheat production comes from autumn plantings
and half from spring plantings.
The different colours highlight the provinces of New Zealand.
Canterbury
is the major wheat producing district for both autumn and spring
wheats. Autumn or spring planting is determined by climatic factors
such as rainfall and environmental factors such as disease. Spring
wheats generally have better bread baking qualities than autumn
wheats, so end-use is also an important consideration.
Wheat
plants grow several side shoots called tillers from a crown
which is just below ground level. Each of these tillers grows
a long stem which bears a flowering head at its top. The length
of these tillers varies greatly between different wheats, some
being extremely short (less than 20cm) while other are extremely
tall (over 1m!). Modern wheats are generally 80cm to 1m tall.
The wheat flowers are self-fertilised by the movement
of pollen from the male part of the wheat flower (stamen) to the
female part (the stigma). Each flowering head fertilises its own
flower. Once this has occurred the grain begins to grow and develop.
Starch and protein are stored in the grain and used as an energy source by the new plant. The grain reaches its maximum size a month after
fertilisation – this is usually in mid summer. Once the grain
is fully developed the wheat plant begins to die and the grain
slowly dries out. It is at this stage that harvesting interrupts
the growing cycle of the wheat plant, as once the grain is dry
enough, the wheat is harvested. The grain is harvested by a machine
(called a combine harvester) which cuts the whole plant and separates
out the grain. Grain can be stored in bulk bins if the amount of
moisture in the grain is kept low.
The
wheat grain
A grain of wheat is a seed which can grow into
a new wheat plant, and is also the part of the wheat plant which
is processed into flour. Wheat grains are generally oval shaped,
although different wheats have grains that range from almost spherical
to long, narrow and flattened shapes. The grain is usually between
5 and 9mm in length, weighs between 35 and 50mg and has a crease
down one side where it was originally connected to the wheat flower.
The grains are commonly a red colour, although
many wheats have white grains and more unusually purple, black,
brown or green/grey varieties exisit. The wheat grain (or kernal)
is divided into several parts, as shown in the diagram.
The
dissection...
The wheat grain (or kernel) is divided into several
parts, as shown in the diagram.
|
The three main parts are:
Bran
The outer coating or "shell" of the wheat kernel is made
up of several layers. These layers protect the main part of the
kernel. Bran is rich in B vitamins and minerals.
Endosperm
This is the main part of the wheat kernel and represents about
80% of the kernel weight. It is from this part that white flour
is milled. The endosperm is rich in energy-yielding carbohydrate
and important protein.
Germ or Embryo
This part grows into a new plant if sown. The germ lies at one
end of the grain and represents only 2% of the kernel. It is
a rich source of B vitamins, oil, vitamin E and natural plant
fat. It needs to be removed during milling because the fat is
liable to become rancid during flour storage. Wheat germ is still
very valuable though and is used in many products.
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Types of wheat
in New Zealand
Wheat is used in many human foodstuffs and for
animal feed. The most important use of wheat in New Zealand is
for breadbaking, which accounts for around 60% of total wheat production.
Other major foodstuffs made using wheat include biscuits and pasta.
The wheat used for pasta is called Durum wheat. Durum wheat is
different from the type of wheat used to make bread and is much
harder, with different cooking properties than bread wheat flour,
making it satisfactory for pasta manufacture.
Biscuit wheats differ from bread wheats in the
hardness of their grains and in the type of doughs which are made
from their flour. Biscuit wheats are soft, which means special
mills are required to extract their flours. Soft wheats in a conventional
hard wheat or bread wheat mill would clog up the sieves used to
separate the white inner part of the grain called the endosperm
from the rest of the grain. The softness of biscuit flours means
they only absorb small amounts of water when mixed into a dough.
Doughs made with biscuit flours spread out sideways when baking,
and so produce high quality biscuits.
The requirements for breadbaking wheats are quite
different. The grains are semi-hard or hard, which produce flours
that flow easily through a conventional milling system. Bread flours
must absorb a relatively large amount of water, and good bread
baking doughs must also have the capacity to stretch into a large
volume. Bread baking doughs are expanded by gas from the fermenting
yeast and then must retain that volume when cooked.
There are also some small amounts of speciality
wheats, such as the purple grain coloured wheat, produced for use
in certain types of breads. Purple wheat, which was first commercially
produced in New Zealand, is a small but significant part of the
New Zealand bread wheat industry. It is used for providing colour
and texture in a number of wholemeal and specialty bread types.
Wheat used for animal feed is commonly bread wheat
which has been rejected for low quality. Animal feeds in New Zealand
are usually compounds of a number of plant and animal products.
Wheat or one of the cereal grains (barley, maize) often provides
much of the physical bulk for these compounds. At present, relative
price is the major factor in deciding which particular cereal grain
is used. However, modern feed manufacturers are beginning to analyse
the properties of their raw ingredients more closely and particular
requirements may soon emerge.
In the future, feed wheat may have its own quality
requirements, just like bread wheat, biscuit wheat and Durum wheat
have.
Canterbury Wheats - April/May sown
Biscuit/Feed |
Claire |
A consistently high yielding
winter wheat with excellent characteristics for soft milling
and animal feed. |
Harbour |
A high yielding winter wheat
with exceptional quality parameters for soft milling characteristics.
Stiff straw and high untreated yields. |
Bread |
Regency |
Bread wheat with medium to
strong quality. Very high yielding autumn/winter wheat
with medium proteins and grain size. |
Feed Wheat |
Alberic
|
Very high yielding & early
maturing, though not as early as Amarok. Good field characteristics. |
Equinox |
Short stiff high yielding feed
variety. Has topped yield trials regularly. Stiff straw
with good standing power, low cost to grow. |
Macro |
The top yielder in Canterbury
irrigated sites over last 2 years. |
Option |
High Yield, especially on dryland
with good test weight. |
Pennant |
High yielding of good feed
quality grain Later maturing variety. |
Phoenix
|
Very high yielding winter feed
wheat. Short strawed and with good grain characteristics. |
Savannah |
A high yielding winter feed
wheat. Good grain size. |
Solstice |
High yield potential winter
wheat. It has short, very strong straw. |
Storm |
A new winter feed wheat with
very high yield potential with short strong straw. |
Other |
Tanker |
High yield potential, Tanker
is a later maturing variety with short straw producing
industry quality grain. |
Weston |
Consistently high yielding,
early maturing variety with short stiff straw, produces
grain of high test wt. |
Canterbury Wheats - May/June sown
Bread |
Amarok
|
High yielding, early maturing
winter wheat. Good on dryland and irrigated farms. Large
grain size. |
Aquilla |
Produces bread with medium-strong
dough properties and consistently good bake scores. Low
risk winter/spring wheat with good grain size, disease. |
Bakker Gold |
Premium bread wheat with excellent
grain, flour and baking results. Good yields. Sow from
autumn to spring. |
Commando |
Medium quality bread wheat.
High yield potential from spring sowing. |
Domino |
High quality bread wheat.
Can be autumn to spring sown. |
Kohika |
Hard milling, producing strong
bread with medium work input. Med. to high yielding. Large
grains. |
Monad |
Very high quality bread wheat.
Suits autumn to spring sowings. |
Regency |
Bread wheat with medium to
strong quality. Very high yielding autumn/winter wheat
with medium grain size and good straw strength. |
Torlesse |
High quality bread wheat with
short straw and good standing power. Can achieve high yields
from autumn and spring sowing. |
Vanquish |
Produces bread dough with medium-strong
properties. High yielding (especially on dry land) autumn/winter/spring
wheat with good grain size. |
Feed |
Morph |
Very high yielding wheat that
can be sown from autumn to spring. |
Raffles |
Above average feed and gristing
variety. |
Milling
of wheat in New Zealand
Wheat arrives at a mill by truck after either
being shipped or hauled from its point of origin. Once at the mill
the incoming wheat is subjected to a series of quality control
tests, then the wheat is unloaded and stored in silos. The diagram
shows a simplified view of the milling process.
The Cleaning of Wheat
Before wheat can be milled the impurities that were gathered up
with the wheat during harvesting must be removed.
Different mills use various makes of machinery
to remove the small stones, husks, weed seeds, etc gathered with
the wheat during harvesting but they all use the differences in
size, weight, shape and density to isolate and remove impurities.
The Conditioning of Wheat
Water is added to the wheat in small amounts to ensure easy separation
of the bran (outer coating) from the endosperm (inner part of
the wheat). The water helps to toughen the outer bran layers
and softens the inner portion. This makes the soft inner portion
easier to remove.
Rolls and Sifters
The whole milling process can be seen as a repetition of two processes
– grinding and sifting. The wheat is first passed over a
series of fluted break rolls. A pair of break rolls do not turn
at the same speed, the higher roll usually turns about twice the
speed of the lower roll.
Wheat travelling between the break rolls is ripped
apart and the white endosperm material is released. After passing
through each set of break rolls the particles are sorted on a sifting
machine. The flour is removed and the coarse branny material is
returned to the break rolls in order to separate out any flour
still attached to the bran.
Semolina, which is chunks of endosperm, is also
produced in the break system and this Semolina is passed onto a
new series of rolls called reduction rolls. Eventually all the
wheat going through the break system is removed as either flour,
semolina or coarse bran.
The reduction rolls are a series of smooth rolls
which grind the semolina particles down into three products, flour,
fine bran and wheatgerm. Each of these products can then be separated
by repeated grinding and sifting.
The flour obtained by the various rolls and sifters
is of differing quality depending upon when it was removed from
the system. Mills can blend flours from the various parts of the
system to obtain a flour suitable for selling. Finally the mill
ends up with wheatgerm and pollard, which is fine bran and flour.
Mills can then either bag these products or send
them off via bulk supplies. Mills can also add value to their product
by making flour into self-raising flours, pastry flours and premixes.
All these are produced by using flours from different parts of
the system and in some cases adding additional ingredients.
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