Cereal Grains
Outline
• Grasses as plants
• Wheat
– domestication
– farming basics
– bread making
• corn
– domestication
– hybrid corn
– ethanol production
• rice
• barley and beer making
• sorghum
pages
• Chap. 12
The Grass Family
• More than 50% of the calories consumed by humans comes from members
of the grass family (Poaceae):
– wheat, corn, rice are the main grains, but also oats, barley, sorghum, millet,
and rye
– corn = maize
• Grasses make up 25% of all vegetation on Earth
• Grasses are monocots
• Tropical grasses (like corn but not wheat or rice) have C4 photosynthesis
– C4 means they can open their stomata at night, store carbon dioxide, and then
close the stomata during the day and fix the CO2 into sugar while the Sun
shines.
Grass Family Characteristics
• Parallel leaf veins (like all monocots)
• fibrous roots
• either annual or perennial
– but crop species are all annuals
• Growing point is below ground until
flowering. For most grasses, the flowers are
at the tip of each branch.
– Branches (tillers) also start below ground.
Grass Flowers
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Grass flowers are small and inconspicuous: they are wind-pollinated so there is
no need to attract pollinators.
Many flowers grouped together (an inflorescence). Each one is called a floret.
All angiosperm flowers have the same basic structure: from outside to inside
there are four whorls, sepals, petals, stamens (male parts), carpels (female parts)
In grasses, the sepals and petals are fused into a small structure (the lodicule) that
swells up to open the flower.
In place of sepals and petals are two bracts (leaves), the palea and the lemma.
Grass Fruits
• Each grain is a fruit: the ovary wall
surrounding a single seed. Grain fruits are dry,
not fleshy, and they are indehiscent: the seed
does not fall out of them.
• The embryo (which grows into the new plant)
is called the germ. It is protein-rich.
• The endosperm is mostly starch, with a little
protein. It provides nutrients for the
germinating seedling before photosynthesis
starts.
• The bran is the outer coat: it consists of the
ovary wall fused to the seed coat.
• In wild grasses (and some domesticated ones),
the grain is surrounded by protective leaves,
the chaff. Chaff has no nutrient value and
must be removed.
Grain Processing
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•
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Most grains are low in some essential amino acids. To get a complete protein, it
is necessary to also eat something else, such as a legume.
White flour, corn starch, white rice: just the endosperm, with the bran and germ
removed.
Brown rice, whole wheat flower, popcorn = the whole grain including bran and
germ.
– It contains much more protein and other nutrients than the endosperm alone.
– But, it spoils faster due to fats in the germ, and bread made with whole flower
doesn’t rise as well.
Wheat
Wheat
• Wheat (Triticum) is the source of most bread, noodles, beer.
• The foundation of Western civilization: Middle East, Egypt,
Mediterranean, Europe.
• Wheat was domesticated at about the same time and place as
barley and rye: the uplands of Turkey, Iran, and Iraq,
roughly 10,000 years ago.
– In the book of Genesis, at the beginning of the Bible, Adam and Eve
are kicked out of the Garden of Eden and forced to grow wheat.
Domestication of Wheat
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Modern bread wheat is a hexaploid: three
different diploid grasses hybridized to form it.
These crosses occurred naturally, but were
noticed and propagated by people.
The starting point: einkorn wheat, which is a
diploid wild grass. This means it was 2 sets of
chromosomes (one set = 7 different
chromosomes), or 14 chromosomes total.
– At first, gains from wild einkorn wheat were
harvested, and probably planted deliberately.
•
Archeological evidence shows that about
10,000 years ago, einkorn wheat with nonshattering heads was grown. This is the first
step in domestication.
– Non-shattering = the grains don't fall off the
stalk spontaneously. Makes it easier for
humans to collect it, but harder for wild plants
to disperse their seed.
Next Steps
• About 8000 years ago (very roughly), someone noticed a spontaneous
hybrid between einkorn wheat and a closely related plant called goat
grass.
– Much bigger grains
– This is emmer wheat, a tetraploid (4 sets of chromosomes, 2 from each of
the parents = 28 total chromosomes)
• further breeding of emmer wheat led to durum wheat, which is also
tetraploid but has "naked grains": the chaff is much smaller and doesn't
surround the grains.
– Durum wheat is the source of pasta flour. It makes up 10% of today's
wheat production in the US.
Final Steps
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Tetraploid emmer wheat x another
diploid goat grass = hexaploid bread
wheat (Triticum aestivum).
– Also a spontaneous event
noticed and cultivated by
humans, about 7000 years ago.
– Six sets of chromosomes, 2 sets
from each of the 3 parents = 42
total
– Bread wheat is about 90% of
today's wheat production.
Wheat cultivation led to permanent
settlements, plus a food surplus that
led to having some people doing
things other than gathering food i.e.
the start of civilization
Wheat cultivation spread out from
this center over the next few
thousand years.
Modern Wheat
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Two types of wheat are currently grown: about 10% is durum wheat (tetrapoid,
goes into pasta) and the rest is bread wheat (hexaploid).
– There are many varieties and cultivars of both of these.
Recent breeding: resistance to diseases, especially stem rust (a fungus), and Green
Revolution traits like dwarf varieties that can efficiently use large amounts of
fertilizer.
– Continued attempts to breed in new traits from other goat grass species
It grows best in relatively cool and dry grasslands, such as the Great Plains west
of the Mississippi River.
– Also, Ukraine, France, Argentina, China
Wheat didn’t become a major US crop until Russian immigrants (dodging the
compulsory military service in Russia) moved to the Great Plains. They brought
wheat varieties with them that grew well: similar climate to Ukraine.
Winter wheat: planted in the fall, needs a cold period (winter) before it can
germinate in early spring, with harvest in late spring or summer
Spring wheat: planted in the spring, harvested in the fall. This is necessary where
the winter weather is too harsh. Germination is controlled by day length.
Farming Basics
• Here are the basic steps involved in crop production. Details vary with the
crop, and modern farmers may through in some other steps to deal with
weeds and insect pests.
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Plowing: the soil needs to be loosened so seeds can be planted.
Cultivating: removing weeds and further breaking up the soil
Planting
Harvesting
Threshing: separating the grains from the stalks and chaff.
• Before about 1700, the basic techniques were more or less unchanged since
very early times.
• Between 1700 and 1850, the Industrial Revolution changed farming by
developing mechanical methods.
– At first, the mechanical implements were powered by horses or oxen. “Oxen”
are bovines, usually castrated males , trained as draft animals.
– Also some use of steam power, but it was cumbersome and dangerous
• Between 1900 and 1950, internal combustion engines replaced animals
Plowing
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Plowing. To loosen the soil for planting.
Better plows also turn the soil over to kill
weeds.
Simple: drag a stick through the ground
Fancier: plowshare and mouldboard. The
plowshare cuts the soil and the mouldboard
turns it over. Requires a lot of weight and
strength to pull: oxen. Developed before
1000 AD.
Sticky soil, especially in western plains of
US. Steel plowshare invented by John Deere
about 1847.
Tractors replaces animals early to mid
1900’s, which allowed multiple plow blades.
Cultivating
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Removing weeds and breaking up
the soil
Can do this with a hoe (and it’s
still done this way for some
vegetable crops).
Drag harrow: run some spikes
through the ground. Needs animal
to pull it.
Cultivators mounted on wheels
control the depth better
As usual, mechanisation has led to
bigger and better.
Planting
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Early: broadcasting: throw the seeds on the ground
An improvement: dig a hole with a stick and drop a seed in
it.
Seed drill. Invented by Jethro Tull in 1701, but not widely
adopted until after 1750.
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It has 3 parts: first, a blade cuts a small furrow in the ground.
Then, a seed wheel drops seeds down a tube into the furrow at
precise intervals, and finally, a rake covers the seeds up.
Much higher rate of seeds turning into plants, not getting eaten
by birds or rotting on the ground.
Automatic seed drill. Pulled by animals or machines;
multiple rows at once. Modern seed drills use compressed
air to move the seeds.
Harvesting
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Reaping is cutting the stalks for harvest.
Hand reaping uses a sickle. The early ones have flint blades
mounted in bone or antler, later ones were made of metal.
You grab a handful of stalks, saw them off, then tie the
stalks into bundles (sheaves) to dry and then thresh later on.
The scythe was invented by the Romans. Full body motion
allowed faster harvesting.. Later versions had a cradle
attached, so the stalks didn’t just fall on the ground.
Mechanical reapers were invented in the 1800’s. The best
know is the McCormack reaper. The stalks fell onto a board
behind the blade, and a set of “sails” pushed the stalks off
into bundles that were tied by hand. Later machines also
bound the sheaves.
Threshing and Winnowing
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Threshing is removing the grain from the stalks; winnowing
is removing the chaff (protective leaves covering the grains).
The original method was to beat on the grain stalks with flails,
then winnowing by throwing it up in the air and letting the
wind carry off the chaff: the heavier grain fell straight down.
A later method was to lay the stalks on a stone floor and let
animals trample it. The grain would fall through properly
spaced cracks and be collected below.
Threshing machines were usually stationary, powered
originally by horses and later by steam.
By 1900, reapers were combined with threshers to become the
combine, which harvests the grain in the field and produces
cleaned grain.
YouTube Videos
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http://www.historylink101.com/lessons/farm-city/reaping.htm
Plowing
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Planting
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http://www.youtube.com/watch?v=4ZEntqFSMJU
Harvesting
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http://www.youtube.com/watch?v=DqhdumfLtJw
Cultivating
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http://www.youtube.com/watch?v=9x-AR5RuO6Y
http://www.youtube.com/watch?v=xuytRXRfyeI
http://www.youtube.com/watch?v=DcDv545uA4c
http://www.youtube.com/watch?v=KW1lxWRY5kE&playnext=1&list=PL1F1B0360104DF6A9&fe
ature=results_video
Threshing
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http://www.youtube.com/watch?v=jleK4pHtQIw
– http://www.youtube.com/watch?v=2-p_2i1p8bA
– http://www.youtube.com/watch?v=iReC7WpveVs
• Grinding
– http://www.youtube.com/watch?v=TZyl7URyn10
Bread
• Wheat (and other grains) is hard to eat raw, and not very digestible.
• In the oldest times, wheat was ground up and cooked with water in a
porridge or stew.
• Bread is far more digestible and storable.
• At its simplest, bread is made by mixing flour with water, then baking
it. Adding salt helps with flavor. And, salt is necessary for humans
but not much found in plants.
Flour
• Flour is finely ground grain.
– At first, grain was ground between
stones. This process leaves stone
fragments in the flour that wear
down the teeth.
– Various improvements: grinding
wheels, use of animal, water, and
wind as power sources
– Modern method: grinding between
metal rollers
Leavened Bread
• Most bread is leavened: yeast is added to the flour and water.
– The yeast is allowed to grow for a few hours, which produces carbon dioxide
gas.
• It is also possible to produce carbon dioxide bubbles with baking soda, or
mechanically by creating a foam
– Why this works: the gluten proteins in the wheat flour are elastic, and they trap
the bubbles of gas. Baking causes the bubble to expand further.
– Kneading the bread increases the elasticity of the gluten. Too much kneading
destroys this property.
– After baking, the bread is lighter and tastier than unleavened bread.
– Discovered by the Egyptians about 4000 years BP.
– Unleavened bread, or flatbread, is made without yeast or other leavening agents
• Leavened bread requires gluten in the flour. Only wheat and rye have
enough gluten to rise properly. Other breads (corn, oat, potato, etc.) all have
some wheat flour in them.
• Refined flour, with bran and germ removed, ground very finely, does the
best job (think of cake flour).
– But, refined flour is less nutritious. It is often supplemented with iron and vitamins to
make up for this.
Maize
He’s outstanding in his field!
Old World vs. New World
• The Old World: Europe, Asia, and Africa
• New World (“discovered” by Columbus and followers): North and
South America
Maize
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Maize (Zea mays) is native to Mexico, and it was grown throughout North and South
America before Columbus.
We call this plant "corn", but that word really just means "the most common grain".
In England, "corn" means wheat, and it Scotland it means oats.
Unlike other grains, maize has the male flowers (the tassel on top of the plant)
separate from the female flowers (the silks and ears, growing out of the sides).
Maize is a tropical grass with C4 photosynthesis. It can grow in hotter conditions
than most other grains.
Maize Domestication
•
Maize is a very unusual grain: the male and female flowers are separate, the
female inflorescence (the ear) is huge, the individual grains are not covered by
bracts but the whole inflorescence is.
– Maize seeds can’t disperse naturally: they are firmly attached to the ear even after
the plant dies.
•
The ancestor of maize is teosinte, a native of Mexico.
– Teosinte ears are small, with kernels alternating on the stem, and each kernel is
covered with a hard shell
– Also, teosinte plants have many stalks (tillers)
•
But, only 5 gene mutations convert teosinte into a single stalked plant whose
ears are multi-rowed with naked seeds: a primitive version of modern corn.
Hybrid Corn
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One of the major developments in agriculture during the early 20th century was
scientific plant breeding based on Mendel's genetic principles.
– Corn yield has increased 5-10 fold since 1900 because of this.
– Traditional method: save the best seed to plant the previous year. Leads to slow
improvement.
Sexual and Asexual Reproduction
• Asexual reproduction is reproduction by
mitosis alone. There is only 1 parent, offspring
are genetically identical to the parent. The
offspring are clones on the parent.
– Most organisms (but not animals) reproduce
asexually some of the time.
– Asexual reproduction preserves good
combinations of genes.
• Sexual reproduction involves meiosis,
fertilization, and two parents. The offspring are
genetically different from both parents.
– Sexual reproduction generates new
combinations of genes. Some of these might be
more successful (fit, in the evolution sense) than
either of the parents.
– Sexual reproduction is useful for finding good
new combinations of genes.
Producing Hybrid Corn
• Hybrid corn is the result of this genetic research. Based on a two-part
process:
• First, inbreed (cross the plant with itself) for several generations.
– Since most bad conditions are genetically recessive, they only appear if
the organism is homozygous, which is what happens in inbreeding.
– Plants with deleterious genes die, leaving a strain that is much healthier.
– However, inbred plants are fairly small and unproductive.
• Then, cross two different inbred lines together: the offspring are
hybrids.
– The resulting plants benefit from hybrid vigor, and it is much larger and
healthier than the inbred parents.
– Also, they are genetically uniform, so they all flower at the same time
ripen at the same time.
• Most farmers buy hybrid seed, rather than saving some ears from the
previous year, because the hybrid seed yields so much better.
Types of Corn
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Different types, based largely on starch quality in the endosperm:
Popcorn has hard starch surrounding water-containing soft starch. When heated, the water
inside boils and blows up the kernel. This method can be used to make hard teosinte
kernels edible. It used to be a breakfast food, sweetened with maple syrup or sugar.
Dent corn has a mixture of hard and soft starch. Most corn grown in the US is dent corn,
which is a hybrid of flint (all hard starch) and flour (all soft starch).
Sweet corn has gene mutations that prevent sucrose from being converted into starch. It is
harvested at an earlier stage than other corn. The plants are smaller than regular field corn.
Pod corn is not grown commercially. It has long glumes (leaves) covering each kernel. It is
probably a primitive form.
Fancy colors in corn, mostly seen as decorations, are the result of several different genes
affecting pigments in different layers of the kernel. These layers are colorless in most corn,
because we like our food that way.
Modern Corn
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Corn is grown very widely in the US and many other countries.
– Described in a Chinese manuscript in 1550. It spread very quickly across the Old World.
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Needs more moisture than wheat. In the western US this means it must be irrigated,
from water stored below ground in the Paleozoic era, which is being used up rapidly
Many different growing regions, each with slightly different cultivars that grow best
there.
Many uses, and mostly not human food.
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About half of the corn in the US is used as animal feed.
We eat sweet corn, popcorn, corn meal
Corn derivatives: corn oil, bourbon whiskey, high fructose corn syrup
Industrial products: ethanol , corn starch
Rice
Rice
• Rice (Oryza sativa) is the most important food crop: it supplies more calories to
humans than all other crops. It is a staple food for nearly half the world’s
population.
– Nearly all rice is grown for human food.
– But unknown in the Western world until Roman Empire days.
• Rice was domesticated about 10,000 years ago in the Yangtze River valley in
eastern China. It spread very quickly to northern India, where very different traits
were selected.
– There is also a related species of rice that was independently domesticated in Africa
– Wild rice grown in the US is another grass species, not closely related to rice. (genus =
Zizania)
Growing Rice
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Rice is a multi-stemmed plant with the inflorescence at the top.
Rice has an adaptation to flooding: the stem contains air chambers that allow
oxygen to get to the roots, as long as the leaves are not underwater. This
allows growth in paddies, covered with water.
– Very few plants can survive flooding, so flooded rice paddies have very
few weeds.
– Rice seedlings are started in dry ground, then transplanted into the
paddies: very labor-intensive.
Rice paddies also grow an aquatic fern (Azolla), which lives in symbiosis with
a nitrogen-fixing bacterium. This provides a natural fertilizer for the rice.
In the US, rice is grown in large, laser-leveled fields, and all work is done
mechanically. Mainly in California, Louisiana, and other southern states.
Rice Varieties
•
Rice was domesticated in two separate locations,
which has led to two major varieties.
– var. indica is tropical. Grains are long and don’t stick
together.
– var. japonica has shorter grains that stick together:
“sticky rice”. This trait in not valued in the US, but
expected in China and Japan. Grown in more
temperate climates.
• The Green Revolution breeding techniques
were used to develop dwarf strains that
efficiently use fertilizer and are resistant to
many diseases. This has increased the area in
which rice can be grown as well as the yield.
• Recently, “golden rice” has been developed by
genetic engineering. It gets its color from
carotene, a precursor to vitamin A. Poor people
living exclusively in rice often developed
blindness from vitamin A deficiency.
Barley
Barley
• Barley may be the oldest domesticated grain, in the Fertile Crescent region.
– But, which crop was first depends on which archeological sites have been
investigated. Agriculture did not spread outward from a single center; no single
person invented the concept of agriculture.
• Like all grains, barley was originally toasted or eaten as a porridge. But, very
early, people learned how to make beer from barley. Laws regulating beer are
found in the Code of Hammurabi (about 1790 BC, Babylonian Empire).
– Most water is contaminated with microorganisms that cause disease, especially
before people knew about microorganisms.
– Making beer sterilizes the water: it was much safer and healthier to drink beer than
water. Also the reason for coffee and tea.
– The desire to be intoxicated seems pretty universal across human cultures.
Malt
• The key to beer making is malt. Malt is used to convert starch into
sugar; yeast then converts the sugar into ethanol.
• Malt is made by soaking barley grains in water and letting them
germinate.
– During germination, enzymes are released into the starchy endosperm to
release nutrients for the developing embryo.
– The germinating barley seeds are then dried and ground up into malt
powder.
– This powder contains amylase enzymes that can break down any starch
into sugar.
• Barley malt is also used to make malted milk products.
Making Beer
• The malted barley can be fermented by itself, or other grains can be added to
it. Any good source of starch will do: wheat, rice, corn, potatoes are all
used. Most American beer uses starch from rice.
1. The first step in beer making is to mix the malt with the grain and let it sit for
a few hours. The starch is converted to sugar, producing a sweet liquid
called “wort”.
2. The wort is then boiled with hops, the female flower of Humulus luputus.
This adds bitterness to the beer and prevents spoilage by killing bacteria.
– Hops addition was invented around 800 AD in Bohemia. Without it beer is too
sweet.
3. Yeast is then added and allowed to grow anaerobically. Yeast uses the sugar
in the wort to produce ethanol and carbon dioxide gas as waste products.
Beer
Making
malt
yeast
Starch  Sugar  Ethanol
Grain  Wort  Beer
Alternative Beer Production
• Many cultures have some form of fermented grain beverage.
• Sake, a traditional Japanese drink, is made by converting the starch in polished
rice to sugars with Aspergillus fungus instead of using malt.
– Polished rice has had the germ and bran removed.
– Yeast is then added to the rice to ferment it
• Chicha is a beer made from corn by the natives of Central and South America.
Instead of malt, they chew the corn kernels briefly. Amylase enzymes in saliva
convert the starch to sugar, and fermenting occurs with naturally-occurring
yeast.
• Modern beer brewing has several additional steps that make the flavor better
and more uniform, with well-engineered equipment to streamline the process.
– Different types of yeast affect the type of beer produced.
Sorghum
• Sorghum is actually a genus name. The
crop species is Sorghum bicolor. The
other species in the genus are not
economically useful.
• native to Africa, where it is still heavily
used.
– Traveled to India and China in ancient
times.
• Closely related to maize, with one major
difference: sorghum has perfect flowers
while maize has imperfect flowers
– Which means sorghum flowers have both male
and female parts, while maize has separate male
and female flowers
– Male flowers of maize = tassel (on top)
– Female maize flowers = ear (on the sides of the
stem)
– Sorghum flowers: tassel, on top of the plant.
Sorghum
Maize
Uses of Sorghum
• Very drought tolerant--it becomes dormant until
water arrives.
– Good food for famines. It grows when better-tasting
grains don’t
– grows in places too dry for maize. Western US, for
example.
– Also, it's a very tough plant that grows well even in hard
ground: needs little cultivation
• Different varieties of sorghum can be used in
different ways:
– As a grain: the tassel produces many seeds, about the size
of a small pea,
– As a sweetener: the canes store sugar, which can be
extracted as molasses
– As fodder for animals: they eat the whole plant (fermented
in a silo: makes it more nutritious and better tasting for the
animals), as well as preserving it for winter use).
– To make brooms. These days most brooms have synthetic
(plastic) bristles.
Sorghum Beer
• Beer made from sorghum is very common in
Africa, often home-brewed in small batches.
– Made from grain and naturally occurring yeast.
– Sipped through long straws to filter out the chaff
– under apartheid in South Africa, Africans were
not allowed to buy alcohol, so they brewed their
own
• Sorghum does not contain gluten, so people
with gluten-free diets can drink it.
• Beer making process: first convert the starch in
the grains to sugar (malting), and then convert
the sugar to alcohol (fermenting).
– Sorghum can be malted just like barley: get the
grains wet, allow them to germinate in a warm
environment, then dry them after sprouting. (or,
you can buy sorghum syrup)
– Fermenting with naturally occurring yeasts, or
add your own.
Sorghum Molasses and Maotai
• Like sugar cane, some varieties of
sorghum store sugar in their stalks.
– Eventually, the sugar gets used to make
the seeds, so harvesting occurs before
the seeds are ripe.
• The juice is squeezed out of the
stalks by running them between
iron rollers.
• The juice is then boiled to remove
most of the water. Impurities are
skimmed off the top.
• In China, sorghum molasses is
fermented and then distilled used to
make maotai, a very popular form of
alcohol there.