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For our farmers, harvest is the busiest,
most important time of the year.
It's the culmination of all their hard work.
I'm Stefan Gates, and I'm completely and utterly,
obsessively fascinated by food -
where it comes from, what it tastes like
and the extraordinary secrets lurking behind it.
But to grow good food, and to grow enough of it, farmers need to
intimately understand the science behind the harvest.
There are almost half a million different
species of plants on Earth.
We cultivate nearly 2,000 of them for food.
These edible plants provide us
with a dazzling variety of things to eat.
We harvest cereals and grains to make our bread.
And fruit and vegetables provide us
with essential vitamins and minerals.
Our ability to feed ourselves all depends on how well farmers
manage the needs of edible plants.
Take the potato - it feeds a vast proportion of the planet.
But it still shares the same basic characteristics
with the rest of the plant world.
Every plant needs its own particular balance of the same
key chemicals, so that it can grow.
And these are absorbed from the soil through the roots.
By adding fertilisers to the soil, farmers give their crops
a very specific cocktail of these chemicals,
and it makes sure they're as healthy as possible.
Phosphorous is essential for healthy roots and shoots.
Potassium strengthens stems, the plant's transport system.
Along with nitrogen, found in nitrates, these nutrients
help plants to create the energy they need to live and to grow.
Plants, unlike animals, are able to create their own food
through the process of photosynthesis.
This is why they're the first step in the food chain for us
and almost all other animals, and successful photosynthesis
is a fundamental part of growing crops for harvest.
But what does the process actually involve?
In order to grow, all plants have to pull off the same incredible trick.
They transform water and carbon dioxide gas into solid matter.
This amazing growth process is powered by the energy in sunlight.
Light enters the chlorophyll,
a green pigment contained within the chloroplasts in the plant's cells.
Here, it provides the energy that drives
the reaction between carbon dioxide and water,
to make glucose.
This provides the sugars that the plant needs to grow.
The by-product is oxygen - the oxygen we all rely on to breathe.
By measuring the speed of photosynthesis,
we can gauge how healthy a plant is.
The process is happening right here to this plant,
but normally it's invisible.
However, there is a way
in which we can see photosynthesis actually happening.
All it takes is a lamp and some aquatic plants.
If you look underwater,
photosynthesis is happening right now, and that oxygen
is being released as these tiny little bubbles.
The intensity of light affects the speed of photosynthesis.
Without enough light, the process will stop.
If I move the light further away...
..the bubbles slow down.
If I move the light closer...
..the bubbles speed up.
More light means more bubbles,
which means that photosynthesis is happening faster.
Faster photosynthesis means that plants can grow more quickly.
So farmers need plenty of sunshine for their crops to do well -
and that's why they say they're harvesting sunlight.
We expect fresh fruit and veg throughout the year.
So how do farmers grow their crops when there isn't much sunshine,
like in winter?
Greenhouses help farmers to grow their crops all year round,
which means that in the middle of winter,
and even in the middle of the night, they can grow tomatoes.
Not in this greenhouse,
but in a slightly bigger one that we found in Kent.
This greenhouse is gigantic -
about the size of ten football pitches.
It may be February,
but inside, it's possible to create the ideal conditions for growth.
The temperature, light and amount of carbon dioxide
can all be controlled to maximize photosynthesis.
Water and fertilisers provide all the minerals the plants need.
Growing crops like this costs money,
but with almost half a million plants in here, they can harvest
about 50,000kg of tomatoes every single week, even in winter.
And this way, they can meet our year-round demand.
Sometimes, with an understanding of exactly what a plant needs,
you can artificially create the ideal conditions for farming.
But farmers can't grow all of their crops inside.
So how does a plant cope
when photosynthesis simply isn't happening, like in winter?
Plants have their own strategies for surviving when it's freezing cold.
During the warmer months,
they save some of the glucose created through photosynthesis.
It's stockpiled in roots, stems and leaves
as a food store for the cold of winter.
We use these as food for ourselves,
and some of them are our most familiar vegetables.
Carrots are actually the plant's winter food supply,
stored in its roots.
Onions are basically energy stored up in swollen leaves.
And the potato is like a swollen, subterranean stem,
called a tuber.
For the plant, it's like an underground larder -
a stash of food to see it through the cold, dark winter.
Any extra sugars that the plant doesn't need to use immediately
are instead used as building blocks to make larger starch molecules.
Starch is insoluble, meaning it doesn't dissolve in water.
This makes starch much better than glucose for storing energy.
If potatoes weren't so starchy, they would draw in lots of water
from the soil, and all that precious food energy would be lost.
Every single potato is like a power cell for the plant,
packed to bursting with starch molecules.
And that means it's full of energy.
The potato uses its stored energy to grow a new plant in spring.
We use it for food.
I know when you taste a potato, you don't think of the energy,
but have a little look.
I'm going to put a couple of teaspoons of starch
into this bit of piping, and then blow it across a naked flame.
See what happens.
What you saw there was the energy being released
in just 30 or 40 kilocalories of starch.
The average potato contains around 150 kilocalories,
so about ten potatoes a day
would supply almost all the energy you need.
It's no surprise that lots of our most important foods
come from plants that are rich in starch.
As well as potatoes, these include grains like rice, barley and wheat.
Hidden in the ears of wheat
are the tiny grains that we use to make flour.
These are actually the plant's seeds.
They're packed full of starch and protein -
all created from the glucose the plant makes during photosynthesis.
So why do plants need to store energy inside their seeds?
Seeds are nature's way of ensuring that plants survive
into the next generation - but what exactly is a seed?
Seeds come in lots of different shapes and sizes,
but within every single one of them, new life has already been created.
This is a broad bean pod.
If I open it up, you find these.
These beans are all actually little seeds.
If I cut open the protective coating...
..and take a little look inside...
This little bit up here is the embryo - it contains all
the genetic information the seed needs to become an adult plant.
All the rest of the bean is the endosperm -
it's a package of energy
to support it on the first stage of its journey.
Given a very precise combination
of the right temperature and enough water,
the seed will germinate
and the plant starts to push up in search of sunlight.
Each bean contains about 1 kilocalorie -
the energy it requires to reach the surface.
Under optimum conditions,
it can grow at a speed of 3cm a day.
So, when farmers sow their crops at the start of the farming year,
each seed goes into the ground with its own store of energy.
But from day one, it's also crucial that farmers get things right.
If they plant their seeds when the ground is too cold
or too dry, they won't germinate.
From the minute they sow their seeds,
farmers must understand exactly what their crops need
to ensure a good harvest.
To produce seeds, plants need to reproduce.
And that's where pollen comes in.
Each microscopic grain carries the male reproductive cells of a plant.
For a plant to reproduce,
its pollen must reach the female parts of another plant.
The trouble is, plants can't really travel,
so finding a suitable mate can be pretty tricky.
And that's why lot of plants rely on animals to act as go-betweens.
To attract animal pollinators, plants entice them
with dazzling displays of flowers, rich with nectar and scent.
Birds, insects, and even mammals feed on the nectar,
and in return provide an invaluable service.
Flowers contain both male and female parts.
If you look at this beautiful lily, you'll see that up here,
these yellowy-brown things, these are called the anthers.
They're utterly drenched in pollen.
The anthers are the male part of the flower.
They stick out, so that any visiting creatures are sure to get
a thorough coating of pollen -
pollen they will then carry to the next plant.
Hopefully it will drop some of that pollen onto this part here -
the stigma, which is the female part.
And when the pollen drops there,
it travels all the way down to the bottom, to the ovaries.
Once it reaches an ovary, the pollen fertilizes an egg -
the flower can now develop seeds.
And with that, the plant has successfully reproduced.
in some plants, the flower will develop into a fruit.
The fruit will only start growing once the plant has reproduced.
So the huge variety of fruit that we eat wouldn't exist
without the help of animal pollinators.
On some large-scale fruit farms,
there are so many trees that an army of insects is needed to do the job.
There just aren't enough bees locally, so at this cherry farm
in Herefordshire, they import bumblebees by the box-load.
These bees are specially bred to do this.
We've relied on bees to pollinate our fruit trees for hundreds
of years, and they're every bit as important today.
Without insects like bees, there'd be no fruit.
And it's not just our fruit trees -
75% of all the crops we grow rely on animal pollinators.
Plants create fruits for one very simple reason -
to spread their seed as far and wide as possible.
The tasty fruit tempts animals to eat it.
The seeds inside the fruit pass through the animal's gut,
and are deposited far away from the parent plant.
But creating that fruit requires
a huge investment of energy for a plant.
That apple contained over a tablespoon of sugar,
which the plant had had to painstakingly create
So plants won't give up their fruits
until the seeds inside them are ready.
And that's why unripe fruit is so unappealing.
These unripe apples are dry and sour.
They are packed with carbohydrates,
but they haven't been broken down into the sweet sugars we can taste.
Until they ripen, most fruits are green,
so that they're well-camouflaged within the plant.
But once they are mature,
the plant produces a syrupy-smelling gas called ethene.
This causes the fruit to become sweeter, darker
and much more appetising.
For the plant, this is the potential for a future generation.
But for us, it's a food
packed full of flavour and essential vitamins.
Once the fruit is ripe,
at harvest time, it's a real mission to get it picked before it goes off.
Cherries are a delicate fruit and need treating with care,
so it all has to be done by hand.
Fresh from the trees, they're brought here, to the pack house.
They're chilled, washed and sorted into different sizes
before being packed into punnets and shipped off to our supermarkets.
From tree to table is a very speedy process.
But strangely enough, the success of the cherry harvest starts
way back in the depths of winter.
Snow in January is great news for our fruit farmers.
It might not look like it, but inside the trees,
there's actually a lot going on.
The trees need the cold of winter
so that they can flower in spring, and then fruit in summer.
If they don't get enough chilling time, they might not fruit at all.
And it's not just about cherries.
All our fruit crops need to go through the cold of winter
if they're going to produce fruit.
So what's actually going on?
Well, it's all to do with the fact that plants really do feel the cold.
When the trees lose their leaves in winter, they become dormant.
That's because they are genetically pre-programmed to shut down.
But what is it that causes the tree to wake up again?
It's all down to a mysterious process called vernalization.
Take this apple tree.
It's only when the plant gets cold for a prolonged period of time
that another set of genes is activated -
and this begins the long process of preparing the plant for spring.
It's a bit like the plant's internal clock is being re-activated.
The long cold of winter triggers the release of hormones,
which kick-start the plant into flowering, and eventually to fruit.
To make an apple, the tree must endure around 700 hours
of temperatures colder than 7 degrees.
Without that, it simply won't flower as well when the weather warms up.
The success of the harvest will always be affected by the weather.
But farmers are constantly coming up with more and more clever
ways of controlling the environment to produce more, and better food.
Good job too.
As farming gets ever more high-tech,
some of our crops lead a really pampered lifestyle.
Polytunnels were first introduced to British farming 20 years ago.
They protect our crops from the worst of the weather.
Inside, it's possible to control the conditions.
These strawberries aren't grown in soil at all,
they're actually sitting in ground-up coconut shells.
They get all the water and food they need through a network of pipes
The amount of nitrogen, potassium,
and phosphorus is carefully measured to make the healthiest plants.
And to grow the very sweetest, plumpest fruit.
So by controlling the environment that they're grown in,
our farmers can increase the amount and the quality
of the fruit and veg that they grow.
Hmmmmm. That is fantastic.
But some farmers have taken it one step further,
and they're experimenting with even wackier techniques.
Miniature-sized versions of everyday veg are a real
favourite at fancy restaurants.
But how do you grow tiny vegetables?
Basically, it's all about density.
The plants are squashed together, with nearly 800 in a square metre.
Provided with the ideal conditions, they take just five weeks to grow.
And it's not just about the size.
Researchers have found that growing vegetables under red lights
speeds up photosynthesis, making them grow faster.
If red light is combined with blue light,
it also speeds up root growth.
And that can alter the taste,
and even make the vegetables better for you.
But in actual fact, our farmers have been experimenting
with how to make better food for thousands and thousands of years.
And to do that they have to understand
the process of natural selection, and then speed it up.
Natural variation in plants is down to chance.
Everything about them
is constantly being changed and refined by evolution.
Sometimes a mutation happens by chance that means a plant
is more likely to survive.
If you have a gene that makes you taller than your neighbours,
you'll get more sunlight, and so you're more likely to thrive.
Natural selection is a lengthy process.
But through artificial selection, farmers can speed things up
by selecting the characteristics we like best.
Mange tout peas are usually green.
The plant's genes act like an internal instruction manual,
telling it to produce a green pod.
But what if there's a chance mutant?
A random plant with purple pods,
and it's the purple colour that I want to keep?
By cross-pollinating the flowers of the purple pea plants with
those of other plants, it's possible to help it reproduce.
So we can artificially spread the genes of the purple pods around.
This increases the chances of purple offspring.
It's a painstakingly slow process
because you have to do this again and again over generations of peas.
But eventually most of my crop should be purple.
Farmers have been selecting plants with the characteristics
we want since farming began,
making them easier to grow as well as producing
a better end result.
Fruit that's sweeter.
Cereals that produce more grain,
or vegetables that are less vulnerable to pests and diseases.
Walk through a field of wheat today
and the crop stands less than a metre tall.
That's very different from the shoulder-high wheat that
farmers grew thousands of years ago.
And that's because farmers have artificially selected
for shorter wheat.
As well as being easier to harvest, it's less likely to be
damaged by bad weather, and creates less waste from the stalks.
So experimenting with new techniques to improve our food
is nothing new.
But there's one thing that really has changed the way
we grow our food in the last hundred years,
and that's the rise of the mega machines.
There's one machine in particular
that's completely changed the way we farm.
The combine harvester.
The first self-propelled
combine harvesters were only introduced to Europe in 1952.
Before that, wheat was harvested in pretty much the same way we'd
done it for thousands of years - by hand.
It took a lot of people power to bring in the harvest,
and the whole community had to pitch in.
But what once relied on an army can now be done with one machine.
This combine harvester has an eight-metre knife section
on the front, which makes around 1,300 cuts per minute.
It can harvest an area the size of a football pitch
in less than ten minutes.
But the real beauty of the combine is that it combines the job
of cutting and threshing the wheat, and that's how it got its name.
Inside the machine,
a set of centrifugal rotors
separate the grain from the rest of the plant.
The grain is collected behind the cab,
and the stems are spewed out the back.
Processed grain is ready
within seconds of the crop being cut.
Because they're so quick, and so efficient, machines like the
combine harvester make it possible to farm on a much bigger scale.
The innovation in the way that we farm never stops.
We'll keep on experimenting,
keep designing new and more efficient machines,
and who knows how we'll be growing our food in centuries to come?
What fascinates me about farming is this extraordinary
combination of technology, chemistry,
the magic of photosynthesis,
and the care and the love the farmer has to show to the crops.
And there lies the secret behind the food on our plates.
Subtitles by Red Bee Media Ltd