Every day 11.5 million of us take packed lunches to work or school.
But how many of us actually think about what's going on with the food that ends up in our lunch boxes?
What is the difference between a cake and a biscuit, other than the way they look?
Just the way they're processed, I guess.
A biscuit's hard.
Why do you reckon you don't see cucumbers like this in the supermarket?
Far too big. That's too big, you think.
That one's completely wrong. Completely out of joint that one.
What do you reckon the connection is between this slime,
a rotting cabbage and a very popular supermarket food?
I'm pretty sure I don't want to know.
I'm going to reveal the secrets in the packed lunch box...
Food Factory style.
MUSIC: "Rubber Biscuit" by The Chips
There are thousands of products to choose from in the supermarket
but most of us wouldn't have a clue what goes into making them.
So I've set up my own food factory inside this barn, to find out what they're doing with our food.
It may look as though it's full of junk, but it's got everything I need
to discover the secrets of supermarket food.
If you decide on a carton of fruit juice for your packed lunch,
there's so many to choose from.
Freshly squeezed, from concentrate, not from concentrate,
with bits, without bits!
But what's really in your fruit juice?
I want to see how many sugar lumps
you think represents the amount of sugar in each glass.
Two? One sugar lump there.
What have you got there? Ridiculous amount.
More sugar than apples.
There are five sugar lumps in cloudy.
In one glass? And there's five in clear.
Oh, the same.
Really?
Boil down a glass of apple juice
and this charred pulp is what's left behind.
Let's taste a bit.
And you see the glistening on the surface, well, that's the sugar.
It's naturally occurring fruit sugar
but there's about the same amount of calories in fruit juice
as there is in a fizzy drink.
Concentrated apple juice is identical to freshly squeezed when it comes to sugar and calories.
So what is the difference?
And why is it cheaper than other apple juices?
What are the factories up to?
Well, to find out, I'm going to make my own.
Here in the barn, I've got everything I need to squeeze out
the Food Factory secrets of apple juice made from concentrate.
Now, the main ingredient of apple juice is of course, apples.
All I've got to do is chop them up.
I could stick them in a juicer but I'd be here all day.
I need to make apple juice on an industrial scale.
This will do the job.
I'm going to chop my apples with a lawnmower and catch the bits in this box.
Let's see if it works.
Apples away!
JIMMY LAUGHS
The factories don't have lawnmowers but they do use lots of sharp rotating blades.
Look at that apple. Beautifully chopped.
All I've got to do now is press it.
To get at the juice, I need a sheet of muslin and a mangle.
I'll wrap up my chopped apples and then squeeze them between the rollers.
The juice will collect in this bucket.
Looks more like vinegar.
This set-up lets me shift lots of apples
just like the factories, and produce bucket loads of juice.
In the UK, we drink 185 million litres a year.
Have a look at that!
There's loads of it!
It does look like muddy water,
or I've been peeling some potatoes in here.
Let's pour some out.
So that's freshly squeezed.
But I want to make the "from concentrate" stuff and that's usually clear.
So I've used filter paper.
Let's have a look.
It's clearer.
It's not crystal clear, but it's not that muddy, muddy sort of apple juice we had before.
But what I'm going to do now is concentrate it, and I'm going to do that by evaporation.
Now as the apple juice heats up, it smells wonderful, really appley!
But that's the problem.
I'm losing all that aroma, the very essence of the apple, into the air.
What a waste. To stop it escaping,
some juice geniuses found a way to capture that appley-ness.
They use something called a steam distiller.
My version is a kitchen pedal bin.
There you go, this is what you call a has-bin.
On top of my bin goes a length of copper pipe.
It'll attach to a clever bit of kit I've got inside.
Hopefully they'll trap the essence of the apples.
The leftover mush from the mangle might lack the juice
but it still has the flavour.
So it goes onto these shelves
and I've attached a couple of wallpaper steamers.
Now the steam is going to rise up through my bin
through the layers of apple.
And then it'll travel through this copper pipe,
hopefully carrying all that lovely essence of apple,
until it reaches this chamber.
Now in this chamber are a series of copper pipes that have
cold water running through them and that will make it condense.
All that steam will condense, just like the hot steam in your bathroom condenses on the cold mirror.
Then it trickles down here and collects in the jug,
and what I should be left with
is some water that's laced with apple essence.
Here we go, first little drop, just arrived there.
There we go, look at that!
Right, let's have a look at this!
Really excited about this.
You know it does... it does smell appley.
I'm adding those intense applely flavours back into the juice which has been boiling away.
So why evaporate the water in the first place?
The answer is money.
By concentrating the juice it's cheaper to store and transport around the world.
There we go, I've made apple concentrate!
But the crazy thing is that having gone to all that effort to get the water out,
I've now got to put it back in.
So I'm adding enough water to turn it back to its original strength.
The water only gets added when the concentrate reaches its destination.
So does THIS affect the taste when compared to the freshly squeezed juice I made earlier?
It's a bit like gravy.
Oh, that's lovely, it's not too sharp.
It's got a lovely sweetness to it and it's a really rich apple taste.
Next, is my clear apple juice.
Believe it or not, made from concentrate.
I mean, it's not really clear, is it? Let's have a little taste.
That is definitely apple-flavoured water.
It hasn't got that richness of the apple juice there,
the really cloudy one, but it's not bad, not bad at all.
But I've got to say, out of both of them, it's this one I prefer.
Both have the same ingredients, apples.
It's how the manufacturers transport the juice
that makes the difference.
That's why concentrate is usually cheaper than its freshly squeezed cousin.
There we go - my very own apple juice made from concentrate.
No packed lunch is complete without a nice slice of cake or a biscuit.
Now to me, they look completely different
but would you believe there was a huge legal battle to sort out the difference between them?
What's the difference between a cake and a biscuit?
Aren't biscuits cooked twice?
Perhaps you can dunk these and you can't dunk these.
You could try and dunk a cake. It would make a mess.
I've watched QI, you see, so I know. Oh, have you, go on.
Cakes go hard when they're stale and biscuits go soft.
Oh, perfect, you're an expert.
He's right.
But why do cakes go hard when they're stale,
while biscuits go soft?
I've come to one of Britain's biggest biscuit factories to find out.
It's home to one of the nation's favourites, the custard cream.
It's Matt Brophy's job to make sure they've got their crunch.
The thing about custard cream, is the custard in the middle. How do you make the custard?
There's no custard in the custard cream.
No custard? So you've been lying to me all these years!
THEY LAUGH
No custard! That takes the biscuit.
As it turns out, quite a lot of biscuit.
The dough is made from, flour, sugar, oil and biscuit crumb,
recycled biscuits from the production line.
So this is the dough after mixing for 30 seconds? Let's have a look at it.
As you can see it's very, very dry.
Cor, it is dry! It's very flaky.
I had some sort of visions of a lovely big old mixing bowl,
like, you'd want to lick the bowl. Very different to a cake, very dry.
You wouldn't want to lick this. Your tongue would disappear, take all the moisture out of it.
This dough is as dry as dust, but that won't stop it
getting the classic custard cream stamp of approval!
So what would happen then, if that mix was a little bit more moist?
If you get too much moisture in what happens is the dough becomes too stretchy.
We don't want it to be stretchy, we want to keep the shape of the biscuit.
And also if it's too moist, it sticks inside the mould. Look at them, there's millions!
You're sure they're not just the same biscuits going round and round? No, every one's a new one!
So how do you give your custard cream its crunch?
Each biscuit treks 80 metres through a blazing hot oven.
I can feel its getting hotter and hotter, it's incredible!
Like a sauna.
How much moisture is in the mix before they go in the oven?
Starts off at 14% when they are in the dough stage,
by the time it's been through the oven it's been dried down to 2%.
How do you test, is it done by tasting? No, it's more scientific than that, we use infrared.
Moisture absorbs infrared light.
So biscuit boffins shine it onto a crushed up biscuit.
Then they see how much infrared is reflected back.
And the computer works out how moist the biscuit is.
Close to 2% is what they want.
So 1.71.
That's an ideal level, that gives us a good snap on the biscuit and a good crumbly texture.
And the kind of biscuit you want to dunk in your tea.
Once the biscuits are cooked they take a trip around the factory to cool, but it's not over yet.
What's a custard cream without the cream?
Now, you can't fool me.
Cream, it's soft, it's wet,
it's going to put moisture in the biscuits. There's actually no water in here. It's a dry mix.
It's made up of vegetable oils, sugar, and some flavourings.
So the secret is to make the cream soft, but in a way, it's still dry.
And that keeps your biscuit nice and crunchy. It does.
At last it's time to introduce the biscuits to the cream.
Here, 250,000 biscuits an hour meet their other half.
It's custard cream speed dating!
So you've spent all this time and trouble keeping your biscuit dry,
even the cream you put in doesn't make it go soggy.
So why does a biscuit go soggy?
Because it's so dry,
it absorbs any moisture that's in the atmosphere.
If there's moisture in the atmosphere, it sucks it into the biscuit.
It's almost like the biscuit is thirsty so it has a drink. It does.
So a biscuit gets soggy because it absorbs moisture from the air.
But a cake goes hard because it contains more moisture than the air.
As this evaporates, the cake dries out.
So that's why cakes go hard and biscuits go soft.
But Matt's biscuits could still end up going stale if he doesn't get them wrapped quickly.
These ladies, they don't count these biscuits, but each time they know exactly how many to put on.
Hours of practice. Fancy having a go?
It makes me quite nervous.
Come on, Jim, get in there.
It's too hard!
Does your sarnie look a sorry state without a dollop of mayo?
Well, mayo is about three-quarter's fat
and one spoonful has about the same amount of calories as a packet of crisps.
But then there's this stuff, "extra light" mayonnaise with just 3% fat.
A spoonful of this is the calorie equivalent of a couple of crisps.
Would you know which is which just by the taste?
We've got two different mayonnaises here, now one is your regular, that's 77% fat,
and the other one is a low fat at 3% fat.
I want you to tell me which one is the low fat one.
You can always tell low fat.
It's usually disgusting. JIMMY LAUGHS
I think that one's the low fat one. You're dead right.
I reckon that one's got the most fat. I reckon that one.
You reckon that one, you reckon that one.
Well, the one that you thought was low fat was actually the normal one.
Cool, I'm more of a salad cream man myself!
So it turns out it isn't that easy to tell the difference between low and full fat mayo.
So how can food manufacturers cut out so much fat and still end up with something mayonnaise-y?
And what do the factories put in instead?
Well, to shed some light on extra light mayonnaise, I'm going to make my own.
Making normal mayonnaise is easy.
Got a little bit of vinegar, that goes in.
Then some egg yolks, mustard...
and a whole jug of oil.
Mix it all together.
How's that for a mixer?
On their own, these ingredients don't sit well on a sarnie,
but whisk them together and they're transformed into silky smooth mayonnaise.
Now oil is an important ingredient in mayonnaise,
but if I want to make light mayonnaise
what can I substitute it with?
Well, the answer's simple...water!
Let's have a go.
The ingredients are almost the same as before.
The big difference is that most of the oil has been replaced with calorie-free water.
Look at this, totally different.
It's more like a milkshake.
Really thin, really runny.
Now the mayonnaise went nice and thick because the oil and the vinegar all stuck together.
But this, look at that.
I couldn't put that on a sandwich.
Using water instead of oil is great news for us, but hard work for the factory.
They still have to fake the consistency of fat, somehow.
Now this is a lovely fresh cabbage,
but when a cabbage begins to go off and become rotten
you often see lots of little black spots appearing that are slimy,
and believe it or not it's that very slime that food manufacturers use to thicken mayonnaise.
That slime is called xanthan gum.
It's made by Xanthomonas campestris bacteria that eat cabbage leaves for breakfast.
It doesn't really taste of anything, but it just feels like wallpaper paste. Ooh!
But I'm not bothered about the taste.
It's texture that matters here.
Xanthan gum has a consistency that's similar to oil.
As disappointing as it may seem, mayonnaise factories don't rely on rotting cabbages.
They use the slime from xanthan bacteria that's been especially grown.
And that's what I'm going to do.
I'm putting together what bacteria boffins call a bio-reactor.
Right, a few more holes.
In this vat will go lots of bacteria,
all keen to make that gooey xanthan gum.
There we go, that works a treat.
Now that's my stirring paddle which is being powered by the motor from an ice cream maker.
Now inside the box will go water and my bacteria and they'll be kept
lovely and warm with these little heating elements here.
Hopefully, I should end up with lots of bacteria and lots of slime.
The first step is to sterilise my bio-reactor.
I'll do that with steam power.
Right, time to switch the steam on.
This should kill off any rogue bugs.
Then in goes the food.
A bacteria-licious cocktail of sugar and yeast extract.
Right, now it's time for my xanthan bacteria.
They've been grown under sophisticated laboratory conditions,
so let's see how they get on in my box.
I reckon you'll be all right.
Right, let's close the lid... and turn on the motor.
It'll take a couple of days for these bacteria to produce the slime
and then they're going to help us make some mayonnaise.
Right, get to it.
There we go, I've got a nice bit of ham, some lettuce,
all I need now is some cucumber.
These weird looking things don't look like the ones you see in the supermarket.
So, would you buy one?
What do you go for? Are you straight or curly?
I'm straight!
Why do you think people choose straight cucumbers over curly ones?
Because it looks nicer and it'll taste better.
It's because that's what they're used to.
That's what supermarkets have. Probably easier to slice.
That's a good idea. So you don't have to go round a corner? Yes!
If you want to know about growing cucumbers,
well, this is the place to come.
This is a monster greenhouse.
It's the biggest cucumber glasshouse in Britain.
Rob James is the man who has to keep all these cucumbers
on the straight and narrow.
Wow, this is incredible. How big is this greenhouse?
This is over six hectares with 185,000 cucumber plants.
That's a lot of cucumbers.
Massive greenhouses like this one, producing straight cucumbers,
are the reason you don't see crooked ones in the shops.
But how bent is too bent in the straight-up world of cucumbers?
There's a very simple test.
If you can get your hand under it, it's too bendy.
Depends how small your hand is. Get me hand under it. That's too bent.
There's one that's just about OK.
Right, that's marginal, that's definitely too bent. OK.
But if you...
Taste it.
Tastes exactly the same as the straight ones.
Only problem with it, it's bent.
It seems crazy that perfectly good cucumbers
never make it to our sandwiches just because they're bendy.
So what stops them growing straight as a die?
One of the things that can affect it is a pest.
And that's the kind of thing that can happen.
So one bite leads to a wonky cucumber.
In there, there's been some damage, the cells have died.
That part of the cucumber has not grown, whereas the rest has carried on growing.
So a little critter has bitten into this and caused it to bend. Can we find the culprit?
I don't think you'll find the culprit because we do everything we possibly can to make sure they are not here.
We employ an army of thousands and thousands of good bugs to eat the bad bugs.
This is one of the good bugs.
Amblyseius swirskii devours the bad bugs by piercing their skin and sucking out their innards.
Harsh, I know, but it's exactly what the bad bugs do to these cucumbers.
It's like having a little squad of assassins that go out
and clear up all your pests.
Rob and his squad of good bugs do a great job.
Right, all aboard.
But hungry bugs aren't the only things that can send a cucumber round the bend.
Rob's cucumbers need to be positioned perfectly.
If something gets in the way of the growing cucumber it'll go bendy,
and here's one, its just got caught,
on the stem below. How bad does the bending problem become?
We don't let it become a problem.
What we do here, the plant is trained, in a V.
All the plants are in the middle, so the idea is the cucumbers hang down vertically unobstructed.
If the vine is hanging like that...
The cucumbers will drop down here.
But if it's like that, the cucumbers will hang in-between the leaves.
So it's all about the angle of your dangle? The angle of dangle is very important for cucumbers.
Rob reckons that only four cucumbers in 100 are rejected by the supermarkets.
But he can encourage his cucumbers to be less straight-laced by growing them in a special mould.
Slice straight through?
Look at that!
Brilliant for sandwiches on Valentine's Day. Look at that.
That's absolutely perfect.
There you are, Rob, I give you my heart.
You didn't have to eat it!
Back at the barn, I'm making low fat mayonnaise.
I've replaced most of the fattening oil with water but, no surprise, it's a bit runny.
In the factory they thicken it with slimy xanthan gum.
Hopefully that's what's growing in my home-made bio-reactor.
Right, it's been a couple of days since I left my bioreactor to do its thing. Let's have a look.
Ooh, it's a bit different.
It's looking a bit like chicken stock.
Oh, hang on. There's something in here that shouldn't be in here.
There's a fly in my soup.
If a fly can get in, then so can all sorts of nasties.
It seems my xanthan bacteria have been killed off.
There's no slime here at all.
It's all down to you, little fly.
That's two days wasted.
Right, time for a good clean down.
Time for Plan B.
I've bought some xantham gum from a professional food supplier.
But on its own it's not enough to make low fat taste full fat.
For that you need another intriguing ingredient.
It's called citrus fibre, and it's made from the pulp of oranges.
It feels a bit like melted fudge
and it's really good at absorbing water
and it's used as a thickener.
And when it's used as an ingredient
it sort of feels like fat in your mouth
and that's why food factories absolutely love this stuff.
Right, let's pop it in here.
A bit of water...
A little bit of Brenda the blender.
# Brenda, my love,
# I keep on telling you
# Brenda, my love
# Brenda, my love. #
Now you wouldn't believe that this has come from oranges that have just been mixed with water.
Look how thick it is!
And in this bucket I've another food thickener, starch.
It looks more like I'm going to be doing some decorating than making mayonnaise, look at it.
My challenge is to turn these buckets of yucky ingredients into luxurious mayo.
This time, the low fat kind.
First in, my xanthan gum,
then it's in with my starch.
It's like a big blob.
Last of the bucket ingredients is the citrus fibre.
Right, well it's definitely beginning to look like mayonnaise,
but it's missing all the normal ingredients.
A tiny amount of oil, in that goes.
Next on the list, eggs...
..mustard, vinegar, and water.
Here we go, that's the most mayonnaise I've ever seen, ho!
Look at that!
Well, it's certainly got the colour of the mayonnaise, it's a little but thin.
Let's have a taste.
Now vinegar comes through and at first you think,
oh, that tastes like mayonnaise.
And then some of the other ingredients come through and then you think,
it's got a funny sort of earthy taste to it.
But you could just about get away with calling that low fat mayonnaise.
There we go. My very own extra light mayonnaise.
It looks the part but what will they think down on my farm?
Don't know whether it's the lettuce or the mayo but it's a bit bitter.
It is quite vinegary. But it is nice.
It's a bit like salad cream.
So out of ten what would you give me?
Five. Seven. I'll have it back!
Seven. Seven, that's not bad.
I don't like mayo!
What are you eating that for? You told me I had to!
Fake fats take the calories out of mayo
and the difference between a cake and a biscuit is water.
It seems to me our packed lunches are packed with secrets.
Subtitles by Red Bee Media Ltd
E-mail: subtitling@bbc.co.uk