NARRATOR: HOW OFTEN DO YOU STOP AND REALLY THINK ABOUT YOUR FOOD?

WHY DOES IT TASTE THE WAY IT DOES?

AND HOW DOES IT AFFECT YOUR BODY... AND YOUR MIND?

IN SEARCH OF ANSWERS, TWO EXPERTS WILL TAKE YOU ON A GLOBAL CULINARY ADVENTURE.

MEDICAL DOCTOR MICHAEL MOSLEY... LOTS OF [SNIFFS] LOVELY AROMA MOLECULES THAT I'M NOT HUNGRILY HOOVERING UP.

NARRATOR: AND BOTANIST JAMES WONG...

THERE'S NOTHING COMING OUT HERE.

NARRATOR: WILL DISCOVER THE HIDDEN SCIENCE IN EVERY MOUTHFUL.

WONG: AND IT IS INCREDIBLE.

IT'S LIKE EATING IN TECHNICOLOR.

NARRATOR: THIS TIME, THEY'RE ON A MISSION TO REVEAL HOW THE BRAIN IS AFFECTED BY OUR FOOD... NOW I'M GETTING SENSORY OVERLOAD.

NARRATOR: HOW OUR MIND SHAPES OUR EXPERIENCE OF WHAT WE EAT... MICHAEL: LIFE AND SOUL.

NARRATOR: WHY WE CRAVE SOME FOODS... THAT IS TRULY DELICIOUS.

NARRATOR: YET FIND OTHERS CHALLENGING AND ULTIMATELY, WHY OUR FOOD HAS SUCH A POWERFUL HOLD OVER US.

MICHAEL: THIS IS DELICIOUS SCIENCE.

MICHAEL: WE HUMANS ARE PECULIAR.

WE EAT FOODS NO OTHER ANIMAL WOULD EAT.

NARRATOR: ON AVERAGE, WE SPEND 67 MINUTES A DAY EATING, WHICH OVER A LIFETIME ADDS UP TO NEARLY 3 1/2 YEARS AT THE TABLE.

BUT WE SPEND EVEN MORE TIME THINKING ABOUT FOOD.

WHEN WE'RE HUNGRY, FOOD BEGINS TO DOMINATE OUR THOUGHTS, AND, OF COURSE, OUR BRAINS.

AND WHAT'S REMARKABLE IS THAT WE'RE BEGINNING TO UNDERSTAND EXACTLY WHY CERTAIN FOODS CREATE SUCH CRAVINGS IN US ALL.

TO START, MICHAEL'S GOING TO GET A MEASURE OF HOW MUCH OUR BRAINS LOVE OR HATE A PARTICULAR FOOD.

RATHER THAN EAT, HE'S GOING TO USE SIGHT AND SMELL ALONE TO MEASURE SOMETHING WE CAN'T STOP OURSELVES PRODUCING-- SALIVA.

SO WHAT I'VE GOT HERE IS A LITTLE SWAB, AND IT WEIGHS 0.68 GRAMS.

PUT THAT IN THERE.

AND I'VE GOT WHAT I'M TOLD IS A DELICIOUS MEAL UNDERNEATH HERE.

SO, LET'S HAVE A LOOK.

IT DOESN'T SMELL DELICIOUS, I HAVE TO SAY.

OH, GOD!

THAT'S REVOLTING.

UGH.

[COUGHS] THAT LOOKS COMPLETELY RANCID.

I HAVE NO IDEA WHAT IT IS.

NARRATOR: THIS IS ACTUALLY A DELICACY IN CHINA.

IT'S A PRESERVED EGG CALLED A CENTURY EGG.

IT REEKS OF AMMONIA AND HYDROGEN SULFIDE, THE SMELL OF ROTTEN EGGS.

SO WHAT WILL THE SALIVA TEST REVEAL?

IN THEORY, THE MORE MICHAEL LIKES THE FOOD, THE MORE HE SHOULD SALIVATE.

SO LET'S SEE WHAT AFFECT THAT HAS HAD ON MY SALIVA.

UH, 0.88.

SO IT'S GONE UP A LITTLE BIT.

I THINK THAT WAS IN ANTICIPATION OF SOMETHING WHICH TURNED OUT TO BE UTTERLY REVOLTING.

NARRATOR: TIME FOR A FRESH SWAB AND A SECOND DISH.

RIGHT.

DISH NUMBER TWO, WHICH I'M ALSO TOLD IS DELICIOUS, ALTHOUGH BY NOW, I'M DEEPLY SUSPICIOUS.

[SNIFFS] SMELLS BETTER ANYWAY.

OK, WHAT IS IT?

AND IT IS CHOCOLATE CAKE.

HURRAH!

[SNIFFING] NOW, YEAH, THAT SMELLS NICE.

AND I THINK I CAN FEEL THOSE SALIVA FLOWING.

LET'S SEE IF IT HAS ANY MEASURABLE EFFECT.

YEP.

WE ARE UP TO 1.83 THIS TIME, SO LOTS OF SALIVA THERE.

NARRATOR: FOR ONE OF HIS FAVORITE FOODS, CHOCOLATE, MICHAEL PRODUCED ABOUT 6 TIMES AS MUCH SALIVA.

SO THIS SHOWS JUST HOW MUCH THE LOOK AND SMELL OF FOOD ALONE CAN FIRE UP OUR BRAINS AND JUICE UP OUR SALIVARY GLANDS.

BUT WHY DO WE DO IT?

WELL, PRODUCING SALIVA HELPS US START DIGESTING OUR FOOD THE MOMENT IT REACHES OUR MOUTHS.

THAT'S BECAUSE SALIVA CONTAINS DIGESTIVE ENZYMES.

AND IT'S PERHAPS NO SURPRISE THAT MICHAEL DROOLED OVER CHOCOLATE, BECAUSE THE CHEMISTRY OF CHOCOLATE MAKES IT THE WORLD'S MOST CRAVED FOOD.

IN THE U.S., WE EAT AN AVERAGE OF ALMOST 10 POUNDS OF CHOCOLATE EVERY YEAR.

THE MERE SIGHT OF IT MAY BE TRIGGERING FEELINGS OF DESIRE IN YOUR BRAIN RIGHT NOW.

BUT JUST HOW DOES IT CREATE SUCH STRONG CRAVINGS?

JAMES HAS COME TO PERU TO DISCOVER HOW WE TRANSFORM CHOCOLATE FROM RAW, BITTER BEANS TO BARS OF DELICIOUSNESS.

HE ALSO WANTS TO UNDERSTAND EXACTLY WHY WE CRAVE IT SO MUCH.

IT'S ESPECIALLY STRANGE BECAUSE IN ITS RAW STATE, THE COCOA PLANT IS NOT AT ALL WHAT WE WOULD EXPECT.

WOW, LOOK AT THAT.

YOU BREAK OPEN THIS BIG HUSK, AND YOU'VE GOT THIS STICKY, IVORY PULP THAT IS... THAT IS TRULY DELICIOUS.

IT HAS THIS INCREDIBLE TROPICAL FLAVOR THAT'S HALFWAY BETWEEN LEMONADE AND A CUSTARD APPLE, IF YOU'VE EVER HAD THAT.

SWEET, ACIDIC, STICKY.

SORRY FOR BEING GROSS, BUT...

THE BIT THAT CHOCOLATE'S MADE OUT OF IS THE BEAN ON THE INSIDE, IF YOU WERE TO SPIT IT OUT, WHICH--AMAZING THAT ANYONE THOUGHT THAT BENEATH STICKY, SWEET, DELICIOUS FLESH, THE ROCK-HARD, SUPER-BITTER BEAN ON THE INSIDE COULD MAKE GOOD EATING.

NARRATOR: THE PROCESSING OF CHOCOLATE BEGINS AS SOON AS THE PODS ARE OFF THE PLANT.

THEY'RE LEFT TO FERMENT IN THEIR OWN JUICES FOR 3 DAYS, WHERE NATURALLY-OCCURRING YEAST BREAKS SUGAR DOWN INTO ALCOHOL, WHICH IN TURN HELPS REMOVE BITTER ALKALOIDS FROM THE BEANS.

THEN OVER A WEEK THE BEANS ARE DRIED, BUT THEY'RE STILL RAW AND QUITE BITTER, NOTHING LIKE THE CHOCOLATE WE KNOW AND LOVE.

BUT WHAT HAPPENS NEXT WILL UTTERLY TRANSFORM THEM.

THE BEANS ARE PUT INTO A KIND OF OVEN.

JAMES: WHAT THIS DOES IS IT ROASTS THE BEANS, AND THAT'S REALLY KEY TO BRINGING OUT THAT KIND OF TOASTY, WARM, CHARACTERISTICALLY CHOCOLATY FLAVOR.

THERE THEY GO.

NARRATOR: THE HEAT FROM THE OVEN TRIGGERS SOMETHING CALLED THE MAILLARD REACTION, IN WHICH SUGARS AND PROTEINS IN THE BEANS BREAK DOWN INTO HUNDREDS OF NEW CHEMICAL COMPOUNDS.

THIS CONVERTS THE OTHERWISE ODORLESS COMPOUNDS INTO VOLATILE AROMA-BEARING ONES.

JAMES: SO THE ROASTED BEANS STILL GOT THESE VERY FINE, THIN SHELLS ON.

THEY'RE GOING IN HERE, AND YOU CAN ACTUALLY SEE ALL THE SHELLS WAFTING UP.

AND FOR THE FIRST TIME, YOU CAN SUDDENLY SMELL CHOCOLATE.

IT'S--OH, IT'S GOOD.

IT'S REALLY GOOD.

NARRATOR: THE COMFORTING AROMA OF CHOCOLATE ACTUALLY COMES FROM 25 DIFFERENT SMELL MOLECULES, LIKE 3-METHYLEBUTANOIC ACID AND DIMETHYL TRISULFIDE.

SURPRISINGLY, ON THEIR OWN, THEY'RE MORE REMINISCENT OF BODY ODOR AND COOKED CABBAGE.

BUT WITH SO MANY TYPES OF MOLECULES WAFTING OUT OF THE COCOA BEANS AND ASSAULTING OUR NOSES, OUR BRAINS CAN'T SEPARATE THEM OUT.

INSTEAD, ONE COMBINED, GLORIOUS SMELL EMERGES-- DELICIOUS CHOCOLATE.

BUT AROMA IS JUST PART OF THE STORY.

JAMES: COCOA BEANS ARE INCREDIBLY RICH IN FAT.

ROUGHLY, LIKE, 50%.

AND IF YOU TAKE A WHOLE BUNCH OF THEM AND SQUISH THAT FAT OUT AND GET IT TO COOL DOWN TO ROOM TEMPERATURE, YOU GET THIS.

THIS IS COCOA BUTTER.

NARRATOR: COCOA BUTTER IS THE ESSENTIAL FATTY INGREDIENT THAT MAKES CHOCOLATE SO IRRESISTIBLE.

AND IT'S NOT JUST COCOA BUTTER.

THERE ARE MANY DIFFERENT TYPES OF FAT, EACH WITH UNIQUE CHARACTERISTICS WHICH CREATE PURE PLEASURE WHEN PAIRED WITH THE RIGHT FOOD.

IMAGINE TOAST WITHOUT BUTTER, FRYING WITHOUT OIL, OR ICE CREAM WITHOUT, WELL, CREAM.

FAT TRANSFORMS OUR ENJOYMENT OF FOOD FROM DRY TO DELICIOUS, AND FOR GOOD REASON.

BEFORE AGRICULTURE, FAT WAS A CRITICAL SOURCE OF ENERGY.

EVIDENCE SUGGESTS THAT OUR BRAINS HAVE EVOLVED TO REWARD US WITH FEELINGS OF PLEASURE WHEN WE EAT IT.

AND WE KNOW EXACTLY WHERE IN THE BRAIN THIS PLEASURE IS FELT-- REGIONS LIKE THE LATERAL HYPOTHALAMUS AND AMYGDALA.

WE'VE EVEN SEEN THAT THE HIGHER THE LEVEL OF FAT IN A FOOD, THE MORE ACTIVE THESE PARTS OF THE BRAIN BECOME.

MICHAEL'S TRAVELED TO AFYON, TURKEY, IN SEARCH OF ONE OF THE RICHEST, HIGH-FAT, MELT-IN-YOUR-MOUTH DISHES IN THE WORLD.

HE'S HOPING TO DISCOVER JUST WHY THIS TYPE OF FAT HAS SUCH A POWERFUL EFFECT ON OUR BRAINS.

THE FOOD MICHAEL'S INTERESTED IN IS MADE FROM THE MILK OF WATER BUFFALO.

TO MAKE THE CREAMIEST FAT, YOU NEED EXTREMELY RICH MILK, AND TO MAKE THAT, WATER BUFFALO NEED TO EAT SOMETHING PRETTY EXTRAORDINARY.

THESE ARE THE POPPY FIELDS THAT SURROUND AFYON.

AT THE HEIGHT OF SUMMER, THE SEED HEADS ARE HARVESTED FOR THE LEGAL PRODUCTION OF OPIATE-BASED MEDICINES.

BUT THE POPPIES ALSO PROVIDE FOOD FOR THE BUFFALO.

HELLO.

ALONG WITH THE HAY, THIS IS WHAT THESE BUFFALO ARE EATING.

IT'S WHAT'S LEFT OVER WHEN THEY'VE TAKEN THE POPPY, THEY'VE EXTRACTED THE OPIUM, AND SENT IT OFF TO BE TURNED INTO MORPHINE AND OTHER PAINKILLERS.

AND THIS IS REALLY WHAT REMAINS.

THERE'S NOT REALLY ANY OPIATE LEFT INSIDE IT, BUT IT'S SAID TO BE EXTREMELY NUTRITIOUS, AND THE REASON THEY FEED IT TO BUFFALO IS ITS SAID TO ADD TO THE FLAVOR, BUT PARTICULARLY SORT OF THE RICHNESS, THE FATNESS, THE OILINESS OF THE MILK.

[BUFFALO MOOING] ARE YOU GOOD?

NARRATOR: THE POPPY IS PACKED FULL OF NATURAL OILS AND FATS, AND SOME OF THIS ENDS UP IN THE BUFFALO MILK.

JUST GIVE IT A GO.

OK. UHH, NOTHING.

SORRY ABOUT THAT.

YEAH, OK. HEH.

I THINK I'LL LEAVE IT TO YOU.

NARRATOR: BUFFALO MILK IS EXTREMELY RICH.

IT HAS TWICE THE FAT OF COW'S MILK.

MICHAEL: SO HERE WE GO.

THAT'S THE PRODUCT OF A BIT OF HARD WORK.

NOT BY ME, I HAVE TO SAY.

NARRATOR: THIS OILY MILK WILL BE TURNED INTO KAYMAK, A RICH, THICK, AND SWEET-TASTING CREAM OFTEN EATEN AS A DESSERT.

MERHABA.

OH, THIS IS WHERE THE MAGIC HAPPENS.

NARRATOR: MILK HAS A VERY PARTICULAR CHEMISTRY.

IT'S MAINLY WATER AND FAT, WHICH TOGETHER FORM WHAT'S CALLED AN EMULSION.

THE FAT IS DISPERSED THROUGHOUT THE WATER IN TINY GLOBULES.

WHEN IT'S HEATED, SOME OF THE WATER IS EVAPORATED OFF, LEAVING A HIGHER CONCENTRATION OF FAT.

THESE BECOME STICKY, AND SOME BIND TOGETHER TO FORM A DELICATE MESH ON THE SURFACE.

IT'S NOW A MATTER OF LETTING IT SIT AND COOL FOR 10 HOURS.

THE HEATING HAS KILLED MOST OF THE BACTERIA THAT COULD SOUR THE MILK, AND THE CREAM SIMPLY RISES TO THE TOP.

AND THEN, IT IS FINALLY READY TO EAT.

YOU'RE INVITING ME TO DIP MY HAND IN AS WELL.

OK, I HAVE WASHED MY HANDS, I PROMISE YOU.

SO IT'S, UM, LIKE SORT OF A KIND OF SOAP.

I COULD IMAGINE SORT OF, YOU KNOW, WASHING IN IT ALMOST.

IT'S GOT A VERY LOVELY SORT OF SILKY TEXTURE TO IT.

OK, SO I THINK... NARRATOR: KAYMAK IS 60% FAT, AND THE WAY IT FEELS ON THE TONGUE DRIVES OUR BRAINS WILD.

SO, WHAT IS IT THAT KAYMAK HAS THAT OTHER FATS ARE MISSING?

WHY IS IT SO MUCH MORE SEDUCTIVE THAN, SAY, BUTTER?

THE WAY THAT KAYMAK IS MADE, OBVIOUSLY, DETERMINES ITS STRUCTURE, AND ITS STRUCTURE, IN TURN, WILL INFLUENCE WHAT IT FEELS LIKE IN MY MOUTH.

SO LET'S GIVE IT A GO.

THAT IS VERY SMOOTH AND CREAMY.

I CAN FEEL IT FLOWING ACROSS MY TONGUE.

THE EASE WITH WHICH SOMETHING FLOWS IS ALSO KNOWN AS ITS VISCOSITY, AND THAT IS SOMETHING YOU CAN MEASURE.

NARRATOR: THIS MACHINE IS A RHEOMETER.

IT ACCURATELY MEASURES VISCOSITY AT CERTAIN TEMPERATURES AND PRESSURES.

AND VISCOSITY TURNS OUT TO BE THE SECRET BEHIND WHY KAYMAK IS SO GOOD TO EAT.

WHAT IS REALLY STRIKING ABOUT THIS GRAPH IS THE COLLAPSE HERE AT AROUND 24 DEGREES, WHEN IT GOES FROM BEING SORT OF THICK AND SOLID AND TURNS INTO A LIQUID.

WE DID THE SAME TEST WITH ANOTHER FAT.

IN THIS CASE, IT WAS BUTTER.

AND AS YOU CAN SEE THERE, BUTTER BEGINS TO CHANGE AT AROUND 24 DEGREES, BUT IT'S A MUCH MORE GRADUAL CHANGE, AND THAT MAY HELP EXPLAIN WHY BUTTER IS NOT ONE OF THOSE THINGS YOU LIKE TO TAKE OUT OF THE FRIDGE AND SORT OF WOLF DOWN.

NARRATOR: KAYMAK MELTS AND FLOWS MORE QUICKLY OVER THE TONGUE THAN BUTTER, MAKING IT FEEL SMOOTH.

MICHAEL: DIG IN?

NARRATOR: AND IT'S THIS SMOOTHNESS THAT OUR BRAINS RESPOND TO, VIA SPECIAL RECEPTORS ON OUR TONGUES.

SOME KAYMAK.

IF TAKE A CLOSE LOOK AT YOUR TONGUE, YOU'LL SEE ITS COVERED WITH LOTS OF LITTLE BUMPS CALLED PAPILLAE.

ON THE SURFACE OF THESE PAPILLAE, YOU HAVE TASTE RECEPTORS, BUT YOU ALSO HAVE TOUCH RECEPTORS.

NOW, IF YOU EAT SOMETHING WHICH IS FAT, THEN THAT FAT CONTAINS TINY, LITTLE GLOBULES WHICH ARE SO SMALL, ONLY A FEW MICRONS ACROSS, THAT YOUR TOUCH RECEPTORS DON'T PERCEIVE IT AS DIFFERENT PARTICLES.

THEY JUST SEE IT AS ONE THING--SMOOTHNESS.

NARRATOR: SINCE FAT TRIGGERS TOUCH RECEPTORS ON THE TONGUE, WE MIGHT THINK THAT THE SIGNALS END UP IN THE TOUCH REGION OF THE BRAIN, AND THEY DO, BUT THE SIGNALS ALSO AFFECT THE TASTE RECEPTORS, SO ODDLY, THE BRAIN PERCEIVES THE FEEL, THE TEXTURE OF FAT, AS A TASTE, WHICH HELPS TO EXPLAIN WHY THE TEXTURE OF SPECIFIC FATS IS SO IMPORTANT WHEN IT COMES TO CREATING THESE WONDERFUL FEELINGS IN THE PLEASURE CENTERS OF OUR BRAINS.

MICHAEL: CHEERS.

THANK YOU.

NARRATOR: IN MUCH THE SAME WAY AS KAYMAK, CHOCOLATE, WITH ITS HIGH FAT CONTENT FROM COCOA BUTTER, ALSO LIGHTS UP THE PLEASURE CENTERS OF OUR BRAINS.

AND THERE'S ANOTHER INGREDIENT THAT WE HAVE LEARNED TO ADD TO THE MIX THAT SUPERCHARGES THE EFFECT OF CHOCOLATE.

FOR GENERATIONS, THE INDIGENOUS PEOPLE ENJOYED CHOCOLATE IN A BITTER LIQUID MIXTURE MADE FROM THE COCOA BEANS.

BUT WHEN THE SPANISH ARRIVED, THEY ADDED ONE MORE INGREDIENT THAT TRANSFORMED THE DRINK INTO A FOOD THAT WOULD SEDUCE THE WORLD.

THAT INGREDIENT WAS SUGAR.

JAMES: THE ADDITION OF SUGAR TO THIS MIX IS SO CRUCIAL TO OUR ENJOYMENT OF CHOCOLATE, BECAUSE IN NATURE, SUGAR AND FAT ARE VERY RARELY FOUND TOGETHER, AT LEAST IN HIGH CONCENTRATIONS.

NARRATOR: WE CAN TURN TO FRUITS, LIKE STRAWBERRIES, WHICH ARE PACKED FULL OF SUGAR, OR CERTAIN CUTS OF MEAT WHEN WE WANT FAT.

BUT IF WE WANT A MIXTURE OF BOTH IN RELATIVELY EQUAL AMOUNTS, THERE IS ONLY ONE PLACE IN NATURE THAT CAN BE FOUND.

JAMES: IT'S ONLY REALLY IN BREAST MILK WHERE YOU END UP WITH THIS PERFECT FUSION OF 50% OF THE CALORIES COMING FROM SUGAR AND 50% COMING FROM FAT.

NARRATOR: SO OUR CRAVING FOR CHOCOLATE MAY GO BACK TO THE BEGINNING OF LIFE, OUR VERY FIRST MEAL.

JAMES: IF YOU THINK ABOUT ALMOST ALL THE FOODS THAT JUST DRIVE PEOPLE CRAZY-- YOU KNOW, COOKIES, DOUGHNUTS, CHEESECAKE, ICE CREAM-- IF YOU LOOK AT THE RECIPES, ALMOST ALL OF THEM HAVE A ROUGH 50/50 SPLIT IN TERMS OF CALORIES BETWEEN SUGAR AND FAT.

IT'S THAT GOLDEN FORMULA THAT JUST BASICALLY SENDS OFF ALL THE PLEASURE SIGNALS IN OUR BRAIN, MAKING FOOD JUST IRRESISTIBLE.

NARRATOR: IT'S A COMFORTING CHEMICAL COMPOSITION THAT WE'RE BIOLOGICALLY SET UP TO LOVE.

SO WHAT EXACTLY ARE CHOCOLATE AND OTHER FAT- AND-SUGAR-FILLED FOODS WITH THAT MAGIC 50/50 CALORIE RATIO ACTUALLY DOING TO OUR BRAINS?

AND WHY DO THESE FOODS BECOME ALMOST ADDICTIVE?

EVEN AS I LOOK AT ALL THIS LOVELY FAT AND SUGAR, I'M BEGINNING TO DROOL.

NARRATOR: MICHAEL'S OWN WEAKNESS IS THE BRITISH VERSION OF KAYMAK, A RICH CLOTTED CREAM WHICH IS SERVED WITH JAM AND SCONES CALLED A CREAM TEA.

I'VE GOT A LITTLE BIT OF A SHAKE.

NARRATOR: OUR DESIRE TO EAT SOMETHING AS DELICIOUS AS A CREAM TEA AND WHY WE CRAVE IT OVER AND OVER AGAIN HAS BEEN MAPPED IN THE BRAIN.

NOW I'M GETTING SENSORY OVERLOAD.

IT RELEASES A WHOLE HOST OF FLAVORS IN MY MOUTH.

THERE'S ALSO LOADS OF THINGS KICKING OFF IN MY BRAIN.

AND I'LL SHOW YOU HERE JUST WHAT'S GOING ON.

WHAT'S HAPPENED IS THE PLEASURE I GET FROM CREAM TEAS HAS ACTIVATED AN AREA HERE.

NARRATOR: BECAUSE, JUST LIKE WITH KAYMAK, IT ALL BEGINS IN THE AMYGDALA, THE AREA IN OUR BRAIN WHICH IS THE CORE OF OUR EMOTIONAL RESPONSE TO FOOD.

IT IN TURN TRIGGERS THE REWARD PATHWAY, PART OF WHICH IS CALLED THE NUCLEUS ACCUMBENS.

MICHAEL: THIS IS WHERE DESIRE FORMS.

I LIKE IT, I WANT IT, I WANT MORE OF IT.

NARRATOR: THE DESIRE CENTER CREATES THE MOTIVATION TO EAT AGAIN BY ACTIVATING TWO OTHER PARTS OF THE REWARD PATHWAY.

THIS AREA HERE IS WHERE MEMORIES ARE LAID DOWN.

IT'S CALLED THE HIPPOCAMPUS.

MEMORIES ARE BUILDING UP FROM THIS OCCASION, BEING HERE IN A NICE TEA SHOP ON A SUNNY DAY IN LONDON.

NARRATOR: OUR BRAIN CREATES A STRONG MEMORY OF THE PLEASURE OF EATING A DELICIOUS TREAT SO WE'LL REMEMBER IT IN THE FUTURE AND WANT IT AGAIN.

THIS AREA OF THE BRAIN IS DIFFERENT.

IT'S MORE COMPLEX.

IT'S THE FRONTAL LOBE.

NARRATOR: THIS AREA CONTROLS OUR BEHAVIORS AND PLANNING.

WHEN THE DESIRE CENTER SIGNALS TO THIS REGION, IT'S REINFORCING THE SEQUENCE OF BEHAVIORS, THE EXACT PROCEDURE REQUIRED TO GET A HOLD OF A DELICIOUS TREAT.

SHOULD WE SEE ANY ONE OF THESE THINGS AGAIN, WE'LL BE REMINDED OF HOW MUCH WE ENJOYED THAT DELICIOUS TREAT, AND WE'LL KNOW EXACTLY WHAT WE NEED TO DO TO GET ONE AGAIN.

IT'S OUR BRAIN'S WAY OF MOTIVATING US, ENSURING THAT THE PLEASURES WE EXPERIENCE IN THE PRESENT ARE REPEATED IN THE FUTURE.

OF COURSE, A VARIETY OF FOODS CAN TRIGGER THE REWARD PATHWAY, BUT NEW RESEARCH HAS REVEALED THAT COFFEE CAN ACTUALLY MAGNIFY ITS POWERFUL EFFECT.

ON AVERAGE, AMERICANS DRINK A LITTLE OVER 3 CUPS OF COFFEE EACH PER DAY.

PART OF THE APPEAL IS COFFEE'S ACTIVE INGREDIENT--CAFFEINE.

AND SCIENTISTS ARE NOW CLOSE TO UNDERSTANDING HOW COFFEE BOOSTS OUR REWARD PATHWAY BY NOT STUDYING HUMANS, BUT, SURPRISINGLY, BEES.

ALONGSIDE CHOCOLATE, PERU IS ALSO A MAJOR PRODUCER OF COFFEE.

THE PLANT RELIES ON THE LOCAL INSECTS FOR ITS POLLINATION, BUT THEREIN LIES A MYSTERY.

IT SEDUCES POLLINATING INSECTS LOOKING FOR FOOD WITH THE PROMISE OF NECTAR FROM ITS FLOWERS.

BUT IT ALSO NEEDS TO DEFEND ITSELF FROM PESTS, SO ITS CELLS SECRETE CHEMICALS TO KEEP THESE INSECTS AT BAY.

PLANTS CAN'T RUN AWAY AND HIDE FROM THEIR PREDATORS, SO WHAT THEY'VE DONE IS DEVELOPED A TOTALLY DIFFERENT EVOLUTIONARY STRATEGY-- CHEMICAL WEAPONS.

SO IN THE CASE OF COFFEE, FOR EXAMPLE, YOU HAVE THESE SEEDS HERE WHICH ARE PACKED FULL OF CAFFEINE, WHICH IS TOXIC TO INSECTS IN LARGE DOSES.

IT'S FOUND IN ITS LEAVES, IT'S FOUND THROUGHOUT THE PLANT, BUT THE WEIRD THING IS IT'S EVEN FOUND IN FLOWERS, AND THE WHOLE FUNCTION OF A FLOWER IS TO ATTRACT INSECTS.

SO IT KIND OF BEGS THE QUESTION IF SOMETHING ELSE IS GOING ON HERE.

NARRATOR: EVEN THOUGH CAFFEINE IS TOXIC TO INSECTS IN LARGE DOSES, THERE MUST BE SOMETHING ELSE ABOUT THIS CHEMICAL THAT INSECTS FIND TEMPTING.

UNDERSTAND THIS, AND IT MIGHT HELP US UNDERSTAND WHY WE HUMANS ALSO FIND COFFEE SO TEMPTING.

BACK IN THE UK, PROFESSOR GERALDINE WRIGHT OF NEWCASTLE UNIVERSITY HAS BEEN STUDYING HOW CAFFEINE AFFECTS THE BRAINS OF BEES.

GERALDINE: BEES ARE ONE OF THE HIGHEST FORMS OF LIFE ON THE PLANET.

THEY HAVE EVOLVED FAIRLY SOPHISTICATED BRAINS THAT ALLOWS THEM TO LEARN FLORAL TRAITS AND ASSOCIATE THEM WITH FOOD.

COFFEE FLOWERS PRODUCE A LOT OF SCENT.

THEY HAVE A BEAUTIFUL FLORAL SCENT THAT'S LIKE JASMINE.

NARRATOR: DRAWN IN BY THE SCENT, THE BEES FEAST ON THE SUGARY NECTAR IN THE FLOWERS, WHICH ALSO GIVES THEM A DOSE OF CAFFEINE.

WHAT GERALDINE HAS DISCOVERED IS THAT THE CAFFEINE HAS A PROFOUND EFFECT ON MEMORY FORMATION IN BEES.

GERALDINE: A LITTLE DOSE OF CAFFEINE IN NECTAR GOES A LONG WAY TO HELPING BEES TO LEARN AND REMEMBER THE SCENT OF FLOWERS.

NARRATOR: THIS IS BECAUSE THE REWARD OF DRINKING THE NECTAR FROM THE COFFEE FLOWER IS BEING REINFORCED.

GERALDINE: CAFFEINE ITSELF IS MAKING THE BRAIN BELIEVE THAT THESE SIGNALS ARE MORE INTENSE.

CAFFEINE IS AMPLIFYING THE EXPERIENCE THE BEES HAVE WITH SUGAR WHEN THEY'RE EATING, AND IT'S MAKING IT SEEM BETTER.

THE RESULTS WE FOUND REGARDING BEE MEMORY CAN BE TRANSLATED TO PEOPLE.

IT'S VERY LIKELY THAT CAFFEINE IS AFFECTING HUMAN MEMORY IN THE SAME WAY, VIA THE SAME MECHANISMS, BASICALLY BY AMPLIFYING REWARD.

NARRATOR: WHEN WE DRINK A COFFEE, THE PLEASANT FEELING OF THE HOT LIQUID IS MADE EVEN BETTER BY THE CAFFEINE, WHICH AMPLIFIES SIGNALS TO OUR REWARD PATHWAY, SO WE CRAVE IT AGAIN.

AND IF WE ADD SUGAR OR SYRUP OR CREAM TO OUR COFFEE, THEN THE CAFFEINE WILL ALSO MAKE THIS PLEASURE MORE INTENSE, SO WE'RE EVEN MORE LIKELY TO GO BACK FOR MORE.

IT COULD BE THAT THIS IS PART OF WHAT MAKES A DAILY CUP SO ADDICTIVE-- OUR BRAINS LEARN TO LOVE THE RITUAL OF MAKING AND BUYING COFFEE.

WE'RE LIKE BEES BUZZING AROUND FLOWERS SEEKING OUT THE EXTRA HIT OF PLEASURE EACH TIME WE ENJOY A CUP.

OUR RELATIONSHIP WITH FOOD IS VERY COMPLEX, BUT THE POWERFUL HUMAN BRAIN IS ALSO VERY ADAPTABLE.

THAT MEANS WE CAN LEARN TO LOVE SOME RATHER UNUSUAL FOODS AND CONTINUALLY ACQUIRE NEW TASTES, FOODS THAT ARE DELICIOUS TO SOME, REVOLTING TO OTHERS, AND THAT OFTEN DEPENDS ON WHERE WE ARE IN THE WORLD.

FOR EXAMPLE, BRAIN.

NOW, AS WELL AS BEING A BRAIN, THIS IS ALSO FOOD.

AND HERE IN TURKEY, A SHEEP'S BRAIN SALAD IS SOMETHING OF A DELICACY.

NOW, THIS BRAIN IS VERY SMALL, AND THAT'S BECAUSE IT COMES FROM A SHEEP, AND A SHEEP DOESN'T HAVE TO MAKE LOTS OF COMPLEX DECISIONS.

I LIKE TO THINK OF SHEEP WANDERING THE FIELDS IN THE SUNSHINE, AND OCCASIONALLY THEY'LL STOP AND HAVE A BIT OF A NIBBLE.

WHEN IT COMES TO FOOD, THE THOUGHT PROCESS GOES SOMETHING ALONG THE LINES OF GRASS, STOP, EAT.

NARRATOR: IT'S SAFE TO SAY THAT SHEEP ARE NOT ADVENTUROUS WITH THEIR EATING HABITS, AND THEY DON'T EXPERIMENT WITH DIFFERENT FLAVOR COMBINATIONS.

THAT'S BECAUSE A SHEEP'S BRAIN HAS A KEY DIFFERENCE TO OURS.

IF I CUT THIS OPEN, YOU CAN SEE THAT IN SOME WAYS IT LOOKS LIKE A HUMAN BRAIN, EXCEPT THAT IN A HUMAN THIS AREA HERE, WHICH IS CALLED THE FRONTAL CORTEX, WOULD BE MUCH, MUCH BIGGER.

AND THAT'S BECAUSE IT'S WHERE WE MAKE ALL OUR IMPORTANT CONSCIOUS DECISIONS, LIKE WHERE AM I GOING TO GO ON HOLIDAY?

DO I REALLY NEED THAT EXTRA BIT OF CHOCOLATE CAKE?

THE FRONTAL CORTEX IS IN MANY WAYS THE AREA OF THE BRAIN THAT MAKES OUR LIVES SO MUCH MORE RICH AND COMPLEX THAN THAT OF A SHEEP.

NARRATOR: IT'S OUR ENLARGED CORTEX THAT HAS LED US TO EXPERIMENT WITH OUR FOOD, INVENTING NUMEROUS DELICACIES ACROSS CULTURES AND CUISINES.

AND THAT'S WHERE IT GETS A LITTLE BIT TRICKY.

I'VE NEVER EATEN A BRAIN BEFORE, BUT THERE'S ALWAYS A FIRST TIME FOR EVERYTHING.

SO, SOME LEMON JUICE, A LITTLE BIT OF OLIVE OIL.

AND HERE GOES.

I THINK THIS IS AN ACQUIRED TASTE, AND IT'S NOT ONE I PLAN TO ACQUIRE.

HMM.

NARRATOR: BUT ACTUALLY, ACQUIRING TASTE IS SOMETHING WE EXCEL AT.

IT SEEMS THAT OUR BRAINS ARE WIRED TO ENJOY NOVELTY IN OUR FOOD AND THAT WE LEARN TO OVERCOME DISGUST.

SOMETIMES, IN THE CASE OF CHILI PEPPERS, EVEN PAIN.

TO INVESTIGATE THE POWERFUL EFFECT THAT CHILI PEPPERS HAVE ON THE BODY AND THE BRAIN, JAMES HAS COME TO THE LARGEST MARKET ON THE PLANET, WHERE NEARLY A HUNDRED TONS OF CHILIES ARE SOLD EVERY DAY.

HE'S IN MEXICO, WHERE PEOPLE FIRST LEARNED TO FARM THE CHILI PLANT SOME 6,000 YEARS AGO.

THE SPICY FLAVOR IN CHILIES IS CAUSED BY THIS CHEMICAL CALLED CAPSAICIN.

NOW, I SAY FLAVOR, BUT IT'S REALLY, LIKE, MORE OF A TEXTURE, ALMOST A FEELING.

AND THIS IS WHERE IT ALL IS.

SO EVERYONE SAYS THAT IT'S THE SEEDS THAT ARE SPICY, AND THAT'S NOT TRUE, IT'S THIS BUSINESS HERE.

THIS WHITE SPONGY LAYER THAT WE CALL THE PLACENTA, THAT BIT.

AND THAT'S WHERE PRETTY MUCH ALL YOUR CAPSAICIN IS MANUFACTURED.

THESE TINY LITTLE DOTS ALONG THERE, EACH ONE OF THOSE IS A GLAND THAT PRODUCES CAPSAICIN.

NARRATOR: AND ALL THIS CAPSAICIN HAS A DIRECT EFFECT ON A VERY PARTICULAR PART OF OUR BIOLOGY... SOMETHING KNOWN AS THE TRPV1 RECEPTOR.

TRPV1 RECEPTORS ARE FOUND IN THE MOUTH, ON THE TONGUE, AND THROUGHOUT THE BODY.

THEIR PURPOSE IS TO DETECT THE SENSATION OF SCALDING HEAT AND RAISE AN ALARM SIGNAL IN THE BRAIN TO PROTECT THE BODY FROM HARM.

BY CHANCE, THE SHAPE OF THE CAPSAICIN MOLECULE HAPPENS TO FIT ONTO THE TRPV1 RECEPTOR LIKE A MASTER KEY IN A LOCK.

THIS TRIGGERS THE RECEPTORS TO ACTIVATE, AND THEY SEND A SIGNAL TO THE BRAIN, FOOLING IT INTO THINKING THAT THE MOUTH IS ON FIRE.

CAPSAICIN, THEN, HAS AN ALMOST UNRIVALLED ABILITY TO GENERATE PAIN IN OUR BODIES.

SO HOW DID A POTENTIAL FOOD SOURCE END UP WITH THIS ASTONISHINGLY POWERFUL IRRITANT?

TO ANSWER THE QUESTION, JAMES IS GOING TO NEED THE HELP OF A, HOPEFULLY, FRIENDLY PARROT.

MAN: YOU LOOK SCARED, JAMES.

I AM VERY SCARED.

TRY NOT TO BE.

GET IT CLOSER.

HA!

WHOA.

OOH!

NO, I DON'T WANT TO DO THIS.

I AM GOING TO GIVE IT TO YOU THERE.

JESUS!

IT'S 'CAUSE YOU'RE SNATCHING IT AWAY.

I KNOW, I KNOW, I KNOW.

OH, AND THEN HE GOT ME.

OK, THERE YOU GO.

HAVE A LOOK AT THAT.

OK. WHAT DO YOU THINK?

YOU LIKE THAT, DON'T YOU?

YEAH?

IN THE WILD, IT'S RELATIVES OF THESE GUYS, BIRDS, THAT ARE THE KEY WAY THAT CHILI PLANTS DISPERSE THEIR SEEDS EVERYWHERE, AND THAT'S BECAUSE BIRDS ARE COMPLETELY IMMUNE TO THE EFFECTS OF CAPSAICIN.

IT'S LIKE IT DOESN'T EVEN EXIST FOR THEM.

BIRDS DO HAVE A TRPV1 RECEPTOR, BUT IT'S A DIFFERENT SHAPE, SO NO LOCK-AND-KEY FIT, NO ACTIVATION, AND NO FEELING WHATSOEVER.

NARRATOR: SO, CHILIES HAVE THEIR SEEDS SPREAD BY BIRDS, WHILE BEING AVOIDED BY OTHER ANIMALS.

BUT THEN WE CAME ALONG AND LEARNED TO LOVE THE BURN.

MICHAEL AND JAMES HAVE COME TO A FOOD AND MUSIC FESTIVAL HERE IN BRISTOL, ENGLAND, WHERE THEY'RE GOING TO COMPETE IN A CHILI EATING CONTEST... A COMPETITION MADE UP OF 12 BRAVE SOULS, INCLUDING A MAN DRESSED AS A CHILI AND ANOTHER DRESSED AS A ZOMBIE...

HOST: GOOD AFTERNOON, BRISTOL.

NARRATOR: TO EXPERIENCE FIRST-HAND THE EFFECT THAT CHILIES HAVE ON OUR BODIES AND OUR BRAINS.

HOST: WELCOME TO OUR CATHEDRAL OF PAIN AND CHAOS.

I'M ACTUALLY FEELING SLIGHTLY NERVOUS.

I DO QUITE LIKE HOT THINGS.

AND ALTHOUGH THIS IS NOT REALLY A COMPETITION, IT IS.

I'D QUITE LIKE TO DO BETTER THAN YOU.

OK. WELL, I GREW UP EATING CHILIES.

I'VE BEEN EATING THEM SINCE I WAS 8 YEARS OLD.

BUT FAMOUS LAST WORDS.

OK.

THERE IS A GOOD CHANCE YOU'LL BEAT ME, THEN.

HOST: BRISTOL, PLEASE GIVE A BIG ROUND OF APPLAUSE TO ALL THE CHILI-EATING CONTESTANTS.

THE THINGS WE DO IN THE NAME OF SCIENCE.

IT'S GOOD TO GO.

GOOD LUCK.

NARRATOR: THE PRINCIPLE OF THE COMPETITION IS SIMPLE.

AT EACH ROUND, THE CHILIES WILL GET HOTTER AND HOTTER, AND THE PERSON WHO LASTS THE LONGEST WINS.

HOST: SOME VERY BRAVE, STUPID PEOPLE.

NARRATOR: THE FEROCITY OF A CHILI PEPPER IS MEASURED IN SCOVILLE HEAT UNITS.

HOST: IT IS CALLED A DUTCH LONG CHILI.

ON MY MARK.

3, 2, 1, EAT!

[CHEERS AND APPLAUSE] THIS WEIGHS IN AT 500 SCOVILLE UNITS.

NARRATOR: THE HIGHER THE SCOVILLE NUMBER, THE MORE CAPSAICIN IN THE CHILI, AND THE MORE FIERY IT BECOMES.

IT'S GOT A BIT OF BITE TO IT.

NARRATOR: THERE'S A LONG WAY TO GO, 18 ROUNDS, BEFORE THEY ENCOUNTER THE WORLD'S MOST FEROCIOUS CHILI, THE CAROLINA REAPER, WHICH WEIGHS IN AT OVER 1.5 MILLION SCOVILLES.

HOST: ON MY MARK.

3, 2, 1, EAT.

NARRATOR: BUT WILL ANY OF THEM MAKE IT THAT FAR?

HOST: SAVOR IT AND ENJOY IT.

3, 2, 1, EAT.

THAT ONE WENT UP THE NOSE.

OH!

HOST: PLEASE GIVE THESE GUYS A ROUND OF APPLAUSE.

[CHEERS AND APPLAUSE] NARRATOR: THEY'VE NOW CONSUMED A CONSIDERABLE AMOUNT OF CAPSAICIN.

AND ALL THOSE CAPSAICIN MOLECULES ARE ATTACHING THEMSELVES TO TRPV1 RECEPTORS IN THEIR MOUTHS...

HOST: GO AND GET IT DOWN YOU.

NARRATOR: SENDING SIGNALS TO THEIR BRAINS, MAKING THEM THINK THEY ARE LITERALLY ON FIRE.

MY EYES ARE REALLY BEGINNING TO WATER AND MY PULSE IS SHOOTING UP.

THIS IS THE FIGHT- OR-FLIGHT RESPONSE.

NARRATOR: THE FIGHT-OR-FLIGHT RESPONSE NORMALLY OCCURS WHEN WE SENSE A THREAT OR DANGER.

[COUGHS] NARRATOR: THE BODY RESPONDS WITH A SHOT OF ADRENALINE.

THE HEART BEATS HARDER AND FASTER, PUPILS DILATE, WE BREATHE DEEPER, AND OUR ARTERIES WIDEN, SENDING A FLOOD OF BLOOD TO OUR MUSCLES TO GET THEM READY FOR ACTION.

IT'S ALL ACCOMPANIED BY A RATHER MORE POSITIVE FEELING THAT MIGHT HOLD THE KEY TO WHY SOME PEOPLE LIKE THIS FIERY SENSATION.

THE THING IS THAT WHEN YOU EAT A REALLY, REALLY HOT CHILI, WHAT YOU ALSO GET IS AN ENDORPHIN RESPONSE, WHICH IS ONE OF THOSE NATURAL OPIATES.

SOMETIMES YOU GET THEM WHEN YOU DO EXERCISE.

BUT IT'S SUPPOSED TO BE A FEEL-GOOD HORMONE.

I'M NOT SURE I'VE GOT THAT YET.

NARRATOR: IT'S PART OF THE CHILI'S ALLURE.

ENDORPHINS ARE POWERFUL PAINKILLERS RELEASED BY OUR OWN BODIES AND SO SHOULD LESSEN THE CHILI'S STING.

BUT CRUCIALLY THEY ARE THOUGHT TO INDUCE A PERVASIVE SENSE OF HAPPINESS, EVEN A RUSH, WHICH CAN BE ADDICTIVE.

YES!

HOST: NICELY DONE.

3, 2, 1, EAT!

HOW ARE YOU DOING?

OH!

NARRATOR: THE FIFTH CHILI IS 15,000 SCOVILLES.

WITH THEIR BRAINS' PAIN CENTERS IN OVERDRIVE, MICHAEL AND JAMES NEED TO DIG DEEP TO STAY IN THE CONTEST.

BUT MICHAEL CAN'T STAND THE HEAT ANYMORE.

HOST: LADIES AND GENTLEMEN, PLEASE GIVE THIS LOT CRAZY LOUD APPLAUSE.

AH, JESUS.

SEE YOU IN A BIT.

HA HA HA!

SEE YOU, MOSLEY.

YEAH.

I CAN FEEL BASICALLY THE TEARS COMING OUT.

THE SNOT IS COMING OUT, AND THOUGHT I WAS GOING TO VOMIT FOR A MOMENT THERE.

SO I THOUGHT IT WAS PROBABLY A GOOD TIME TO WITHDRAW.

HOST: LADIES AND GENTLEMEN, PLEASE GIVE MR. MICHAEL MOSLEY A ROUND OF APPLAUSE.

NARRATOR: THE BEST THING TO SOOTHE THE BURN IS NOT WATER, BUT MILK.

IT HELPS NEUTRALIZE CAPSAICIN BECAUSE DAIRY MILK CONTAINS SOMETHING CALLED CASEIN.

CASEIN MOLECULES ARE ATTRACTED TO OILY SUBSTANCES LIKE THE CAPSAICIN IN CHILIES.

THEY SURROUND THE CAPSAICIN, PREVENTING IT FROM LATCHING ON TO THE TRPV1 RECEPTORS IN OUR BODIES, AND IT JUST GETS WASHED AWAY.

SO IF YOU EVER ENCOUNTER SPICY FOOD YOU CAN'T HANDLE, DON'T BOTHER WITH WATER, REACH FOR DAIRY.

HOST: 3, 2, 1, EAT!

NARRATOR: JAMES IS STILL IN THE RUNNING AND ON TO THE SIXTH CHILI, AND THIS ONE IS 30,000 SCOVILLES, 60 TIMES HOTTER THAN THE FIRST.

THE REASON WHY PSYCHOLOGISTS THINK WE LIKE EATING CHILIES IS IT'S A MINOR FORM OF SADO-MASOCHISM, A BIT LIKE RIDING A ROLLER COASTER.

AND I CAN CONFIRM THAT IT'S DRIVEN BY THE HUMAN RUSH FOR EXCITEMENT.

NARRATOR: IT'S THRILL SEEKING, FEEDING OUR BRAINS' DESIRE FOR STIMULATION.

HOST: HONESTLY.

LADIES AND GENTLEMEN, PLEASE GIVE JAMES WONG A ROUND OF APPLAUSE.

[CHEERS AND APPLAUSE] HOST: EXCELLENT WORK.

OH, THAT MILK'S GOOD.

NARRATOR: WE STILL DON'T KNOW WHY PEOPLE HAVE DIFFERENT TOLERANCES TO SPICY FOODS, BUT WE CAN SPECULATE THAT PEOPLE WITH THRILL-SEEKING PERSONALITIES ARE MORE LIKELY TO EXPOSE THEMSELVES TO THE BURN AND MAY BUILD UP A TOLERANCE TO CAPSAICIN.

OUT OF 12 PEOPLE, MICHAEL AND JAMES FINISHED 11th AND 12th.

HOST: RIGHT, SO NEXT UP WE HAVE THAI RED CHILIES.

3, 2, 1, EAT!

NARRATOR: AND THE REST ARE SOON DROPPING LIKE FLIES.

HOST: THESE ARE NAUGHTY.

JERRY'S DONE.

THE LAST TWO CONTESTANTS HAVE OVERCOME INTENSE PAIN TO REACH THE LATER ROUNDS.

THEY NOW FACE THE INFAMOUS JAYS RED GHOST CHILI, AT A STAGGERING 1.2 MILLION SCOVILLES.

IT'S TOO MUCH.

GRABBING THE MILK GIVES HIS OPPONENT THE VICTORY.

SPARING THEM BOTH FROM ENCOUNTERING THE CAROLINA REAPER.

OUR LOVE FOR CHILIES SHOWS AN EXPERIMENTAL SIDE TO OUR EATING HABITS.

REWARDED BY ENDORPHINS AND A RUSH OF PLEASURE, WE'VE BECOME CULINARY ADVENTURERS, CONSTANTLY SEEKING OUT NOVEL FOOD EXPERIENCES.

IT'S EVEN LED US TO CONSUME A CHEMICAL THAT, IN ITS PURE FORM IS, FRANKLY, POISONOUS-- ALCOHOL.

IT COMES IN MANY GUISES.

AND IT CAN PASS RIGHT THROUGH THE BLOOD-BRAIN BARRIER, A WATERTIGHT MEMBRANE WHICH PROTECTS THE BRAIN FROM SUBSTANCES THAT CAN INTERFERE WITH IT.

THIS IS RED WINE.

SMELLS RATHER NICE, AND I'M SURE IT'S THE PRODUCT OF YEARS OF HARD WORK AND EXPERIENCE.

BUT I'M NOT GOING TO DRINK IT.

I'M GOING TO SEND IT OFF TO BE EVAPORATED.

NARRATOR: ALCOHOL HAS A LOWER BOILING POINT THAN WATER, SO GENTLY HEATING THE WINE IN A ROTARY EVAPORATOR TURNS IT INTO A VAPOR, WHICH RISES AND CAN BE COLLECTED.

ALCOHOL IS A PACKED WITH ENERGY.

MICHAEL: HERE IT IS BACK AGAIN, SMELLING COMPLETELY DIFFERENT.

AND BY NOW IT SHOULD BE ALMOST PURE ALCOHOL.

AND IF WE DIM THE LIGHTS DOWN, WE SHOULD BE ABLE TO SEE IT BURN.

NARRATOR: EVERY QUARTER OUNCE RELEASES 7 CALORIES OF ENERGY, SO DRINKING ADDS CALORIES TO OUR DIET.

BUT ENERGY IS NOT WHY MOST OF US DRINK.

ALCOHOL'S POPULARITY COMES FROM WHAT IT DOES TO OUR BRAINS, WHICH MEANS AROUND THE WORLD, ALMOST EVERY CULTURE HAS INVENTED ITS OWN UNIQUE ALCOHOLIC DRINK.

NORTHERN PERU IS NO EXCEPTION.

THE LOCALS HERE HAVE PRODUCED AN EXTRAORDINARY BREW CALLED MASATO.

THESE ARE THE CANCHA PEOPLE.

THEY'VE BEEN HERE FOR OVER 700 YEARS.

AND THROUGHOUT THEIR HISTORY, THEY HAVE IMPROVISED A UNIQUE WAY TO PRODUCE A STEADY STREAM OF ALCOHOL.

LIKE ALL CULTURES, THEY USE WHAT'S ON HAND, AND FOR THEM, THAT'S THE ROOT OF THE YUCCA PLANT.

[SPEAKS NATIVE LANGUAGE] HELLO.

[SPEAKS NATIVE LANGUAGE] HI THERE.

NARRATOR: TODAY, MICHAEL'S JOINED THEM TO HELP MAKE THE NEXT BATCH OF MASATO.

ONCE THE YUCCA ROOTS ARE PEELED, THEY'RE BOILED TO SOFTEN THEM UP, THEN THEY'RE CRUSHED.

[LAUGHTER] THEY'RE OBVIOUSLY HAVING A GOOD LAUGH, BUT I'M NOT ENTIRELY SURE WHAT IT'S ABOUT.

ALL YOURS.

NARRATOR: MICHAEL'S HOPING HE'LL BE BETTER AT THE NEXT BIT, WHEN THEY ADD THEY ADD THE OTHER CRUCIAL INGREDIENT-- SPIT.

[ALL SPEAKING NATIVE LANGUAGE] [LAUGHTER] YES, THIS IS HOW IT'S DONE.

EWW.

[LAUGHTER] APPARENTLY THIS IS NORMALLY JUST FEMALE-ONLY ACTIVITY.

I'M NOT SURE ADDING A BIT OF SORT OF GRINGO MALE SPIT TO IT IS ADDING TO THE FLAVOR.

THIS MAY LOOK ABSOLUTELY DISGUSTING, BUT IT'S ACTUALLY PART OF THE PROCESS BECAUSE THE SALIVA IS ACTUALLY AN INTRINSIC PART OF THE WHOLE THING.

WHAT HAPPENS IS THE SALIVA IN YOUR MOUTH CONTAINS AN ENZYME CALLED AMYLASE, AND THIS STUFF IS ALL STARCH.

WHAT THE AMYLASE DOES IS IT BREAKS DOWN THE STARCH AND RELEASES THE SUGARS INSIDE IT.

IF YOU'VE EVER STUCK A CRACKER IN YOUR MOUTH AND LEFT IT THERE, OR PERHAPS YOU'VE STUCK SOME WHITE BREAD IN YOUR MOUTH AND LEFT IT THERE, WHAT YOU'LL NOTICE AFTER A LITTLE WHILE IS IT STARTS TO TASTE RATHER SWEET.

AND THAT'S BECAUSE THE AMYLASE IN YOUR MOUTH IS BREAKING DOWN THE STARCHES AND RELEASING SUGAR.

SO YOU HAVE TO STICK IT IN, RUN IT ROUND, AMYLASE SPRINGS INTO ACTION, AND THEN, AH, YOU GOB IT OUT.

NARRATOR: THE POINT IS TO GET SOME SUGAR.

ONCE WE HAVE SUGAR, ALL WE NEED TO TURN IT INTO ALCOHOL IS A LITTLE FRESH AIR.

THAT'S BECAUSE OUR ATMOSPHERE CONTAINS MANY FORMS OF TINY SINGLE-CELLED MICRO-ORGANISMS, INCLUDING YEAST.

WHEN ONE OF THESE YEAST CELLS LANDS ON THE CHEWED YUCCA, IT STARTS TO FEED ON THE SUGAR AND BEGINS TO MULTIPLY.

IT'S A PROCESS CALLED FERMENTATION.

THE YEAST STARTS DIGESTING THE SUGARS IN THE YUCCA.

IN THE PROCESS, EACH SUGAR MOLECULE IS CONVERTED INTO 4 SMALLER MOLECULES, TWO OF CARBON DIOXIDE AND TWO OF ALCOHOL AS WASTE.

THE SMALL SIZE OF THE ALCOHOL MOLECULE IS CRUCIAL TO OUR ENJOYMENT.

BEING SMALL HELPS IT PASS THROUGH THE WATERTIGHT BLOOD-BRAIN BARRIER AND STRAIGHT INTO THE BRAIN ITSELF.

NOW, FERMENTATION IS AT THE HEART OF LOTS OF THE THINGS WE LOVE, NOT JUST BOOZE, BUT CHOCOLATE, YOGURT, AND, OF COURSE, BREAD.

NOW, WITH BREAD THE PRODUCT OF THE FERMENTATION YOU REALLY WANT IS NOT THE ALCOHOL, BUT THE CARBON DIOXIDE BECAUSE THAT'S WHAT MAKES IT RISE AND PRODUCES THAT LOVELY SPONGY TEXTURE.

THERE IS A SMALL AMOUNT OF ALCOHOL IN THE DOUGH, BUT THAT GETS EVAPORATED OFF WHEN THE BREAD IS BAKED.

[THUNDER] NARRATOR: YET IN MASATO, IT'S ALL ABOUT THE ALCOHOL, AND IT'S BEGINNING TO BUILD.

BUT THERE'S A LIMIT TO HOW STRONG IT CAN BECOME.

AFTER ABOUT A WEEK, THE ALCOHOL LEVEL REACHES AROUND 6%, AND IT BECOMES CONCENTRATED ENOUGH TO POISON MANY TYPES OF YEAST, WHICH DIE.

AND THAT IN TURN SLOWS THE FERMENTATION PROCESS.

AND IT'S AT THIS POINT IT'S READY TO ENJOY.

THE VILLAGERS HAVE INVITED MICHAEL TO SHARE A MEAL WITH THEM.

AND THAT ALSO MEANS SAMPLING SOME OF THEIR YUCCA BEER.

RIGHT.

OK.

IT'S THE MOMENT OF TRUTH.

I'M A LITTLE APPREHENSIVE.

HMM.

WASN'T WHAT I WAS EXPECTING.

IT'S KIND OF GOT A BIT OF AN ALCOHOLIC KICK TO IT.

AND IT'S QUITE BITTER.

IT'S ALMOST SORT OF YOGURTY.

[SPEAKING SPANISH] MICHAEL: OK. YOU DRINK IT PRETTY WELL EVERY DAY, DO YOU?

CHEERS.

CHEERS.

SALUD.

SALUD.

IT'S NOT TERRIBLY ALCOHOLIC.

I GUESS IT'S PROBABLY ABOUT 4% OR 5%, THOUGH, I SUSPECT, YOU DRINK ENOUGH OF IT, YOU GET FAIRLY JOLLY.

[LAUGHS] AHH.

THAT'S-- HA HA!

OK. [LAUGHTER] NARRATOR: AFTER A FEW BOWLS, MICHAEL'S STARTING TO FEEL THE EFFECTS.

MICHAEL: AHH.

WHEN IT GETS INTO YOUR BLOODSTREAM, IT HITS YOUR BRAIN, AND THERE IT REALLY STARTS TO DO THE BUSINESS BECAUSE ONE OF THE THINGS IT DOES IS IT AFFECTS A NEUROTRANSMITTER CALLED GABA.

NARRATOR: GABA IS A NEUROTRANSMITTER, OR CHEMICAL MESSENGER, THAT'S PRESENT THROUGHOUT THE BRAIN.

NORMALLY, IT REGULATES THE BRAIN'S ACTIVITY.

ITS FUNCTION IS TO ACT RATHER LIKE A BRAKE ON BRAIN CELLS, STOPPING THEM FROM FIRING AT THE WRONG TIME.

BUT ALCOHOL INTERFERES WITH THIS SYSTEM.

THE MORE WE DRINK, THE MORE RECEPTIVE OUR BRAIN CELLS BECOME TO GABA.

AS THE POTENCY OF GABA INCREASES, SO DOES THE DAMPENING EFFECT ON THE BRAIN, SWITCHING OFF AREAS ONE BY ONE.

AT FIRST THIS CAN MAKE US FEEL LIBERATED, EXCITED, AMUSING BECAUSE THE ALCOHOL STARTS BY SWITCHING OFF THE AREAS THAT CONTROL OUR INHIBITIONS.

YEP.

LIFE AND SOUL.

NARRATOR: THESE REGIONS HAVE BRAIN CELLS WITH THE GREATEST NUMBER OF GABA RECEPTORS, SO THEY'RE MOST SENSITIVE TO THE EFFECTS OF ALCOHOL.

THE EMOTIONAL REGIONS ARE NEXT TO BE SUPPRESSED.

THEY HAVE ALMOST AS MANY GABA RECEPTORS.

THEY ARE FOLLOWED BY OUR MOTOR CONTROL REGION, AND THEN MEMORY.

[INDISTINCT CHATTER] NARRATOR: FINALLY, WHEN WE ARE BLIND DRUNK, WE ARE LEFT WITH ONLY THE MOST BASIC PARTS OF OUR BRAIN OPERATING.

THEY HAVE THE LEAST GABA RECEPTORS, AND FORTUNATELY, THEY GO ON KEEPING US BREATHING AND OUR HEART BEATING, EVEN WHEN WE ARE UNCONSCIOUS.

BUT MICHAEL'S NOT AT THAT STAGE TONIGHT.

MOST OF THE TIME, ALCOHOL JUST INHIBITS OUR BRAINS ENOUGH TO LOOSEN OUR INHIBITIONS AND MAKE US MORE SOCIABLE, AT LEAST WHEN DRUNK IN MODERATION...

WHICH IS PERHAPS WHY IT'S BEEN EMBRACED BY MANY CULTURES AROUND THE WORLD.

[SINGING IN NATIVE LANGUAGE] NARRATOR: OUR RELATIONSHIP WITH FOOD IS INCREDIBLY COMPLEX.

[LAUGHS] WHOA.

YET WE NOW UNDERSTAND HOW OUR EXPERIENCE OF FOOD IS FUNDAMENTALLY INTERTWINED WITH OUR BRAIN... THAT'S INTENSE.

NARRATOR: HOW CERTAIN FOODS CAN DIRECTLY AFFECT IT AT THE MOLECULAR AND CELLULAR LEVEL.

IT'S PART OF OUR EVOLUTIONARY STORY.

WE INDULGE OUR SENSES, WHICH IN TURN REWARD US WITH FEELINGS OF PLEASURE, KEEPING US COMING BACK TO THE TABLE FOR MORE.

MMM.

MEANWHILE, AROUND THE WORLD, FOOD SCIENTISTS WILL CONTINUE TO DELVE INTO THE CHEMISTRY AND BIOLOGY OF OUR FOOD TO TRY AND UNDERSTAND HOW IT WORKS IN OUR BODIES AND ON OUR MINDS, AND ALL THE WHILE, OUR LOVE AFFAIR WITH FOOD CONTINUES TO EVOLVE.

AND THAT'S BECAUSE WE'RE CONSTANTLY PUSHING THE BARRIERS, LOOKING FOR NEW WAYS TO STIMULATE OUR INCREDIBLY DEMANDING HUMAN BRAINS.

NARRATOR: NEXT TIME, WE EXPLORE THE BOUNDARIES OF TASTE.

WONG: THEY ARE IRRESISTIBLE.

NARRATOR: WE REVEL IN THE SUMPTUOUS FOOD THAT DAZZLES OUR TASTE BUDS AND EXCITES OUR NOSES.

[SNIFFS] WONG: HO HO HO!

NARRATOR: AS WE DISCOVER THAT TASTE IS ULTIMATELY ALL ABOUT SURVIVAL.

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