Why Does Asparagus Make Your Pee Smell?
Fascinating food trivia explained with science
Copyright © 2016 Andy Brunning. All rights reserved. Any unauthorized duplication
in whole or in part or dissemination of this edition by any means (including but not
limited to photocopying, electronic devices, digital versions and the Internet) will be
prosecuted to the fullest extent of the law.
Published in the US by
P.O. Box 3440
Berkeley, CA 94703
First published as Why Does Asparagus Make Your Wee Smell? in Great Britain
in 2015 by Orion, an imprint of the Orion Publishing Group Ltd., an Hachette UK
Library of Congress Control Number: 2015952141
10 9 8 7 6 5 4 3 2 1
Printed in Korea by WE SP through Four Colour Print Group
US editor: Alice Riegert
Design concept by Grade Design
Cover design by what!design @ whatweb.com
Cover photos from Shutterstock.com: asparagus © ksulee; beer © Serhiy Shullye;
bacon © Joe Belanger; © GMEVIPHOTO; red onion © Amero; red hot pepper
© Timmary; abstract background © Tusiy
Interior photo credits: see page 143
Distributed by Publishers Group West
IMPORTANT NOTE TO READERS: This book is independently authored and
published and no sponsorship or endorsement of this book by, and no affiliation
with, any trademarked brands or other products mentioned or pictured within is
claimed or suggested. All trademarks that appear in ingredient lists, photographs
and elsewhere in this book belong to their respective owners and are used here
for informational purposes only. The authors and publishers encourage readers to
patronize the quality brands mentioned and pictured in this book.
To Anna, for her continued support and
enthusiasm throughout the creation of this book.
8 A Brief Introduction to Organic Chemistry
9 Functional Groups in Organic Chemistry
Why Do Some People Hate Brussels Sprouts?
Why Do Artichokes Make Drinks Taste Sweeter?
How Do Miracle Berries Make Sour Foods Taste Sweet?
Why Does Orange Juice Taste Bitter
After Brushing Your Teeth?
Why Does Smoking Meat Change Its Flavor?
What Causes the Sour Taste of Spoiled Milk?
Why Does Cilantro Taste Soapy to Some People?
What Do Dill and Spearmint Have in Common?
What Causes the Bitterness of Coffee?
What Causes the Bitterness and Taste of Beer?
Why Does Garlic Give You Bad Breath?
Why Does Asparagus Make Your Pee Smell?
Why Does Durian Fruit Smell So Bad?
Why Does Bacon Smell So Good?
What Causes the Smell of Fish?
What Causes Blue Cheese to Smell So Strong?
Why Do Beans Make You Fart?
Can Carrots Help You See in the Dark?
Why Do Beets Turn Urine Red?
Why Do Potatoes Turn Green?
Why Do Avocados Go Brown So Quickly?
Why Are Salmon and Prawns Pink?
Why Does Tonic Water Glow under a Black Light?
Why Are Raw Kidney Beans Poisonous?
Why Are Some Mushrooms Poisonous?
Do Apple Seeds Really Contain Cyanide?
What Causes Shellfish Poisoning?
Why Is Eating Pufferfish a Risky Move?
Why Is Chocolate Poisonous to Dogs?
Can Mixing Drinks make Your Hangover Worse?
Why Do Onions Make You Cry?
What Makes Chilies Spicy?
Why Does Mint Make Your Mouth Feel Cold?
How Does Pop Rocks® Candy Work?
What Causes the Pungency of Wasabi?
Does Eating Turkey Make You Sleepy?
Why Can Nutmeg Act as a Hallucinogen?
Why Do the Stimulant Effects of Tea and Coffee Differ?
Does Drinking Absinthe Cause Hallucinations?
How Do Energy Drinks Work?
Why Can’t You Eat Grapefruit with Some Medications?
Why Do Lemons Help Prevent Scurvy?
Why Are Some People Allergic to Nuts?
Can a Tick Bite Make You Allergic to Meat?
Why Can Clove Oil Be Used as an Antiseptic?
Does MSG Cause “Chinese Restaurant Syndrome”?
Why Are Sweeteners Sometimes Used in Place of Sugar?
What Are Sulfites And Why Are They in Alcoholic Drinks?
123 Do Bananas Help Other Fruit Ripen Quicker?
124 Why Does Adding Some Fruits to
Jelly Stop It from Setting?
127 Why Does Whipping Cream Make It Thicker?
128 Should You Keep Chocolate in the Fridge?
131 Why Are Beer Bottles Usually Made with Darkened Glass?
132 What Chemical Compounds Make Jams Set?
134 What Causes the Bitterness and Dry
Sensation in Red Wine?
137 How Do Bubbles Enhance the Taste of Champagne?
143 Photo Credits
Food plays a huge part in our everyday lives, but we hardly
ever stop to think about the science behind it. We all know that
chopping onions makes you cry, that eating garlic gives you
bad breath and that mint makes your mouth feel cool, but most
people don’t have a clue how to describe the chemical reasons
behind these strange effects. The aim of this book is to look at
the quirky and sometimes downright weird properties that food
and drink can exhibit, and explain in simple terms the chemistry
that leads to them.
In our explanations, we’re going to be talking primarily
about organic chemistry. This use of the word “organic” is
different from the one that we usually associate with food in
supermarkets; in chemistry, it refers to chemical compounds
based on carbon. There are many millions of possible organic
compounds, with a wide range of different properties. You,
yourself, are made up of organic compounds, and so are the
foods we eat. These compounds are responsible for the flavor
and aroma of the foods and drinks we consume on a daily
basis, and can also help explain some of the different effects
that we see.
The hope is that the material in this book will be accessible
even to those who only have a basic understanding of
chemistry. There is a brief introduction on the next page
to some of the chemistry, to help with interpretation of the
structures and descriptions later in the book.
If you do have a background in chemistry, and want to read in
further detail on some of the topics examined here, references
to the studies consulted during the writing of this book are also
given at the end.
Whatever your interests or curiosities, I hope that the chemistry
in this book will turn the everyday into the extraordinary for you.
A BRIEF INTRODUCTION TO ORGANIC CHEMISTRY
H C H
H C H
Organic chemistry is the study of carbon-based
compounds. Organic compounds usually contain
primarily carbon and hydrogen, but we’ll also see
some containing the other elements shown here.
The chemical bonds in organic compounds are formed by the atoms sharing a pair of electrons
with each other. Carbon can form four bonds to other atoms; oxygen usually forms two bonds,
while hydrogen can only form one bond. Bonds are shown as lines; two lines between atoms
indicates a double bond, or two shared pairs of electrons.
H C C OH
H C C OH
Dashed bond (into page)
Wedged bond (out of page)
Organic compounds can be drawn showing all their bonds and
all their atoms, as on the left. However, for bigger molecules,
this can end up looking pretty messy so we commonly use the
skeletal formula to represent molecules.
The skeletal formulas show each carbon atom as a bend in the
chain of the molecule. Hydrogen atoms attached to carbons
aren’t shown, to make the structure easier to interpret. Atoms
other than carbon and hydrogen are shown.
While chemical structures are shown in two dimensions on the
page, obviously they are three dimensional in real life. In some
cases, it is useful to indicate this in structures, so for this purpose
we sometimes use dashed bonds, to show a bond going away
from you and into the page, and wedged bonds, to show a bond
coming toward you and off of the page.
Functional groups are groups of atoms in organic compounds that are responsible for the characteristic reactions and
properties of those compounds. In many compounds in this book, you will see several of these groups in one molecule. The
functional groups present in a molecule are usually reflected in its name, as indicated here.
Functional Groups in Organic Chemistry
You may also see “R” used in some molecules—this represents a further part of the molecule that may be variable. If you see
“X” used, it indicates a halogen atom (the halogens are the elements fluorine, chlorine, bromine and iodine). Some typical
functional groups are shown here.
R1 C C R2
Naming: haloe.g., chloroethane
Naming: -oic acid
e.g., ethanoic acid e.g., ethanamide
Naming: -amine Naming: -ylbenzene
e.g., ethanamine e.g., ethylbenzene
Metabolism product of
PTC TASTES BITTER TO 70% OF PEOPLE
It’s thought that cruciferous vegetables can induce a similar eff ect,
as their breakdown products, isothiocyanates, are chemically similar.
EXAMPLES OF CRUCIFEROUS VEGETABLES
Brussels sprouts generally have higher levels of glucosinolates
compared to other cruciferous vegetables
Found in all cruciferous vegetables
(R group varies)
There’s one vegetable at the Christmas dinner table that’s
always bound to elicit strong and contrary opinions: brussels
sprouts. Much like black licorice, they seem to conjure up a
“love it or hate it” sentiment; however, if you fall into the latter
camp there may be a chemical and genetic reason why you
can’t stand the taste.
Before discussing brussels sprouts specifically, we actually
need to look at a chemical that isn’t even found in them,
phenylthiocarbamide (PTC). This compound is an oddity in that
it tastes bitter—but only to around 70 percent of people. To
the other 30 percent it’s completely tasteless. This property
of PTC was discovered by accident in 1931, when Arthur
Fox, a chemist working for the chemical company DuPont,
accidentally spilled some of the compound while he was
working with it. His colleague working nearby complained of the
bitter taste, but Fox couldn’t detect it.
Fox went on to carry a series of taste tests with his friends and
family, further confirming that it tasted bitter to some, but not
all. These studies, along with further work, confirmed the ability
to taste PTC as a dominant genetic trait, and one that can be
inherited. Before the advent of readily available DNA testing,
the ability to taste PTC was commonly used in paternity cases.
Another compound, propylthiouracil (PROP), is similar in that it
also tastes bitter to some and not others, and is now the more
commonly used compound in taste research.
WHY DO SOME PEOPLE HATE BRUSSELS SPROUTS?
At this point, you’re probably wondering what this has to do
with brussels sprouts. While PTC and PROP aren’t found in
vegetables, they contain a thiocyanate group (nitrogen, carbon
and sulfur bonded in series) which is thought to be related to
its bitter taste. This same group is also present in compounds
called glucosinolates that occur naturally in brussels sprouts,
as well as broccoli, cabbage and kale (collectively known
as cruciferous vegetables). There also seems to be a strong
association between the ability to detect the bitter taste of
PROP and a sensitivity to the bitterness of these vegetables.
It’s not the case that sensitivity to PTC and PROP automatically
implies a dislike of cruciferous vegetables; other environmental
factors may also have an effect. However, if you’re a brussels
sprout hater and you are berated for your perceived vegetable
prejudice, you can now suggest a chemical reason for your
WHY DO ARTICHOKES MAKE DRINKS TASTE SWEETER?
Artichokes have an unusual claim to fame—they’re the only
known plants consumed on a large scale across the world that
have taste-modifying properties. To some people it can cause
drinks to taste sweeter straight after eating it, which apparently
causes great difficulty when pairing dishes containing
artichokes with wine. This effect comes down to particular
chemical constituents contained within artichokes.
This strange effect was first noted in research at an American
Association for the Advancement of Science dinner. Artichokes
were included in one of the courses, and after it was said
that 60 percent of the 250 people attending reported that the
water being served tasted sweeter. Decades later, a researcher
investigated this effect by exposing subjects to artichoke
extract, as well as individual constituents of the extract, and
recording the perceived impact on the taste of water.
It was found that, of the constituent compounds in artichokes,
potassium salts of chlorogenic acids and cynarin were major
causes of the effect. Potassium ions are the dominant metal
ions present in artichokes, hence why potassium salts of the
compounds were used. Cynarin in particular was found to
have a sweetening effect equivalent to adding two teaspoons
of sugar to ¾ of a cup (170 milliliters) of water. That said,
although these compounds were found to be the major sources,
they still didn’t account for the full effect of artichoke, so other,
lesser compounds may also be implicated.
We still don’t know exactly how these compounds cause other
substances to taste sweeter, but we do know it’s a result of
them interacting with sweet-detecting taste buds on the tongue
in such a way that non-sweet substances taste sweet. It also
doesn’t affect everyone, as the survey taken at the dinner
which initially highlighted the effect showed—it’s assumed that
there must be some form of genetic basis to the effect.
So, the next time you get a chance, why not try eating an
artichoke and see if it works for you?
Estimated percentage of the
population who experience
the sweetening effect of
Major compound that
THE COMPOUNDS IN ARTICHOKES HAVE A SIMILAR
SWEETENING EFFECT ON TASTE BUDS TO ADDING
TWO TEASPOONS OF SUGAR TO ¾ cup OF WATER
HOW MIRACULIN WORKS
NUMBER OF AMINO
ACIDS THAT MAKE
UP THE MIRACULIN
Binds to sweet taste
First documentation by
explorer Chevalier des
Marchais while exploring
receptors to be
activated by acids
The effect lasts
A BRIEF HISTORY OF
MIRACULIN IN OTHER PLANTS
Areas in which miracle fruit can be grown are
limited due to its tropical origins. Scientists
have attempted to produce miraculin in other
plants, with mixed success rates.
Robert Harvey’s hope
to market miraculin as a
sweetener is thwarted by
the FDA, who deem it can’t
be classified as “generally
recognized as safe.”
isolated from miracle
fruit by Professor Kenzo
Miraculin purified and
sequenced by Professor
Researchers find that
miraculin improves insulin
sensitivity in diabetics.
Miraculin piloted as a
taste-masking agent for
Miracle berries (Synsepalum dulcificum) grow on a shrub native
to West Africa, and have curious taste-modifying abilities. After
chewing the fruit, it can make sour food and drink taste sweet
for up to an hour after. For example, eating miracle berries
before drinking lemon juice removes the sourness completely.
This effect is due to the presence of a particular protein which
is only found in miracle berries, named miraculin.
As a protein, miraculin has a very large molecular structure—
too large to be shown here. To give an idea of its size, it’s
made up of 191 amino acids, amino acids being the molecular
building blocks of proteins. The molecule isn’t sweet by
itself, and we actually still don’t fully understand how it
produces its taste-altering effect. Your tongue is covered in
receptors capable of detecting different tastes, and what we
do know is that miraculin can bind to the taste receptors that
detect sweetness very strongly. Then, when you eat or drink
something sour, it can react with the miraculin. This reaction
has a knock-on effect, causing the shape of the sweet taste
receptors to distort. This distortion makes them much more
sensitive, and the signals they relay to the brain overpower
those of the sour tastes, causing you to experience a sweet
taste even with sour foods. This lasts until the miraculin is
eventually uncoupled from the receptors.
HOW DO MIRACLE BERRIES MAKE SOUR FOODS TASTE SWEET?
While this effect might seem like nothing more than a curiosity,
food scientists have for many years been looking at ways in
which miraculin could potentially be used as a sweetener. There
are a number of problems to overcome—first, miraculin isn’t
heat stable, and above 212° F (100°C) it loses its taste-altering
properties, so it isn’t possible for it to be used in any foods that
require cooking. Another problem is the duration of its effect,
though scientists have succeeded in creating a version of the
protein whose effect is much shorter lived, which could make
its use much easier.
The FDA (Food and Drug Administration) has ruled that
miraculin is an additive, and cannot be given the status of
“generally recognized as safe,” meaning it will likely require
several years of testing before it can be included in food
WHY DOES ORANGE JUICE TASTE BITTER AFTER BRUSHING YOUR TEETH?
Most people have probably made the mistake of drinking
orange juice immediately after brushing their teeth. The effect
generated isn’t a pleasant one—the resulting taste is bitter,
with none of the original sweetness of orange juice. Research
suggests that this effect can last up to 30 minutes after the
use of toothpaste, and it can also be subtly noticed with other
The root of the effect can be found in one of the chemical
constituents of toothpaste. Sodium lauryl sulfate is a compound
commonly used in personal care products, including toothpaste,
shampoo and shower gel. It acts as what chemists call a
“surfactant.” Essentially, the molecule has one end which will
dissolve in water and one end which is insoluble in water, but
soluble in grease and oils. This helps it dissolve and remove dirt
when you wash your hair. It also stimulates foaming; in toothpaste,
it lowers the surface tension of saliva, allowing a foam to form.
Sodium laureth sulfate is a chemical commonly used instead of
sodium lauryl sulfate, but it performs exactly the same role. Some
rumors have falsely claimed that these chemicals are cancer
causing, but there is scientific evidence that they are completely
safe at the concentrations we usually encounter.
The presence of sodium lauryl sulfate (or its alternative) in
toothpaste is thought to be the cause of its effect on the taste
of orange juice. The commonly accepted explanation for this
effect is that sodium lauryl sulfate suppresses the receptors
in your mouth that help you detect sweetness. At the same
time, it’s also thought they can alter membranes formed by
compounds called phospholipids, which usually inhibit your
bitter taste receptors to an extent. As a consequence, when
you drink orange juice immediately after toothpaste, the sweet
taste is dulled and the bitter taste is emphasized, producing the
somewhat unpleasant effect.
If, for whatever reason, you want to avoid this unfortunate effect
of toothpaste (instead of never brushing your teeth again), there
are alternatives to sodium lauryl sulfate toothpastes. These
often use glycyrrhizin, a compound isolated from licorice root,
in order to produce their foaming effect.
The surfactant molecules in toothpaste
aﬀ ect our sense of taste.
Alters phospholipid membrane
structures, which usually inhibit
Surfactants inhibit sweet taste
receptors, reducing sweetness.
SODIUM LAURYL SULFATE
aka SLS, foaming agent in many toothpastes
SODIUM LAURETH SULFATE
sometimes used in place of SLS
DURATION LASTS FOR UP TO 30 MINUTES
Author Andy Brunning Isbn 9781612435510 File size 13MB Year 2016 Pages 128 Language English File format PDF Category Chemistry Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare FOOD QUESTIONS ANSWERED WITH COLORFUL GRAPHICS AND FUN, EASY-TO-UNDERSTAND SCIENTIFIC EXPLANATIONS Have you ever wondered… Why bacon smells so good? Why onions make you cry? If eating turkey makes you sleepy? If mixing drinks makes a hangover worse? How energy drinks work? Why chocolate is poisonous to dogs? Why coffee makes you more wired than tea? Why cilantro tastes soapy to some? The answers to these baffling questions and more are revealed in this friendly, informative collection of trivia. Not a scientist? No problem. This books colorful graphics and easy-to-understand explanations make these food facts fun for everyone. Download (13MB) Bitter: A Taste of the Worlds Most Dangerous Flavor, with Recipes Handbook Of Mineral Elements In Food Your Brain on Food: How Chemicals Control Your Thoughts and Feelings How Life Works : The Inside Word From a Biochemist Chemistry and Technology of Soft Drinks and Fruit Juices, 3rd Edition Load more posts