HOW TO FOSSILIZE YOUR HAMSTER (Chapter One)1 In the Kitchen
Can you make plastic in your kitchen?
You would imagine that you'd need some pretty noxious, smelly chemicals to make plastic, but you can actually find the things you need to make malleable, doughy pieces of it in your own home. Instead of putting vinegar on some fish and chips and crying over your spilled milk, use them to become a polymer chemist.
WHAT DO I NEED?
a pint of milk
a sieve or colander
a spoon for stirring
four teaspoons of white vinegar
WHAT DO I DO? Pour the milk into the pan and gently warm it. When the milk is simmering (don't let it boil), stir in the white vinegar until you notice whitish yellow rubbery lumps beginning to curdle in the mixture and the liquid clearing. Turn off the heat and let the pan cool.
WHAT WILL I SEE? First of all you'll smell the vinegary reaction, which is the key to the process at work. As the vinegar is added and stirred, the liquid gets clearer, and the yellowy rubbery lumps form. When the pan has cooled you can sieve the lumps from the liquid, pouring the liquid down the sink. Put on the rubber gloves and wash the lumps in water. You can then press them together into one big blob--they will be squishy and will feel as if they are going to fall apart, but they will stick together after some firm kneading. You can now use your artistic skills to fashion the material into the shapes of your choice--the New Scientist staff came up with balls, stars, a heart shape for a pendant, and even dinosaur footprints. Leave the material to dry for a day or two, and it will become hard and plastic enough to paint and varnish.
WHAT'S GOING ON? You have used the combination of an acid--in this case vinegar, which contains acetic acid--and heat to precipitate casein (a protein) from the milk. Casein is not soluble in an acid environment, and so when the vinegar is added to the warm milk, it appears in the form of globular plastic-like lumps. Casein behaves like the plastics we see in many objects around us, such as computer keyboards and phones, because it has a similar molecular form. The plastics in everyday objects are based on long-chain molecules called polymers. These are of high molecular weight and get their strength from the way their billions of interwoven crisscrossing molecules tangle together.
P.S. Some forms of cheese making rely on a similar technique--the name "casein" comes from caseus, the Latin for cheese. The Indian cheese known as paneer is made in a very similar way to the plastic you have just made, although in this case lemon juice is the acid used rather than vinegar. Afterward, unlike our plastic milk, it is not dried out and allowed to harden to tooth-breaking consistency, and so remains soft and edible.
Breakfast cereals often claim to be fortified with iron. Well, are they?
They are and, more amazingly, if you have a magnet you can extract it, too! So ponder the ingredients list on your box of cornflakes while you are munching breakfast, and then set about removing one of them.
WHAT DO I NEED?
breakfast cereal fortified with iron (cornflakes work, but check on the side of the box to see what the iron content is--the higher, the better)
a plastic cup
a spoon or pestle to crush the cereal (better still, a blender)
a very strong magnet
clean white paper
a clear, sealable plastic sandwich bag
WHAT DO I DO? Fill the cup to about two-thirds full with cereal, and with the spoon or pestle crush the cereal into a fine powder. It is worth spending a lot of time on this stage--the finer the powder, the better. Put the crushed cereal into the sandwich bag and add hot water. Leave the mixture for about fifteen to twenty minutes. Now gently tilt the bag forward so that the cereal collects on one side, and place the magnet along the outside of the bag near the cereal, running it over the bottom, because the iron tends to sink. Tilt the bag back so that the cereal runs away from the magnet. You can also lay the bag flat on the table and stroke the magnet across it toward a single corner of the bag.
Alternatively, if you are using a blender, put the cereal straight into the blender and add hot water until the cereal is submerged. Wait for about fifteen to twenty minutes until the cereal is soft, then blend it all together. While the blender is whirring, place the magnet on the outside of the blender near the mixture, and keep it there as you turn the blender off.
WHAT WILL I SEE? The magnet will attract a black fuzz of iron. Move the magnet over the surface of the bag or blender and the tiny pieces of iron will follow it.
WHAT'S GOING ON? The black stuff really is iron in your cereal--the same stuff that is found in nails and trains and motorbikes. And it's quite heavy, which is why you need to make sure you run your magnet along the bottom of the bag. The iron is added to the mix when the cereals are being made, and you really do eat it when you devour your cornflakes.
The reason it is added in a form that you can extract is that iron ions (iron that would more easily combine with other molecules in the cereal) increase the spoilage rate of the food. Using iron in its pure metal form gives the cereal a longer shelf life.
The hydrochloric acid and other chemicals in your stomach dissolve some of this iron, and it is absorbed through your digestive tract, although much of it remains untouched and is excreted.
P.S. Humans need iron for many important bodily functions. Red blood cells carry hemoglobin, of which iron is a key constituent. Hemoglobin transports oxygen through the blood to the rest of the body by binding oxygen to its iron atom and carrying it through the bloodstream. As our red blood cells are being replaced constantly, iron is an essential part of our diet.
Can you maintain the fizz in champagne overnight if a teaspoon is suspended in the neck of the bottle?
I have included this experiment not because it is spectacular or even because it actually works, but to illustrate the use and importance of controlled conditions when attempting to prove or disprove a theory. For any experiment in this book, you can add a control for comparison to test whether a particular ingredient is the cause of the reaction you are observing.
WHAT DO I NEED?
at least two bottles of champagne
WHAT DO I DO? Open two bottles of champagne. Drink some from each, then place a teaspoon into the neck of one of the bottles, with the handle dangling downward and with no part of the teaspoon touching the liquid. Drink a little more if it is. The other bottle should be left open. To maintain a true control, keep the amount of champagne in each bottle equal. Now place both in the fridge and leave them overnight. Test them at regular intervals, noting how fizzy each bottle is and whether there is any significant difference between the two. I suggest you test them the following morning, lunchtime, and evening, and again on subsequent days, until the champagne in both bottles has lost all its fizz.
WHAT WILL I SEE? You'll need to be objective in your assessment of the fizz quotient of each bottle, but you will find, especially if you repeat the experiment as any decent scientist would, that both bottles are equally fizzy at each stage of testing. As an objective measure you could see how much champagne needs to be added to the champagne flutes for the bubbles to reach the rim, but for this to work you'll have to make sure you pour all glasses at the same rate.
WHAT'S GOING ON? This question is a classic example of being misled by uncontrolled experiments.
Because people rarely have two bottles open at the same time, if they have stored an unfinished bottle with a suspended spoon in its neck they attribute the following day's unexpected longevity of fizz to the spoon. However, in your tasting experiments you will have found that the truth of the matter is that champagne--surprisingly--keeps its fizz for three days or more, with or without the teaspoon.
The opened bottle without the teaspoon acts as a control against which you are able to gauge the fizziness of the bottle with the teaspoon in its neck. Both bottles decrease in fizziness at exactly the same rate.
It's not uncommon to attach significance to apparently linked events when there is no control data to compare them with. Often you'll hear people saying things like, "How incredible, I was just thinking of you when the phone rang and it was you." Telepathy is not involved here. We merely ignore the huge number of times we think of people and the phone does not ring.
P.S. If your budget doesn't stretch to champagne, the experiment will work just as well with cava, Asti Spumante, or a domestic sparkling wine.
If a strand of dried spaghetti is held at both ends and bent, why does it always break into three or more pieces?
This is, indeed, a strange phenomenon. Surely holding a strand of dried spaghetti at both ends and bending it until it breaks should produce just two pieces, but it hardly ever does--usually three or even more pieces are the result. This conundrum first appeared in New Scientist in 1995 and was repeated in 1998. Even so, we didn't get to the bottom of it until 2006. It's a problem that has taxed greater minds than ours, including that of the Nobel Prize-winning physicist Richard Feynman.
WHAT DO I NEED?
strands of dried spaghetti
something to catch them in
WHAT DO I DO? Hold a strand of spaghetti at both ends and bend it until it breaks. Count the pieces. Repeat with the other strands.
WHAT WILL I SEE? In nearly all cases the spaghetti will break into three or more pieces. Even on the rare occasions when it seems to break into only two you'll often find a stray shard or splinter has flown off into the nether regions of your kitchen.
WHAT'S GOING ON? Back in 1998, a New Scientist reader tried to come to grips with the issues involved and came very close to solving the problem.
First, when you bend a piece of spaghetti, it does not usually break at the apex of the bend where the stresses are highest, because failure in the spaghetti is controlled by defects in the pasta. The first break occurs at a point near the apex where the combination of stress level and defect size reaches a critical value. This breaks the original piece into a long and a short piece. After the break, as the longer piece snaps back, the whipping action sends the tip beyond the neutral point (the original straight state of the piece of spaghetti) and activates the next defect on what was the long side. This defect has already been opened up on the outside of the curved spaghetti by the first bending, so it doesn't take much to finish off the crack by bending it in the other direction.
both strands subject to flexual waves after snapping
flexual wave causes spaghetti to spring back after breaking; already weakened here by previous bending
third piece snaps off after springing back
Second, the sequence of events can be determined by looking at the broken ends of the spaghetti pieces. When a break occurs, the fracture starts cleanly on the stretched convex side and ends slightly raggedly on the compressed concave side where a small splinter--or spicule--is usually torn away from one side of the break. Additionally, careful inspection of the ejected middle piece of spaghetti will reveal evidence of spicule formation at both ends and that these are on opposite sides. This shows that the two breaks that generate the middle piece occur while the spaghetti is bending in opposite directions, which is consistent with the dynamics of linear spaghetti structures.
While being very much on the right track, the reader's observations only partly answered the conundrum. It took Basile Audoly and Sébastien Neukirch to verify what was going on in their paper "Fragmentation of Rods by Cascading Cracks: Why Spaghetti Does Not Break in Half," published in Physical Review Letters (volume 95, number 9, December 22, 2004, page 95505).
Audoly and Neukirch broke strands of spaghetti of varying thicknesses and lengths by clamping one end and bending them from the other. They found that the unexpected three-part breakage occurs because of what are known as flexural waves. When the curvature of the spaghetti reaches a critical point, the first break appears. The shock of this causes a flexural wave to ripple down each of the two resulting lengths of pasta at high speed and amplitude.
The two halves formed by the initial break do not have time to relax and straighten before being hit by the flexural wave, which causes them to curve even further and suffer more breaks, leading to a cascade of cracks in the pasta. Often more than three pieces are created when this happens.
While spaghetti snapping is in itself a rather humdrum if fun pastime, Audoly and Neukirch's work also provides important information about failures in other elongated, brittle structures, including human bones and bridge spans.
P.S. In No Ordinary Genius, the illustrated biography of Richard Feynman published in 1994, Danny Hills describes his and Feynman's experiments with spaghetti: "If you get a spaghetti stick and break it, it turns out that instead of breaking in half, it will almost always break into three pieces. Why is this true--why does it break into three pieces? Well, we ended up at the end of a couple of hours with broken spaghetti all over the kitchen and no real good theory about why spaghetti breaks into three." This seems to have been a common occurrence--apparently visitors to Feynman's home were often presented with sticks of spaghetti and asked to help solve the problem.
There is, therefore, a delicious irony in the fact that while this puzzle drove Feynman, a Nobel Prize winner, in physics, to distraction, those who discovered the reason why it happened were awarded the antithesis of Nobel fame, the Ig Nobel Prize for Physics in 2006, forty-one years after Feynman won his Nobel Prize. Nobel Prizes are awarded for supreme achievements in scientists' chosen fields, while Ig Nobels, from the opposite end of the research spectrum, are awarded for success in the areas of improbable research, humor, and, quite often, silliness.
WANT TO READ MORE? A video of breaking spaghetti can be seen at http://www.lmm.jussieu.fr/spaghetti/index.html, where you can also find out more about Audoly and Neukirch's research.
No Ordinary Genius (1994) was edited by Christopher Sykes and published by W. W. Norton & Company.
What's the best way to store bananas to keep their skins from turning brown quickly?
This is counterintuitive to those of us brought up to believe that chilling foodstuffs slows decay, but a simple experiment will show us if it's true or not.
WHAT DO I NEED?
two or more bananas (and possibly some fresh banana skins)
a fridge (or a domestic freezer)
WHAT DO I DO? Place one banana in the fridge and leave the other at room temperature (approximately 68°F). Observe each banana three or four times a day and note the relative discoloration of the skins. As a side experiment, rub a third banana with lemon juice before subjecting it to the fridge conditions.
WHAT WILL I SEE? The banana in the fridge will brown or blacken faster than the one at room temperature. However, a banana rubbed with lemon juice and placed in the fridge will not decay at the same rate as the untreated one.
WHAT'S GOING ON? While many fruits are stabilized by refrigeration, most tropical and subtropical fruits, and bananas in particular, exhibit chill injury. Tests show that the ideal temperature for long-term banana storage is 56°F. Below 50°F, spoilage is accelerated because their cells' internal membranes are damaged, releasing enzymes and other substances. Banana skin can blacken overnight as it softens and breaks down.
The membranes that keep separate the contents of the various compartments inside a cell are essentially two layers of slippery fat molecules or lipids. Chill these membranes and the molecules get more sticky, making the membranes less flexible. Bananas adjust the composition of their membranes to give the right degree of membrane fluidity for the temperature at which they normally grow. They do this by varying the amount of unsaturated fatty acids in the membrane lipids: the greater the level of unsaturated fatty acids, the more fluid the membrane at a given temperature. If you chill the fruit too much, areas of the membrane become too viscous, and it loses its ability to keep the different cellular compartments separate. Enzymes and substrates that are normally kept apart therefore mix as the membranes collapse and hasten the softening of the fruit flesh.
Skin blackening involves the action of a different enzyme from those involved in flesh softening. In the skin, polyphenol oxidase breaks down naturally occurring phenols in the banana skin into substances similar in structure to the melanin found in suntanned human skin. So the browning starts sooner in refrigerated bananas because of chill-induced membrane damage that allows the normal process of decay--which would have occurred anyway at room temperature--to begin earlier. The cold itself does not speed up the browning part of the reaction. Indeed, if chill damage in a fridge is induced first, removing the banana from the fridge then hastens the process as the reaction that causes the browning, once it is under way, is speeded up by heat.
This can be demonstrated by putting a banana skin in a freezer for a few hours. The inner surface will stay creamy white because, although the membranes are destroyed by the freezing process, the oxidases cannot work at such low temperatures. Then let it thaw overnight at room temperature. In the morning it will be pitch-black due to the damage the cell membranes suffered in the freezer. Yet had the cold itself caused the blackening, it would have turned dark while it was being frozen.
Decay can be slowed by acids, which prevent the release of the polyphenol oxidase enzyme. This is why adding lemon juice--which is rich in citric acid--to skins can slow the browning process. A similar slowing of the breakdown process can be seen if bananas are coated in wax; this prevents oxygen from reaching the skin and speeding up decay.
P.S. In commercial storage of tropical fruit, chilling injury is a big problem. Unlike temperate fruits such as apples and pears, which can be stored at temperatures close to freezing, tropical fruits break down faster in the cold. Because tomatoes, now commonplace in northern Europe and North America, are actually a semitropical fruit, the evidence suggests that they will last longer out of the fridge than in it. I look forward to hearing from readers about their home experiments on tomatoes and any number of other fruits whose growing environments straddle temperate and tropical climes.
Why does a grain of cooked rice in a glass of lemon-lime soda repeatedly rise to the surface and fall to the bottom?
I have fond memories of fooling gullible schoolmates with this "magic" trick, telling them that for a modest sum I could make objects at the bottom of the glass mystically rise to the surface. That was until I was outed by the head of chemistry and forced to hand back my ill-gotten proceeds.
WHAT DO I NEED?
a glass of lemon-lime soda (other fizzy drinks will work just as well, but transparent drinks are better than opaque ones if you want to see the rice)
grains of cooked and uncooked rice
WHAT DO I DO? Drop a grain of cooked rice into the soda and wait. For comparison, put a grain of uncooked rice in a glass of soda. As a control (discussed in the "Fizz Fallacy" experiment), put a grain of cooked rice in a glass of still water.
WHAT WILL I SEE? The cooked rice will sink to the bottom of the glass of soda. Then, after a short while, it will begin an inexorable cycle of rise and fall between the surface and the glass bottom. The uncooked rice will also rise and fall, but more slowly. The rice in the control will do nothing.
WHAT'S GOING ON? Initially, the grain of rice sinks in the soda because it is denser than the liquid around it. However, once the grain has reached the bottom of the glass, bubbles of carbon dioxide begin to collect around it. This is because bubbles in fizzy drinks tend to form preferentially around rough surfaces, which provide what are known as nucleation sites. Nucleation sites are hydrophobic (they repel water) and allow gas pockets to form without first forming the tiny bubbles. The uncooked grain has fewer rough edges and fewer nucleation sites, so the process takes longer.
Eventually, the bubbles of carbon dioxide begin acting as if they were airbags inflated underwater and attached to the grain. The rice then becomes buoyant and starts rising. When it reaches the surface, the bubbles burst and it sinks again, restarting the process. If you leave the soda and rice for long enough, the drink will go flat and the rice will stop ascending.
P.S. The New Scientist team is indebted to the students of the Aberdeen University Scottish Country Dance Society who were kind enough to send in their extensive research in this field carried out over a number of years in controlled laboratory conditions (the student bar) using a variety of drinks and bar snacks. They tell us that the most consistent effects were usually obtained using salted peanuts and cheap lager. In fact, a handful of peanuts rising and falling in a pint of lager can produce an effect similar to the lava lamps popular in the 1960s and 1970s. Unfortunately, but not surprisingly, the salt on the nuts makes cheap lager unpalatable, so do this only if you have no intention of consuming the beer later.
Interestingly, Newcastle Brown Ale and many bottled ciders are so fizzy that bubbles form too quickly, and the salted peanuts never have time to sink back to the bottom but remain at or near the surface. Dry-roasted peanuts are far too dusty to work properly, and potato chips and pork rinds don't sink in the first place but float soggily at the surface.
Green Eggs and Cabbage
Why does the juice from cooked red cabbage turn fried egg whites green?
Chef Heston Blumenthal, one of the founding fathers of molecular gastronomy, would love this one. So would Dr. Seuss. You need only a small amount of red cabbage juice to change the color of fried eggs from white to green. Your kids and brunch guests will be completely taken aback.
WHAT DO I NEED?
shredded red cabbage
a frying pan
WHAT DO I DO? Boil the cabbage in a pot for twenty minutes and let it cool. Squeeze the juice from the cooled cabbage into a jug. Heat the oil in a frying pan and begin to fry the egg until the white is just turning from clear to white. Drip a small amount of cabbage juice into the setting egg white.
WHAT WILL I SEE? The egg white will turn lurid green where the juice hits it.
WHAT'S GOING ON? Red cabbage juice is a good indicator of whether a substance is an alkali or an acid. If added to an alkali, such as ammonia, it will turn green; if added to an acid, such as lemon juice, it will turn red. In neutral substances it is purple, the natural color of red cabbage. Because egg white (mostly the protein albumen) is alkaline, it turns green. Any number of substances can be tested in this way, although take care to avoid strongly corrosive chemicals such as drain cleaners or bleach, because these can be dangerous.
The experiment works because red cabbage contains water-soluble pigments called anthocyanins (also found in plums, apple skins, and grapes). These change color depending on whether they are in the presence of an acid or an alkali. These change the number of hydrogen ions attached to the molecule--acids donate hydrogen ions while alkalis remove them--and it is the presence or absence of hydrogen ions that is responsible for creating the different colors. This explains why red cabbage that is pickled turns red rather than its natural purple. Pickling takes place in vinegar, which is acidic.
Red cabbage juice breaks down quite quickly, so if you are going to use it to test the acidity or alkalinity of other household foods or products, use it sparingly and fast.
P.S. A trick that will prove popular with children is to create "magic" paper. Soak cheap absorbent paper in boiled red cabbage water and leave it to dry. Then paint it with household substances such as vinegar, orange juice, or powdered clothes detergent dissolved in water. A range of colors will appear on the paper depending on the acidic or alkaline nature of the paints used.
Why does brown or whole wheat bread char more quickly than white bread when you toast it? (Which may explain why I burn the toast but my wife doesn't....)
WHAT DO I NEED?
slices of brown or whole wheat bread
slices of white bread
You may also want to have butter and jam or jelly handy to ensure your efforts are not wasted.
WHAT DO I DO? Place the brown bread in the toaster. Check it every fifteen seconds to see when it starts to burn (you'll need to set a clear if subjective measure of what you consider to be charred bread in advance). Take a note of the time. Repeat with the white bread.
WHAT WILL I SEE? You'll notice that the brown or whole wheat bread toasts much faster than the white bread.
WHAT'S GOING ON? During heating, a complex reaction occurs between the proteins and sugar contained in the bread. This is known as the Maillard reaction, and it produces the typical flavor we know from toasted bread as well as the color formed as the bread toasts.
The Maillard reaction is a chemical one between an amino acid and a reducing sugar. It usually requires the addition of heat, as in the case of toasting bread. The reaction is widely used in the food industry, producing different flavors and odors according to the type of amino acid involved in the reaction.
Because brown and whole wheat bread contain more sugar and protein than white bread, they undergo more rapid Maillard browning than white bread does.
One other factor may help to explain why white bread chars more slowly: albedo, the proportion of incident light or radiation that is reflected by a surface. White bread reflects more radiation than brown bread, which is why it appears whiter. Because darker breads absorb more radiation in the form of heat from the toaster, they heat up and burn more quickly.
P.S. While you have the loaves of bread out, you can try another experiment. Take a fresh, untoasted slice of bread and spread it with honey. Then set it aside. If you leave it for a few minutes, you'll see that it becomes concave on the side spread with honey. This is because bread is approximately 40 percent water while honey is a strong solution containing approximately 80 percent sugar. Sugar is hygroscopic, which means that it soaks up moisture. This causes moisture to be drawn out of the bread and into the honey by osmosis. Extracting the water makes the bread shrink, but only on the side exposed to the honey. This explains why the bread becomes concave.
This is less likely to happen if you butter your bread before spreading on the honey. Butter forms a fat-rich, water-impermeable layer that protects the bread from dehydration by the honey.
WANT TO READ MORE? The chemistry of different bread types is discussed in The Composition of Foods by Robert Alexander McCance and Elsie Widdowson (Elsevier/North-Holland Biomedical Press).
Most hard cheeses such as cheddar go stringy when grilled, yet Indian paneer and Greek-Cypriot halloumi don't melt at all; they just char while maintaining their shapes. Why is this?
All cheese is made from milk, so that obviously cannot be the reason. When you try this out, keep a slice of toast from the "Burnt Offerings" experiment on hand--there's no point in wasting melted cheese.
WHAT DO I NEED?
cubes of cheddar
cubes of paneer or halloumi cheese
an oven broiler
bread to eat the results with
WHAT DO I DO? Thread the cheese cubes onto the skewers, place under the broiler, heat at a high temperature, and watch what happens.
WHAT WILL I SEE? The cheddar will start to go stringy and drip into the broiler's pan. (This is where some bread, slowly toasting below the cheese skewer, will come in handy.) Meanwhile, the paneer or halloumi will retain its cube shape and often char. Fortunately, it, too, can be eaten after it has cooled a little.
WHAT'S GOING ON? Uncooked cheddar contains long-chain protein molecules curled up in a fatty, watery mess. It also has a low melting point which means it becomes runny before it burns. As the fats and proteins melt and drop under the weight of gravity, they are dragged into dripping strings--just as they are if you take a bite from a grilled cheese sandwich or from the bread that has collected the drippings from your cheddar skewer. As the cheese softens, the long-chain protein molecules unravel and form fibers. From eating pizza, you'll know that mozzarella displays this quality even better and can string out to a foot or more. In fact, string length is a measure of protein content--the longer the string of cheese, the more protein it contains.
However, in addition to melting and becoming stringy, the protein in cheddar is denatured by the heat. This is why previously molten cheddar turns into an unpleasant rubbery lump after it cools. Paneer, halloumi, and similar cheeses are produced by taking advantage of this process. They have already been partially cooked--some with heat and others with exposure to acid--while they are made, so important changes have already taken place before you put them under your grill. The denaturing effect means the cheese is already in a rubbery state and so keeps its shape. That ensures that the paneer in Indian dishes doesn't ooze all over the place and makes halloumi perfect for use in kebabs. Of course, these cheeses can still burn easily, so keep a close eye on this experiment at all times.
P.S. Try reheating cold, previously molten cheddar to see whether its properties have become like those of paneer and halloumi. You'll find you've produced your own denatured cheese in the kitchen, even though it's just about inedible.
In the Dumps
Why do matzo balls and gnocchi dumplings float while uncooked ones remain close to the bottom of the pot?
I have happy memories of my mom's home-cooked beer and beef stew with dumplings, which has flour-based dumplings not unlike matzo balls and gnocchi, so this question offered me the perfect opportunity to revisit a favorite childhood dish. If you don't have a family recipe for matzo balls or gnocchi that you'd like to cook up to test this principle, I've provided a recipe for dumplings below, courtesy of Mom, who has always been an expert at traditional English fare.
WHAT DO I NEED?
uncooked matzo balls, gnocchi, or other dough-based dumplings
a pot of simmering liquid of your choice (a stew or soup stock works well for converting your research into a sublime culinary experience)
a slotted spoon
WHAT DO I DO? Lower the uncooked dumplings carefully into the simmering liquid with a slotted spoon.
WHAT WILL I SEE? The uncooked dumplings will initially sink to the bottom of the pan. As they cook, they will rise to the surface. While I admit that this is easier to see if you are using boiling water, it's more efficient to cook them in a stew or soup since, of course, you'll end up with dinner after the experiment has been completed.
WHAT'S GOING ON? Two factors are at work. It seems the main reason the dumplings float once they are cooked is because bubbles become trapped in their dough matrix--held together with the gluten in the flour or meal--and provide buoyancy. Similar foodstuffs, such as meatballs made from minced meat, egg, bread crumbs, and herbs, have the same propensity. First they sink, then they rise. This is because the air spaces bound up in the dough matrix expand when they are placed in boiling liquid, making the mixture less dense. This is what makes them buoyant. Consequently, if left to cool, various dumplings and meatballs will return to the bottom of the pan as the air spaces shrink, so the golden rule is eat them while they are hot. And they taste far better that way.
There is, however, another factor at work, especially in the case of flour-based dumplings like the ones in my mom's stew, and that is the presence of baking powder. Most varieties of this style of dumplings are made with plain flour and a large quantity of baking powder or with self-rising flour. Baking powder is a leavening agent containing an alkali, most commonly sodium bicarbonate, and an acid plus starch to prevent the mixture from becoming damp. When it is dissolved in water, the alkali reacts with the acid to produce carbon dioxide, which creates bubbles in the dumplings. Self-rising flour has a similar effect, although in this case the leavening agent is already part of the mixture (so there is no need to add baking powder).
Try making two batches of dumplings, one with a leavening agent and one without, and you'll find the ones without leavening are far more reluctant to float. Given enough time and heat, though, the air spaces in their dough matrix will ensure they eventually reach the surface.
P.S. This recipe for dumplings has been in the O'Hare family for generations. We cannot claim its superiority over other dumpling recipes, but I do know that it leads to dumplings that follow the experimental rules outlined above. First they sink, then they float.
1 cup self-rising flour
5 tablespoons plus 1½ teaspoons shredded suet (you can use a vegetarian version if you prefer, or substitute solid vegetable shortening)
Decent-sized pinches of salt and pepper
1 teaspoon dried herbs
Approximately 3 tablespoons of water
Sift the flour into a bowl and mix it well with the suet, salt, pepper, and herbs. Add the water a little at a time to make a slightly soft but not gooey dough. Lightly flour your hands and form your dough mixture into six to eight balls. Using a slotted spoon, carefully place them in a simmering stew or soup of your choosing (or water) over medium to medium-high heat and allow them to cook for twenty-five to thirty minutes. Check them after twenty minutes--if the cooking liquid is boiling vigorously, they'll be cooked sooner.
If you have family recipes of your own, you can compare and contrast the buoyancy or lack thereof of your own dumplings with the O'Hare version.
Why is cornstarch mixed with cooking oil attracted to a balloon?
With its very high proportion of starch, cornstarch gives rise to a number of weird effects that make it the perfect ingredient for use in scientific demonstrations. In addition to showing off the properties of starch molecules, this experiment shows the strength of even very small electrical charges. (For another experiment involving charges, see "Wayward Water" in chapter 5.)
WHAT DO I NEED?
an inflated balloon
a wooden spoon (the spoon must be wooden because you need an electrical insulator)
WHAT DO I DO? Mix the cornstarch and oil together until the mixture resembles a thick cream. Rub the balloon on your clothing to create a charge on its surface (as in the old party trick of rubbing a balloon and sticking it to the wall). Pick up some of the cornstarch-and-oil paste on the wooden spoon. This works best if a few stable dribbles are hanging from the spoon. Slowly move the spoon and its dribbles closer to the balloon.
WHAT WILL I SEE? When the spoon gets close enough, the paste thickens and moves, independently of the spoon, toward the balloon.
WHAT'S GOING ON? When you rub the balloon, the electrical charge you create on its surface is positive. When the tiny particles of starch that make up the cornstarch come near this positive charge, their negatively charged electrons are pulled toward the balloon. Electrical charges act like magnetic poles--a negative charge attracts a positive one and vice versa. The sides of the starch particles facing the balloon are now more negative (and consequently the sides of the starch particles facing away from the balloon are more positive). The positive sides of the starch particles have no balloon or similar charge to attract them and are therefore dragged along for the ride.
In addition, the whole mixture thickens because, although the charges cannot move from one starch particle to another since they are insulated by the oil, they will pack tightly next to one another as the negative sides of the particles nearest to the balloon are attracted to the positive sides facing away from the balloon.
P.S. Cornstarch is an incredibly versatile product. It is widely used for thickening sauces, but its great culinary benefit is that it only works when heat is applied. If you simply add cornstarch to a small amount of cold water, no thickening occurs; however, pour the mixture into a heated soup or casserole and the water and starch molecules begin to bond. The starch particles enlarge, trapping the water as they grow. At about 150°F, the structure of the starch breaks up and forms a mesh of bonded starch and water molecules, preventing free movement of the water molecules and creating a thick sauce. To learn firsthand about these curious properties of cornstarch, check out the "Mixing Madness" experiment in chapter 7.
And if you aren't familiar with the party trick, here's how it works. Rub an inflated plastic balloon on your clothing and then stick it to the wall. The static electricity generated by the motion will suspend it there since the negative electrons collected by the balloon are attracted to the positive areas of the wall.
Aim and Pour
Why does milk dribble down the underside of its carton if you pour it too slowly?
It's not only milk, of course. Many liquids poured from cartons, such as orange juice, result in a sticky floor or ruined shoes. And it's difficult to avoid the effect because when the carton is full, you have little choice but to tip it gently when trying to fill your glass.
WHAT DO I NEED?
cartons of milk or other liquids
a cloth (for cleaning up afterward)
If you want to demonstrate the effect further, you'll need:
a vertical cylinder (a liquid dishwashing soap bottle or a wine bottle will do)
a lighted candle
And, if you are feeling very confident, you'll need:
a hair dryer
a table tennis ball
WHAT DO I DO? Open the carton and pour the milk into the glasses. Vary the speed at which you pour so that you range from just a dribble to a rapid stream.
WHAT WILL I SEE? At low pouring speeds, the milk will cling to the edge of the carton and dribble its way down the container before depositing liquid on the floor--this is where the cloth will come in handy. At faster speeds, the liquid will pour freely, allowing you to fill your glass with aplomb.
WHAT'S GOING ON? When the carton of liquid is tipped, the surface of the liquid in the container is raised and moves toward the opening of the container. As the carton is tipped further, liquid pours from the opening, creating pressure at the opening. In addition to this pressure force, there are surface tension forces acting on the fluid that tend to draw it toward the surfaces of the container. At high pouring speeds, the pressure force is much greater than the surface tension forces, and the fluid will leave the carton in an orderly fashion, following a predictable parabolic path to your glass.
However, at low pouring speeds, a point is reached where the surface tension forces are sufficient to divert the path of the fluid jet so that it fails to leave the opening cleanly and becomes attached to the top face of the carton. Once attached, a jet of liquid will tend to stick to that surface thanks to the surface tension forces and a phenomenon known as the Coanda effect. This occurs when a fluid jet on a convex surface (such as water from a tap curving around the back of a spoon) generates internal pressure forces that effectively suck the jet along the surface.
The combination of surface tension and the Coanda effect enable an errant flow of fluid to negotiate the bend from the top face of the carton onto the carton's side and, ultimately and rapidly, onto the floor--or your shoes.
The Coanda effect (also known as "wall attachment") is named after Henri Coanda (1886-1972), who invented a jet aircraft that was to be propelled by two combustion chambers, one on either side of the fuselage and pointing backward. These were positioned near the front of the aircraft. To Coanda's horror, when the engines were ignited, the jets of flame, instead of remaining straight and pointing directly out of the back of the engines, clung to the sides of the fuselage all the way to the tail. While this discovery was obviously troublesome at the time, Coanda has since been immortalized, with the effect now bearing his name.
You must also take into consideration one more effect that causes erratic emission of liquid from cartons. This is the "glugging" that occurs as air is sucked into the carton to replace the lost fluid. This causes the fluid jet to oscillate, leading to intermittent surface attachment and wet shoes even at relatively high pouring speeds.
P.S. The Coanda effect is seen in many circumstances because of the general tendency for fluid flows to wrap around surfaces. Another demonstration that you can try consists of taking a vertical cylinder (this is where the liquid dishwashing soap or wine bottle comes in handy) and placing a lighted candle on the far side away from you. When you blow against the near side of the bottle, the candle is extinguished despite being apparently protected from the breeze. The current of air wraps around the bottle and links up again on the far side rather than being deflected away.
Now take the hair dryer, switch it on to a cool setting, and aim the air stream vertically upward. The effect works best if the hair dryer's nozzle is roughly the same size as the table tennis ball. You'll be able to take the table tennis ball and position it in the air flow above the hair dryer so that it will bob about quite happily without falling (you may need a few attempts to position it because finding the right spot can be difficult). Again, this is a case of the air stream sticking to a surface, this time to the table tennis ball, and the ball is held in place by the Coanda effect. Because this effect is so powerful, you'll have to tilt the hair dryer steeply away from the vertical before gravity can win out.
WANT TO READ MORE? A photograph of the Coanda, the first true jet aircraft, built in 1910, can be found at http://www.allstar.fiu.edu/aero/coanda.htm, alongside information about the designer.
Sink or Swim
Sauce packets in a plastic bottle filled with water can be made to act like submarines. How?
This astounded the New Scientist research team when we read about it, so we tried it out in the office and it's true. You can make a sauce packet--the kind you find in fast-food restaurants for serving ketchup, mustard, and mayonnaise--rise and fall in a plastic bottle just by squeezing the bottle.
WHAT DO I NEED?
a two-liter plastic bottle
unopened packets of ketchup, mustard, mayonnaise, or any other sauce
WHAT DO I DO? Fill the bottle to the very top with water and add the packets. It helps if you have more than one packet to experiment with because you need to find one (or more) that floats beneath--but just touching--the surface. (Racing different sauces to the bottom of the bottle can become quite addictive.) Screw the bottle top on as tightly as you can. Then squeeze the bottle hard.
WHAT WILL I SEE? The sauce packet will sink to the bottom of the bottle. It's quite amazing. And when you release the pressure on the bottle, it will rise again.
WHAT'S GOING ON? When the bottle is squeezed, pressure is applied to the water. But because liquids are generally very resistant to compression, this pressure is transferred to the packet, which in addition to the liquid sauce contains a small amount of gas. Gas is easily compressed, and as the packet is squeezed by the surrounding water, the space taken up by the packet is reduced. As its volume shrinks, it becomes denser and reaches a point at which it can no longer float. The packet then sinks to the bottom of the bottle, returning to the surface only when the pressure falls--that is, after you stop squeezing the bottle.
P.S. As a floating object falls or rises in liquid, the forces around it change, as does the object's volume. At the surface, it is less compressed (and therefore less dense) than it is at depth. In fact, a suitably compressable object can sit in a liquid at equilibrium neither rising nor falling. Much of this was discovered by Archimedes in the third century BC.
Try squeezing the bottle with differing pressures until you get a packet to hover halfway between the top and the bottom of the bottle. (If you find this tiring, try using a G-clamp or even squeezing the bottle gently between a door and its jamb.) This is essentially how a submarine operates. To control its buoyancy, a submarine has ballast tanks that can be filled with air or water. On the surface, the tanks are filled with air and the submarine's density is less than that of the surrounding ocean. To dive below the surface, the submarine's tanks are filled with water and the air vented until its overall density is greater than the surrounding water. A supply of compressed air (much reduced in volume from normal atmospheric pressure and similar in pressure to the air in the sauce packets after the bottle is squeezed) is kept on board. This is used to force water from the ballast tanks and refill them with air to allow the submarine to resurface. In order for the submarine to operate at precise levels between the surface and the seabed, special trim tanks carry a fine balance of air and water. These carefully adjust the overall density of the submarine to allow it to achieve neutral buoyancy at whatever depth the captain chooses.
Why does lemon juice stop cut apples and pears from browning?
Lemon juice might not improve the flavor of the other fruits, but it certainly works, as many cooks know. And if you want to eat the apples or pears afterward, you can always wash off the lemon juice.
WHAT DO I NEED?
If you want to take this experiment further, you need:
filter paper (you can cut up a paper coffee filter)
a vitamin C drink
WHAT DO I DO? Slice the apples or pears so they have large areas of their inner flesh exposed to the air. Place half of them on one plate and half on the other. Sprinkle the fruit on one of the plates with lemon juice, and leave the other untouched.
WHAT WILL I SEE? The fruit on the plate that has not been sprinkled with lemon juice will turn brown on its exposed surfaces much faster than the fruit covered in the juice.
WHAT'S GOING ON? To understand why this happens, you first need to understand why some plant tissues turn brown in the first place. Plant cells have various compartments, including ones known as vacuoles and plastids, which are separated from each other by membranes. The vacuoles contain phenolic compounds that are sometimes colored but usually colorless, while other compartments of the cell house enzymes called phenol oxidases.
In a healthy plant cell, membranes separate the phenolics and the oxidases. However, when the cell is damaged--by cutting, for example--phenolics can leak from the vacuoles through the punctured membranes and come into contact with the oxidases. In the presence of oxygen from the surrounding air, these enzymes oxidize the phenolics to produce enzymes such as polyphenol oxidase, which helps to protect the plant and heal the wound--a process also mentioned in "Banana Armor" in chapter 1. The drawback is that they also turn the plant material brown.
However, this browning reaction can be blocked by one of two agents, both of which are present in lemon juice. The first is vitamin C, a biological antioxidant that gets oxidized instead of the apple's phenolics. The second agent is organic acids, especially citric acid, which make the pH more acidic than the oxidases' optimum level and thus slow the browning. Lemon juice not only has more than fifty times the vitamin C content of apples and pears, it is also much more acidic than apple or pear juice, as a quick taste will tell you. This means lemon juice will immediately prevent browning.
You can also prevent cut apples from browning without lemon juice by putting them in an atmosphere of nitrogen or carbon dioxide, thereby excluding the oxygen required by the oxidases, but this option is clearly not open to the home experimenter or cook.
An excellent vegetable for observing browning is celeriac. Cut a large, relatively uniform slice of this root and then lay several small filter paper discs on the cut surface, each soaked in different solutions with varying levels of vitamin C and citric acid, such as the lemon juice, apple juice, orange juice, and vitamin C drink. If the disc is carrying an agent that blocks the action of oxidases, it will leave a white circle on the otherwise brown surface of the celeriac. Check the differences in browning prevention among the different solutions.
P.S. The pH of a solution is the measure of how acidic or alkaline it is. Most substances fall on a scale of 1 to 14 with 7 being neutral. Distilled water is neither acidic nor alkaline, so it registers a pH of 7, while acids, such as citric acid, fall between 1 and 7, and alkalis, such as sodium bicarbonate, fall between 7 and 14. The more acidic a solution is, the lower its pH, while the more alkaline a solution is, the higher its pH.
Polyphenol oxidase was discovered in mushrooms by Christian Schönbein, a Swiss chemist. It is found in humans, most animals, and many plants. In plants, its function is to protect against insects and microorganisms when the skin of the fruit is damaged. The dark brown surface formed by the skin is not attractive to insects or other animals, and the compounds formed during the browning process have an antibacterial effect.
In some foodstuffs made from plants, this browning effect is desirable. For example, in tea, coffee, or chocolate, it produces their characteristic flavor. However, in other plants and fruits, such as avocados, apples, and pears, browning is a problem for farmers because brown fruit is not acceptable to consumers and, even more important, it doesn't taste as good.
Can you wash your clothes with chestnuts?
Not all detergents come in packets; some grow on trees. Take horse chestnuts, for instance. When you're not roasting them on an open fire or baking them into stuffing, you could be using them to make your whites whiter.
WHAT DO I NEED?
a handful of chestnuts
a kitchen knife
a chopping board
a dish towel
a washing basin
a bottle with a screw top
some dirty socks
WHAT DO I DO? Remove the brown outer casing of the chestnuts, chop them up into small pieces, and put them in the pan. Add a cup or two of water and boil the chestnuts for a few minutes, then let them cool. Strain the mix through the dish towel into the basin to remove the solids while keeping the liquid. Pour this liquid into a bottle and shake it. Now put it back in the basin and wash your socks in it.
WHAT WILL I SEE? You should see a soapy lather form on the liquid you pour into the basin. And, if you give your socks a good scrub, you'll see how clean they emerge.
WHAT'S GOING ON? This highlights a property of chestnuts that few people are aware of. Horse chestnuts contain saponin, a natural soap or surfactant. Many other plants, including soapwort, produce saponins, which help protect them against disease because they are toxic to bacteria and fungi. As you have seen, they can be extracted with water--a trick that has been used for centuries to make a soapy liquid for cleaning linen.
Surfactant molecules have a polar region that is attracted to water molecules (it is hydrophilic) and a nonpolar region that is repelled by water (hydrophobic). They can therefore be dissolved in water as well as other kinds of organic solvents, including the substances that make your socks dirty. It also makes them very similar to synthetic detergents and very good for cleaning.
Because saponins are very mild surfactants, they are less damaging to materials than stronger, synthetic detergents. This is why they are popular with art conservators, who use them to clean delicate fabrics or ancient manuscripts.
Surfactants also play a role in firefighting. They are, along with a number of chemicals, a constituent of Light Water, a substance produced by the company 3M. As a dilute solution in water, it forms a light, stable foam used primarily to fight fires that involve flammable organic liquids such as oil. The foam floats on the surface of the burning liquid (hence its name), covering it with a thin surfactant film that prevents further evaporation of the liquid and extinguishes the fire by cutting off the oxygen supply.
P.S. You need to be aware that the horse chestnut extract you have created is mildly poisonous, causing coughing and sneezing if drunk, and that it can also be a skin irritant (you may want to use kitchen gloves while you do your laundry). Close adult supervision of children is required. And when you've finished, wash all the utensils you used to make sure there are no traces of saponin left.
Can you measure the speed of light using nothing more than a chocolate bar and a microwave oven?
Yes, although a counter theory says that all you need is a chocolate bar and a classroom of schoolchildren just waiting to pounce.... This is a marvelous experiment that actually allows you to measure one of the fundamentals of science--the speed of light--in your own home.
WHAT DO I NEED?
a bar of chocolate (the longer the better)
a metric ruler
a microwave oven
WHAT DO I DO? Remove the turntable mechanism from your microwave oven--the bar of chocolate needs to be stationary. Put the chocolate on a plate in the microwave and cook at a high setting until it starts to melt in two or three spots--this usually takes about forty seconds. You should stop after sixty seconds maximum, for safety.
WHAT WILL I SEE? Because the chocolate is not rotating, the microwaves are not evenly distributed throughout the bar, and spots of chocolate will begin to melt in the high-intensity or "hotspot" areas. Remove the bar from the microwave and measure the distance in centimeters between adjacent globs of melted chocolate.
WHAT'S GOING ON? The frequency of the microwaves is the key here. A standard oven will probably have a frequency of 2.45 gigahertz (GHz). If your oven is 2.45 GHz, this means the microwaves oscillate 2,450,000,000 times a second. You will need to adjust this figure depending on your oven's frequency, which should be printed on the back of the oven or in its instruction manual. (If the frequency is given in megahertz [MHz], you simply need to know that 1,000 MHz is equal to 1 GHz.) Microwaves are a form of electromagnetic radiation and therefore travel at the speed of light. Once you know the frequency of the microwaves in your oven, finding out their wavelength will allow you to calculate how fast they are traveling.
This is where the chocolate comes in. The distance between the globs of molten chocolate is half the wavelength of the microwaves in your oven, so double the measurement you have taken of the gap between the molten globs to find the microwaves' wavelength. In the New Scientist microwave oven, the distance between the globs of molten chocolate was six centimeters, so the wavelength in our 2.45 GHz oven is twelve centimeters.
To calculate the speed of light in centimeters per second, you need to multiply this wavelength by the frequency of the microwaves: 12 × 2,450,000,000 × 29,400,000,000, which is astoundingly near to the true speed of light of 29,979,245,800 centimeters per second (or 299,792,458 meters per second, as it is usually expressed). Since scientists have universally adopted the metric system for measurements, the speed of light is defined in meters per second.
Try it yourself, measuring as accurately as possible to get a figure even nearer to the true speed. If your chocolate bar is chilled beforehand, the molten areas tend to be more distinct when they first appear. Of course, you may find testing a variety of different chocolate bars, all of which taste delicious slightly melted, as an aid in your research. Dedicated scientists know that they must always double-check results.
How can you force an egg into a bottle?
This classic experiment has been repeated many times through the years, but the forces at play are often misunderstood. In fact, the illuminating part of this experiment isn't getting the egg into the bottle, but getting it out....
WHAT DO I NEED?
a hard-boiled egg
a glass bottle with an opening slightly smaller than the circumference of the egg when it is placed upright atop the bottle (milk bottles are ideal; wine bottle necks tend to be too narrow)
Vinegar and syrup will allow you to carry out a second experiment.
WHAT DO I DO? Shell the egg so you have the fresh, rubbery white exposed. Place the bottle on a flat, flame-resistant surface. Light a match and drop it into the bottle, making sure it stays lit. Add a few more burning matches as quickly and as safely as possible--if you can, add all the matches at once. Put the egg, pointed side down, over the neck of the bottle.
WHAT WILL I SEE? The matches will soon go out, because they are starved of oxygen once the egg seals the bottle, and the egg will be forced into the bottle, looking rather peculiar as it contracts in order to slide down the inside of the neck.
WHAT'S GOING ON? Inside the bottle, the lighted matches heat up the air, causing it to expand. This means that some of the expanded air escapes from the bottle. When the matches go out after the egg has been placed on top of the neck, the air contracts, creating a lower pressure inside the bottle than exists outside. The pressure outside the bottle forces the egg inside, and it plops to the bottom.
While it seems as though the egg is being pulled or sucked into the bottle, in reality it is pushed by the outside pressure. The greater pressure outside forces the egg down into the lower-pressure area in the bottle.
While many people were taught that the egg is sucked into the bottle when the burning matches use up the oxygen in the air inside the bottle, this is just plain wrong. It's the change in the temperature of the air after the matches go out that causes the air in the bottle to contract. An egg works well because its moist, rubbery surface forms an effective seal around the neck of the bottle. If you repeat this experiment with a chocolate egg or an unpeeled, uncooked new potato that doesn't completely seal the neck of the bottle, air will be able to return to the bottle and equalize the pressure between the inside and outside without carrying the object with it.
You can confirm this when it's time to get the egg out of the bottle. Hold the bottle on its side and carefully jiggle the egg so that its narrow end is resting against the bottle's neck. Turn the bottle upside down and form a seal between your mouth and the bottle opening. Now blow hard, which will increase the air pressure inside the bottle and force the egg out. But be careful: the egg can come out at quite a speed!
P.S. While you have your eggs out, you can try another experiment, especially if you've saved some vinegar after trying out the "Plastic Milk" experiment.
Place a whole uncooked egg in a jar of vinegar and leave it for a couple of days. When you return you'll see the shell has disappeared and the egg has swollen to perhaps twice its size. This is because the shell, which is made of calcium carbonate, reacts with the vinegar's acetic acid to create carbon dioxide, water, and calcium ions. The water passes into the egg through its now exposed membrane, driven by the pressure of osmosis (the passage of water from a region of high water concentration through a semipermeable membrane to a region of low water concentration, reducing the difference in concentrations). The white of the egg has a very high concentration of protein, and water passes from the vinegar into the egg in an attempt to equalize the concentrations on either side of the membrane.
To reverse this process, place the egg in a solution of 75 percent sugar syrup and 25 percent water. After a couple of days the egg will shrink to less than its original size as osmosis works in the opposite direction, and water leaves the egg to equalize the concentration between the egg and the sugary syrup mix surrounding it.
HOW TO FOSSILIZE YOUR HAMSTER Copyright 2007, 2008 by New Scientist