Do Polar Bears Get Lonely?: And Answers to 100 Other Weird and Wacky Questions about How the World Works

Do Polar Bears Get Lonely?: And Answers to 100 Other Weird and Wacky Questions about How the World Works

by New Scientist

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Amazing and intriguing questions and answers from the team behind the international phenomenon Why Don't Penguins' Feet Freeze?

The popular-science magazine behind the runaway international bestsellers Why Don't Penguins' Feet Freeze? and Does Anything Eat Wasps? takes on another irresistible batch of the strange, silly, and

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Amazing and intriguing questions and answers from the team behind the international phenomenon Why Don't Penguins' Feet Freeze?

The popular-science magazine behind the runaway international bestsellers Why Don't Penguins' Feet Freeze? and Does Anything Eat Wasps? takes on another irresistible batch of the strange, silly, and mind-boggling questions that plague curious minds the world over:
- Can pigeons sweat, can fish get thirsty, and can insects get fat?- Could a person commit the perfect murder by killing someone the day after receiving a full blood transfusion?- Is there a way to beat the odds of the lottery by using math?- How much mucus does a nose produce during the average cold?- If forced to eat parts of yourself to survive, which non-vital organs would be the most nutritious?
Culled from New Scientist's popular "The Last Word" column and edited by Mick O'Hare, the author of How to Fossilize Your Hamster, Do Polar Bears Get Lonely? is guaranteed to amuse and amaze as much as it informs.

(And if a polar bear appears to be lonely, it probably means there wasn't enough walrus for dinner.)

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Editorial Reviews

From the Publisher

“Mad science is back. Only here, it's less evil and not just for kids. Eighty simple and charming experiments meant to be conducted in the comfort of one's own home illustrate scientific principles in action.” —Science News on How to Fossilize Your Hamster

“Forget graduate school. New Scientist... outlines how you can eat and drink your way to scientific discovery.... It's a funny and very adult twist on the classic baking-soda volcano projects of our childhood.” —Wired Magazine on How to Fossilize Your Hamster

“If you have ever wondered why hair turns grey, fingers get crinkled in the bath or if the Great Wall of China really is visible from space, Mick O'Hare has the answers.” —CNN on Why Don't Penguin's Feet Freeze?

“Extraordinary book…. Responsible for putting popular science back on its feet.” —BBC Radio 5 Live on Why Don't Penguin's Feet Freeze?

“Hold the answers to all the world's little mysteries.” —Evening Standard (London) on Why Don't Penguin's Feet Freeze?

“At last, the mysteries of the world are explained… The book everyone is taking about.” —Independent on Sunday (London) on Why Don't Penguin's Feet Freeze?

School Library Journal
Adult/High School—This compilation of questions and answers taken from the "Last Word" column of New Scientist magazine includes many that may seem lightweight, ridiculous, or downright gross, but the answers are always dealt with in well-reasoned scientific terms, sometimes with a twist of humor. Answers often come from subscribers, the majority of whom are associated with respected institutions such as the American Institute of Physics, University of Glasgow, University of Sussex, University of Sydney, and Trinity College (Cambridge). A United Kingdom perspective is evident, particularly in the abundance of pub-related questions. Some of the questions seem to spring from a childlike curiosity: Do elephants sneeze? What causes "pins and needles" in arms and legs? Other questions are just gross and disgusting: What is the volume of snot produced during an average cold? Why is poop from breast-fed babies less odorous than that of bottle-fed infants? And then there are the downright silly questions that come from people with too much time on their hands: How long would it take an average cow to fill the Grand Canyon with milk? The random nature of the questions makes the book more of an amusing entertainment than a source for research assignments. However, it will have great appeal to adolescent boys, science geeks, trivia buffs, and reluctant readers. And finally, we have an answer as to whether it is more fuel efficient to drive with the windows down or with the air-conditioning on.—Paula Dacker, Charter Oak High School, CA

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Do Polar Bears Get Lonely?




Upon cracking open my breakfast boiled egg, I found a whole new egg inside. It was not a double-yolked egg, it was a double-egged egg—a completely new egg with a shell and yolk inside another. Can anybody explain it?

Liam Spencer


An egg within an egg is a very unusual occurrence. Normally, the production of a bird's egg starts with the release of the ovum from the ovary. It then travels down the oviduct, being wrapped in yolk, then albumen, then membranes, before it is finally encased in the shell and laid.

Occasionally an egg travels back up the oviduct, meets another egg traveling down it, and then becomes encased inside the second egg during the shell-adding process, thus creating an egg within an egg. Nobody knows for sure what causes the first egg to turn back, although one theory is that a sudden shock could be responsible. Eggs within eggs have been reported in hens, guinea fowl, ducks, and even Coturnix quail.

Incidentally, it is especially unusual to encounter thisphenomenon in a shop-bought egg, because these are routinely candled (a bright light is held up to them to examine the contents), and any irregularities are normally rejected.

Alex Williams


As the curator of the British Natural History Museum egg collection, I've come across quite a few examples of egg oddities. Double eggs (as opposed to multiple-yolked eggs) are less common than some other oological anomalies and consequently the "ovum in ovo," as the phenomenon described here is known, has attracted specific scholarly attention for hundreds of years.

The Dominican friar and polymath Albertus Magnus mentioned an "egg with two shells" as far back as 1250 in his book De animalibus, and by the late seventeenth century pioneering anatomists like William Harvey, Claude Perrault, and Johann Sigismund Elsholtz had also given the phenomenon their attention.

Four general types occur—variations of yolkless and complete eggs—but this form in which a complete egg is found within a complete egg is relatively rare. Several theories have been proposed for the origin of these double eggs, but the most likely suggests that the normal rhythmic muscular action, or peristalsis, that moves a developing egg down the oviduct malfunctions in some way.

A series of abnormal contractions could force a complete or semi-complete egg back up the oviduct, and should this egg meet another developing egg traveling normally down the oviduct, the latter can engulf the former; more simply, another layer of albumen and shell can form around the original egg.

Often when no yolk is found within the "dwarf" or interioregg, a foreign object is found in its center. This object has served as a nucleus around which the albumen and shell were laid down, in a process not dissimilar to the creation of a pearl.

Anybody interested in learning more about this subject should try to find a copy of The Avian Egg by Alexis Romanoff and Anastasia Romanoff (New York: John Wiley & Sons, 1949) and read pages 286-95.


Douglas Russell

Curator, Bird Group, Department of Zoology The Natural History Museum, Hertfordshire, United Kingdom


Why do bottle caps on beer bottles—at least the few hundred thousand that I have drunk from—always have twenty-one sharp bits?

Volker Sommer


We have three explanations for this one. We're still waiting for a bottle-top aficionado (of which there seem to be many) to rule between them.—Ed.


The bottle cap on any bottle is regulated by the internationally accepted German standard DIN 6099, ensuring all bottle caps are the same. Along with specifying the diameter of the bottle neck, the form of the rim around which the cap is crimped, and the materials the cap may be constructed from, this document specifies the form of the crimp. One requirement is that the closure be sufficiently circular to maintain a tight seal all around the circumference, which implies a highnumber of crimps (and thus points). It must also be robust, however, which implies reducing the number of crimps to give each crimp a larger bearing surface. Using twenty-one crimps is a good compromise between these requirements and is mandated in the standard. As to why it is twenty-one crimps rather than twenty or twenty-two, the best answer is simply "because it is."

S. Humphreys


Through trial and error, William Painter, the inventor of the crown cork, or bottle cap, discovered that the optimum number of teeth on a mold made of steel for securing carbonated drinks was twenty-four. He registered a patent for his design and for many years the twenty-four-tooth capping mold was standard. However, around 1930 the steel mold came under threat from a cheaper version made of tinplate. This newer mold could not win a patent if it also had twenty-four teeth, so it was changed to twenty-one to avoid infringing the original design. The new figure is the smallest number of teeth needed to prevent leaks and is now used across the world.

Chitran Duraisamy


The crown cap was patented by Painter on February 2, 1892 (U.S. patent 468,258). It originally had twenty-four teeth and a cork seal with a paper backing to stop drink and metal touching. The current version has twenty-one teeth.

The twenty-four-tooth caps were originally fitted to bottles one by one using a foot-operated press. When automatic machines were adopted, the crown caps were loaded into circular feed tubes and the twenty-four-tooth caps frequently jammed. With an uneven number of teeth this doesn't happen, and because the sealing quality of twenty-three teethwas no better than twenty-one, the smaller number was adopted.

The height of the crown cap was also reduced and specified in the German standard DIN 6099 in the 1960s. This also defined the "twist-off" bottle cap that is widely used in the United States.

Barry Painter


Most healthy people I know eat cereal or fruit for breakfast. This gives complex carbohydrates for long-term energy. But I have a physical job as a gardener and I know if I rely on this intake I'll be ravenous by 10 A.M. On the other hand, if I have eggs, I'll be fine until midday. Clearly I need protein, but that shouldn't give me energy. What is going on, and is this common?

Steve Law


It may be that your hunter-gatherer ancestry is responsible for the favorable response to your morning serving of eggs. In the course of human evolution we have become physiologically adapted to the diet that prevailed for most of that time: that of a hunter-gatherer. This diet is assumed to have been dominated by lean meats, fruits, and vegetables. Cereal grains, on the other hand, are a relatively new addition to our diet, having found their place on the dinner table with the onset of the agricultural revolution only ten thousand years ago.

It has been suggested that our pre-agricultural diet is the best way to support healthy physiological function, including improved energy production and appetite control. One of the characteristics of this diet is a low "glycemic load,"which means glucose is released slowly into the blood as food is digested. Another is a higher level of lean protein than that eaten by modern humans. These characteristics are found in your eggs, whereas most breakfast cereals and fruit have higher glycemic loads and lower protein content.

The low glycemic load of your meal may help to stabilize your blood sugar level, sharp drops of which precede an increase in appetite. The protein in eggs is also a strong inducer of cholecystokinin, a gut-derived satiating hormone. And carbohydrate is not the only source of energy in our diets. The fat in your breakfast eggs provides approximately double the energy of carbohydrate, albeit in a slow-release form.

Benjamin Brown

Technical Research Officer Health World, Queensland, Australia


Animals and plants share a common genetic ancestry, so perhaps vegetarians who refuse to eat meat on ethical grounds should avoid anything that has DNA at all. Is this feasible? Could anybody suggest a menu?

Richard Ward


I'm not aware of any living organisms that don't have DNA, so you'd have a hard time eating any tissues or cell cultures. You could try eating RNA viruses, but you'd need to produce them in a cell culture, which generally requires animal serum to keep the cells alive. Your food wouldn't contain DNA, but you would have used dead animals to produce it.

One cheat that springs to mind is red blood cells. In many species, including humans, the nucleus and mitochondria are removed from these cells during the maturation process. This is to make room for more hemoglobin, the iron-bound protein that carries oxygen. Because the nucleus and mitochondria contain all the cell's DNA, you could argue that provided you don't kill the animals, drinking their blood is the ultimate vegetarian diet. You'd need to filter out the white blood cells, which still have plenty of DNA, but the rest of the blood components would be fine. They'd provide you with protein, some sugars, and vitamins, but probably more iron than is healthy.

If that doesn't sound appealing, consider totally (bio) synthetic foods. Biologists routinely construct yeast and bacterial lines designed to churn out large quantities of a specific protein or other biological molecule. I assume it would be possible to scale this production up to produce sufficient quantities of purified proteins, sugars, and so on to act as a food source. Don't expect it to be tasty, though: the proteins and sugars produced would be purified from the culture as crystalline powders. I'm not sure whether it's possible to produce fats like this without killing the cells, but if you did the result would either be oil or a pretty nasty goo. Also, maintaining the cultures required to produce this stuff would rely on antibiotics to kill contaminant organisms, so going against the spirit of the idea.

Many, perhaps all, of the various vitamins and other nutrients we require could probably be synthesized in similar ways, given time and cash. The various mineral compounds we need—iron, copper, zinc, iodine, and so on—are probably available from a good synthetic chemist. And, of course, you could drink milk. It's a complex mixture of secretedproteins, fats, sugars, and pretty much everything else you need to stay alive. It may contain cells from the animal which produced it, but you could probably centrifuge these out.

Christopher Binny


All I can come up with is a dish of baked retrovirus served on a water biscuit made from purified starch, fried in a purified fat of choice, and seasoned with salt and vinegar. For the sweet course you might try a sorbet of snow sweetened with a purified sugar, honey, or syrup, a touch of citric acid for bite, and with added vitamins, trace elements, and essential oils to taste. It should be washed down with any spirit, or any wine or beer filtered to remove yeast traces.

Bryn Glover


I found the following information on the wall of the Johnson Space Center in Houston, Texas. One cubic meter of lunar soil contains enough of the right elements to make a cheeseburger, an order of fries, and a fizzy drink. That would contain no DNA, but might be a little expensive.

Graham Kerr


I considered this some years ago and put my conclusions in the form of a cookery book, available online at

Norman Paterson


To whet your appetite, here's a recipe from Norman Paterson's book.—Ed.

For four malachite burgers you will need:

Four slices of Welsh slate 1 kilogram of malachite


Cut the slates in two. Break up the malachite with a sledgehammer. Divide the malachite equally among four slates and cover with the remaining four. Bake at 2200°F for twelve hours, by which time the malachite should be a beautiful bubbly green. Cool and eat. Excellent for picnics, as they can be prepared the century before. A dry, gritty flavor.

Most people who are vegetarian on ethical grounds oppose killing animals. They are rejecting the senseless deaths of the animals and the inhumane way the animals are treated, rather than worrying about similar DNA. Vegetarians have nothing against eating vegetable matter and fungi because these have no central nervous system and thus cannot experience pain.

Ceridwen Fitzpatrick


If all plants and animals have common DNA ancestry, then perhaps we are all vegetarians. Or if we are all also vegetables, maybe the world is awash with cannibalism.

Or perhaps vegetarians can eat their neighbors without feeling too much guilt. By the "common DNA" logic this is no more or less cannibalistic than eating a radish. The only solution to all these dilemmas would be for every creature to subsist purely on nonliving minerals and nutrients. Nonhuman animals, however, are unlikely to stop eating what they want.

Brian Falconer


I cooked some poultry stuffing and left it in a bowl in the fridge overnight, covered with aluminum foil. In the morning there were holes in the foil where it had touched the stuffing, which was stained black under each hole. Uncooked stuffing does not produce this effect, and it makes no difference whether the stuffing is cooked inside the bird or separately. What is going on here, and are the black stains poisonous?

Andrew Stiller


Without its submicroscopic insoluble skin of oxide, aluminum cookware would catch fire easily. Fortunately, this is not usually a problem. Normally, breaks in the oxide skin of aluminum heal instantly when the exposed metal reacts with, say, air or water. But if, for example, mercury or certain alkalis or acids dissolve this skin, the exposed underlying metal reacts vigorously. So, while aluminum cookware and foil are safe and useful in the kitchen, it is important to keep them away from strong salt solutions or caustic soda, for example, and also from wet food when it is not actually cooking.

This is because wet, fatty materials, such as cooked lard, form fat-soluble detergents that penetrate microscopic chinks in the oxide layer, exclude air that otherwise would reseal the skin, and corrode pinholes into the metal. If floating fat has coated the metal, even cold chicken soup can eat through a thick aluminum pot overnight.

The black stain is mainly from small amounts of iron in the aluminum. It is not deadly, but it is better not to eat food contaminated with high levels of metals, which alsospoil the taste. For wrapping cooked fatty or acidic food for more than short periods, plastic film is much better.

Jon Richfield


The mineral water in my local shop has a label telling me it is from a three-thousand-year-old source, yet there is still a "best before end" date on it approximately two years in the future. If the water has been in its aquifer for three thousand years, why should it go bad in a sealed bottle?

Lewis Smith


Mineral water has passed through layers of rock that have different effects on the water. Some minerals dissolve in the water, supposedly improving both its taste and health-giving properties, hence the demand for it.

The small pore size of the rocks that the water passes through acts as a filtration system, improving the purity of the water by removing larger molecules such as biological contaminants. As soon as the water emerges it is vulnerable to contamination again. The "best before" dates are based on the amount of time the bottler believes the water will remain without measurable levels of contamination due to the lack of completely sterile conditions in their bottling plants.

If the water is stored in a plastic bottle the date might also relate to contamination from the constituents of the plastic, which may change the taste of the water.

John Thompson


The reason for the "best before" date on bottled spring water is not the contents but the container. Most mineral or spring water is packed in polyethylene terephthalate (PET) bottles. During the manufacture of the bottles, traces of catalyst or plasticizer, which may include antimony, remain in the plastic and are leached out into the water over time. To avoid this, glass bottles, which have stood the test of time, are preferable.

Rob Davids


"Pure" water does not decompose or suddenly go bad. However, manufacturers of foods and beverages have to give "best before" dates to cover their backs. If the bottle sat around for long enough the plastic might decompose or the seal might degrade, allowing bacteria to enter and contaminate it.

As for the water being three thousand years old, in fact most of the water we drink has probably been in existence as water molecules for millions of years. What is important is the purity of the water, not its age: three thousand years in an underground aquifer may have filtered out all the organic matter, but it may still contain harmful dissolved chemicals such as arsenic.

Simon Iveson


Why do cooked foods taste different after they have cooled from the way they tasted when they were hot?

Alan Parson


Cooked, solid foods are not static substances. Chemically and physically they are complex dynamic systems, continuouslychanging without stopping to suit anybody, so there are penalties for eating them too early or when they are past their best.

Cooking or cooling changes various substances in foods, affecting composition and flavor. Yesterday's leftovers have undergone reactions, including oxidation and the evaporation of aromas and flavor components. Food also changes physically on cooling, by congealing, crisping, or crystallizing, for example. These changes may prevent some substances from reaching the nose or the tongue, or expel or redistribute fluids. Few such changes reverse precisely on reheating, just as one cannot uncook food by chilling it.

Some changes are desirable, such as the setting of jelly or ice cream, but it is not for nothing that various foods are prepared at a particular temperature. Fresh hot food presents copious aromas in particular balances that reheating can never recapture.

Colin Collinson


Only a small amount of the taste of food is detected by the tongue, where taste buds recognize just five specifics: bitter, salt, sour, sweet, and umami (or savory). The majority of what we call "taste" is more specifically described as "flavor" and it comes from odor identified by nasal olfactory cells. That requires the flavor molecules to be wafted up from the mouth. This is more readily achieved when food is hot, creating convection currents and making odor molecules—as well as water molecules—volatile and mobile.

Water from food and saliva can dissolve flavor molecules so those more readily reach the taste buds while flavor vapors hit the nose. Having a cold that blocks the nose is evenmore effective in reducing flavor than eating food cold, and can make apples and onions indistinguishable.

Elisabeth Gemmell


Why are fizzy drinks such as cola or champagne far more appealing than the same liquid once it has gone flat?

Olaf Lipinski


Most fizzy drinks are made so by injecting carbon dioxide into the liquid at high pressure. Carbon dioxide dissolves readily at atmospheric pressure, but the high pressure allows even more to be dissolved. It forms carbonic acid in the drink, and it is this which gives the drinks their appealing "fizzy" taste—not the bubbles, as many people believe. When the drink goes flat, most of the dissolved carbon dioxide has been released back into the atmosphere, so the amount of carbonic acid is also reduced.

The fizzy taste is more appealing than the flat one simply because the drink was meant to be fizzy. Cola and champagne are concocted with the fizz in mind, using the carbonic acid as an essential ingredient in the flavor, so they will naturally taste better when the drink is still fizzy. When they go flat, this means that one of the main flavors has disappeared, and the overall taste will change—usually for the worse.

Martin Roos


A good taste is a matter of blended, often contrasting, sensations and expectations. These include temperature—for hot and cold drinks, say—sound and texture for chips or creams,plus aroma, flavor, and stimuli on the tongue. Fizz is generally created from carbon dioxide, though pressurized air also lends some noncommercial spring waters a certain liveliness. A good fizz tickles the nose and splashes minute stimulating droplets around the mouth as you drink.

Dissolved carbon dioxide has a distinct taste of its own, which is slightly sharp. Flat beverages have lost this bite. Going flat upsets the balance of the flavors and other stimuli, and without them such a drink is likely to taste insipid or too sweet, and ... well ... flat.

Jon Richfield


A side effect of taking the drug acetazolamide is that all carbonated drinks taste flat. Acetazolamide is used to help prevent altitude sickness by pre-adjusting the acidity of the blood to acclimatized levels. This also counteracts the acidity caused by carbonic acid in fizzy drinks, making them taste as if they were flat. I experienced this odd phenomenon firsthand last summer while drinking a soda before climbing Tanzania's Mount Kilimanjaro.

David Clough

University of Cambridge, United Kingdom


How do they get the smooth, round chocolate coating on confectionery like Whoppers?

BBC Radio 5 Live listener


I spent six months making Smarties, a similar type of confectionery, in 1977. The chocolate centers were tumbled in adevice resembling a cement mixer that gave them repeated coatings that alternated between sweet starchy liquid and powdered sugar, blow-dried after each coat. It took a week or two to learn the knack of ensuring an even coating: we had to remove clumped material, get the right combination of wet and dry, and keep the layers thin. Trainees' lumpy sweets were sold off cheap.

I handled about a ton of chocolate centers a day, putting on the white inner coat. More experienced workers did the outer candy coating, in similar "cement mixers," and the finished product was polished by tumbling the sweets in powdered beeswax, except for the black ones, for which petroleum jelly was used, apparently to avoid a whitish bloom.

Significantly, this was not a conveyor-belt manufacturing process. Each worker controlled their own rate, taking anything from an hour to an hour and a half per batch, depending on experience.

Peter Verney


I have heard that a family of four can be kept fed 365 days a year using only about 9.5 square yards of land. Is this really possible anywhere in the world? Could it really take only two hours a week as was suggested, and what would be on the menu?

Jan Horton


Opinions differ. There may be no definitive answer until somebody measures the output from 9.5 square yards of land—an experiment which is of necessity almost certainly going on in many poor countries.—Ed.


Energy flow is a key issue. The sun's intensity at the Earth's surface depends on latitude and season. The average value over a twenty-four-hour period across the whole of the Earth's surface is about three hundred watts per square yard. Therefore each day, a 1-yard-square plot receives an average of about twenty-six megajoules of energy—more close to the equator. The recommended dietary intake is about two thousand kilocalories a day. So, in theory, an average 1-yard-square plot receives enough solar energy to support three people. However, photosynthesis has an efficiency of only 10 percent so you would need more than 3.5 square yards per person. The figure of 2 square yards per person might just be achievable near the equator, although this seems optimistic.

There are also difficulties in getting the required nutrients and minerals, and in seasonal reductions in output.

Simon Iveson


I don't weigh my garden produce, but this year I did grow enough to fill a freezer, plus the produce my family ate fresh. All of this was grown on two small patches of land totaling about eight square yards. I believe I could have grown the minimum daily requirements for two, or possibly even four, if that had been my intention.

The produce—interspersed and rotated—included runner beans, sugar snap peas, onions, parsnips, raspberries, strawberries, spinach, broccoli, cauliflower, and blackberries. I grew carrots, tomatoes, cucumbers, peppers, zucchini, and herbs in pots on a one-square-yard shelf in my greenhouse.

I grow more intensively than advised by seed packets, and I start most of the outside crops in a heated greenhouse in winter. Some crops, such as beans, take up very little ground space, and crop rotation makes good use of space. Inaddition we eat wild fare, such as rabbits, and we could have supplemented our diet in various other ways had we not preferred to encourage the wildlife rather than eat it. Two hours a week on a plot this size is plenty of time.

But could it work anywhere? The soil in my garden has been cultivated for generations. I recently started a vegetable patch in an uncultivated part of the garden and the result was poor. And I'm not sure I could have grown enough to feed us out of season without a greenhouse or freezer.

Tony Holkham


My family has decided that it would be possible to feed a family of four from 9.5 square yards of ground for a year if we were only producing vegetables.

You can grow climbing beans up poles along the rear of the plot and freeze the surplus. You can also grow trailing plants, such as pumpkins or cucumbers, within the plot, but let them trail outside it. Silver beet can be cropped continuously and potatoes can be grown in a stack of old car tires. Similarly, tomatoes and Brussels sprouts grow upward and you can bottle or freeze surplus tomatoes.

Herbs can be grown in pots with multiple openings, as can strawberries. Carrots, parsnips, rutabaga, and turnips can be grown between the tall plants. You need to stagger the plantings a little and freeze any surplus. Radishes are fast growing, so they need little space at any time, while celery is a "narrow" plant and the surplus can be frozen.

Keep seeds each year and store or barter the surplus seeds or grown vegetables for goods to preserve.

My garden is a little bigger than 9.5 square yards, but I haven't had to buy green vegetables (or eggs) for a family of three for longer than I can remember. In our case we alsohave chickens, which fertilize the soil and enter the equation themselves because they provide food (but take up space).

The vital part of this equation, however, is growing vegetables that can be stored or preserved.

Sandra Craigie


The difficulties inherent in calculating the food output of land are shown by the fact that our first correspondent above, Simon Iveson, later revised his calculations:


Since answering this question, I have thought of two important additional points.

First, the human body is not able to metabolize 100 percent of the energy stored in the plant material that it eats, so this would increase the land area needed to feed a person. Presumably the exact percentage we can metabolize depends on food type.

Second, cloud cover would reduce the amount of direct solar radiation that reaches the Earth's surface, further increasing the land area needed per person.

Two square yards is starting to look unfeasible.

Simon Iveson


Why does red wine become lighter in color as it ages, but white wine become darker?

Volker Stuck


Color maturation in wines is just one small aspect of a very complicated chemical process. When red wines age theygradually turn from a deep purple color to a light brick red. Red wines are kept in contact with the grape skins throughout fermentation. During this process, blue/red-colored phenolic compounds called anthocyanins leach from the skins into the wine. As the wine ages, small amounts of oxygen react with anthocyanins and other, mostly colorless, phenolic compounds, causing them to polymerize and form pigmented tannins. Over time, these produce the brick-red color. Often tannin complexes grow as they react with other wine constituents, such as proteins, and many become too large to stay in solution and precipitate out, leading to the sediment you may find in aged wines.

White wines start out in bottles with a greenish tinge (young wines in Portugal are called vinho verde) and end up with a browner hue. White wines are not fermented with the grape skins, so they contain vastly lower levels of phenols, and therefore tannins. Also, white grapes do not contain anthocyanins—otherwise they would not be white. Consequently those few tannins found in whites are nonpigmented. It is presumed that white wines become browner with age because of the slow oxidation of what few phenols are present. A similar process can be observed in the discoloration of a half-eaten apple.

One interesting side note is that anthocyanins are only found in the skins, so it is possible to make white wine from red grapes if the skins are removed. White zinfandel, common in the United States, is an example of this.

Oliver Simpson


It was stated in a previous answer that "young wines in Portugal are called vinho verde." This is in fact incorrect. Vinho verde is a wine made with certain types of grapes ina certain region of Portugal, and there are white and red vinhos verde.

Although vinho verde should indeed be drunk while young (with the possible exception of alvarinho styles), the name itself does not imply youth.

Antonio Brito


Why does garlic make your breath smell in a way that, say, lettuce or potatoes do not?

Chris Goulding


Garlic produces a potent antifungal and antibacterial compound called allicin when the clove is cut or crushed. This is created by the enzyme alliinase acting on a compound called alliin. Allicin is responsible for the burning sensation you experience if you eat garlic raw.

However, allicin is not stable and generates numerous smelly sulfur-containing compounds, hence its pungent smell. After ingestion, allicin and its breakdown products enter the bloodstream through the digestive system and are free to leave again in exhaled air or through perspiration. This is the first effect of garlic.

In addition, the chemicals in garlic change the metabolism of the body and trigger degradation of fatty acids and cholesterol in the blood: this generates allyl methyl sulfide, dimethyl sulfide, and acetone. These are all volatile and can be exhaled from the lungs, giving you garlic breath the morning after a meal. It is not necessary to eat garlic to have garlic breath because allicin can be absorbed through the skin. Justrubbing garlic on the surface of the body can be enough to generate smelly breath because it exits the body via the lungs.

The only real solution to smelly breath from garlic is for us all to eat it.

Peter Scott

School of Life Sciences University of Sussex, United Kingdom


Garlic owes its pungency and subsequent halitosis-producing qualities to a variety of sulfur-containing compounds that are produced after cutting the cloves, some more transient than others and with a variety of health-giving properties. Sulfur is responsible for some of the smelliest substances known, from the brimstone stench beloved of vulcanologists and the rotten-egg smell of hydrogen sulfide to the potent secretions of the skunk.

Geoffrey Chaucer made a comment on alchemists of the fourteenth century in his own inimitable way:

Evermore where that ever they gone Men may hem ken by smell of brimstone; For al the world they stinken as a gote ...

Paul Board


Mold has always been a menace on my blocks of Gouda and Edam cheese, which I store under a cheese cover. Recently my wife told me to put a lump of sugar under the cover with the cheese, and I have not seen mold since. The sugar gets moistand slowly dissolves, but nothing else seems to happen to it. My wife learned this from her mother, and so it must be an old and possibly widespread remedy. Why and how does it work?

Georg Thommesen


This habit is also common in northern Germany, where the explanation given is quite simple. The sugar lump takes up moisture from the air trapped under the cheese cover, slowly dissolving as it does so. The relatively dry air reduces the suitability of the environment for cheese molds.

David Fleet


The sugar cube absorbs water, lowering the relative humidity, so that mold can no longer grow on the surface of the cheese. Salt would work just as well, as would saturated solutions of sugar or salt—saturated solutions are those that still contain some undissolved sugar or salt.

This forms the basis of humidity control in museum display cabinets. If the humidity is too high, undesirable molds grow, but if it is too low, wood and leather might crack. Saturated solutions of different salts can peg the relative humidity anywhere from 10 percent to 90 percent. For example, a saturated solution of lithium chloride will maintain a relative humidity of 11 percent, while a saturated solution of common salt keeps the relative humidity at around 70 percent.

John Hobson


The sugar will draw liquid from the air by its intrinsic hygroscopicity—its tendency to absorb moisture. This is the reason sugar cakes in the damp, and in the process it will suppress the growth of mold or bacteria.

The mechanism is related to the one that protects honeyfrom microbial growth. Honey is so effective at this that it was once spread on wounds to prevent infection. Honey suppresses mold and bacterial growth thanks to its high concentration of sugar. By drawing water away from its surroundings, the sugar desiccates any fungal and bacterial cells and spores in the honey. Cells must feed to reproduce and so they absorb food in contact with their cell membranes or which their excreted enzymes have released. Sugar in the honey will draw water out of the cell, which will either kill it or encourage it to live on in the spore phase and eschew reproduction until it encounters a more benevolent environment. This is the spore's job, and so it sits and waits and ceases to be active in the honey.

Bill Jackson


I discovered a pear that had started to go bad in my fruit basket. The first evening it had a perfect bull's-eye pattern of mold. Sixty hours later it had grown more (partial) rings of mold. Another forty-eight hours later it had grown still more partial rings, always separated by the same gap and all still roughly concentric. At that point it was getting pretty rotten, so I threw it away. But what causes the mold to grow in rings? I've seen it in other similar fruit.

Bob Ladd


The pear is suffering from brown rot disease, which is caused by the pathogenic fungus Monilinia fructigena. This is a very common and widespread disease of apples, pears, and stone fruits and spreads through the air as spores. The sporesgerminate on areas of damaged fruit, attacking it where the fungus has easy access to the unprotected, nutrient-rich, fleshy parts inside.

The fungal threads, or hyphae, grow and branch within the tissue and degrade the flesh. At first, the disease is invisible to the naked eye, but as it spreads, the pear responds with the typical "browning" reaction that gives the disease its name.

As it grows, daylight prompts the fungus to produce more spores on specialized hyphae that grow back out of the skin, forming gray-brown pustules.

A new crop of fungal spores is therefore produced with each period of daylight, and the fungus continues to grow as the flesh forms successively larger rings each day, giving the typical appearance described by the questioner.

A parallel situation can be seen in the "fairy rings" of dense, green grass growth and toadstools that appear in lawns—again it is a visible manifestation of a microscopic fungus growing beneath the surface. In this case, however, it is the fungus breaking down organic matter in the soil which causes the release of nutrients to stimulate grass growth and provide the essential energy to form the spore structures of the fairy-ring toadstool.

Peter Jeffries

Technology and Medical Studies University of Kent, United Kingdom


It is accepted among Australian beer drinkers that a glass of cold draft lager holds its head for longer if the beer is pulled intwo or three separate pours rather than in one continuous pull. What causes this effect and does it also apply to beers served at cellar temperature?

Justin Swain


If you pour the beer in one pull, the foam grows under uniform conditions, producing relatively few bubbles and mostly large ones. Large bubbles pop quickly, so the head doesn't last. By pausing during pulling, one gives the first bubbles time to grow larger and more flexible before the turbulence of the next pull shears some of them into more numerous, smaller bubbles. Furthermore, the concentration of carbon dioxide in the poured beer surrounding a large bubble has had a chance to drop, so that the bubbles stop growing so rapidly. The effect of the extra pulls is to reduce the size of the bubbles and increase their number. This means a smoother, finer, firmer froth. Because smaller bubbles do not pop as easily as large ones, the finer froth lasts longer too.

Qualitatively, warmer beer behaves in much the same way, but it froths too violently and briefly, which masks the effect. Bubbles in warmer beer are larger and more fragile anyway, so the overall improvement is less worthwhile.

Billy Gill


Once when I was reducing red wine and olive oil in a flat frying pan on the stove, the mixture exploded with an audible pop, spraying the wine—but not the oil—up to two yards away from the pan. Significantly, the wine was not hot enoughto scald me. I hadn't stirred the pan for at least a minute, and the wine and oil had separated. What happened?

Alan Gammons


There are several ideas about what could explain this. If any reader feels the urge to find out for themselves which scenario is correct, please exercise extreme caution.—Ed.


I don't know if chefs have their own term for this phenomenon, but chemists call it "bumping." It occurs when a liquid is heated above its boiling point but does not boil due to a lack of nucleation sites—scratches, sharp corners, or solid particles where bubbles form easily.

You can observe nucleation sites in a flute of champagne. They are the spots on the inside of the flute where bubbles are continuously forming before streaming upward. They usually mark the location of a tiny scratch or a speck of dust: a very clean flute, with few or no nucleation sites, will keep your champagne fizzy much longer.

When there are no good nucleation sites in the frying pan, the temperature can rise well above the liquid's normal boiling point, until it is so high that bubbles can form even without a nucleation site. Once a bubble forms, however, it acts as a nucleation site for the adjacent liquid. When such superheated liquid suddenly finds itself adjacent to a nucleation site, it boils explosively. This often happens in the chemistry lab because chemical glassware is so clean and defect-free that it often has no nucleation sites at all.

To prevent bumping, a chemist might deliberately scratch the inside of a flask to create nucleation sites, or may add chemically inert "boiling chips" to a solution. In other cases,bumping is a necessary evil and the chemist tries to catch or deflect the resulting spray using a "bump trap"—usually in the form of a protective glass screen.

Nucleation is an important concept in many disciplines. In meteorology, for example, seeding clouds involves providing nucleation sites for the condensation of water vapor. And in metallurgy, the way that atoms crystallize into grains around nucleation sites greatly affects the strength and other properties of a metal or alloy.

In the case mentioned above, my guess is that the wine in the frying pan bumped. It may be that oil stuck to the surface of the pan, creating a completely smooth surface, free of nucleation sites, or it may be that the pan was simply very clean and smooth. The wine was presumably hot enough to scald when it left the pan, but tiny droplets flying through the air cool rapidly. To prevent bumping in your kitchen, you might provide some nucleation sites, perhaps by dropping a sprig of rosemary into your oil and wine before heating it.

Ben Haller


The mixture had not been disturbed and so had separated into oil on top and wine on the bottom, next to the heat. The alcohol in the wine would boil off well before the water in the wine could reach its boiling point and would bubble gradually through the layer of oil. Being heavier than air, the gaseous alcohol would sit on top of the oil, somewhat contained by the edges of the pan and mixing with the surrounding air to form an explosive mixture. After a while this mixture would overflow from the pan and slip down into contact with the heat source, igniting it, and the whole gaseous mixture above the oil. The resulting explosion would send a shock wave in all directions, causing the audible pop. The shock wave travelingdownward would hit the viscous oil layer and force it downward too, pushing on the wine, which would have nowhere to go except sideways, up the sides of the pan and out over the kitchen.

David Levien


It looks like the red wine became superheated and flash-boiled explosively. Liquids start to boil when their vapor pressure equals the ambient pressure—in this case it was one atmosphere above the open pan. Usually the heat is released relatively smoothly, but two-phase liquids, such as this mix of oil and wine, boil at a lower temperature than either liquid, or phase, would boil on its own. Each phase generates its own vapor pressure and the mixture boils when the combined vapor pressure reaches ambient pressure. However, if the mix is allowed to separate before getting hot, as this one did, the temperature of the phase below—the red wine—can then exceed the two-phase boiling point before the red wine has even started to boil. When the wine does boil, it causes remixing, which results in a swift drop in boiling point and a rapid or instantaneous boil-off.

The wine was expelled rather than the oil because it provides almost all of the generated vapor. It was probably also hotter than the oil but fortunately hit your skin at a cool temperature because it was probably dispersed in a rapidly cooling aerosol by the force of its vapor expansion.

Paul Gladwell

Copyright © 2009 by New Scientist All rights reserved.

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New Scientist is a science magazine for everyone, young and old, amateur and professional. With a worldwide readership of more than half a million, it is among the most popular of all popular-science magazines.

Mick O' Hare is the production editor of New Scientist and the editor of the magazine's previous international bestsellers Does Anything Eat Wasps? and Why Don't Penguins' Feet Freeze? He lives in London.

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