Onion Gastronomy

Monday 9 February 2009

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In the UK when people want to say that someone knows what he/she is talking about, they say “He knows his onions.” The purpose of this page is to assist anyone to develop an increased awareness of food, its properties and how best to deal with it in the kitchen and at the table. What happens at the table can include your learned explanation as to the dish you have created or topics which arise during conversation. Your guests will say that you know your onions!

Cynthia Nelson knows her onions, too. Go to this website to learn about her Onion Gastronomy.
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http://www.tasteslikehome.org/2008/06/immature-onions.html

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We continue from above where it said "Your guests will say that you know your onions!"

The material broadens to topics such as middle-age spread and vegetarianism.

This page is for general readership. The student of Gastronomy should benefit as well and the topics here are to raise questions in the student mind. He/she is in easy contact with the appropriate library and is supported by specialists who can supplement the information here and answer questions demanding scientific etc knowledge. When further information comes to light or you have an opinion, please send it in for inclusion.

It follows that professionals within the domain of Gastronomy can use the type of information on this page in staff training, marketing, purchasing and other aspects of their work. It also follows that those who cook at home, who entertain, who appreciate food and drink in a wide framework can benefit from the knowledge and advice herein.

Sources

At the back of The New Scientist magazine, there is a page where readers send their questions about the peculiarities of life and specialists reply. There has been a lot of interest in the topics and at the time of writing [January 2009], the publisher has produced three books devoted to the questions.

The books are:.
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Does Anything Eat Wasps? .... 2005
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Why Don’t Penguins’ Feet Freeze? ... 2006
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Do Polar Bears get Lonely? .... 2008

Edited by Mick O’Hare
Profile Books

It was tempting to create three pages – Penguin .. Wasp … and Polar Bear Gastronomy but more sensible to divide the extracts into Food, Beverage, etc pages with suitable headings. Once an extract is on the correct page, it is referenced as, say, Penguins – pages Y – Z. Additional notes are within [ .. ] or different colour text.

Each question is given a number to be used for indexing an referencing. Thes numbers are nothing to do with the sources books.

.Most of the extracts form part of the overall contributions made by the experts who answered. The purpose here is to render the flavour and not the full account. The names of the questioners and the experts have been omitted.

Text in green is the question, text in blue gives the answer(s). Red text is to highlight items of significance and black text is my comment on anything needing it.

---o--- indicates the end of one answer before continuing to include another. In many cases, a selection has been made from a lot of material. The reader can read the book for the entire answer(s).

Let us begin with that vexed question concerning tears and onions.

1 - Slice crisis

Penguins - pages 85 – 86

What is the irritant that causes eyes to water when slicing onions? Is there any way to prevent this?

Onions and garlic both contain certain derivatives of sulphur-containing amino acids. When an onion is sliced, one of these compounds, S-1-propenylcysteine-sulphoxide is decomposed by an enzyme to form the volatile propanthial S-oxide, which is the irritant or lacrimator.

Upon contact with water – in this case your eyes – the irritant hydrolyses to propanol, sulphuric acid and hydrogen sulphide. Tearfully, the eyes try to dilute the acid. However, it is these same sulphur compounds that form the nice aroma when onions are being cooked.

To prevent watering eyes, I would suggest one of the following: stop using onions (but you would lose the tasty aroma); wear goggles (you will look slightly silly); slice the onion under water (you will wash some of the aroma out); before slicing the onion wash it, and keep it wet.

[There are several other techniques mentioned including holding a bread crust between your lips. Many more can be found on the internet. No guarantees are offered for anything on any topic here or there.]

2 - Strings attached

Penguins - pages 105 - 6

Why does grilled cheese go stringy?

The uncooked cheese contains long-chain protein molecules more or less curled up in a fatty, watery mess. When you heat the cheese, the fats and proteins melt and if you fiddle with the fluid, the chains can get dragged into strings. Grab a bit of molten cheese and pull, and you get a filament, in much the same way that you can draw and twist cotton wool into yarn.

You can do similar things with polythene from plastic bags by heating or stretching the plastic to curl or stretch the long-chain molecules. When the molecules are curled up, the plastic is softish and waxy. When they are stretched into fibres, the result is elastic and strong in the direction of the stretch, although it splits easily between the chains lying among the fibre.

3 - Stale tale

Penguins - pages 103 - 105

Why does a biscuit that is left in the open overnight become soft by the morning but a baguette left out for the same length of time become so hard that one could knock someone out with it?

Biscuits contain much more sugar and salt than baguettes. The finely divided sugar and salt are hygroscopic and soak up moisture from the atmosphere – the osmotic pressure in a sweet biscuit is quite high. The dense texture of a biscuit helps maintain the moisture by capillary effects.

The baguette, on the other hand, contains little salt or sugar, and has a very open structure. The flour doesn’t care if there’s moisture around it or not. So, because of their different make-up, one attracts water, the other doesn’t. Try a series of different biscuits, varying from very sweet, dense ones to light, fluffy sponge biscuits. The ‘overnight sogginess index’ - put both traditional Italian biscotti (not very sweet and fairly open-textured) and dense, sweet ginger biscuits in a sealed container, the biscotti go rock hard and the ginger biscuits end up very soft.

4 - Green ham common
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[A variant of Greenham Common - one of the Open Spaces Society's most famous campaigns saved Greenham and Crookham Commons in the UK from development. – wiki]

Penguins - pages 107 - 9

What causes the greenish iridescent sheen that I often notice on bacon and ham? Is it harmful, and why does it vanish when the product is heated? Does this occur on any other foodstuffs?

The green colour that is sometimes observed on bacon and ham is the result of the action of non-pathogenic bacteria which break down the oxygen transport protein myoglobin to produce porphyrin derivatives. These derivatives are large heterocyclic compounds which can have greenish colours.

5 - Red or White?

Penguins - pages 71 – 72

Why is red meat red and white meat white? What is the difference between the various animals that makes their flesh differently coloured?

The colour is governed by the concentration of myoglobin in the muscle tissue which produces the brown colouring during cooking.

Chickens and turkey are always assumed to have white meat, but free-range meat from these species (especially that from the legs) is brown. This is because birds reared in the open will exercise and become fitter than poultry grown in restrictive cages. The fitter the bird, the greater the ease of muscular respiration, and hence the increased myoglobin levels in the muscle tissue, making the meat browner.

All beef is brown because cattle are allowed to run around in fields all day, but pork is whiter because pigs are lazy.

6 - In black and White

Penguins – page 231

While working at a factory that produces carbon powder, I noticed I had a large black thumbprint on one of my sandwiches. This set me wondering why bread, or for that matter potatoes, rice and sugar, which are mostly carbon, are not black.

The best way to explain is with an example. Sodium reacts violently on contact with water, while chlorine is a highly toxic greenish-yellow gas. However, sodium chloride, the compound which contains these two elements, is harmless common salt, showing the properties of an element are very different from the properties of the element’s compound.

7 - Eggsactly

Penguins – pages 67, 68

Why are most eggs egg-shaped?

Eggs are egg-shaped as a consequence of the egg-laying process in birds. The egg is passed along the oviduct by peristalsis – the muscles of the oviduct, which are arranged as a series of rings, alternately relax in front of the egg and contract behind it.

[Changes in text size are due to the way Google deals with text. The website is, as has been stated earlier, at the experimental stage.]

At the start of its passage down the oviduct, the egg is soft-shelled and spherical. The forces of contraction on the rear part of the egg, with the rings of muscle becoming progressively smaller, deform that end form a hemisphere into a cone shape, whereas the relaxing muscles maintain the near hemispherical shape of the front part. As the shell calcifies, the shape becomes fixed, in contrast to the soft-shelled eggs of reptiles which can resume their spherical shape after emerging.

Advantages in terms of packing in the nest and in the limitation of rolling might play a role in selecting individuals which lay more extremely ovoid eggs (assuming the tendency is inherited) but the shape is an inevitable consequence of egg-laying process rather than evolutionary selection pressure.

When you buy eggs, you probably look at them for those that are cracked. Some eggshells these days are very thin so press each one slightly. Also, check that the eggs are the correct way up. The “airspace” should be at the top, rounded end. The narrow end should be down. Also, some shops may prefer the narrow ends uppermost since it is more difficult to check for thin shells since there is a different surface structure.

Another aspect of egg knowledge concerns the way the yolk is held within the centre. Stronger threads of the white called chalaza attach to the yolk and the inside of the shell. Look at a cut hard-boiled egg. If the yolk is not central the egg is stale. Look at the egg in the pan when frying it and before it sets. If the white is thin and spread out because of weak chalaza, (which remains relevant even though it is no longer attached to the shell) and other factors, the egg is stale. Experiment using eggs which vary in freshness.

8 - A matter of taste

Penguin, pages 113 - 114

How does temperature affect the taste of food and drink? For example, white wine, tap water, cointreau, lager and even chocolate taste much better cold. On the other hand, tea, coffee and brandy, as well as most cooked meals, taste much better warm or hot. English beer and red wine are better at room or cellar temperature, why?

What we normally refer to as ‘taste’ is more correctly termed flavour, which is made up of taste, irritation and aroma. Taste per se consists only of the five sensations that can be detected by the tongue: salt, sweet, sour, bitter and umami*. These are not affected by temperature and nor is irritation from, for instance, chilli peppers. But aroma, which is sensed in the nose, is strongly affected by food temperature because it depends on the release of volatile oils. The higher the temperature, the more volatiles are released, and the stronger the aroma and thus the total sensation.

* Umami is detected by specialised receptor cells present on the human tongue. The specialisation is focused on detecting glutamic acid or glutamates present in meat, cheese, and other protein foods. One way of putting it is that umami concerns the detection of savouriness in the same way that other detectors are concerned with sweetness, sourness etc.
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Umami is described on pages 86.87, 97 - 99, 283 and in the editor's preface in "Molecular Gastronomy ..."by Herve This, 2006. On page 29, hard-boiled eggs are dealt with which furthers the previous item Number 7. There are other topics relevant to this Onion Gastronomy page well worth investigating.
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See also Number 18 as umami is relevant but not mentioned.

9 - A sting in the mouth

Wasps - pages 85-86

In a recent conversation about food chains, a colleague wondered if anything ate wasps. Someone suggested ‘very stupid birds’. Does anyone know any more about this?

The lowly wasp certainly has its place in the food chain. Indeed, the question should possibly be ‘what doesn’t feed, in one way or another, on this lowly and potentially dangerous insect?

This has been included to introduce this source but also to provide an unusual perspective of the food-chain aspects of our diet.

10 - Honey, I’m bendy

Wasps - page 124

Why does a slice of bread spread with honey gradually become concave?

My wife has assured me that her bread doesn’t have time to go concave when spread with honey. However, for those folk, who chomp their honeyed bread in a more leisurely fashion, there is a simple explanation.

Bread is approximately 40 per cent water while honey is a strong solution containing approximately 80 per cent sugar. This means that moisture is drawn out of the bread and into the honey by osmosis. Removing the water makes the bread shrink, but only on the side exposed to the honey. This causes the bread to become concave.

This is less likely to happen, of course, if you butter the bread before spreading the honey. Butter forms a water-impermeable layer that protects the bread from dehydration by the honey.

11 - Toxic Tatties

Wasps - pages 62-63

When I was a child my grandmother told me that I should never eat the green areas of skin on old or damaged potatoes. I’ve since learned that this contains a toxin similar to that found in deadly nightshade. But how much green potato skin would I have to eat before falling ill, and what would the toxin actually do to me? Do similar problems lurk in species related to potatoes, such as yams or aubergines?

Potatoes are a member of the solanaceae family of plants that include tomatoes, peppers, aubergines, tobacco and deadly nightshade. They are characterised by their ability to produce toxic alkaloids such as solanine in their leaves, roots and fruit. Unfortunately, solanine does not dissolve so it cannot be removed by soaking the potato and it is not destroyed by cooking.

Even in edible varieties, a high concentration of glycoalkaloids is present in the leaves, shoots and fruit and these should never be eaten. Potato tubers should always be stored where it is cool, dry and dark, because those exposed to light may develop unacceptable concentrations of glycoalkaloids, indicated by the green colour you find in aging potatoes.

People have died from solanine poisoning. A report by Canada’s Bureau of Chemical Safety for the World Health Organization concluded there is no safe level of solanine in food, though levels found in correctly stored potatoes between 10 and 100 milligrams per kilogram are acceptable.

A lethal dose might be 3 milligrams of glycoalkaloids per kilogram of a person’s body mass. Therefore, an adult with a mass of say 70 kilograms might consume a fatal dose by eating around 2 kilograms of potatoes. Even if one were hungry enough to eat a meal this large, the more likely outcome would be gastrointestinal or neurological symptoms and not death. Besides, if concentrations in the potato had reached hazardous levels this would most likely be detected from the bitter taste or the burning sensation in your throat.

12 - Whisking Disaster

Wasps - pages 93-94

For years, whenever my family have come to visit, I have made meringues, which involves whisking egg whites until they are thick. I have always used free-range eggs, but recently I bought organic free-range ones, and no matter how much I whisked these whites they would not thicken. Why should organic eggs behave in this way? Is something missing from the birds’ organic diet that prevents the whites of their eggs thickening?

A good, stiff meringue froth demands a complex interconnection of suitably distorted protein molecules. Anything that interferes with the interlinking of the molecules leaves the whites an unappetising slush. Oil is the usual culprit. Use clean, dry utensils, free of detergent. Before the whites have formed a stiff froth, the merest drop of cooking oil, cream or oily yolk getting into the whites can ruin the meringue.

13 - Banana armour

Penguins, page 77

The skin of bananas in the fridge turns brown faster than those in a room, but the fruit is still edible. I thought the browning was oxidation, but if so why does it happen faster than in the cold?

Number thirteen is unlucky for some. If you have been lulled into the answers on a plate, ask yourself about the temperature of the fruit's environment "at home". Then consider the way enzymes might vary in their release depending on the surrounding temperature. If that exhausts you, buy the book(s).

We will now return to normal.

14 - Pickled Poser

Wasps - page 96

I love pickles and chutneys. But I’d like to know what nutrition is conserved and what is lost when vegetables are prepared and preserved in this manner?

Pickles and chutneys were originally a means of preserving fruit and vegetables using a combination of heat processing to kill bacteria, fungi and yeasts, with added sugar, acid (in the form of vinegar) and salt acting as a preservative.

In some cases the raw fruit or vegetable is fermented for weeks or months in a brine containing lactobacillus bacteria, which produce the natural preservative lactic acid. Mango and cabbage can be preserved in this way. This also develops the texture and flavour of the fruit or vegetable.

Vitamins, minerals and nutrients are lost when the cooked or fermented plants are washed during processing. Unstable vitamins start to break down soon after harvesting, a process which is accelerated at high cooking temperatures and the acidic pH typical for these types of product.

15 - Spice attack

Wasps - pages 99 – 100

Why does turmeric stain everything an indelible yellow, including surfaces that appear impermeable to other substances? Other powdered spices such as cinnamon, paprika and chilli do not leave the same legacy. And what is the best way to remove turmeric stains?

Turmeric, the powdered rhizome of Curcuma longa, and paprika, which is obtained from the fruits of sweet peppers, Capsicum annuum, are examples of spices used in cooking as much for their colour as for favour.

The yellow colour of turmeric is caused by curcumin, which makes up around 5 per cent of the dry powder. The red pigments in paprika are a mixture of carotenoids, principally capsanthin and capsorubin, and in dried paprika they amount to a maximum of 0.5 per cent of the weight.

The red carotenoids, which consist of long, chain-like molecules, are soluble in organic solvents such as petroleum spirit. Curcumin consists of smaller molecules with terminating phenyl groups. It is insoluble in water but dissolves in solvents like methanol. Therefore you might expect that both paprika and turmeric would stain paintwork and plastics, because they dissolve in organic solvents. You would also expect them to migrate to the oily part of food during cooking.

16 - Citric secret

Wasps - page 102

Why does lemon juice stop cut apples and pears from browning?

To answer this question first we need to understand why some plant tissues go brown when cut. Plant cells have various compartments, including vacuoles and plastids, which are separated from each other by membranes. The vacuoles contain phenolic compounds which are sometimes coloured but usually colourless, while other compartments of the cell house enzymes called phenol oxidases.

17 - Honey monster

Wasps - pages 110-111

How can an unopened jar of runny, clear honey suddenly begin to turn into a hardened block of sugar with no obvious stimulus? Jars that have remained clear for years can, over the space of a couple of weeks, change into solid sugar while the jar remains motionless on its shelf.
Temperature does not seem to be a factor – the process can occur in winter or summer?

Bee-keepers argue about this, as honeys from different sources behave differently. Honey is a supersaturated solution of various proportions of sugars (mainly glucose and fructose), and is full of insect scales, pollen grains and organic molecules that encourage or interfere with crystallisation. Glucose crystallises readily, while fructose stubbornly stays in solution. Honeys like aloe honey, which is rich in glucose and nucleating particles, go grainy, while some kinds of eucalyptus honey stay sweet and liquid for years.

18 - Changing tastes

Wasps - pages 114-115

Monosodium glutamate is a common flavour enhancer that is used particularly in Chinese and Japanese cooking. Why is it so popular in these cuisines and, more pertinently, how does it enhance the flavour of food?

Monosodium glutamate or MSG is presumably most commonly used in oriental cooking for traditional reasons. For thousands of years the Japanese have incorporated a type of sea weed known as kombu in their cooking to make food taste better. It was not until 1908, however, that the actual ingredient in kombu responsible for improvement in flavour was identified as glutamate.

From then until 1956, glutamate was produced commercially in Japan by a very slow and expensive means of extraction. Then large-scale industrial production began and has continued, mainly involving the fermentation of natural substances such as molasses from sugar beet or sugar cane. Today, hundreds of thousands of tonnes of MSG are produced all over the world.

Monosodium glutamate contains 78.2 per cent glutamate, 12.2 per cent sodium and 9.6 per cent water. Glutamate, or free glutamic acid, is an amino acid that can be found naturally in protein-containing foods such as meat vegetable, poultry and milk. Roquefort and parmesan cheese contain a lot of it. The glutamate in commercially produced MSG, however is different from that found in plants and animals. Natural glutamate consists solely of L-glutamic acid, whereas the artificial variety contains L-glutamic acid plus D-glutamic acid, pyroglutamic acid and other chemicals.

19 - Bluto strikes back

Wasps - pages 89-90

My Italian recipe book says that I should cut cooked spinach with a stainless steel knife to avoid discoloration. Which would become discoloured if I don’t – the knife or the spinach? And what would be the chemistry at work?

The reason you should always use a stainless steel knife to cut your spinach is intriguing and is a major stumbling block to the fortification of food with iron. Remember that a lack of iron is the world’s most prevalent nutritional deficiency.

Both iron blade and spinach will become discoloured because of the reaction between the polyphenols in the spinach, and the iron blade. If you want to see a dramatic illustration of this, make yourself a cup of tea and add a few crystal of soluble iron salt such as ferrous sulphate (don’t drink it).

The black discolouration you see is caused by the reaction between polyphenols, called tannins, in the tea, and in the iron. The resulting black compound is highly insoluble. The implications for iron absorption in the body are huge because iron in this form is virtually unavailable for absorption, it is not the iron.

Polyphenols are found in many vegetables and, together with phytates, are the reason why many people who subsist on cereal and vegetable diets have iron deficiency. Fortifying such diets with iron salts creates two problems. Firstly the iron is not absorbed, and secondly the coloured iron-polyphenols made the food look unattractive.

20 - Cereal Killer

Bears, page 5

Most healthy people I know would 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 am. 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?

It may be that your hunter-gatherer ancestry is responsible for the favourable response to your morning service 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 10,000 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 ‘glycaemic 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 glycaemic loads and lower protein content.

21 - Sacred DNA

Bears, page 6

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?

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.

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Page 7

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.

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Page 8

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

www.cs.st-and.ac.uk~norman/Shorts/inorganic.html

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Page 9

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.

22 - Tasteful matters

Bears, pages 12 & 13

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

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

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

23 - Twin Chicks

Bears, page 14

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?

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 travelling 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.

24 - Colour of Custard

Bears, p16

Why is custard powder pink until you add the liquid, upon which it becomes yellow?

Custard powder is often coloured with a blend of tartrazine yellow or quinoline yellow food dyes, mixed with sunset yellow. In solution with water, these colours are true to their names, but in their pre-dissolved solid phase the sunset yellow portion is more orange-red, and this colour tends to dominate.

When mixed with the other custard powder components, which are white, the result is a pastel orange-red, or pink. Many pure colourants, both dyes and pigments, have a very different shade from that required in their final state.

25 - Question of taste

Bears, page 24

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

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 fro the burning sensation you experience if you eat garlic raw.

However, allicin is not stable and generates numerous smelly sulphur-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.

26 - Cheese scrub

Bears, pages 25 & 26

Mould 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 the mould since. The sugar gets moist and 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?

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 moulds.

27 - Shapely pear

Bears, page 149

Why are pears pear-shaped and not spherical like apples?

Apples, pears, medlars, quinces, and the fruits of related plants such as Pyracantha are known as pomes. The fleshy part of the pome grows from tissue between the stem and the carpels, the female reproductive parts of the flower.

Plant hormones called auxins, whose distribution is genetically controlled, guide all plant tissue growth and form, including fruit shape. As long as the final product does not put the plant at a disadvantage, selection has no influence on the fruit’s appearance.

So if the question is attempting to address what purpose or function the shape of a pear serves, the answer is probably none.

28 - No swimming

Bears pages 54 & 56

Everyone I know was told as a small child not to swim within an hour of eating. Why is this?

One possible rational explanation for the idea is that because both exertion and digestion demand extra blood supply, swimming after heavy eating may be dangerous for anyone prone to fainting. Anyway, why risk vomiting during a strenuous swim instead of waiting a while? The stomach absorbs very little food, so it is an uncomfortable handicap when full, whereas food in the small gut continuously maintains your stamina while you assimilate it.

29 - Dodgy tummy

Bears, page 67

Tripe is the stomach lining of cows and other animals. So how is tripe digested by humans? You would assume that it would not be broken down by the normal digestive process. If it is, why is it an effective stomach lining?

Our digestive juices can break down tripe because it has lost the protection it had when it was part of a living animal. Inside our own digestive tract it is broken down by gastric acid in the form of hydrochloric acid produced by parietal cells, and enzymes such as pepsin.

These substances could eat away at our own stomach lining too, were it not for the fact that it is covered in a layer of thick bicarbonate–rich mucus produced by so-called goblet cells. Bicarbonate is alkaline, so it neutralises the acid secreted by the parietal cells. Without the continuous bicarbonate supply your stomach would digest itself.

30 - Middle-age spread

Bears, pages 92 & 93

Why, as we age, do we find it easier to gain body fat and, of equal importance, why is it so much more difficult to get rid of it?

There is a number of contributing factors at work here. As we age we tend to reduce our active pursuits and, above the age of 20, our resting metabolic rate reduces by about 3 per cent per decade, allowing our bodies to go further and further on the same amount of food. On top of this, as we age, we use less energy to digest and process the food that we eat.

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If you have reached this point, you may well have improved your knowledge about certain foodstuffs. Gastronomy is knowledge. It is also experience and you can now consolidate your knowledge by putting what you have learned into practice.