Ingredient Focus: Nuts and Seeds

Written by Science Knowledge on 7:59 PM

Nuts and seeds pack quite a few vitamins (such as folate and vitamin E) and minerals, along with fiber and protein, in their small sizes. Nuts, in particular, also contain quite a bit of fat. Luckily, most of the fat (except in walnuts) is monounsaturated. Walnuts and flaxseed are rich in the omega-3 fatty acid linolenic acid, an essential fatty acid. One ounce of many nuts contains from 13 to 18 grams of fat, making them also a relatively high-kcalorie food. By comparison, seeds contain less fat and more fiber but still quite a few kcalories. Nuts and seeds also contain many phytochemicals.

Nuts usually grow on trees and are characterized by a hard, removable outer shell. Some commonly used nuts include the following:

  • Almonds were common ingredients in the cuisines of ancient China, Greece, Turkey, and the Middle East. Today much of the world's supply of almonds is grown in California. Almonds are sweet with a delicate butterlike flavor.
  • Brazil nuts are the firm but tender fruit of a South American tree. They have a clean, slightly oily taste. They are high in calories.
  • Cashews form on the bottom of a pear-shaped fruit. Because of the process needed to remove the shell, they are not readily available in the shell.
  • Macadamia nuts are grown in Hawaii, Australia, and Central America. They are high in cost and very high in fat (store in the refrigerator).
  • Peanuts probably originated in Brazil and are grown in the southern United States, among other places. Three types of peanuts are most commonly grown: Virginias and runners, which have red skins, and Spanish, which are smaller and have a skin that is more tan.
  • Pecans grow on huge trees native to the Mississippi River Valley. Georgia is the main source of pecans, which are wonderful all-purpose nuts. Kernels are best stored in the refrigerator.
  • Pine nuts, also known as pignoli, are popular in Italian cuisine, where they are used in rice, sauces, and cakes. They are also used in Turkish, Middle Eastern, and Mexican cooking. There are two varieties: the Mediterranean or Italian pine nut, with a light flavor, and the Chinese pine nut, with a stronger flavor.
  • Pistachios, originally from the Middle East and Asia, are now grown in California. The pistachio shell splits naturally as part of the ripening process. Pistachios were originally dyed red by importers to cover stains in imported nuts. Most California pistachios are sold with their natural ivory shell.
  • Walnuts were introduced to California by the Franciscan fathers in the 1700s. The mellow flavor of the walnut works well with a variety of foods. Most walnuts marketed in the United States are the English variety. The black walnut is sweet and has a deeper flavor. Walnuts are a good source of omega-3 fatty acids.

Nuts in the shell can be stored at room temperature in a cool, dry location. Once shelled, most nuts need to be refrigerated.

Nuts are used in all their forms and styles (whole, sliced, pieces, ground, butters, oils) in baked goods, in stews and ragouts, and as toppings for salads, cooked vegetables, and entrées. Nuts often add eye appeal and an unexpected change in texture. In part due to their high calorie and fat content, nuts are often used in small amounts. By toasting or roasting nuts, you can bring out a more intense flavor and use less. Small amounts of flavorful nuts and seeds can often replace fats such as butter or margarine. Other foods, such as pumpkin seeds or roasted chickpeas, can also be used to replace part or all of the nuts in a dish and still provide a crunchy texture.

Seeds are versatile as well.

  • Pumpkin seeds are common in the cuisines of Austria and parts of Mexico, where people like their zesty flavor. Pumpkin seeds can be coated with olive oil and roasted to bring out their nutty flavor, then tossed on salads. Pumpkin seeds can also be pulverized into a thick powder or paste and used as a thickener, or toasted and used as a crust. In Austria, pumpkin seed oil, which has a very strong flavor, is used in small amounts in salad dressings. It is used in the United States now as well by some chefs.
  • Sunflower seeds are large compared to seeds such as sesame and caraway. They can be used in casseroles, stews, vegetables, stuffings, or salads.
  • Sesame seeds and caraway seeds are often used in baking. Toasted sesame seeds can be sprinkled on soups, fish, and cooked vegetables for flavor and texture.

Seeds should be stored in a tightly covered container in a cool, dry, dark area.


Written by Science Knowledge on 4:03 PM

The average adult's body weight is generally 50 to 60 percent water—enough, if it were bottled, to fill 40 to 50 quarts. For example, in a 150pound man, water accounts for about 90 pounds and fat about 30 pounds, with protein, carbohydrates, vitamins, and minerals making up the balance. Men generally have more water than women, a lean person more than an obese person. Some parts of the body have more water than others. Human blood is about 92 percent water, muscle and brain tissue about 75 percent, and bone 22 percent.

The body uses water for virtually all its functions: digestion, absorption, circulation, excretion, transporting nutrients, building tissue, and maintaining temperature. Almost all body cells need and depend on water to perform their functions. Water carries nutrients to the cells and carries away waste materials to the kidneys.

Water is needed in each step of the process of converting food into energy and tissue. Water in the digestive secretions softens, dilutes, and liquefies the food to facilitate digestion. It also helps move food along the gastrointestinal tract. Differences in the fluid concentration on either side of the intestinal wall enhance the absorption process.

Water serves as an important part of body lubricants, helping to cushion the joints and internal organs; keeping tissues in the eyes, lungs, and air passages moist; and surrounding and protecting the fetus during pregnancy.

Many adults take in and excrete between 8 and 10 cups of fluid daily. Nearly all foods have some water. Milk, for example, is about 87 percent water, eggs about 75 percent, meat between 40 and 75 percent, vegetables from 70 to 95 percent, cereals from 8 to 20 percent, and bread around 35 percent.
The body gets rid of the water it doesn't need through the kidneys and skin and, to a lesser degree, from the lungs and gastrointestinal tract. Water is also excreted as urine by the kidneys along with waste materials carried from the cells. About 4 to 6 cups a day are excreted as urine. The amount of urine reflects, to some extent, the amount of an individual's fluid intake, although despite the amount consumed, the kidneys will always excrete a certain amount each day (about 2 cups) to eliminate waste products generated by the body's metabolic actions. In addition to the urine, air released from the lungs contains some water, and evaporation that occurs on the skin (when sweating or not sweating) contains water as well.

If normal and healthy, the body maintains water at a constant level. A number of mechanisms, including the sensation of thirst, operate to keep body water content within narrow limits. You feel thirsty when the blood starts to become too concentrated. Unfortunately, by the time you feel thirsty, you are already much in need of extra fluid. It is therefore very important not to ignore feelings of thirst, a concern that is particularly appropriate for the elderly, whose thirst mechanism is compromised. The well-known recommendation to drink 8 cups of fluid daily is too much for some, like many elderly, and too little for others, like athletes.

There are, of course, conditions in which the various body mechanisms for regulating water balance do not work, such as severe vomiting, diarrhea, excessive bleeding, high fever, burns, and excessive perspiration. In these situations, large amounts of fluids and minerals are lost. These conditions are medical problems to be managed by a physician.

Factors Influencing Food Selection

Written by Science Knowledge on 8:58 AM

Why do people choose the foods they do? This is a very complex question, and there are many factors influencing what you eat, as you can see from this list:

  • Flavor
  • Other aspects of food (such as cost, convenience, nutrition)
  • Demographics
  • Culture and religion
  • Health
  • Social and emotional influences
  • Food industry and the media
  • Environmental concerns

Now we will look at many of these factors in depth.

The most important consideration when choosing something to eat is the flavor of the food. Flavor is an attribute of a food that includes its appearance, smell, taste, feel in the mouth, texture, temperature, and even the sounds made when it is chewed. Flavor is a combination of all five senses: taste, smell, touch, sight, and sound. From birth, we have the ability to smell and taste. Most of what we call taste is really smell, a fact we realize when a cold hits our nasal passages. Even though the taste buds are working fine, the smell cells are not, and this dulls much of food's flavor.

Flavor— An attribute of a food that includes its appearance, smell, taste, feel in the mouth, texture, temperature, and even the sounds made when it is chewed.

Taste comes from 10,000 taste buds—clusters of cells resembling the sections of an orange. Taste buds, found on the tongue, cheeks, throat, and roof of the mouth, house 60 to 100 receptor cells each. The body regenerates taste buds about every three days. They are most numerous in children under six, which may explain why youngsters are such picky eaters. These cells bind food molecules dissolved in saliva, and alert the brain to interpret them.

Taste— Sensations perceived by the taste buds on the tongue.

Taste buds— Clusters of cells found on the tongue, cheeks, throat, and roof of the mouth. Each taste bud houses 60 to 100 receptor cells. The body regenerates taste buds about every three days. These cells bind food molecules dissolved in saliva and alert the brain to interpret them.

Although the tongue is often depicted as having regions that specialize in particular taste sensations—for example, the tip is said to detect sweetness—researchers know that taste buds for each sensation (sweet, salty, sour, and bitter) are actually scattered around the tongue. In fact, a single taste bud can have receptors for all four types of taste.

If you could taste only sweet, salty, sour, and bitter, how could you taste the flavor of cinnamon, chicken, or any other food? This is where smell comes in. Your ability to identify the flavors of specific foods requires smell.

The ability to detect the strong scent of a fish market, the antiseptic odor of a hospital, the aroma of a ripe melon, and thousands of other smells is possible thanks to a yellowish patch of tissue the size of a quarter high up in your nose. This patch is actually a layer of 12 million specialized cells, each sporting 10 to 20 hairlike growths called cilia that bind with the smell and send a message to the brain. Our sense of smell may not be as refined as that of dogs, who have billions of olfactory cells, but we can distinguish among about 10,000 scents.

You can smell foods in two ways. If you smell coffee brewing while you are getting dressed, you smell it directly through your nose. But if you are drinking coffee, the smell of the coffee goes to the back of your mouth and then up into your nose. To some extent, what you smell (or taste) is genetically determined.

All foods have texture, a natural texture granted by Mother Nature. It may be coarse or fine, rough or smooth, tender or tough. Whichever the texture, it influences whether you like the food. The natural texture of a food may not be the most desirable texture for a finished dish, so a cook may create another texture. For example, a fresh apple may be too crunchy to serve at dinner, so it is baked or sautéed for a softer texture. Or a cream soup may be too thin, so a thickening agent is used to increase the viscosity of the soup, or, simply stated, make it harder to pour.

Food appearance or presentation strongly influences which foods you choose to eat. Eye appeal is the purpose of food presentation, whether the food is hot or cold. It is especially important for cold foods because they lack the come-on of an appetizing aroma. Just the sight of something delicious to eat can start your digestive juices flowing.

Other Aspects of Food
Food cost is a major consideration. For example, breakfast cereals were inexpensive for many years. Then prices jumped, and it seemed that most boxes of cereal cost over $3.00. Some consumers switched from cereal to bacon and eggs because the bacon and eggs became less expensive. Cost is a factor in many of the purchasing decisions at the supermarket, whether one is buying dry beans at $0.39 per pound or fresh salmon at $8.99 per pound.

Convenience is more of a concern now than at any time in the past. Just think about the variety of foods you can purchase today that are already cooked or can simply be microwaved. Even if you desire ready-to-eat fruits and vegetables, supermarkets offer cut-up fruits, vegetables, and salads that need no further preparation. Of course, convenience foods are more expensive than their raw counterparts, and not every budget can afford them.

Everyone's food choices are affected by availability and familiarity. Whether it is a wide choice of foods at an upscale supermarket or a choice of only two restaurants within walking distance of where you work, you can eat only what is available. The availability of foods is very much influenced by how food is produced and distributed. For example, the increasing number of soft drink vending machines, particularly in schools and workplaces, has contributed to increasing soft drink consumption year-round. Fresh fruits and vegetables are perfect examples of foods that are most available (and at their lowest prices) when in season. Of course, you are more likely to eat fruits and vegetables, or any food for that matter, with which you are familiar and have eaten before.
The nutritional content of a food can be an important factor in deciding what to eat. You have probably watched people reading nutritional labels on a food package, or perhaps you have read nutritional labels yourself. Current estimates show that about 66 percent of Americans use nutrition information labels. Older people tend to read labels more often than younger people.

Demographic factors that influence food choices include age, gender, educational level, income, and cultural background (discussed next). Women and older adults tend to consider nutrition more often than men or young adults when choosing what to eat. Older adults are probably more nutrition-minded because they have more health problems and are more likely to have to change their diet for health reasons. People with higher incomes and educational levels tend to think about nutrition more often when choosing what to eat.

Culture and Religion
Culture can be defined as the behaviors and beliefs of a certain social, ethnic, or age group. Culture strongly influences the eating habits of its members. Each culture has norms about which foods are edible, which foods have high or low status, how often foods are consumed, what foods are eaten together, when foods are eaten, and what foods are served at special events and celebrations (such as weddings). For example, some French people eat horsemeat, but Americans do not consider horsemeat acceptable to eat. Likewise, many common American practices seem strange or illogical to persons from other cultures. For example, what could be more unusual than boiling water to make tea and adding ice to make it cold again, sugar to sweeten it, and then lemon to make it tart? When immigrants come to live in the United States, their eating habits do gradually change, but they are among the last habits to adapt to the new culture.

Culture— The behaviors and beliefs of a certain social, ethnic, or age group. Food Practices of World Religions

Have you ever dieted to lose weight? Most Americans are either trying to lose weight or keep from gaining it. You probably know that obesity and overweight can increase your risk of cancer, coronary heart disease, diabetes, and other health problems. What you eat influences your health. Even if you are healthy, you may choose foods based on a desire to prevent health problems and/or improve your appearance.

A knowledge of nutrition and a positive attitude toward nutrition may translate into nutritious eating practices. Just knowing that eating lots of fruits and vegetables may prevent heart disease does not mean that someone will automatically start eating more of these foods. For some people, knowledge is enough to stimulate new eating behaviors, but for most people, knowledge is not enough and change is difficult. There are many circumstances and beliefs that prevent change, such as a lack of time or money to eat right. But some people manage to change their eating habits, especially if they feel that the advantages (such as losing weight or preventing cancer) outweigh the disadvantages.

Social and Emotional Influences
People have historically eaten meals together, making meals important social occasions. Our food choices are influenced by the social situations we find ourselves in, whether in the comfort of our home or eating out in a restaurant. For example, social influences are involved when several members of a group of college friends are vegetarian. Peer pressure no doubt in fluences many food choices for children and young adults. Even as adults, we tend to eat the same foods that our friends and neighbors eat. This is due to cultural influences as well.

Food is often used to convey social status. For example, in a trendy, upscale New York City restaurant, you will find prime cuts of beef and high-priced wine.

Emotions are closely tied to some of our food selections. You may have been given something sweet to eat, such as cake or candy, whenever you were unhappy or upset. As an adult, you may gravitate to those kinds of foods, called comfort foods, when under stress.

Food Industry and the Media
The food industry very much influences what you choose to eat. After all, the food companies decide what foods to produce and where to sell them. They also use advertising, product labeling and displays, information provided by their consumer services departments, and websites to sell their products.

On a daily basis, the media (television, newspapers, magazines, radio, etc.) portray food in many ways: paid advertisements, articles on food in magazines and newspapers, or foods eaten on television shows. Much research has been done on the impact of television food commercials on children. Quite often the commercials succeed in getting children to eat foods such as cookies, candies, and fast foods. Television commercials are likely contributing to higher calorie and fat intakes.

The media also report frequently on new studies related to food, nutrition, and health topics. It is hard to avoid hearing sound bites such as "more fruits and vegetables lower blood pressure." Media reports may influence which foods people eat.

Environmental Concerns
Some people have environmental concerns, such as the use of chemical pesticides, so they often, or always, choose organically grown foods (which are grown without such chemicals—see Food Facts on page 31 for more information). Many vegetarians won't eat meat or chicken for ecological reasons, because livestock and poultry require so much land, energy, water, and plant food, which they consider wasteful.

Food Contaminants

Written by Science Knowledge on 8:20 AM

There is a greater reason than aesthetics to insist on clean hands at all times. Salmonella, the most common form of food poisoning and one that can kill the elderly and infirm, is often transmitted by urine. Diarrhea and dysentery often come from feces.
However, the good news is that the least likely source of food poisoning is a dirty person. The classic case of “Typhoid Mary,” an itinerant dishwasher who spread typhoid wherever she worked, is long gone.

Far more dangerous are bad food storage disciplines. Raw meat and cooked meat must not collide. A butcher or chef who has handled raw meat must not handle any other food item until he’s washed his hands thoroughly in serious soap and water. The quick rinse under the faucet doesn’t do it.

Food stored in a refrigerator must be placed in a way that will not allow accidental drippings from one item to another.

What saves society from regular epidemics of food poisoning is the cooking process. Germs insinuated into food by dirty workers or natural deterioration are destroyed by heat.
Other germs may be present in food from other sources. Chicken has been targeted as the main source of salmonella in the United States. That’s why it should be thoroughly cooked, though it’s not unusual in dubious restaurants to see a little ooze of blood as one cuts into a chicken breast! Such a sight is likely to extinguish the heartiest appetite, so make sure your chicken—and all other appropriate items—are properly cooked, or you’ll lose customers and even risk lawsuits. Apart from the fact that pork tastes better when well cooked (though the French sometimes eat pork chops medium rare!), there is the danger of trichinosis, a common disease carried by pigs that can be fatal to humans. The dietary laws of some religions preclude the consumption of pork, and originally the reason for this may have been practical rather than religious.

The most dangerous food is that which, having been cooked, is then reheated. At certain temperatures germs spring to life with a vengeance, particularly in meat and quite horrifically in sausage. The simple way to avoid this danger is to make sure that food is served either thoroughly cooked and piping hot, or cold. Of course, this leaves your poor old salade de canard tiède (warm salad of medium rare duck breasts and vegetables) out in the cold, but some gourmets are happy to take a chance.

Sadly, fish is a well-known source of poisoning, and fish allergies are common. Although it’s not likely to be a danger to Westerners, there is some curio value in mentioning the highly dangerous puffer fish, so called because when threatened, it gulps water and doubles its mass, making it harder to swallow. The trade-off is a 50 percent reduction in speed of withdrawal. Other names for this fish, of which there are more than a hundred species worldwide, ranging in size from a few inches to two feet, are blow fish, swell fish, globe fish and, in Japan, where it’s considered a great delicacy, fugu. Many parts of this fish, including the liver, skin, and ovaries, contain a strong paralyzing poison, 1,000 times more deadly than cyanide, called tetrodotoxin. There is no known antidote for this poison. The immediate symptoms of ingestion are a slight numbness of the lips and tongue. Diarrhea, vomiting, collapse, and paralysis follow. Eventually, the central nervous system is destroyed, and the patient dies between 20 minutes and eight hours later, often remaining mentally lucid to the end. In Japan, only specially trained and licensed chefs are allowed to prepare fugu. There have been many casualties over the years. Some call this dish the gourmet’s Russian Roulette. Read that sushi menu carefully.

At the risk of sounding gruesome, it should be mentioned that ordinary (i.e., ghastly but non–life-threatening fish poisoning) will often produce the same immediate symptoms, as well as fierce facial flushing, which will sometimes reduce the sympathy factor as beholders assume the poor victim is simply drunk.

Fortunately, there is usually no mistaking fish that has deteriorated, but accidents do happen, and even the strong smell of rotting fish might get lost in the jumble of aromas that pervades the kitchen at busy times. Interestingly, fish inspectors at central markets are often allergic to the histamines that occur in deteriorating fish. Their noses are thus super-sensitive. One threatening whiff will define the quality of a batch of fish.

A properly trained Western cook simply follows the maxim, “When in doubt, throw it out.” But anyone unfamiliar with the fundamentals of hygiene should make an effort to acquire them.

The Main Types of Alternative Fuels

Written by Science Knowledge on 9:38 AM

In this section we will look at the main types of alternative fuels. We start with Biofuels as this constitutes probably the most popular AF currently in use.


Much recent attention has been focused on biofuels. This is highlighted economically by the fact that worldwide investment in biofuels rose from US$5bn in 1995 to US$38bn in 2005, owing to substantial investments by companies such as BP, Shell and Ford, and by Richard Branson (Grunwald, 2008).

Biofuels are essentially fuels produced from renewable plant material and oils. The International Energy Agency (IEA, 2004: 26) defines biofuels in the following way: 'Either in liquid form such as fuel ethanol or biodiesel or gaseous form such as biogas or hydrogen, biofuels are simply transportation fuels derived from biological (eg agricultural) sources.'

There are two main types of biofuel:

Biodiesel (or Alkyl Esters)
Biodiesel is made from plant and animal oils through a process called transesterification (ie the production of esters from oil or fat). In this process, the fat or oil is reacted with alcohol in the presence of a catalyst to produce biodiesel and glycerine ( The main sources of oil used in the production of biodiesel vary according to country, depending on local growing conditions. In Asia palm oil is the norm, in the United States it is soybean oil and in Europe the norm is rapeseed oil (or canola). Other plant oils that can be used include sunflower oil, cottonseed oil, mustard seed oil, coconut oil and hemp oil. In 2006, the United States produced 250 million gallons of biodiesel, up from 2 million gallons in 2000, but this still only represented less than 1 per cent of total highway diesel fuel used (Union of Concerned Scientists, 2007).

Bioethanol can be produced from any biological foodstock that contains sugar, or materials such as starch or cellulose that can be made into sugar (IEA, 2004). The main sources of sugars for bioethanol are wheat, corn, sugar beet, straw, maize, reed canary grass, cord grass, Jerusalem arti-chokes, myscanthus, sorghum, sawdust and willow and poplar trees (ESRU, 2007), although sugar beet and corn account for 80 per cent of all bioethanol produced in the world in 2007 (Sperling, 2008). Bioethanol has been used as a fuel for decades. Brazil has been using bioethanol made from sugar cane since the 1930s, and indeed in the 1980s was selling cars that ran exclusively on such fuel (Sperling, 2008). The United States has also been using bioethanol (produced from corn) for many decades (not so much for environmental reasons as to reduce its dependence on imported conventional oil).

Both biodiesel and bioethanol are usually blended with existing fuel to make them usable. Biodiesel is usually blended with conventional diesel and bioethanol is usually blended with conventional petrol ('gasoline' in the United States), although it can be blended with diesel after some modification (IEA, 2004). Thus, B20 means there is a 20 per cent blend of biodiesel with conventional diesel and similarly E20 means that there is a 20 per cent blend of bioethanol with conventional petrol. As the percentage blend of ethanol increases, so its corrosive impact increases, and over about 10 per cent susceptible conventional vehicle components (particularly the rubber elements) need to be replaced by ethanol-resistant components. However, with biodiesel this problem is reduced. In the United States, the most common blend is B20, but in Germany, Austria and Sweden 100 per cent pure blended biodiesel is used in goods vehicles and buses with only very minor engine modifications (IEA, 2004). Vehicles that can use conventional fuel or any blend of biofuels are known as flexible-fuel vehicles (sometimes called flex-fuel vehicles).

One of the main reasons why biofuels have gained so much attention is that low blends (generally agreed to be up to about 10 per cent) can be used directly in existing cars with no engine modifications, and the refuelling infrastructure is exactly the same as for conventional fuel (ie through fuel pumps). In early 2008, there were 165 biodiesel and 16 bioethanol stations around the UK (Anon, 2008). This makes it very convenient and cheap compared with the development of other renewable fuel alternatives (such as hydrogen, electric power or LNG/CNG), which require major modifications to both vehicles and refuelling distribution systems.

Attention on the environmental impacts of transport is not new. In the 1970s and 1980s the focus was on the use of non-renewable resources (ie oil) following the OPEC oil crisis and an increasing understanding of the effects of transport on the local environment (particularly the health impacts of sulphur and lead). Since the 1990s, however, attention has been focused on the global impacts of pollution, and in particular on the impact of greenhouse gas emissions (particularly CO2) on climate change. The EU Biofuels Directive was adopted in May 2003. Its aim was to promote the use of transport fuels made from biomass and other renewable sources. The directive sets a reference value of 5.75 per cent (by energy) for the market share of biofuels by 2010. In the case of the UK, a conditional target of 10 per cent for the energy content share of biofuels in petrol and diesel was set for 2020. As part of the UK's 2006 Climate Change Programme, a further target of 5 per cent (by volume) was set for the proportion of road transport fuel to be derived from renewable sources by 2010. To aid in the achievement of this target, a Renewable Transport Fuel Obligation (RTFO) was established for fuel suppliers (which started in April 2008). Under the RTFO, companies are required to measure and report on how much carbon their fuel has saved on a life cycle basis (including land-use changes) (DfT, 2007). In 2008, the government announced that from 2010, the RTFO will reward fuels according to their carbon savings in order to encourage technological advances.

Environmental Impacts of Biofuels


Hydrogen is a second key potential alternative energy source for transport. In the early 2000s, hydrogen was being viewed as a panacea for the future and in 2003 the International Partnership for the Hydrogen Economy, established by the US Department of Energy with signatories from around the world, aimed to accelerate the transition to a hydrogen economy (see The impetus towards this shift has, however, slowed as problems have emerged.

To date, much of the research into hydrogen as an AF has focused on passenger cars and buses rather than freight vehicles, although there is considerable interest in the potential for hydrogen use in the light goods vehicle (LGV) sector. As the technology improves, and as long as it is viewed as being successful, transferral of this energy source to larger vehicles is likely.

The main form of hydrogen to be used in transport is the hydrogen fuel cell. This is a device that converts hydrogen gas and oxygen into water via a process that generates electricity. Fuel cell vehicles are generally powered by pure hydrogen which comes in the form of compressed hydrogen gas, metal hydrides stored in cylinders or as liquid hydrogen, though any hydrogen-containing feedstock (such as petrol and diesel oil) could be used (DfT, 2000). Proton exchange membrane fuel cells (PEMFC) are being developed for both transport and stationary applications (such as power for warehouses). PEMFCs are not new; they were invented in the 1950s by General Motors and were used by NASA in the Gemini space project. The PEMFC works by harnessing the chemical energy that results from the reaction of hydrogen and oxygen and transforming it into electrical energy. It is very efficient at energy production and is almost totally recyclable.

The main environmental benefit of hydrogen is that its only real tailpipe emission is water vapour. For use in cities this can be very beneficial and it is for this reason that bus companies all over the world are currently trialling them (for instance through the Clean Urban Transport in Europe (CUTE) initiative).

As more research into the use of hydrogen is carried out, however, major doubts have crept in concerning its environmental credentials. The principle issues of contention are fivefold:

- Hydrogen is 'an energy carrier not an energy source' (EurActiv, 2006). This means that it has to be produced from other sources (coal, nuclear etc), so it is only as clean as these source fuels. It can be made from renewable energy sources, such as wind power, but there is concern that if there is a global switch to the use of hydrogen, there will be insufficient supplies of renewables, whose price will increase as a result, encouraging the use of non-renewables again. Even if renewables can be used, in a major study of the benefits of hydrogen fuel for the DfT, Eyre, Fergusson and Mills (2002: 6) concluded: 'until there is a surplus of renewable electricity it is not beneficial in terms of carbon reduction to use renewable electricity to produce hydrogen — for use in vehicles or elsewhere.' They suggest that it is more efficient to use renewables for purposes other than hydrogen formation.

- The pollutant emissions from hydrogen have also been challenged. A report to the DfT (2002: 4) by AEA Technology suggested that 'direct emissions of hydrogen to the atmosphere from human activity may alter the natural chemistry of the atmosphere and exacerbate problems relating to the impacts of photochemical pollution (ozone) and climate change.' Hydrogen is an indirect greenhouse gas with a potential global warming effect, because emissions of hydrogen lead to increased burdens of methane and ozone (Collins, Derwent and Johnson, 2002). It appears that the precise impact of hydrogen on the environment is not yet clear.

- In order to be able to produce hydrogen fuel cells, a small amount of platinum is required (to act as a catalyst). There are substantial negative environmental effects associated with the mining and refining of platinum, including atmospheric emissions of SO2, ammonia, chlorine and hydrogen chloride (estimated to be around 180 kg of carbon per ounce), but also long-term groundwater and disposal problems (DfT, 2002). If recycled platinum can be used, this reduces the environmental footprint significantly.

- A whole new refuelling infrastructure needs to be developed. Hydrogen filling stations need to be set up globally, requiring a considerable investment and a great deal of environmental pollution. For vehicles, hydrogen would be purchased in liquid form and the oxygen would be obtained from the air. However, because of its low energy-to-volume ratio, hydrogen is difficult to carry in vehicles as well as to store and distribute (NREL, 2003).

- At present the fuel cells do not allow long-distance travel (ie their range is limited).

In conclusion, hydrogen does not appear to be the 'dream ticket' it was expected to be. Until there is a surplus of renewables from which it can be produced, and until the platinum problem is dealt with, it seems that hydrogen merely transfers the environmental effects from the tailpipe to the electricity generation. In the future, it may be possible to produce hydrogen by 'splitting' water (ie by electrolysis). If this can be done using sunlight, either through photoelectrochemical or photobiological processes, the lifecycle impact of hydrogen production is virtually nothing (NREL, 2003). At present, this technology is not well understood (or some would say that the big oil producers are not in favour of it, so less investment is being made in it). It seems likely that the majority of hydrogen energy will continue to be produced from non-renewables in the foreseeable future.

Gas-Fuelled Vehicles

Electric Vehicles

About Me

In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.

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