IELTS Academic Reading Practice Test 39

At the end of the eighteenth century, France was at war with much of Europe, and its commanders faced a problem as old as warfare itself: how to keep large numbers of soldiers and sailors supplied with food that would not rot. Salting, drying and smoking could preserve some foods, but they changed their taste and texture and offered a limited diet. In 1795 the French government announced a prize of 12,000 francs for anyone who could devise a better method of preserving food for its armies and navy.

The prize was eventually won by Nicolas Appert, a Paris confectioner who had spent years experimenting. His technique was simple. He placed food in thick glass bottles, sealed them tightly with corks, and then heated them in boiling water for a period that depended on the contents. Food treated in this way remained edible for months. In 1810 Appert received the prize on condition that he make his method public, and in the same year he published a book describing it in detail. Remarkably, he had no idea why his method worked. The existence of the microorganisms that cause food to decay was not yet understood, and Appert believed that heating simply drove out the air that he assumed was responsible for spoilage.

Glass bottles were heavy and easily broken, and the next step was taken in Britain. Also in 1810, Peter Durand was granted a patent for preserving food in containers that included vessels of tin-plated iron. Durand does not seem to have manufactured anything himself; instead, he sold the patent to Bryan Donkin and John Hall, who set up a canning works in Bermondsey, in London, around 1812. For sailors on long voyages, whose diet was otherwise dominated by salted meat and hard biscuit, such food offered welcome variety. Their tins were supplied to the Royal Navy and were carried on several voyages of exploration. Each can was made by hand from sheets of metal joined with solder, and the containers were so thick and heavy that some had to be broken open.

Indeed, for several decades nobody produced a dedicated tool for opening cans. Some were labelled with instructions to cut around the top with a chisel and hammer. The first can opener is generally credited to Robert Yeates, an English maker of cutlery and surgical instruments, who patented a hand-held, claw-ended device in 1855. In 1858 Ezra Warner of Connecticut patented an opener with a curved blade that was forced into the lid and worked around its edge. It was considered too dangerous for use at home, but it was used by soldiers during the American Civil War, a conflict that greatly increased demand for canned food in the United States. Later in the nineteenth century, openers with a rotating cutting wheel were developed, leading eventually to the familiar designs found in kitchens today.

The scientific explanation for canning arrived only gradually. In the 1860s Louis Pasteur showed that microorganisms cause food to spoil, and later research revealed that some bacteria form spores, tough dormant structures that can survive boiling. The most dangerous of these is Clostridium botulinum, which can grow in sealed containers without oxygen and produce a toxin that causes the often fatal illness known as botulism. Early canning also carried other risks. Lead was commonly used in the solder that sealed cans, and some researchers have suggested that lead from poorly made tins contributed to the deaths of the members of Sir John Franklin's Arctic expedition of 1845, although this theory remains debated.

Modern commercial canning is designed around this knowledge. Food is first washed, sorted and cut, and many vegetables are blanched – briefly heated in hot water or steam – to inactivate the enzymes that would otherwise cause changes in colour, flavour and texture. The cans are then filled, leaving a small headspace at the top, and air is removed to create a partial vacuum.

The lid is attached by a double seam, in which the edges of the lid and the can body are rolled together in two separate operations to form an airtight joint. Next, the sealed cans are heated under pressure in a large vessel called a retort. For foods that are low in acid, such as meat and most vegetables, temperatures of about 121 degrees Celsius are used, high enough to destroy bacteria and their spores. Finally, the cans are cooled rapidly in water to prevent overcooking, and then dried and labelled.

Canned food is sometimes regarded as inferior to fresh produce, but the reality is more complicated. The heating process causes some loss of vitamins that are sensitive to heat, such as vitamin C, yet much of the nutritional value of the food is retained, and because produce is often canned soon after harvest, it may lose less than fresh food that has been transported and stored for long periods.

In the late nineteenth century, machines that could make cans automatically replaced much of the skilled hand labour that early canning had required, and canned food became cheap enough for ordinary households. Properly processed cans can remain safe for years without refrigeration. More than two centuries after Appert's experiments, his invention remains one of the most important ways of storing food and moving it around the world.

For engineers, spider silk is one of nature's most enviable materials. The dragline silk that a spider uses to build the frame of its web and to hang from when it drops is, weight for weight, comparable in strength to high-grade steel, and it is considerably tougher than Kevlar, the synthetic fibre used in body armour. Toughness measures how much energy a material can absorb before it breaks, and silk achieves it by combining strength with the ability to stretch. Just as impressively, spiders produce this material at ordinary temperatures from a solution of proteins in water, whereas the manufacture of many synthetic fibres depends on high temperatures and harsh chemicals. Spiders have been producing silk for hundreds of millions of years, and they use it not only to catch prey but also to build shelters, protect their eggs and, in the case of some young spiders, to travel through the air on the wind.

Spiders do not make just one kind of silk. An orb-weaving spider can produce as many as seven different types, each from its own set of glands and each suited to a particular job: strong silk for the frame of the web, extremely stretchy and sticky silk for the spiral that captures prey, and tough, protective silk for wrapping eggs. All are made of proteins known as spidroins. These contain long, repetitive sequences, some of which fold into tightly packed crystalline regions that give the fibre its strength, while others form looser, disordered regions that allow it to stretch.

The record for toughness is held by a species from Madagascar, Darwin's bark spider, which was formally described in 2010. This spider builds enormous webs across rivers and streams, anchored by bridging threads that can be up to 25 metres long. In the same year, a study by Ingi Agnarsson and colleagues reported that its dragline silk was more than twice as tough as any silk previously described and over ten times tougher than Kevlar. The researchers suggested that this exceptional toughness evolved alongside the spider's unusual habit of building webs over water, where a broken line would be disastrous.

Why, then, has spider silk not replaced synthetic fibres? The main obstacle is supply. Unlike silkworms, which have been farmed for thousands of years, spiders are territorial and often cannibalistic, so they cannot be kept together in large numbers, and each individual produces only a small amount of silk. The difficulty was illustrated by a golden cape created by the textile specialists Simon Peers and Nicholas Godley in Madagascar. Over a million female golden orb-weaver spiders were collected from the wild, their silk was drawn out using a hand-operated machine, and the spiders were then released. The rich golden colour of the finished textile is entirely natural, coming from the silk itself. The cape, which took years to make, was exhibited at the Victoria and Albert Museum in London in 2012.

Scientists have therefore tried to persuade other organisms to make spider silk proteins. In 2002 the Canadian company Nexia Biotechnologies announced that it had produced goats carrying spider genes, whose milk contained silk proteins that could be extracted and spun into fibres. Goats were chosen partly because the milk glands of mammals are well suited to producing large quantities of complex proteins. The company's work did not lead to a commercial product, but the research was continued by Randy Lewis and his colleagues at the University of Wyoming. In 2010 researchers at the University of Notre Dame and the University of Wyoming, working with a private company, announced that they had genetically engineered silkworms to spin fibres containing spider silk proteins. These fibres were stronger than ordinary silkworm silk, though still not as strong as the real thing.

Other groups use microorganisms. The Japanese company Spiber, founded in 2007 by researchers who had begun experimenting as students at Keio University, ferments sugar and nutrients with genetically modified microbes in steel tanks, in a process similar to brewing beer. The resulting proteins are then spun into fibres, which have been used in limited collections by clothing brands. Other companies, such as AMSilk in Germany, have taken similar approaches, using bacteria to produce silk proteins for products ranging from cosmetics to textiles. Yet producing the proteins is only half the challenge. Inside a spider, the protein solution is transformed into a solid thread as it is drawn along a narrow duct, where its acidity changes, water is removed and the molecules are pulled into alignment. Reproducing this delicate process in a factory has proved extremely difficult, and most artificial fibres remain weaker than natural silk.

Despite these difficulties, interest in the material remains strong. Because silk proteins are biodegradable and rarely provoke a reaction from the immune system, researchers are investigating their use in surgical stitches, in coatings for medical implants and as scaffolds to help damaged nerves regrow. Others hope that silk-based textiles could offer an alternative to fibres made from oil, and silk-based materials have also been explored for lightweight protective equipment, although such applications remain at an experimental stage. Enthusiasts have been promising a spider silk revolution for decades, and the timetable has repeatedly slipped. But each advance in genetics and materials science brings the prospect of spinning like a spider a little closer.

For many young people, the year between leaving school and starting university has become an opportunity to do something different: to work, travel, volunteer or simply pause. Once regarded as a peculiarly British habit, the gap year is now encouraged by some of the world's most selective universities; Harvard, for example, has for years suggested in its letters of admission that new students consider deferring their entry for a year. Yet the gap year also attracts fierce criticism, as an expensive indulgence for the privileged or a waste of valuable time. In my view, both enthusiasts and critics are asking the wrong question. Whether a gap year is worthwhile depends far less on taking one than on what it contains.

The modern gap year has its roots in the 1960s. In 1967 a former army officer, Nicholas Maclean-Bristol, founded Project Trust, a charity based on the Scottish island of Coll, which sent three young volunteers to Ethiopia in its first year. Other organisations followed, offering school leavers placements as teaching assistants or community workers overseas. As air travel became cheaper towards the end of the century, the gap year gradually turned into something closer to a rite of passage for many middle-class British teenagers, and an industry of commercial providers grew up to serve them.

What does the evidence say about its effects? One of the most frequently cited studies was published in 2010 by Andrew Martin, an educational psychologist at the University of Sydney, who examined data from more than 2,800 students. He found that young people who chose to take a gap year had often shown lower motivation at school than their peers, but that once they reached university they tended to display greater motivation and better habits, such as planning and persistence. This is encouraging, and it suggests that a year away from formal study may help students who have lost their way. However, such research cannot easily show that the year itself caused the improvement. Students who take a gap year differ from others in many ways, and it is possible that some would have matured anyway.

Critics make several reasonable points. A gap year delays entry into the workforce by twelve months, which has a financial cost, and some students find it hard to return to the discipline of study after a long break. There is also the possibility that a student who intended to start university after a year will decide not to go at all, although for some this may reflect a well-considered change of direction rather than a failure. These risks are real, but they are not arguments against gap years as such. They are arguments against unstructured years, in which a young person drifts without any clear purpose or plan.

A more serious concern is the growth of what has been called voluntourism, in which young people pay commercial companies for short volunteering trips abroad. Untrained volunteers who spend a few weeks teaching in a school or building a house may do little good, and they can sometimes take work away from local people who need it. The most troubling example is orphanage tourism. Many children living in orphanages in poorer countries have at least one living parent, and campaigners have argued that a steady supply of well-meaning foreign visitors and donations has encouraged some institutions to recruit children in order to attract money. In 2018 Australia became the first country to recognise orphanage trafficking as a form of modern slavery in its legislation. Students considering a placement of this kind should think very carefully before taking part.

There is also the question of who can afford a gap year at all. Travelling the world or paying for an overseas placement is far beyond the means of most families, and if the benefits of a gap year are real, they risk being concentrated among those who are already advantaged. This is why it matters that a gap year need not involve foreign travel. A year spent working in a local business, caring for relatives, volunteering in one's own community or training as an apprentice can develop exactly the qualities – independence, responsibility and a clearer sense of direction – that make gap years valuable in the first place.

Universities can make a real difference here. By allowing students to defer their places, and by recognising the value of experience gained close to home rather than only abroad, they can help ensure that a gap year is a genuine option rather than a privilege. Some institutions go further and fund structured programmes for students who would otherwise be unable to take part. Princeton University, for example, has run a Bridge Year programme that allows some of its incoming students to spend a year on service projects, with the costs largely covered by the university.

The gap year, then, is neither a guaranteed path to maturity nor an inevitable waste of time. Its value lies in purpose, structure and reflection. A young person who sets clear goals, takes on real responsibility and thinks seriously about what they have learned is likely to benefit, wherever they spend the year. One who simply postpones decisions may gain very little. Schools, too, could do more to help students plan such a year rather than treating it as an absence from education. The aim should be to make the first kind of gap year available to everyone who wants it.