Matching information to paragraphs

In a former warehouse on the edge of a large city, lettuces are growing in trays stacked twelve levels high. There is no soil and no sunlight. Instead, the plants' roots sit in water containing carefully measured nutrients, and rows of LED lamps glow pink and purple above them. This is vertical farming: growing crops indoors in tall, climate-controlled buildings. Over the past fifteen years, the idea has attracted large amounts of investment and a great deal of attention.

Supporters list several advantages. Because conditions inside are controlled, crops can be grown all year round, whatever the weather, and a harvest is never lost to drought, floods or a late frost. Pests are rare, so few or no chemical sprays are needed. Water that the plants do not take up is collected and reused, which means that a vertical farm may use only a small fraction of the water needed in a field. And because the farms can be built inside cities, vegetables can reach shops within hours of being picked rather than after a long journey by lorry.

The greatest problem is energy. In a field, sunlight is free; indoors, every hour of light must be paid for, and the lamps produce heat that then has to be removed by air-conditioning. When energy prices rose sharply in many countries in 2022, a number of vertical farming companies struggled to cover their costs, and some closed altogether. Critics also point out that if the electricity comes from coal or gas, the environmental benefit of growing food close to consumers may disappear.

There are also limits on what can be grown profitably. Leafy greens such as lettuce, and herbs such as basil, are ideal: they grow quickly, are small enough to fit on shelves, and almost the whole plant can be sold. Staple crops such as wheat and rice are a different matter. They need a lot of space and light, take months to mature and sell for a low price per kilogram. At current electricity prices, a loaf of bread made from wheat grown indoors would cost far more than an ordinary loaf.

Some researchers believe the answer lies in combining indoor and outdoor growing rather than choosing one or the other. Young plants could be raised indoors for their first few weeks, when they are most at risk from cold and pests, and then moved to fields or greenhouses. Others are experimenting with building farms next to power stations or factories so that waste heat can be put to use, or with running the lights mainly at night, when electricity tends to be cheaper.

Whether vertical farming will ever produce more than a small share of the world's food remains uncertain. Most analysts expect it to remain a specialist method, supplying fresh salads and herbs to wealthy cities rather than replacing traditional agriculture. Even so, the technology may prove especially valuable where farmland is scarce or the climate is extreme, such as in desert regions or remote northern communities that currently depend on expensive imported vegetables.

Chilli peppers contain a chemical called capsaicin, which does something unusual. It activates the same nerve receptors in the mouth that respond to high temperatures, so the brain receives the message that the mouth is, in a sense, on fire. No real damage is done, but the body reacts as if it were: the face turns red, the eyes water and many people start to sweat. The strength of the effect varies enormously from one variety to another: a mild pepper may barely be noticed, while the hottest can be painful even in tiny amounts.

Given these unpleasant effects, it is surprising that so many people actively seek out spicy food. Most other mammals avoid chillies altogether. Young children usually reject them at first, and adults who enjoy them have often learned to do so gradually, starting with mild dishes and moving on to hotter ones over months or years. In this respect, a taste for chilli resembles a taste for black coffee or bitter vegetables, which also tends to develop with repeated experience.

Psychologists have offered several explanations. One is that eating chilli is a safe thrill, similar to riding a roller coaster or watching a frightening film: the body signals danger, but the mind knows there is none, and the gap between the two is enjoyable. Another focuses on the brain's response to pain, which may include the release of natural chemicals that produce a mild feeling of pleasure. A third suggests that personality plays a part, since people who enjoy new and intense experiences in general also tend to say they like spicier food.

Culture matters too. In parts of Mexico, Thailand and India, for example, chilli is added to many ordinary dishes. In regions like these, where spicy food is part of everyday cooking, children are exposed to chilli early and often, and by adulthood they may barely notice levels of heat that visitors find painful. Some researchers have also suggested that spices became popular in hot climates partly because certain spices slow the growth of bacteria in food, although this idea remains controversial. What seems clear is that, for most people, a love of chilli is not present at birth but develops over time.