The Knowledge: How to Rebuild Our World From Scratch by Lewis Dartnell Page B
Authors: Lewis Dartnell
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work, but without any underlying theory as to why. Retaining this kernel of understanding after the apocalypse (see here for how to build a microscope capable of revealing these microbes) will be enormously beneficial to maintaining a reliable food supply and avoiding infectious disease—both critical to sustaining a population increase after a cataclysm.
Not only does all life on Earth require liquid water to grow and reproduce; organisms can also tolerate only a particular range of physical or chemical conditions. More specifically, the enzymes in a cell—the molecular machinery that drives the reactions of biochemistry andcoordinates the processes of life—are active only over particular ranges of temperature, salinity, and pH (how acidic or alkaline a fluid is). Preservation can be achieved by pushing any of these three factors away from the optimum for microbial growth.
The easiest method of preserving food is simply to desiccate it. Without much available water, microbes struggle to grow (this is why it’s also critical to dry your harvested grain before storing it in silos). The traditional technique is air- or sun-drying, suitable for fruit such as tomatoes as well as meat to make biltong or beef jerky, but it is a slow process and not suitable for large bulks of food.
Without being commonly considered as desiccated, many other foodstuffs are also preserved by low water availability. Large amounts of dissolved compounds like sugars make a solution very concentrated, which acts to draw water out of microbial cells and stop all but the hardiest strains from growing. This is exactly the principle behind jams: the saccharine fruitiness tastes great on toast in the morning, but the very reason for the creation of preserves in the first place is to protect fruit by the antimicrobial action of the concentrated sugar solution. Sugar can be extracted from tropical sugar cane or the root of the temperate-growing sugar beet by trickling water through the crushed plant to dissolve the sugar and then recovering the crystals of it by drying. Honey is extremely long-lasting for the same reason.
Salt is needed in small amounts for the healthy functioning of the human body—which is why our palate craves it—but a far greater quantity is used for preservation. Salted foods are protected in the same manner as preserves: concentrated briny fluids draw water out of cells and hamper growth. Fresh meat can be effectively preserved by packing it in dry salt for several days, or keeping it submerged in a heavy brine solution—about 180 grams of salt dissolved into every liter of water creates a brine solution roughly five times more concentrated than seawater. Salting has been a crucial preservation technique throughout history, so it is worth looking at in more detail.
In principle, producing salt is childishly simple, provided you’re anywhere near the coast. Seawater contains about 3.5 percent dissolved solids, the vast majority of which is common salt (sodium chloride), which can be extracted by evaporating off the water solvent. If you live in sunny climes, you can simply allow seawater to flood shallow pans and evaporate in the heat of the day to leave a crust of salt precipitated behind. In very cold temperatures, you can allow shallow ponds of seawater to freeze, leaving a concentrated brine solution at the bottom. But temperate conditions, as are prevalent across much of Europe or North America over the year, require burning fuel to heat cauldrons of saline to drive off the water. In the case of salt, then, the availability of a valuable commodity is not due to the rarity of the substance itself—three-quarters of the Earth’s face is sloshing with saline solution—but to the energetic costs of extracting it in large amounts, or of finding and exploiting minable deposits. *
Salting is often used in combination with another preservation technique, whereby naturally toxic antimicrobial compounds are generated and
Not only does all life on Earth require liquid water to grow and reproduce; organisms can also tolerate only a particular range of physical or chemical conditions. More specifically, the enzymes in a cell—the molecular machinery that drives the reactions of biochemistry andcoordinates the processes of life—are active only over particular ranges of temperature, salinity, and pH (how acidic or alkaline a fluid is). Preservation can be achieved by pushing any of these three factors away from the optimum for microbial growth.
The easiest method of preserving food is simply to desiccate it. Without much available water, microbes struggle to grow (this is why it’s also critical to dry your harvested grain before storing it in silos). The traditional technique is air- or sun-drying, suitable for fruit such as tomatoes as well as meat to make biltong or beef jerky, but it is a slow process and not suitable for large bulks of food.
Without being commonly considered as desiccated, many other foodstuffs are also preserved by low water availability. Large amounts of dissolved compounds like sugars make a solution very concentrated, which acts to draw water out of microbial cells and stop all but the hardiest strains from growing. This is exactly the principle behind jams: the saccharine fruitiness tastes great on toast in the morning, but the very reason for the creation of preserves in the first place is to protect fruit by the antimicrobial action of the concentrated sugar solution. Sugar can be extracted from tropical sugar cane or the root of the temperate-growing sugar beet by trickling water through the crushed plant to dissolve the sugar and then recovering the crystals of it by drying. Honey is extremely long-lasting for the same reason.
Salt is needed in small amounts for the healthy functioning of the human body—which is why our palate craves it—but a far greater quantity is used for preservation. Salted foods are protected in the same manner as preserves: concentrated briny fluids draw water out of cells and hamper growth. Fresh meat can be effectively preserved by packing it in dry salt for several days, or keeping it submerged in a heavy brine solution—about 180 grams of salt dissolved into every liter of water creates a brine solution roughly five times more concentrated than seawater. Salting has been a crucial preservation technique throughout history, so it is worth looking at in more detail.
In principle, producing salt is childishly simple, provided you’re anywhere near the coast. Seawater contains about 3.5 percent dissolved solids, the vast majority of which is common salt (sodium chloride), which can be extracted by evaporating off the water solvent. If you live in sunny climes, you can simply allow seawater to flood shallow pans and evaporate in the heat of the day to leave a crust of salt precipitated behind. In very cold temperatures, you can allow shallow ponds of seawater to freeze, leaving a concentrated brine solution at the bottom. But temperate conditions, as are prevalent across much of Europe or North America over the year, require burning fuel to heat cauldrons of saline to drive off the water. In the case of salt, then, the availability of a valuable commodity is not due to the rarity of the substance itself—three-quarters of the Earth’s face is sloshing with saline solution—but to the energetic costs of extracting it in large amounts, or of finding and exploiting minable deposits. *
Salting is often used in combination with another preservation technique, whereby naturally toxic antimicrobial compounds are generated and
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