The Knowledge: How to Rebuild Our World From Scratch

by Lewis Dartnell

  Butter is a good way of preserving the energy-rich fats of milk by removing much of its water. The essence of butter making is to first extract the fat-rich cream; you can either allow it to naturally rise to the top for a day or so in a cool container, or accelerate the process with a centrifuge (a whirling bucket will do the trick). The process of churning is simply to get the droplets of fat to stick together and exclude the remaining fluid, or buttermilk. This can be achieved by rolling a jar back and forth across the floor, or shaking it, but a more effective post-apocalyptic makeshift solution would be to use an electric drill with a paint-stirring paddle. Strain the butter out of the buttermilk, add salt for preservation, and then knead it until all the water has been squeezed out and the salt mixed throughout.

  Yogurt and butter are stable for a few days to around a month, respectively, whereas cheese can safely preserve the nutrients of milk for many months: it is the perfect rickets-busting storage medium. Cheese making is more involved, but the crucial point is to preserve the nutrients in milk by removing its water component. Rennin, an enzyme from the first stomach of a calf, is used to break down the proteins in milk and so curdle it. The curds are strained off and pressed into a solid lump, which is then allowed to mature; it’s the action of various fungi that gives different cheeses their characteristic appearance and flavor.

  PREPARATION OF CEREALS

  Let’s turn our attention now to the preparation of cereal crops. The prehistoric domestication of wheat, rice, corn, barley, millet, and rye represents one of the crowning glories of human accomplishment. The reproductive strategies of these cultivated strains have been reprogrammed through artificial selection to bear easily recoverable grain—they are the solution that we found to the challenge of consuming grass species without the biological benefit of a ruminant digestion like that of the cows and sheep we husband.

  Corn can be cooked and eaten as corn on the cob,* and rice can be dehusked and simply boiled or steamed for eating. But the small, hard kernels of most cereal crops cannot be eaten as is, unlike many cultivated fruits or vegetables; they have to be technologically prepared for consumption.

  The grain must be pulverized into a fine powder: flour. The simplest method is to place a handful of grain onto a smooth, flat rock on the ground, and then lean forward and use your body weight to crush and grind it beneath a handheld pestle stone. But this is backbreaking and enormously time-consuming labor: a far better system is to mill it between two squat cylindrical stones or steel disks, with the grain introduced (grist for the mill—another common phrase with ancient agricultural roots) into the sandwich through a hole in the middle. The weight of the top millstone provides the crushing pressure, and its rotation works the flour outward to be collected. In this way, the millstone represents a technological extension of our molar teeth, crushing and grinding hard foodstuffs to render them more digestible. You can ease your own manual toil by yoking a draft animal to drive this slow rotation, or even better, harnessing water or wind energy (we’ll see how in Chapter 8). Even so, the pulverizing of a harvest’s worth of grain will represent an enormous expenditure of energy for a recovering society.

  The simplest, but least appetizing, way to consume ground flour is to mix it with a little water into a thick porridge or gruel. But there is a far more tasty, and versatile, starch-delivery mechanism that requires just a little more preparation. Bread is essentially no more than a cooked gruel, but as an effective pathway for nourishment it has underpinned civilization since its very birth. The basic recipe is ludicrously simple: grind some grass seeds into a powdery flour, mix with water into a pasty dough, then roll out and cook slowly, perhaps even just on a hot stone by the fire. This makes an unleavened flatbread, which is still exceedingly common today as chapati, naan, tortilla, khubz, and pita bread.

  The type of bread we are most familiar with in the Western world, though, is risen bread, and this requires one further ingredient. Yeast is a microbe, a single-celled fungus not far removed from the toadstools sprouting from a rotting tree trunk, that is applied to the fermentation of flour dough, breathing out carbon dioxide that gets trapped in bubbles to produce a light, fluffy loaf. One particular strain of yeast, Saccharomyces cerevisiae, is used for producing almost all leavened bread today. Indeed, you’d do very well to have the presence of mind to rescue a starter stock of this organism, as vital and hard-working in its own way as the ox or horse, before it is lost in the turmoil of the apocalypse; it can be found in supermarkets dried, in packets, but won’t persist indefinitely. How might you go about re-isolating bread-making microorganisms from scratch if you have to?

  The yeast required for raising bread, as well as other fermentation bacteria, are naturally present on cereal grain and thus also in milled flour. The trick is to isolate these beneficial bugs among all the others that might do you harm: you need to play primitive microbiologist and create a selection process that favors the desired bugs. The guide given here is for isolating the correct microbes for baking a sourdough, the first leavened bread to be baked, around 3,500 years ago in ancient Egypt, and still popular today among craft bakers.

  Make up a mixture of one cup of flour (whole-grain is best for this initial process) and half to two-thirds of a cup of water; cover and allow it to sit in a warm place. Check after twelve hours for signs of growth and fermentation, such as bubbles forming. If none are apparent, stir and wait another half day. Once you get fermentation, throw half of the culture away and replace with fresh flour and water in the same proportions, repeating this refill twice a day. This gives the culture more nutrients to reproduce and continually doubles the size of the microbial territory to expand into. After about a week, once you have a healthy-smelling culture reliably growing and frothing after every replenishment, like a microbial pet thriving on the feed left in its bowl, you are ready to extract some of the dough and bake bread.

  By running through this iterative process you have essentially created a rudimentary microbiological selection protocol—narrowing down to wild strains that can grow on the starch nutrients in the flour with the fastest cell division rates at a temperature of around 20°–30°C. Your resultant sourdough is not a pure culture of a single isolate, but actually a balanced community of lactobacillus bacteria, able to break down the complex storage molecules of the grain, and yeast living on the byproducts of the lactobacilli and releasing carbon dioxide gas to leaven the bread. Such a mutually supportive marriage between different species is known as a symbiotic relationship and is a common feature of biology from nitrogen-fixing bacteria hosted in the roots of legume plants, to the bacterial digestion assistants in our own gut. The lactobacilli additionally excrete lactic acid (just as in yogurt production), which gives this bread its tasty sour tang, but also act to exclude other microbes from the culture, keeping the symbiotic sourdough community wonderfully stable and resilient against incursion.

  Not all flours can be used for leavened bread, however, as it requires the presence of gluten to create a malleable dough able to trap the bubbles of carbon dioxide breathed out by the growing yeast. Wheat grain contains lots of gluten and so makes a divinely light-textured loaf, whereas barley flour has barely any. Barley has a far more pleasing application than daily bread, however.

  Yeasts growing in an environment with plenty of oxygen, such as in a dough, are able to break down their food molecules all the way to carbon dioxide (just as human metabolism does). But culture yeasts under anaerobic conditions, with restricted oxygen, and they can only partially decompose sugars, instead releasing ethanol (alcohol) as a waste product: this is the essence of brewing. Since its discovery, alcohol has been helping revelers have a good time, but it has a myriad other uses and is well worth the effort of purifying in the interests of rebuilding civilization. Concentrated ethanol is valuable as a clean-burning fuel (such as in a spirit burner or biofuel car), a preservative, and an antiseptic. It is also a versatile solvent for dissolving a variety of compou
nds insoluble in water, such as in the extraction of chemicals from plants for perfumery or creating medical tinctures. And when alcohol is exposed to air for a while it turns vinegary, as any wine drinker is surely familiar with after a bottle has been open for a few days. New bacteria colonize the fluid and convert the ethanol into acetic acid: cooking or table vinegar is commonly between 5 and 10 percent acetic acid diluted in water, and more concentrated solutions can be used for pickling, as we have seen.

  Unlike the mixed microbial community of a sourdough, the pure yeast culture used in brewing cannot itself break down the complex starch molecules in the grain, which must therefore first be converted into fermentable sugars. The biological function of starch is as an energy source to support the young sprouting plant until it has become established with leaves, and so the grain’s own mechanisms are activated to disassemble the starch. The barley grains (or indeed those of any other cereal) are steeped in water and encouraged to germinate for a week in a warm damp room, and thereby break apart their starch into accessible sugars (the starch molecule is a long chain of sugar subunits linked together), before being dried or partially roasted—to vary the color and flavor of the final brew—in a kiln. This malt is then mashed with hot water to dissolve out all of the sugars, and filtered to produce a sweet-tasting wort. The wort is first boiled, both to evaporate off some of the water in order to concentrate the sugars, and also to sterilize it and so offer a blank slate for adding the desired fermentation microbes afterward. Finally the wort is cooled and inoculated with yeast from a previously brewed batch, and then fermented for around a week.

  One exceedingly useful item to scavenge from the supermarket shortly after the Fall would be a bottle of craft ale that contains a sediment of live yeast at the bottom, so as to save this handy bug for posterity. But yeasts suitable for brewing are also prevalent in the environment and can be re-isolated using a selection technique similar to that described above. In fact, the pure-culture yeasts used for commercial bread making today are descended from cells originally found in the froths of beer-brewing fermenters, and were isolated using the microbiological tools of agar plates and microscope that are described in Chapter 7. So next time you’re warmly tipsy, remember that your brain has been mildly poisoned and impaired by the excrement of a single-celled fungus. Cheers!

  Pretty much any sugar source (or starch disassembled back into sugar) can be fermented into an alcoholic product: honey, grapes, grain, apples, and rice are transformed into mead, wine, beer, cider, and sake, respectively. But regardless of the nutrient source, alcohol from fermentation can only reach a concentration of around 12 percent before the yeast cells essentially poison themselves with their own ethanol excretion. The process of purifying alcohol to higher concentrations, by separating ethanol from the water and everything else in the messy ferment, is known as distillation and is another truly ancient technology.

  As with extracting salt from saline solution, separating alcohol from the watery soup of the ferment exploits a difference in the properties of the two components—in this case the fact that ethanol has a lower boiling point than water. At its simplest, a still need be no more complicated than that used by Mongolian nomads to make their hooch. A bowl of the fermented mash is held over a fire, with a collection vessel on a ledge above it, and then a third, pointy-bottomed pot full of cold water positioned directly above both; a hood is then draped over the entire arrangement. The fire heats the mash, and the ethanol is driven off first, the vapor condensing on the cool underside of the water pot and running down to drip into the middle dish. Modern laboratories merely replicate this basic setup with dedicated glassware, a thermometer to check that the steam boiling off the mash doesn’t exceed 78°C (the boiling point of ethanol), and a gas burner with a controllable air inlet. The efficiency of the process can be improved by using a fractionating column, an upright cylinder packed with glass beads, so that the vapor coming off the mash repeatedly condenses and re-evaporates, further concentrating the alcohol relative to water each time, before a final condenser with a water-cooled jacket collects the distillate.

  MAKING USE OF HEAT AND COLD

  Finally, we’ll look at how the mastery of temperature—using extremes of heat and cold—has become invaluable for food preservation.

  The preservation techniques used throughout history—drying, salting, pickling, smoking—are pretty effective but often change the flavor of the food, and are not perfect in maintaining the nutritional content. A new method was devised by a French confectioner in the early years of the nineteenth century: sealing the food in glass jars with a cork stopper and wax, and then standing the jars in hot water for several hours. Soon after, airtight metal cans began to be used (the reason that we use tin cans, or at least tin-coated steel, today is that this is one of the few metals that will not corrode with the acidity of foods).* Encouragingly for an accelerated reboot, there was no missing prerequisite technology that prevented the development of canned food centuries earlier in our history—perhaps even skilled Roman glassworkers could have made reliably sealable airtight vessels—so survivors can start canning food soon after the Fall.

  The key principle of the canning process is to inactivate microbes already present using heat and apply an airtight seal to prevent any more from recontaminating the food to cause decomposition. A related procedure, called pasteurization, involves briefly heating foodstuffs to 65–70°C so as to deactivate spoilage or pathogenic microbes. This has been particularly effective in treating milk (without curdling it) to prevent the transmission of tuberculosis or gastrointestinal diseases to humans. For the safest preservation, food that isn’t already acidic or pickled should be pressure-canned, exposing it to temperatures above the normal boiling point, as this completely sterilizes the contents and kills even temperature-resistant spores of microbes like those responsible for botulism.

  That’s how high temperatures can be used to preserve vital stockpiles of food for many years. But what about the cold?

  As temperature drops, the activity and reproduction of microbes are slowed, as are the chemical reactions that turn butter rancid and soften fresh fruit. The preserving effect of low temperature has been known for a long time. At least 3,000 years ago the Chinese were gathering ice in winter to preserve food in caves through the year, and in the 1800s Norway was a major exporter of its ice to Western Europe. But being able to artificially create cold is a fundamental advance of modern civilization—and is much trickier to pull off than generating heat. The application of the principles known as the gas laws to create refrigerators is handy for keeping fresh food from spoiling rapidly and for freezing for long-term preservation, but can also be applied to the safe storage of hospital stocks of blood or transportation of vaccines, as well as to building air conditioners or distilling air to produce liquid oxygen. We’ll take quite a detailed look at how refrigerators work, because it also illustrates an interesting point about the adoption of technology and how a recovering society could end up taking very different paths from our own.

  The key operating principle behind refrigeration is that as a liquid vaporizes to gas, it removes the heat required for that transition from its surroundings. This is why our bodies perspire to keep cool, and a low-tech solution for refrigeration is essentially a sweating clay tub. The Zeer pot, common in Africa, consists of a lidded clay tub inside an unglazed larger one, with the gap between them filled with damp sand. As the moisture evaporates it draws heat out of the inner container, lowering its temperature, so the Zeer pot can postpone the spoilage of fruits or vegetables at market by a week or more.

  All mechanical refrigerators work on the same basic principle: controlling the vaporization and recondensation of a “refrigerant.” Vaporization (boiling) requires heat energy, whereas condensation releases that thermal energy. If you arrange for the vaporization part of the cycle to happen in pipes within an insulated box, you draw heat out of this closed space and so cool the insides, all
owing you to export that heat out into the surrounding air through black radiator fins at the back of the appliance.

  Practically all modern refrigerators force the condensation step—returning the refrigerant to a liquid so that it can be vaporized again and remove more heat from the compartment—by using an electric compressor pump. But there are alternative methods, the simplest of which is known as an absorption refrigerator (Albert Einstein himself co-invented one version). In this system, a refrigerant such as ammonia is condensed not by pressurizing it but simply by allowing it to dissolve, or be absorbed, into water. The refrigerant is returned to the cycle by heating the ammonia-water mixture to separate the ammonia, which has a far lower boiling point (the same principle of distillation we saw here), using either a gas flame, an electric filament, or just the Sun’s warmth. In this way, an absorption refrigerator ingeniously uses heat to keep things cool. Indeed, without the need of an electric motor for the compressor pump, this design has no moving parts, thus slashing the need for maintenance and the risk of breakdown. And it operates silently.

  If history is just one damn thing after another, then the history of technology is just one damn invention after another: a succession of gadgets each beating off inferior rivals. Or is it? Reality is rarely that simple, and we must remember that the history of technology is written by the victors: successful innovations give the illusion of a linear sequence of stepping stones, while the losers fade into obscurity and are forgotten. But what determines the success of an invention is not always necessarily superiority of function.