The Knowledge: How to Rebuild Our World From Scratch by Lewis Dartnell Read Free Book Online Page A

weaker dilution to disinfect drinking water. A single teaspoon of this calcium hypochlorite powder is enough to disinfect 200 gallons of water (but again, be careful it doesn’t contain any antifungal agents or clarifier additives). Later on in the rebooting process, once all the readily available chlorinating agents are gone, you’ll need to create your own from scratch using seawater and chalk as raw materials, as we’ll see in Chapter 11.
    Plastic bottles can be used not just for storing water, but for sterilizing it as well. Solar water disinfection, or SODIS, employs only sunlight and transparent bottles, and is recommended by the World Health Organization for decentralized water treatment in developing nations—a perfect low-tech option for the post-apocalyptic world. Tear the labels off clear plastic bottles—but don’t use bottles bigger than two liters, as the crucial part of the Sun’s rays won’t be able to penetrate all the way through—fill them with the water to be disinfected, and lay them down outside in full sunlight. The ultraviolet component of the Sun’s rays is very damaging to microorganisms, and if the water warms up to above 50 degrees Centigrade (122°F), thisdeactivating effect is greatly enhanced. A good system is leaning a sheet of corrugated iron angled to the Sun and stacking the water bottles in the grooves. Painting the sheet black helps the heat sterilization effect.

    However, glass and some plastics, such as PVC, block out the UV rays. Check the bottom of the plastic bottle: most are now manufactured with a recycling symbol, and you want to pick out those marked with a (1), indicating they are made of PET. If the water is too murky for the sunlight to penetrate, you’ll need to filter it first. In bright, direct sun, this method can disinfect water in around six hours, but if the sky is cloudy it’s best to leave it for a couple of days.

FOOD
    How long will you be able to continue dining out on the leftovers of our civilization? The expiration date on modern packaging is only a guideline and often underestimates deterioration by a considerable margin. So how long would different food types actually remain edible? Some products will last more or less indefinitely, including salt, soy sauce, vinegar, and sugar (as long as it stays dry), and we’ll see in Chapter 4 how these substances can be used to preserve food.
    Other staples of our diet won’t fare as well on the shelves of deserted supermarkets. Most of the fresh fruit and vegetables will have wilted and rotted within weeks, but tubers will persist much longer, since they evolved to store energy over winter for the plant. Potatoes, cassava, and yams will all have a good chance of lasting more than six months if they’re in a cool, dry, and dark place.
    Cheese and other treats on the delicatessen counter will be moldy within weeks, and after a matter of months the butcher’s unpackaged meat cuts will have decomposed to leave only the odd T-bone or rackof ribs. Eggs are actually surprisingly resilient and can remain edible for more than a month without refrigeration.
    Fresh milk will be spoiled within a week or so, but “shelf safe” milk in UHT packs (pasteurized at ultra-high temperatures) will last years, and powdered milk even longer. Since it’s the fat content of dried foodstuffs that often spoils first as it undergoes rancidification, fat-free powdered milk will remain potable the longest. Lard and butter will spoil quickly within defunct refrigerators, and cooking oils will also turn rancid over time. (But once unfit for human consumption, their lipid content can still be used to make soap or biodiesel, as we’ll see later on.)
    White wheat flour will keep for only a few years, but longer than whole wheat flour, which, due to the much higher oil content, goes rancid quickly. Flour products such as dried pasta will also last for a few years. The nutritional content survives far better if the grains have not been