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Home : FOOD : Preservation |
| Food preservation is one of the most important stages of food production. Without efficient preservation, we would never be able to make it through the winter or the hungry gap of the early spring. There are many ways to preserve food, but the easiest methods for the self-producer are refrigeration, drying, and canning. Different foods have different methods applied, due to the different efficiencies of each method. For example, refrigerated apples are not the same as dried apples, and dried apples can last much longer and retain more of the nutrition value than refrigerated apples. Refrigeration Refrigeration is one of the most used method of preserving food. It consists of keeping food chilled, which delays the decomposition. But wait a second, don't refrigerators and freezers use an enormous amount of energy? The answer to that is a resounding maybe... like most things, it depends on the design of the appliance. Your standard upright, 110 AC, compressor powered refrigerator/freezer will probably eat you right out of your energy efficient status. However, a chest freezer/fridge can save you over 50% in energy requirements. Why? Because of the design and the inherent nature of cold air. Cold air moves down, so every time you open an upright design, your cold air spills out of the box, and requires additional input to re-cool the interior. With a chest design, every time you open the box, very little cold air escapes. This is an easy concept to test. Open your fridge while wearing no shoes. Can you feel the cold air rushing out? That is wasted energy pouring onto your feet. Another concept is timed energy consumption rather than the standard on-demand energy use. Refrigerators have a thermostat installed to tell the compressor pump when to turn on. When the temperature inside the box rises above 40 degrees, the compressor kicks on and cools the box down. As the temperature approaches 35 or so, the compressor turns off. At first glance, it appears to be a fairly good system, but in actuality, it wastes a lot of energy. The reason for this waste is that every time you start a motor (compressor) you must apply extra energy to initiate the turn, breaking the stationary inertia. This is called a surge, and some motors require a substantial surge to get them moving. The surge itself doesn't use all that more energy because it is short-lived. However, if you start and stop a motor repeatedly throughout the day, then the surges add up, and you end up using a lot of extra energy. The alternative approach is to time the motor to run for a set amount of time. So, for example, you start the motor at 9 am, and it runs until 10 am. You only have one surge during this time, and the box gets progressively colder as time wears on. Then, you start the compressor once again around 1 pm and run for another hour. Then once more right before night. All in all, you have only 3 surges a day versus the normal 60 or more with a thermostat control. You achieve the same end result, but use less power. So, for the off-grid home, you want a chest design with a timed compressor. Or you can use a heat based system instead of the conventional pressure-based system. A propane refrigerator works on this principle. Heat one end of the system, and cool the other end. Your heat can be an different source that propane, like solar thermal, geothermal, wood fire or any other heat source. For more information on these system see the zeolite system, ammonia absorption, and solar ice-maker.  DryingDrying food is very simple. You cut the food as thin as possible, then lay it out where it can get good, dry air flow. Keeping the bugs off is another good idea. A screened box with trays is a great design, but there are many other designs that use the sun to dry the food faster. I prefer the low-tech screen box method, but it can take a few days to fully dry most foods. The best foods to dry are those with a low raw water content. Any food can be dried, but ones that have low water content to begin with will dry faster. Squash, beans, apples, bananas, peppers, eggplant, and pumpkin are good driers. The goal with drying is to dry the food as fast as possible to avoid nutrient loss or rotting. Drying is not limited to veggies, and is a good way to preserve meat. Salt the meat and cut it thin. Keep the flies off of meat! They will bring in rot-causing bacteria. Canning Canning food is a popular traditional method of preservation. Although it requires energy, the nutritional value is well preserved, and most foods can be store for quite some time (years) with this method. Botulism The problem with canning is that it can be extremely dangerous if done incorrectly. There can be various kinds of bacteria, molds or yeasts present naturally in your food, however the most common danger is considered botulism. Although this bacteria is killed easily by heat and won't grow when cold, its spores are extremely resilient. Canning safely depends on how many micro-organisms are in the food to begin with, not using too big of a can (as the center can resist the heat better than the extremity), acidity of the food (high acid kills spores), the temperature reached and for how long. To avoid the possibility of poisoning yourself and your family, it's a good idea to read up on the dangers of canning before you start the process - it is well worth the effort!! Water-Bath Canning This method is used only for fruits and high acid tomatoes.
If you are canning low acid foods such as meat and vegatables, you will need a pressure canner, as it must be heated to 240°F to kill botulism spores. Follow directions for your particular pressure canner. |
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