A food dehydrator is a device that removes moisture from food to aid in its preservation. Food drying is a method of preserving fruit, vegetables and meats that has been practiced since antiquity. [1]
A food dehydrator is a device that removes moisture from food to aid in its preservation. Food drying is a method of preserving fruit, vegetables and meats that has been practiced since antiquity. [1]
Most modern food dehydrators are low-power convection ovens that use heated air flow to reduce the water content of foods. The water content of food is usually very high, typically 80–95% for various fruits and vegetables and 50–75% for various meats. Removing moisture from food restrains various bacteria from growing and spoiling food. Further, removing moisture from food dramatically reduces the weight and often volume of the food, making it easier to storage. Thus, food dehydrators are used to preserve and extend the shelf life of various foods. [2]
Food dehydrators require heat sources such as solar energy, electric power or biofuel, [3] and vary in form from large-scale dehydration projects [4] to do-it-yourself projects or commercially sold appliances for domestic use. A commercial food dehydrator's basic parts usually consist of a heating element, an electric fan, air vents which allow air to circulate, and food trays to lay food upon. As shown on the right, the trays most commonly have slits to provide more surface area between the food and the air. A dehydrator's heating element, fans and vents simultaneously work to direct hot air over the food, accelerate surface evaporation and warm the food causing moisture to be also released from its interior. This process continues until the food is dried to a substantially lower water content, usually less than 20%.
Most foods are dehydrated at 130 °F (54 °C), although meats being made into jerky should be dehydrated at a higher temperature of 155 °F (68 °C) — or preheated to that temperature — to guard against pathogens that may already be in the meat. These temperatures are similar to those used in pasteurization, and achieve similar effects. The key to successful food dehydration is the application of a constant temperature and adequate air flow. Too high a temperature or too low of airflow can cause hardened foods: food that is hard and dry on the outside but moist, and therefore vulnerable to spoiling, on the inside.
Solar food drying involves the use of a solar dryer designed and built specifically for this purpose. Solar drying is distinctly different from open-air "sun drying", a simple technique that has been used for thousands of years. A good solar food dryer may dry food much faster than some air driers. Some solar driers can achieve higher food drying temperatures than some air driers. However, direct sun drying can chemically alter some foods making them less appetizing. [5]
Food drying is an excellent solar energy application since food drying primarily requires heat, and solar radiation is easily converted to heat. A clear or translucent glazing allows sunlight to enter an enclosed chamber where it is converted to heat when it strikes a dark interior surface. Airflow is typically achieved with natural convection (warm air rises). Adjustable venting allows regulation of airflow and temperature.
Solar food drying is effective and practical in most of the populated places of the world. [6] A general rule is that, if you can grow a successful vegetable garden, then there is enough solar energy to dry the food you produce (some overcast, northern maritime climates are the exception).
Some solar food dryer designs employ a separate solar collector to generate the heated air, which is then directed into a food chamber or cabinet. This type of solar food dehydrator is called an indirect solar dryer. [7] [8] [9] Other designs combine the collector and food cabinet and allow direct heating of food (these are called direct solar dryers). [10] [11] [12] [13] It is said that the indirect dryers allow much better drying, but the downside is their larger size. Backup electric heating can be incorporated into some solar food dehydrators to provide an alternative heat source if the weather changes.
Solar food dehydrators are often cited as viable tools in the search for agricultural sustainability and food security. [14]
Smoking is the process of flavoring, browning, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood. Meat, fish, and lapsang souchong tea are often smoked.
A Trombe wall is a massive equator-facing wall that is painted a dark color in order to absorb thermal energy from incident sunlight and covered with a glass on the outside with an insulating air-gap between the wall and the glaze. A Trombe wall is a passive solar building design strategy that adopts the concept of indirect-gain, where sunlight first strikes a solar energy collection surface in contact with a thermal mass of air. The sunlight absorbed by the mass is converted to thermal energy (heat) and then transferred into the living space.
In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.
Food drying is a method of food preservation in which food is dried. Drying inhibits the growth of bacteria, yeasts, and mold through the removal of water. Dehydration has been used widely for this purpose since ancient times; the earliest known practice is 12,000 B.C. by inhabitants of the modern Middle East and Asia regions. Water is traditionally removed through evaporation by using methods such as air drying, sun drying, smoking or wind drying, although today electric food dehydrators or freeze-drying can be used to speed the drying process and ensure more consistent results.
A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.
A clothes dryer, also known as tumble dryer or simply dryer, is a powered household appliance that is used to remove moisture from a load of clothing, bedding and other textiles, usually after they are washed in a washing machine.
Freezing food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved grains and produce in unheated buildings during the winter season. Freezing food slows decomposition by turning residual moisture into ice, inhibiting the growth of most bacterial species. In the food commodity industry, there are two processes: mechanical and cryogenic. The freezing kinetics is important to preserve the food quality and texture. Quicker freezing generates smaller ice crystals and maintains cellular structure. Cryogenic freezing is the quickest freezing technology available due to the ultra low liquid nitrogen temperature −196 °C (−320 °F).
Dried fruit is fruit from which the majority of the original water content has been removed either naturally, through sun drying, or through the use of specialized dryers or dehydrators. Dried fruit has a long tradition of use dating back to the fourth millennium BC in Mesopotamia, and is prized because of its sweet taste, nutritive value, and long shelf life.
A convection oven is an oven that has fans to circulate air around food to create an evenly heated environment. The increased air circulation causes a fan-assisted oven to cook food faster than a conventional non-fan oven, which relies only on natural convection to circulate the hot air. Fan-assisted convection ovens are commonly used for baking as well as non-food, industrial applications. Small countertop convection ovens for household use are often marketed as air fryers.
An evaporative cooler is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning systems, which use vapor-compression or absorption refrigeration cycles. Evaporative cooling exploits the fact that water will absorb a relatively large amount of heat in order to evaporate. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation). This can cool air using much less energy than refrigeration. In extremely dry climates, evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.
A clothes line, also spelt clothesline and also known as a washing line, is a device for hanging clothes on for the purpose of drying them. It is any type of rope, cord, or twine that has been stretched between two points, outside or indoors, above the level of the ground. Clothing that has recently been washed is hung along the line to dry, using clothes pegs or clothespins. Washing lines are attached either from a post or a wall, and are frequently located in back gardens, or on balconies. Longer washing lines often have props holding up sections in the middle due to the weight of the usually wet clothing.
Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.
A heat gun is a device used to emit a stream of hot air, usually at temperatures between 100 and 550 °C, with some hotter models running around 760 °C, which can be held by hand. Heat guns usually have the form of an elongated body pointing at what is to be heated, with a handle fixed to it at right angles and a pistol grip trigger in the same pistol form factor as many other power tools.
Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet, long pieces, particles or powder. A source of heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water. Desiccation may be synonymous with drying or considered an extreme form of drying.
A ground-coupled heat exchanger is an underground heat exchanger that can capture heat from and/or dissipate heat to the ground. They use the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential, agricultural or industrial uses. If building air is blown through the heat exchanger for heat recovery ventilation, they are called earth tubes.
A combo washer dryer is a combination in a single cabinet of a washing machine and a clothes dryer. It should not be confused with a "stackable" combination of a separate washing machine and a separate clothes dryer.
Laboratory ovens are a common piece of equipment that can be found in electronics, materials processing, forensic, and research laboratories. These ovens generally provide pinpoint temperature control and uniform temperatures throughout the heating process. The following applications are some of the common uses for laboratory ovens: annealing, die-bond curing, drying or dehydrating, Polyimide baking, sterilizing, evaporating. Typical sizes are from one cubic foot to 0.9 cubic metres (32 cu ft). Some ovens can reach temperatures that are higher than 300 degrees Celsius. These temperatures are then applied from all sides of the oven to provide constant heat to sample.
Solar dryers are devices that use solar energy to dry substances, especially food. Solar dryers use the heat from the Sun to reduce the moisture content of food substances. There are two general types of solar dryers: direct and indirect.
Grain drying is process of drying grain to prevent spoilage during storage. The grain drying described in this article is that which uses fuel- or electric-powered processes supplementary to natural ones, including swathing/windrowing for drying by ambient air and sunshine, or stooking before threshing.
Vacuum drying is the mass transfer operation in which the moisture present in a substance, usually a wet solid, is removed by means of creating a vacuum.
