Subtitle: Drying Foods
If you are low on space, dehydrated or dried foods take up little space and can last a long time - up to 5 years in some cases. If you want food to store at work in case of an emergency - you get iced in, for example - a stash of dehydrated food can supplement what’s in the vending machines. Where I work, the vending machines only contain juices and soda. We have drinking fountains, though, so bringing a few jars of dried foods to keep in the freezer or even at my desk (it’s a balmy 65ºF at my desk most days and rarely rises above 70ºF - ideal storage temperature for dried foods).
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The best temperature for drying food is 140 ̊F. If higher temperatures are used, the food will cook instead of drying. When the food cooks on the outside and the moisture can’t escape, "case hardening" can occur. The food will mold. The lesson here is to never hurry the drying process by raising the temperature.
Low humidity aids the drying process. Food contains a lot of water. To dry food, the water must move from the food to the surrounding air. If the surrounding air is humid, then drying will be slowed down. If your dehydrator doesn’t come with a built in fan, or if you’re using a solar or outdoor drying method, the use of a fan to increase air circulation is practically a must.
Most foods can be dried indoors using modern food dehydrators, counter-top convection ovens or conventional ovens. Microwave ovens are recommended only for drying herbs, because there is no way to create enough air flow to dry denser foods.
Sun Drying is not the same as Solar Drying. See Solar Drying below.
Vegetables (with the exception of vine-dried beans) and meats are not recommended for out-of-doors drying. Vegetables are low in sugar and acid, which increases the risks for food spoilage. Meats are high in protein, making them ideal for microbial growth when heat and humidity can’t be controlled. Both of these benefit from some other drying method.
The high sugar and acid content of fruits make them safe to dry out-of-doors when conditions are favorable for drying. It takes several days to dry foods out-of-doors, and because the weather is uncontrollable, this method can be risky. Hot, breezy days with a humidity below 60 percent are best, but usually these ideal conditions are not always available. A minimum temperature of 85 ̊F is needed with higher temperatures being better. Fruits dried out-of-doors must be covered or brought under shelter at night. The cool night air condenses and could add moisture back to the food, thus slowing down the drying process.
Equipment: Racks or screens placed on blocks allow for better air movement around the food. Because the ground may be moist, it is best to place the racks or screens on a concrete driveway or if possible over a sheet of aluminum or tin. The reflection of the sun on the metal increases the drying temperature.
Screens need to be safe for contact with food. The best screens are stainless steel, teflon-coated fiberglass and plastic. Avoid screens made from "hardware cloth." This is galvanized metal cloth that is coated with cadmium or zinc. These metals can oxidize, leaving harmful residues on the food. Also avoid copper and aluminum screening. Copper destroys vitamin C and increases oxidation. Aluminum tends to discolor and corrode.
Because birds and insects are attracted to dried fruits, two screens are best for drying food. One screen acts as a shelf and the other as a protective cover. Cheesecloth could also be used to cover the food, but birds and insects will find their way through cheesecloth.
Recent efforts to improve sun drying have led to solar drying. Solar drying uses the sun as the heat source, but a specially designed dehydrator increases the temperature and air current to speed up the drying time. Shorter drying times reduce the risk of food spoilage or molding. Mother Earth News had a good article on building your own solar dryer. You can get more information on solar drying by going to Build It Solar, or reading Solar Food Drying or The Solar Food Dryer.
Another method of drying outdoors is vine drying. To dry beans (navy, kidney, butter, great northern, lima, lentils and soybeans) leave bean pods on the vine in the garden until the beans inside rattle. When the vines and pods are dry and shriveled, pick the beans and shell them. No pretreatment is necessary. If beans are still moist, the drying process is not complete and the beans will mold if not more thoroughly dried. If needed, drying can be completed in the sun, oven or a dehydrator.
Pasteurization: Sun-dried fruits and vine-dried beans need treatment to kill insects and their eggs.
Freezer Method: Seal the food in freezer-type plastic bags. Place the bags in a freezer set at 0 ̊F or below and leave them at least 48 hours.
Oven Method: Place the food in a single layer on a tray or in a shallow pan. Place in an oven preheated to 160 ̊F for 30 minutes.
A food dehydrator is a small electrical appliance for drying foods indoors. A food dehydrator has an electric element for heat and a fan and vents for air circulation. Dehydrators are efficiently designed to dry foods quickly at 140 ̊F. Food dehydrators are available from department stores, mail-order catalogs, natural food stores, and seed or garden supply catalogs. Costs vary from $50 to $350 or above depending on features. Some models are expandable and additional trays can be purchased later. Twelve square feet of drying space dries about a half-bushel of produce. The major disadvantage of a dehydrator is its limited capacity.
Dehydrator Features to Look For:
* Double wall construction of metal or high-grade plastic. Wood is not recommended, because it is a fire hazard and is difficult to clean.
* Enclosed heating elements.
* Counter-top design.
* An enclosed thermostat from 85 to 160 ̊F and a dial for regulating temperature.
* A fan or blower.
* Four to 10 open mesh trays made of sturdy lightweight plastic for easy washing.
* A timer to turn the dehydrator off and prevent scorching if the drying time is completed during the night.
* UL seal of approval, a one-year guarantee and convenient service.
Types of Dehydrators: There are two basic designs for dehydrators; horizontal and vertical. In horizontal air flow units, the heating element and fan are located on the side, whereas the vertical air flow dehydrators have the heating element and fan located at the base. The major advantages of horizontal flow are: it reduces flavor mixture so several different foods can be dried at one time; all trays receive equal heat penetration; and juices or liquids do not drip down into the heating element. Search Amazon for dehydrators in all price ranges and types.
Everyone who has an oven has a food dehydrator. By combining the factors of heat, low humidity and air current, an oven can be used as a dehydrator. An oven is ideal for occasional drying of meat jerkies, fruit leathers, banana chips or for preserving excess produce like celery or mushrooms. Because the oven may also be needed for everyday cooking, it may not be satisfactory for preserving abundant garden produce. Unless you have a convection oven or an oven with a convection setting, most ovens take a long time to dry foods. It takes twice as long to dry food in an oven than in a dehydrator, and it uses more energy, so buying a dehydrator is actually a cost-effective move.
To Use Your Oven: First, check your dial and see if it has a reading as low as 140 ̊F. If your oven does not go this low, then your food will cook instead of dry. For air circulation, leave the oven door propped open 2 to 6 inches. Circulation can be improved by placing a fan outside the oven near the door. CAUTION: This is not a safe practice for a home with small children. Because the door is left open, the temperature will vary. An oven thermometer placed near the food gives an accurate reading. Adjust the temperature dial to achieve the needed 140 ̊F. When you dehydrate food in a regular oven, you need to watch it constantly.
Trays should be narrow enough to clear the sides of the oven and should be 3 to 4 inches shorter than the oven from front to back. Cake cooling racks placed on top of cookie sheets work well for some foods. The oven racks, holding the trays, should be 2 to 3 inches apart for air circulation.
This method of drying differs from sun drying since it takes place indoors in a well-ventilated attic, room, car, camper or screened-in-porch. Herbs, hot peppers, nuts in the shell and partially sun-dried fruits are the most common air-dried items. Herbs and peppers can be strung on a string or tied in bundles and suspended from overhead racks in the air until dry. Enclosing them in paper bags, with openings for air circulation, protects them from dust, loose insulation and other pollutants. Nuts are spread on papers, a single layer thick. Partially sundried fruits should be left on their drying trays.
I grow a lot of herbs, and so I have bundles of them hanging from my ceiling all through the house. I hung nets - fishing nets - across the ceilings and can hook the bundles as needed with adequate drying space around them. With fans (floor or ceiling), air circulates enough to dry herbs and flowers very well.
Dehydrofreezing is a new method of food preservation that combines the techniques of drying and freezing. Fruits dried at home normally have had 80 percent of their moisture removed; vegetables, 90 percent. However, by removing only 70 percent of the moisture and storing the fruit or vegetable in the freezer, a tastier product results. The low temperature of the freezer inhibits microbial growth. Also, the food takes up less room in the freezer. Dehydrofrozen fruits and vegetables have good flavor and color. They reconstitute in about one-half the time it takes for traditionally dried foods.
Dehydrofreezing is not freeze-drying. Freeze-drying is a commercial technique that forms a vacuum while the food is freezing. Freeze-drying is a costly process that can’t be done in the home.
The drying chamber of a freeze drying machine has to be vacuum tight. To freeze dry an object or solution it first has to be frozen so the water separates off from the other material as ice crystals. A vacuum is then created in the drying chamber that radically lowers the boiling point of the frozen water. Heat going into the frozen product while under vacuum promotes a process known as sublimation in which the ice comes away as vapour rather than melting. This leaves all the other material such as minerals, nutrients, volatiles etc. intact and eventually dry.
A separate, colder area of the freeze drying machine attracts the vapour to it where it condenses back to ice and is collected.
It is not energy-efficient or eco-friendly. It takes 1.2 times more energy than canning, and 1.7 times more energy than freezing.
It requires expensive specialized equipment (the cheapest system I saw started at $5,000 new, and around $4,000 used). 8 years ago, we could take food to companies that did freeze-drying and they'd freeze dry our food along with their things for a fee. I can no longer find companies in the US that will freeze dry your own prepared foods for you, like you could bring your own prepared food to a tin canning facility and have your own food canned in tins by them. The only ones I can find are in other countries.
That said, you can mimic freeze drying to an extent. Let me tell you how.
Chicken jerky treats for pets are very popular, but also very unsafe as most of the freeze dried jerky treats for dogs come from China, where they aren't too careful about food preparation and dogs have died eating food produced in China. So let me tell you how to freeze dry your own chicken jerky treats for your dogs (and cats - I know a few cats who love them, too).
You will need an oven that can get to 180*F, a vacuum sealer, dry ice, a small ice chest, and a freezer.
Slice the chicken into thin slices (partly freezing it before slicing makes a huge difference in how thin you can get). Because we have a dog that needs glucosamine, we marinate the chicken strips in a solution of glucosamine (get with your vet to determine the correct dosage for your dog). You can marinate the chicken strips in any flavoring that is dog-safe.
Pat the strips dry and lay in a single layer on a perforated tray and slipinto an oven pre-heated to 180*F. Let the strips dry for 3 - 4 hours.
Vacuum seal the food - this pulls any further moisture out. Remove from the vacuum sealed bags, pat dry, and vacuum seal again, this time in individual portion sizes. If it pulls more moisture out, remove from bags, pat dry, and re-seal again. You want the food as dry as possible.
Place a layer of dry ice in the bottom of the ice chest. Place a layer of sealed chicken strips on the dry ice and top with a layer of dry ice. If you have more than one layer worth of chicken strips, place that onto top of the layer of dry ice and top with another layer of dry ice. Close the ice chest and let the chicken freeze among the dry ice for 30 - 60 minutes.
Remove from the ice chest and store in the freezer until you give it to your dog. With a commercial freeze-dryer, you wouldn't have to store it in the freezer. I let the treat achieve room temperature or re-heat it slightly because Itzl and Xoco prefer it warmed up to still frozen. Some dogs love it frozen, though, so see how your dog likes it.
PACKAGING AND STORING DRIED FOODS
Dried foods are susceptible to insect contamination and moisture reabsorption and must be properly packed and stored immediately. First, cool completely. Warm food causes sweating which could provide enough moisture for mold to grow. Pack foods into sterilized, dry, insect-proof containers as tightly as possible without crushing. I like canning jars for practically everything, and once in the jars, a vacuum sealer with a jar sealing attachment can provide further preservation. I use the Tilia Foodsaver with the jar sealer attachments because it keeps its seal. I’ve tried the Reynolds Handivac and the Packmate Vacu-Seal and the Ziploc Vacuum Pump and all of those lost their vacuum seal over a matter of days. I don't trust them and won't use them, but if you have one and test it and it holds its seal, by all means use it. I may have just gotten defective merchandise.
Glass jars, metal cans or boxes with tightly fitted lids or moisture-vapor resistant freezer cartons make good containers for storing dried foods. Heavy-duty plastic bags are acceptable but are not insect-and rodent-proof. If you use these, they can be then stored in metal containers or frozen.
Pack food in amounts that will be used in a recipe. Every time a package is re-opened, the food is exposed to air and moisture that lower the quality of the food.
Fruit that has been sulfured should not touch metal. Place the fruit in a plastic bag before storing it in a metal can. Sulfur fumes will react with the metal and cause color changes in the fruit, along with taste and texture changes. It’s not dangerous in the short term, it’s just not pleasant. Since the fruit will absorb some of the metal, it’s not advised to eat this food unless you are truly desperate.
Dried foods should be stored in cool, dry, dark areas. Recommended storage times for dried foods range from four months to one year. Because food quality is affected by heat, the storage temperature helps determine the length of storage; the higher the temperature, the shorter the storage time. Most dried fruits can be stored for one year at 60 ̊F, six months at 80 ̊F. Vegetables have about half the shelf-life of fruits.
Foods that are packaged seemingly "bone dry" can spoil if moisture is reabsorbed during storage. Check dried foods frequently during storage to see if they are still dry. Glass containers are excellent for storage because any moisture that collects on the inside can be seen easily as droplets inside the shoulder of the jar. Foods affected by moisture, but not spoiled, should be used immediately or redried and repackaged. Moldy foods should be discarded.
Moisture in jar or container:
1. Incomplete drying - test several pieces for dryness before storing
2. Food cut unevenly, thus incomplete drying - be sure food is all the same size when drying
3. Food left too long at room temperature before storing - cool quickly and store immediately
Mold on food:
1. Incomplete drying - test several pieces before storing
2. Food not checked for moisture within 7 days - check containers within 7 days and re-dry
3. Containers not airtight - check seals, get new lids, make sure container is air-tight
4. Storage temperature too warm plus moisture in food - check for moisture, store below 70ºF
5. Case hardening - food dried too hot food cooked on outside but not inside - dry at 140ºF
Brown spots on vegetables:
1. Too high a drying temperature used - dry at 140ºF
2. Over-dried and too crisp - check for doneness sooner
Insects in jars:
1. Lids don’t fit jars well - get new lids
2. Foods dried outdoors but not pasteurized - pasteurize by drying in oven at 160ºF 30 minutes or by freezing for 48 hours
Holes in plastic bags:
1. Insects or rodents ate through the bags - don’t store food in plastic bags, use airtight glass or hard food-grade plastic containers.
Smoking is a type of drying, and it will be addressed in a diary of its own as it requires a lengthier discussion.