How to Preserve Food by Drying

Food drying is one of the oldest methods of preserving food. Since drying reduces the moisture in foods making them lightweight and convenient to store, it can easily be used in place of other food preservation techniques. In fact, one can even use drying along with other food preservation techniques such as freezing or canning, which would make the process of food preservation even better.

Drying food is simple, safe and easy to learn. The early American settlers practiced drying food using the natural forces of sun and wind and today, the use of technology has revolutionized this method of preserving food. With modern food dehydrators, foods such as fruit leathers, fruit chips, dried nuts and seeds and meat jerky, can all be dried year-round at home.

Being easy to store and carry and requiring no refrigeration makes dried foods ideal for domestic use as well as for use in the rough outdoors.

Moreover, dried foods are good sources of quick energy and wholesome nutrition, since the only thing lost during preservation is moisture. For instance, meat jerky, dried nuts and seeds are good sources of protein for a snack or a meal. The fruit leathers and chips provide plenty of quick energy. Dried vegetables, too, can be used to prepare wholesome casseroles and soups and the nutritional value can be enhanced by using the soaking water for cooking. Therefore, dried foods are an easy food option for busy executives, hungry backpackers and active women and children, all of whom can benefit from the ease of use and nutritional content of dried foods.

Here are some useful resources for basics of food drying

• Introduction to Drying Food
• How to Dry Food
• History of Food Drying

How Drying Preserves Food

Drying basically dehydrates or removes the moisture from the food and this simple action inhibits the growth of bacteria, mold and yeast. Moreover, it slows down the enzyme action without deactivating them. These factors ensure that food does not spoil easily and hence, makes drying an effective food preservation technique. 

Since drying removes the water from the food, the weight of the food item also reduces. This not only makes it lighter but also shrinks it in size. In order to use the food, all one has to do is add water to it.

The best temperature to dry foods and preserve them is 140 deg F. However, for meats and poultry, the USDA Meat and Poultry Hotline recommends heating meat to 160 deg F and poultry to 165 deg F before starting the drying process. Once the heating is done, the dehydrator temperature should be consistent at 130 to 140 deg F. Using temperatures higher than this will result in cooking the food instead of drying it. The food will cook on the outside and the moisture will remain trapped within. Drying is a slow process and one shouldn’t try and speed it up by raising the temperature.

Another factor that helps with drying food is humidity. Since drying involves extracting the moisture from the food items and expelling it into the surrounding air, low humidity will help with the drying process. If the humidity is high, drying will be slower simply because the surrounding air would also be laden with moisture. By increasing the currents or flow of air, one can speed up the drying process.

There are several ways of drying foods – in the sun, in an oven or in a commercial dehydrator. However, in either case, it is important to have the right temperature, air flow and level of humidity.

Here is some useful information on drying meats and the right temperature –

• Drying Meats

Drying Foods Out-of-Doors

Sun Drying

Drying food in the sun is a safe and economical way to preserve food, especially fruits. Meats and vegetables, however, cannot be dried outdoors since they have a low sugar and acid content. Fruits have a high sugar and acid content, which makes sun drying safe and easy. Meats and vegetables are best dried indoors in a controlled oven or dehydrator since temperature and humidity are essential when preserving these food groups.

In order to dry food in the sun, one needs to have both warm temperatures and a constant breeze. A minimum temperature of 85 deg F is essential while higher temperatures are obviously better. The high temperature will extract the moisture while the breeze would help to dispel it into the surrounding air. A low level of humidity is also essential for successful sun drying. The high humidity levels in the South make sun drying difficult. Humidity of below 60 percent is ideal.

Raisins dried in the sun are probably the most widely known of dried fruits. The sunny region of California produces a large portion of these raisins and the reason is simple. The temperatures in the San Joaquin valley are warm, the humidity is low and there is a constant breeze. These conditions are ideal for drying and preserving fruits, especially grapes.

Sun drying is a slow and time-consuming process since the unpredictable and uncontrollable weather is the drying agent. Moreover, it is this unpredictability, that also makes sun drying a risky process. For instance, in California, sudden rains can ruin the entire supply of raisins. Not only that, having the ideal mix of temperature, humidity and air flow is often difficult to achieve and this prompts one to look for other methods of drying food.

Fruit that is being dried in the sun needs to be protected from the cool night air that could add the moisture back to the fruit. Therefore, the fruits must either be brought in every night or put under some form of shelter to protect them from the night dew.

Equipment

For drying food in the sun, one needs racks or screens that are placed on blocks or on a concrete surface. This arrangement and equipment ensures adequate flow of air around the food. To prevent transfer of moisture from the earth, place the racks or screens on a concrete surface or over a sheet of aluminum, which will help to increase the temperature.

It is essential to use food-grade quality materials for the screens or racks. Ideally one should use screens made of stainless steel, Teflon-coated fiberglass or plastic. Avoid screens made of copper, aluminum or “hardware cloth” which is basically galvanized metal coated with zinc or cadmium. All these metals are unsafe since they can oxidize, leave residue on food or affect the nutritional quality of food items.

To protect the drying fruits from birds and insects, it is important to protect the fruits with some form of covering. To do this, one can simply use either another screen or a covering of cheesecloth.

Solar Drying

Solar drying is the result of technological advances made in the field of sun drying. Solar drying is a process of drying foods by harnessing the heat energy of the sun in a special dehydrator that not only increase the temperature but also, improves the air flow. This speeds up the process of drying the food and reduces the risk of food getting moldy or spoilt.

A solar dryer increases the temperature by using a reflector such as glass or aluminum while air flow is improved with the help of vents at each end. The technique and system is fairly simple. Cool air enters the dryer, removes moisture and escapes. The reflector surface helps to increase the heat by 20 deg F to 30 deg F. A cover of plastic protects the food, prevents rain or dew from dampening it and screens over the vents prevent birds and insects from attacking the fruit.

One may need to change the position of the solar dryer throughout the day in order to maximize the heat received from the sun. Also, one will have to stir the food several times to ensure uniform drying.

Solar dehydrators are available easily and in many variants. One can even make them at home after getting the requisite directions.

Vine Drying

Vine drying is yet another simple and effective way of drying food outdoors. This method is especially useful for beans and lentils. All one needs to do in order to dry beans such as kidney, soy, lima, navy and lentils, is to leave the bean pods on the vine till the beans inside rattle. It is relatively simple since no pretreatment of food is required. Once the bean pods are completely dry, simply pick them and shell. If required, further drying may be completed by drying them in the sun, oven or a commercial dehydrator.

Pasteurization

It is important to treat fruits and beans dried in the sun or on the vines and kill any insects and their eggs. One can use any one of these two methods for this purpose. The first is the freezer method. For this, one can simply seal the dried food in freezer plastic bags and place them in a freezer set at 0 deg F or below and leave them at least 48 hours.

The second is the oven method. For this place the food in a single layer on a tray or in a shallow pan, and then place the tray or pan in an oven preheated to 160 deg F for 30 minutes.

Here are some useful resources on outdoor drying –

• Solar Dryers
• Tips for Solar Drying Food

Drying Foods Indoors

Drying foods indoors is easy and possible with the help of modern gadgets such as food dehydrators, conventional ovens or countertop convection ovens. While one can dry herbs in a microwave, it isn’t possible to dry other foods simply because there isn’t adequate air flow.  

Food Dehydrators

Food dehydrators are small electrical appliances that can be used to dry and preserve food indoors. A dehydrator has an electric element for the heat and a fan and vents for air flow and circulation. Most dehydrators are designed to dry foods at 140 deg F, which makes them efficient and quick.

These days, one can buy a food dehydrator from department stores, natural food stores, mail-order catalogs or garden supplies stores and catalogs. Dehydrators can cost anywhere from $50 to $350 or above depending on features. While most have standard features, some models may be expandable with provision for extra trays. The only possible disadvantage that a dehydrator may have is its limited capacity and therefore, expandable dehydrators may be a better option.

Dehydrator Features to Look For

Here are some standard features that one should look for when buying a food dehydrator.

Double wall construction of metal or high-grade plastic with enclosed heating elements and an enclosed thermostat with temperatures from 85 deg F to 160 deg F.

• A dial for regulating temperature and a timer to prevent food from over-drying and scorching.
• An easy-to-use, counter top design.
• A fan or blower to ensure flow of air and circulation.
• Four to ten open mesh trays made of sturdy lightweight plastic. Trays should be easily washable and low on maintenance.
• The UL seal of approval with a one-year guarantee.
• Easy to maintain and use with proven after-sales service. 

Types of Dehydrators

Usually, dehydrators come in two designs where one has a horizontal air flow since the heating element and fan are located on the side while the other model has a vertical air flow with the element and fan located at the base.

Dehydrators with a horizontal flow of air have several advantages – mixing of flavors is reduced which allows several foods to be dried simultaneously, there is no dripping of liquid or juices and all trays are heated equally. Vertical flow dehydrators cannot prevent mixing of flavors and this can increase the time for drying different types of foods. 

Homemade Dehydrators

It is possible to build a dehydrator at home after getting the required instructions from the county Extension offices. A homemade dehydrator will be cheaper however; it may not be as convenient and efficient as a commercial one.

Oven Drying

An oven can easily and effectively be used to dry food. Ovens have all the three elements needed for food drying – heat, low humidity and air flow. However, while it can be possible to dry small amounts of fruit leathers, meat jerky, banana chips or mushrooms, it is indeed difficult to use a home oven to dry large quantities on a regular basis.

Moreover, drying food in the oven is a slow and time-consuming process. Most ovens do not have an in-built fan and therefore, they end up taking more time and energy to dry relatively small quantities of food.

To Use Your Oven

If one decides to use the oven to dry fruits and vegetables, here are the steps.

Check the oven dial to see if it has a reading as low as 140 deg F. If the oven does not have this temperature, it will end up cooking the food rather than drying it out.

To ensure and facilitate air circulation, leave the oven door propped open 2 to 6 inches. It is also possible to improve air circulation by placing a fan outside the oven near the door. However, this is not recommended for homes with small children.

Since the door is left open, the temperature inside will vary. So, place an oven thermometer near the food for a more accurate idea. Adjust the dial to achieve the required 140 deg F.

Use trays that stay away from the sides of the oven and are at least three to four inches shorter than oven from front to back. The racks should be two to three inches apart to allow airflow.

Room Drying

Drying food in the room is different from sun drying. Here the food that has to be dried is placed in a well-ventilated room or covered space. Fruits, nuts, herbs and hot peppers are usually dried in this manner.

To dry herbs and hot peppers, either suspend them from a string or tie in bundles and suspend them from overhead racks. Keep the herbs and peppers covered in paper bags with small openings to allow air circulation. The paper covering will protect them from dust, insects and other pollutants. To air dry nuts in the room, simply spread them on a single layer of paper while for partially sun dried fruits, one can simply leave them on their drying trays. 

Dehydrofreezing

Dehydrofreezing is a new method of food preservation that uses both the techniques of drying and freezing. Fruits that have been dried at home usually have 80 percent of their moisture removed while vegetables have 90 percent. However, if only 70 percent of the moisture is removed and then, the fruit or vegetable is stored in the freezer, the final product will definitely be better tasting. Dehydrofreezing achieves this by combining freezing and drying.

However, it is important to understand that dehydrofreezing is not the same as freeze-drying. Freeze-drying is an expensive commercial technique that creates a vacuum while the food is freezing. This technique of food preservation cannot be performed at home.

In dehydrofreezing, the foods are partially dried and then, frozen. The low temperatures in the freezers prevent food from mold, bacteria and general spoiling. Moreover, since they have been dried, they take less space. In addition, the taste and color of such foods is definitely better than foods that have only been dried. Another great advantage of dehydrofrozen foods is that they reconstitute in about one-half the time it takes for dried foods, making the former a quicker and easier option. If one requires more information on dehydrofreezing food at home, do get in touch with a county Extension agent.

Here are some helpful resources on indoor drying of food items.

• About Electric Dehydrators
• Commercial Dehydration of Foods

Packaging and Storing Dried Foods

It is important to pack and store dried foods properly since they are prone to insect contamination and moisture re-absorption. 

Begin by cooling the foods completely. Foods that are warm tend to give off moisture, which could cause mold and bacteria. After cooling, tightly pack the dried food into clean and dry insect-proof containers. While packing them tightly, do ensure that the food does not get crushed or broken.

One can use glass jars, metal cans, boxes with tight fitted lids or moisture-vapor resistant freezer cartons to pack foods. While it is possible to use heavy-duty plastic bags, these cannot protect the food from insects and rodents. To keep out moisture, use plastic bags with a 3/8-inch seal. Fruit that has been sulfured should not be placed in metal containers directly. Fumes from sulfur can react with the metal and cause discoloration. So, place the fruit first in a plastic bag and then, store it in a metal canister.

It is a good idea to pack foods according to serving -or recipe-size amounts. Reopening the package several times will expose the dried food to air and moisture, therefore reducing its shelf life and quality.

Store dried food in cool, dark areas and most dried foods have a storage time from 4 months to a year. The storage temperature plays an important role in determining shelf life. Higher storage temperatures mean lower storage time. Most dried fruits can be stored for a year at a temperature of 60 deg F and for 6 months at a temperature of 80 deg F. Dried vegetables can be stored for half the storage period of that of fruits.

Keep a close eye on stored dried food to check for moisture that may creep in during storage. Glass containers make this easily possible. If one spots moisture on food, it is a good idea to dry and package them again. Moldy foods, however, should be discarded immediately.

Here are some more useful resources for dried food.

• Drying Foods – Introduction, Techniques, Instructions and Nutritional Content
• Remedies for Drying Problems