Understanding Dehydrating


Dehydration which is popularly known as ‘drying’ is a long-practiced method for preserving foods. It can also be referred as the process of removing water through evaporation from a solid or liquid food. The aim of this is to arrive at a solid material that has been sufficiently water-reduced. This process consists of reducing the level of food moisture into smaller levels in order to extend the lifespan of the food. It requires adding different forms of energy to the food.

Note that dehydration does not include mechanical pressing of liquid foods. In most cases, Hot-air is used to add heat to the food and to reduce its moisture.

It is very easy for pathogenic bacteria to survive comfortably in the unfavorable environment of dried foods. This means that once your dried food is rehydrated and eaten, it could cause you food poisoning. Of course, you would not want to suffer food poisoning, all in the name of preserving your foods for later use.

What should you do then to prevent this when drying your food? Make use of high-quality materials with low contaminants when drying your foods.  High-quality materials with low contaminants are materials and tools specifically made for dehydrating foods. Also, ensure proper sanitation of all tools and surfaces and ensure that the storage condition of the dried food is one that prevents contact with dust, rodents, insects and other house insects.

When you decide to dehydrate your food to make it last longer, then you have numerous options available for you. You could dry your food by air, vacuum, inert gas, steaming, or by directly applying heat to the food. Usually, the most popular and acceptable means of drying is by air. This is okay for obvious reasons. Using this method allows your food to dry gradually, plus it is very convenient. And, yes, air is very plentiful, and free! Allowing your food to dry gradually by using air prevents scorching and discoloration of your food, which is popular with other drying systems.

Slices of dehydrated persimmon on dark background

Dehydrating foods started as far back as times when early men spread their harvests or hunts out in the sun for sun drying. It is one of the oldest methods of preservation, as the prehistoric men were fond of drying some seeds before planting.

Fish, meats and food plants have been preserved over the years by drying them in the sun or naturally spreading them in the desert heat, across different desert areas.

In more recent times, American Indians stored their meats by laying them under the sun. The people of China also dried their eggs from the sunshine and the Japanese dried rice and fish under the sun’s rays as well. During the Second World War, there was a great need to move food in bulk from place to place and this challenge ignited the developments of modern strategies on preserving foods, hence dehydration. In the year 1975 however, the French made a major breakthrough in the development of hot-air dehydration, which is the drying of foods through the method of blowing hot air over them.

Browning reactions are one of the most common chemical reactions that occur in dried foods. They occur when chemical compounds in the food being dried react with compounds in the air. Browning is usually considered undesirable because it can change the taste of the food as it changes its appearance. A little known fact about browning is it can sometimes damage the nutritional value of the food as the color changes.

Many fruits and vegetables undergo enzymatic browning when they’re cut open and their flesh is exposed to the air. This sort of browning also occurs when produce is dropped, hit with something or otherwise damaged. It’s a stress response brought on by the rapid conversion of chemical compounds in the flesh into brown melanin. The enzymes that cause browning can be deactivated through careful use of heat, acids or chemicals like sulphites. Blanching foods and/or exposing them to citric acids before setting them out to dry can inhibit browning enough to where it isn’t much of a problem.

The Wonder of Dehydrating

Assorted dehydrated citrus slices on wooden surface

A centuries-old technology, dehydrating removes moisture from fresh food so bacteria cannot grow. Dehydrating preserves your food for a year or more, without refrigeration. With 90 percent of the moisture removed, the food intensifies in flavor, concentrates its nutritional value, and takes up less room in your pantry.

In areas where the relative humidity is 30 percent or less, fruit naturally dries on the tree or vine, right in the garden. Airflow and heat are both essential to the dehydrating process. When left to nature, grapes turn into raisins slowly, dependent on local weather conditions. But in many areas the humidity is too high for this natural process to be successful. A food dehydrator controls the variables of temperature and humidity, speeding up the drying process and ensuring an end product that is safely preserved. Getmore information about safety in home fermentation: the facts.

The first food-drying machine was invented in France in 1795 to aid Napoleon’s war efforts. It used circulating airflow and temperature control to speed up the dehydration process. Dried food was useful for traveling armies because it was lightweight, retained its nutritional value, and took up less space than its fresh counterpart.

During the two world wars, dehydrated food was essential to provisioning the troops, leading to an increased demand and further innovation on an industrial scale. In fact, instant mashed potatoes were born from the war effort with the technology gained from dehydrating food for the troops.

Interest in home dehydrating was slower to take hold until the mid 1970s, when the back-to-the-land movement increased interest in home-scale food preservation. In response to this increased demand, several electric dehydrators for home use were patented that offered both airflow and heat.

When a recipe calls for blanching fruit or vegetables, it’s usually done to stop or slow enzymatic action on the produce. Foods that need blanching should be processed quickly after cutting into them. The enzymatic action will initiate as soon as the flesh of the fruit or vegetable is exposed to oxygen. If you’re planning on drying large amounts of produce, it’s best to do so in smaller batches. Trying to do it all in one batch might result in the produce you cut in the beginning degrading to the point it can’t be used by the time you get around to blanching it.

Color loss can also come about as a result of drying. This effect is especially pronounced when high heat or sunlight is used to dry leafy greens and brightly-colored vegetables that get their color from carotenoids, which are fat-soluble pigments. Pigments will often fade during drying and can further fade during storage.

Dried foods change texture when the moisture is removed. This is due to a number of factors, including the loss of moisture, changes to the cellulose material and degradation of some of the compounds found in the food. When foods are dried at too high a temperature, the outside of the food can dry before all the moisture leaves the inside, creating what’s known as case-hardened foods. They appear dry on the outside, but there’s still too much moisture inside the hard outer shell.

While it may sound like food drying is an invasive process that drastically changes food, it actually isn’t that bad once you get past the physical changes. It’s the least damaging food preservation technique and foods that are dried retain most of their nutritional value. Other preservation techniques involve the use of extreme heat or extreme cold, which is even more damaging to the structure and chemical composition of foods subjected to them.

From a technical standpoint, most food starts degrading as soon as it is harvested. Once a plant or animal is no longer alive, it starts to lose nutritional value. This loss is slow at first, but quickly accelerates into rapid degeneration once the food begins to spoil. Anything done to prepare the food like heating it, washing it, slicing it or otherwise processing it further damages the food.

Dehydrators for home use offer continuous circulating airflow, temperature control, food-safe tray materials, and special aftermarket add-ons like silicone sheets to make it easier to make leathers and snacks. The latest digital models allow for temperature control between sections of the dehydrator, as well as programmable temperature and time variations for different foods. With electronic precision, you can put the food in, set the cycle, and go about your day. Read most important topic about food safety basics.

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