In summary, dehydrators use a combination of low, regulated heat and controlled air-flow to gradually remove the moisture from the food, thus causing it to dry out – often to less than 20% of its original water content.
Application of heat
In a way food dehydration is a form of cooking because heat is applied. But it is done so slowly that it doesn’t really cook the food in a conventional manner at all.
The key is to apply a very low temperature over a long period of time to allow the moisture to escape very slowly without allowing the food to actually cook in the normal way.
The idea behind dehydrators came from ancient times when people would simply use the power of the sun to dry out food. Of course the temperature was very unpredictable, airflow could not be controlled and the food would be at the mercy of the elements which was not desirable!
Modern electric dehydrators follow the same principles but in a controlled way to provide a safe, predictable outcome.
Controlling the air flow
If you dry out your food in the sunshine you should have a pretty large surface to work with – a good chunk of the planet! But of course, kitchen appliances need to be a bit smaller than that so dehydrators usually use a collection of trays that are stacked on top of each other in order to minimise the counter top space taken up by the unit.
The problem with this arrangement is that those trays that are furthest away from the heating element will get the least amount of heat. Most systems use a fan that blows the heat away from the heating element and over the trays. Take a look at our buying guide for a diagram of how this works.
Another important factor in controlling the air flow is the arrangement of the food. Ideally you would would want to cut it into small pieces and arrange them so that none are touching or overlapping. The trays are usually some kind of mesh and so this allows air to flow in, over, under and around every individual piece of food therefore drying each piece effectively and evenly.
Removing the moisture
So if the water is being removed from the food then where does it go? It evaporates of course but with the aid of well placed air vents. The vents allow the moisture in the air to escape outside of the unit. If these vents get blocked the air would remain damp and the system would not work.
Most modern types of dehydrators come with an adjustable thermostat which will regulate the temperate inside the unit and keep it even throughout the drying process.
This is a useful feature to have as some foods, such as meats (commonly used for jerky), require a higher temperature to effectively kill any bacteria than lighter, more delicate items such as herbs.
Food safety and long term storage
There are many reasons why people use dehydrators these days – because they want to make delicious jerky or fruit leather, or perhaps they simply enjoy dried apple rings more than eating a fresh apple. But in a lot of cases, dehydration is a method of food preservation, and as a bonus, because so much moisture is removed, it is also much lighter in weight and takes up a lot less space.
These last two points make dried food an excellent source of nutrition for those who need to store food over the long term without traditional food preservation methods. Hikers, backpackers, campers, other outdoor enthusiasts, and preppers all find dehydrated food to be extremely useful and efficient!
What makes the food safe to eat without freezing or refrigeration is the removal of the moisture. Bacteria, mold and anything else which causes food to spoil works in the presence of water. When that moisture is removed it will last much, much longer.
These are the basics of how these great little appliances work. They come in all shapes and sizes and can vary a lot but the basics will always remain the same.
Dehydrators remove the moisture from food slowly over time by applying gentle heat, allowing that hot dry air to slowly dry the food whilst eliminating the damp air with a ventilation system. After a few hours you’ll have a delicious, healthy snack that will last for months!