Although it may sound very technical and scary, it is really very easy to dehydrate food. All it requires is cooking the food for a long time at a very low temperature to get rid of all the moisture. People dehydrate food for many different reasons. Some take it hiking with them1, some use dehydration as a way to preserve seasonal foods, some to make seasoning for cakes and sauces. And then of course there's jerky. Foul rotten evil stuff, it's spiced raw meat - anything from beef to duck - just cooked so that it stays in a leathery state. If you want to learn more about it you will have to go elsewhere!
Shop-bought dehydrators look a bit like a sprouter - between three and five round aerated shelves stacked on the heating device, with a lid on top and a hole straight up through the middle to allow the air to escape. If you're lucky, you'll get a fruit-leather sheet with it - these are indispensable when dealing with juicy fruits or any sort of sauce. If your machine doesn't come with one, baking paper will do, but some sort of tough plastic you can grease (such as the bag from a packet of cereal) is better.
You don't need to go out and buy a fancy machine - your oven will work fine. The only drawback with an oven (unless it's relatively new) is that it's hard to be precise with the temperature - depending on the food it should be anywhere from 35 - 63°C (95 - 145°F). The concept is still the same, just a bit more fiddly. The important thing to remember is to keep the oven door open to let the heat escape, otherwise you will cook the food.
It's also possible to make a dehydrator - it's a good way to get something which will perfectly suit your needs!!
Pretty much anything can be dehydrated - keep in mind that the more water it has to start off with, the longer it will take to dehydrate, and the smaller it will be when you rehydrate it. Sloppy sauces and watermelons won't work too well.
Slice evenly, possibly use a food processor. Uneven chunks will dry irregularly.
If it's sloppy, grease the tray with olive oil to prevent hassle getting it off.
Be careful with dairy products - they can curdle if left too long between cooking and dehydrating.
Use the best produce you can find - lean meats work a lot better than fatty ones, and fresh fruit and veggies are much nicer and more nutritious than something which is going off.
Be very liberal with your spices!
Air temperature and moisture will affect the amount of time your food takes to dehydrate.
The last half hour is the most important - make sure you don't burn your food!
Store dehydrated food in the freezer to give it an even longer life.
Fruits are great to dehydrate - cheaper than buying from the store and excellent as snacks in a trail mix, they're the simplest thing to do. Depending on the fruit, you can either peel it or leave the skin on - the skin is where most of the nutrients are found, but it is tough and stringy to eat. Make sure the fruit is fresh, wash it, and cut it in to slices between half and one centimetre thick. Fruits such as apples and pears should be soaked in either pineapple or lemon juice for five or so minutes to stop them from browning. Garnishes can be a nice touch - sprinkle some coconut over the pineapple or mango, sugar over strawberries. Just experiment!
Veggies follow the same method as fruits - slice them evenly and thinly and spread them across the tray. If it's something a bit juicy, it may be worth greasing the tray with some olive oil to prevent it from sticking. If the vegetable is moist, like a tomato or courgette (zucchini), sprinkling herbs over it is a good way to add a bit of flavour.
To make a fruit leather, whizz up your favourite fruit with some apple puree to make a chunky sauce, spread it on the tray about 5mm thick, and voilà! Couldn't be easier.
Yoghurt leathers can be made in the same way but be careful which yoghurt you use. Vanilla becomes very sour - the berry ones work best. Experiment until you find one you like.
Meat and Fish
Meat is a bit iffy. Things like duck and chicken go rubbery, and beef becomes globby and unappetizing. If you simply can't go without meat, then be careful which cuts you use. Mince works best.
Pasta and Sauces
The best way to dehydrate a pasta sauce is with the pasta - this way some of the flavour will stick to the pasta and not be lost in the scrape from dehydrator to container. Be generous with your spices; a lot is lost in the dehydration/rehydration process.
To rehydrate your food, add water three or so hours before you want to eat. If you're camping, a see-through wide-mouthed bottle is your best option; you'll be able to see the food rehydrate and it's easy to get in and out. A rough guide is about a cup (250ml) of water to every cup of dry product, but it really depends on what it is you're trying to rehydrate. If you're going to cook it after it's been rehydrated you may want to add extra to allow for evaporation.