The purpose of dehydration is to take out enough water from the material (and therefore in the case of fruits raise the natural sugar level) so that spoilage organisms are not able to grow and multiply during storage. Although drying, dehydrating and evaporating are often used casually to mean the same thing, dehydrated food is understood to contain only 2.5% - 5% water. "Dried" food still contains roughly 10% - 20% water and in order to keep it, some preservative needs to be added (or be kept frozen).
Advantages of dehydrated food:
- It takes up only 8-30% of its original volume
- Does not rely on power to be stored
- Long shelf life
- Preserving without the need of any additives
Some points about dehydrating using a dehydrator:
- Drying herbs: <35`C (higher temps cause loss of flavour)
- Drying Fruit and Leathers: <55`C
- Drying Veg: <50`C
Use fruit with good flavor: select fresh fruit at the peak of ripeness (if it tastes like cardboard because a fruit is unripe it will taste like a very dry piece of cardboard later). Wash thoroughly and dry if the fruit has been sprayed or has been picked up off the ground.
Cut or slice fruit evenly so it dries all at the same time. Remove stones, pips, stems. Blemishes can very easily be cut away, as long as an off flavour hasnt developed through the fruit. If there are uneven pieces allow for extra drying time for the thicker parts.
Pretreatment: It is suggested that some vegetables should be blanched prior to dehydrating to stop the enzyme action that causes flavour loss. Fruit does not need any pre- treatment. However, if you like to keep bananas and apples very pale they can be dipped in lemon juice immediately after slicing (Conventionally, ascorbic or citric acid are used as is sodium meta-bi-sulphite).
'To peel or not to peel' thats the question - entirely up to you!
Drying time will depend on temperature of weather and dehydrator, humidity, thickness and moisture content of produce. Apples sliced in approximately 5mm slices might only take 8-10 hrs. Mulberries left whole, 2-3 days. Generally its better to over-dry than under-dry.
To test for adequate dryness, let a piece of produce cool, bend it and then squeeze it. If there is any moisture showing the product is not dry enough and should be further dried so moulds dont develop during storage.
Storage in a cool and dark place. Use clean glass jars or food grade plastic buckets with good fitting lids. If you are dealing in very large quantities, cherry barrels (200L) are excellent; they keep moisture and dried fruit moths out. Even though you might not have seen any moths, the eggs may already have been laid and hatch after you have put the fruit in storage. Nothing is more devastating than to discover hours and hours of work eaten away by these destructive creatures. So check regularly for any sign of life. We use food grade carbon dioxide gas (available from BOC Gases Ltd) to suffocate any living creatures in the storage containers and to stop the development of any eggs laid (CO2 will also suffocate you if used inappropriately so follow safety directions carefully). Freezing will also kill most insect eggs.
Its good policy to specifically check for moisture after a few weeks - Was your product truly dry enough? Condensation in the containers indicates it isnt (or moisture is getting in). Moulds, bacteria and fungi need to be treated with respect! Some are dangerous.
Also note that plastic containers may keep the smell of previously stored food (eg pickles) for a long time and taint the flavor of your new harvest.
Fruit Leathers: over ripe fruit can be stewed, pureed and spread out on a lightly oiled sheet of plastic. Drying times vary but are speeded up by turning the leather after a day.
Herbs can be dried. Temp should not exceed 35`C.
A wicked hint: orange dipped in chocolate is simply delicious.
Hygiene: Commonsense hygiene rules need to be taken into account. Contact your local council Environmental Health Officer for interesting and detailed information on Food and Hygiene.(Applicable to home situation, compulsory reading if you are thinking of selling produce). All the above information is easily used when you have an electric dehydrator.
Other methods of drying:
- Sun drying: trays protected with cheesecloth to keep insects off . Watch out for dew, rain, birds, rats and ants!
- Oven drying: care should be taken to not exceed 55-60`C-leave door ajar- frequent turning helps drying
- Solar drying: Various driers are available - you can also build your own
- Freeze drying: Generally not used in domestic situation.
- Refrigerated drying, using a special, new type of machine.
- DIY Fruit Dryer, Alternative Technology Ass., 247 FlindersLane, Melbourne VIC 3000
- Jura Sol, Jura Heights, Gowan via Bathurst, NSW 2795
- Solar Safe,RMB 2317 Euroa ,Vic 3666
- Ezidri , Ezi Concepts, 9 Commercial St, Marleston, SA ph 08 8371 1611 They also market the apple peeler and corer.
- Nara, Shop 11, Albyn Tce, Strathalbyn, SA 5255
- Sunbeam and other small dryers in local stores
- The Permaculture book of Ferment and Human Nutrition, Bill Mollison, Tagari
- Department of Agriculture Fact sheets on drying fruit
- Food Poisoning and Food Hygiene, Betty Hobbs, Diane Roberts, publ. Edward Arnold
- Drying Food, Ricky M, Gribling, Hyland House Publishing
A solar dehydrator designed by Chas Martin of Willunga.
It features a tiny electric fan to speed up drying time and is weatherproof. Dehydration of most fruit in summer takes 2-3 days.
Chas lives in a solar/wind powered home at Willunga in South Australia and besides running a mechanical workshop he can export power to his neighbours. He installs power systems and composting toilet/reedbed systems for others.