Dehydration temperatures for long-term preservation

Question

I am dehydrating fruits and vegetables with a home dehydrator. I found in the internet varying recommendations about dehydration temperatures, ranging from 45 to 65 C (113 to 150 F). However, since dehydration is used also for short-term consumption (by raw-food enthusiasts), I am not sure the recommendations are good for long-term preservation.

So, my questions are:

• If I dehydrate in 45 C (113 F), for about 24 hours, and keep the dehydrated stuff in tightly closed glass jars - can I expect them to be preserved for about 2 years?
• If the answer is no - what is the minimal temperature that I should use in order to guarantee preservation for 2 years?

Answer 1

The temperature varies not by how long you want to keep the item, but by what you are dehydrating. Consider a carrot. A raw carrot will keep for literally months. A cooked one at room temperature will not even keep for days. So, when you're dehydrating carrots (for example to reduce the weight of the food you take camping) you want to be sure not to cook them in the process. Now, consider raw meat such as jerky. This has a LOT of water in it. If you dry it at too low a temperature, it will spoil before you have reduced the water content enough. Same for a fruit puree. But herbs, if you have it too hot you will draw out the flavours and just keep dehydrated dust.

My dehydrator came with a book telling me what temperatures to use for what products. There are also words on the temperature dial. This is a cropped shot of my model on the manufacturer's website:

While you can't read the words, they say "fruit", "vegetables" etc. The coolest temps are for herbs, then it goes raising bread, making yogurt, then dehydrating veg, then fruit, and finally jerky.

And just as you can't choose one temperature to use for dehydrating any and all food, nor can you assume one keeping time for any and all food. My book also tells me which things keep for months, and which for years. I don't think there's anything that will let your dried meat keep for years, but you should do ok with legumes and some vegetables.

Answer 2

In terms of the science, it is not the temperature to which you set the dehydrator which is important, but the percentage of water remaining in the dehydrated food which will control its shelf life (along with other factors). The dehydrator temperature influences, instead, how long it will take the food to dehydrate, and the quality of the product (how much of a cooked flavor, for example, the food picks up).

Still, home dehydrated food is not recommended for long term preservation. They recommend jerky, for example, be held at room temperature for no more than two weeks; fruits can be held up to six months to a year.

This is because perfect quality control and stronger dehydration is difficult to achieve with home type equipment.

See the National Center for Home Food Preservations guide to dehydration, which links several in house and university supported articles about home dehydration.