Tuesday, October 9, 2012

Variables in Dehydrating Times

“I did what the book said, but it isn’t dry!” 

Most dehydrating books will give you a specific range of drying times at a particular temperature. You followed the directions, but your food isn’t dry.  What happened? 

This is a common lament, especially for newbies. The problem is, most dehydrating books don’t seem to take into account the variables that affect the time it takes to dehydrate your food.   

Applesauce Plops


Four Variables that Affect Drying Times

Moisture Content in the Food:
  • Moisture content in the food can vary considerably. It can vary from crop to crop, from variety to variety, or from the part of the country in which it was produced.
Thickness of the Pieces of Food:
  • Thin pieces of food will dehydrate more quickly than thick pieces of food. Sometimes, with different varieties of foods, such as grapes and other fruits, the thickness of the skin will affect how quickly the moisture evaporates.
Ambient Humidity Where You Live:
  • Let’s face it. This country is too big. What works in Florida won’t necessarily work in California. If you live in a humid climate, or if it’s raining when you decide to dehydrate something, it will take longer than it will in an arid climate or if it’s not raining.
Equipment Performance Variables:
  • Thermostat readings may vary from model to model. Even though several machines might have the same setting, there can be slight differences in the actual heat they generate.
  • Different wattages of machines can have blowers that push air at different volumes. A slow blowing machine won’t circulate (and remove as much moisture) as a faster blowing machine.
For those reasons, you need to recognize by touch and taste when your food is dry.

Apple Puree Plops

The general rules of thumb are:
  • Fruits and sweet things generally tend to be leathery rather than brittle. They will bend, not snap.
  • Most vegetables generally tend to be brittle. They will snap rather than bend.
  • Some foods will become brick hard when dry.
  • If you have treated something with sugar, honey or other sweeteners, the food will tend to take substantially longer to dry. If it’s sticky, you need to continue drying it.
  • In spite of what the books may say, some things can take several days rather than several hours to dehydrate.

A Word of Caution:
  • This bears repeating – high temperatures can cause case hardening.  This happens when the surface dries before moisture has had time to escape from the inside of a piece of food. If that happens, the food will appear to be dry, but before long, you will have moldy food.
  • It is much better to dry at a lower temperature rather than take the risk of case hardening.
    • Fruits and veggies – 115º to 120º degrees
    • Meats – 140º

Until you become familiar with how it works in your area, you might want to make a note of the time and date you started dehydrating an item and when it finished. You might want to jot down other information that you observe, perhaps about the weather and such. 

Linda’s Note: you can find more information on my post Testing for Dryness. 

Applesauce ready to dehydrate
As you can see, the applesauce is very thin.  It spreads out on the fruit leather tray. It doesn't take long for this to dry. It will become waifer-like in its consistency.

Apple Puree ready to dehydrate
whereas, the apple puree is much thicker and will take a good bit longer to dry. Both have the same sized portions, 1/4 cup each.  But the puree became leathery and pretty much held its shape, even after soaking in water for an hour.

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