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Food Dehydration - Step 3 - Testing for Dryness

Food Dehydration - Step 3 - Testing for Dryness

Dry your own fruits, vegetables and other foods

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Before you take the foods out of the dryer, it is important to test a representative sample for dryness. Take a look at this page that describes typical drying problems.

Testing for dryness by observation

Know when your food is dry:
Some foods are more pliable when cool than warm. Foods should be pliable and leathery, or hard and brittle when sufficiently dried. Some vegetables actually shatter if hit with a hammer. At this stage, they should contain about 10 percent moisture. Because they are so dry, vegetables do not need conditioning like fruits.

How to test for dryness:

Take a few cooled pieces (pick from the middle, edges, etc. You want to get samples that are fully representative of all pieces. Cut the pieces in half. There should be no visible moisture and you should not be able to squeeze any moisture from the fruit.
Fruits may remain pliable, (e.g., leathery) but they should not be sticky or tacky. They also should not be hard.  If a piece is folded in half, it should not stick to itself. similarly, when a few pieces are squeezed together they should fall apart when the pressure is released. They should have a leathery or suede-like feel.  High sugar fruits, like figs and cherries, may feel slightly sticky. Fruit leathers can be peeled from the plastic wrap. Dried fruits are generally eaten without being rehydrated, so they should not be dehydrated to the point of brittleness. Most fruits should have about 20 percent moisture content when correctly dried.
Berries should be dried more; until they rattle when shaken.

Vegetables are generally brittle or tough when they are dry enough. If there is a question as to whether vegetables are dry enough, reduce the temperature and dry the product a little longer, using a low temperature toward the end of the drying period. Unlike fruits, there is little danger of damage being done to vegetables by this extra drying time.  The USDA says "Some vegetables would actually shatter if hit with a hammer. At this stage, they should contain about 10 percent moisture. Because they are so dry, they do not need conditioning like fruits."

Vegetables	Characteristics when properly dry
Beans, green	Leathery, brittle
Beets	Brittle
Broccoli	Crisp
Cabbage	Brittle
Carrots	Tough to brittle
Cauliflower	Crisp
Celery	Very brittle
Corn, cut	Dry, brittle
Eggplant	Leathery
Horseradish	Brittle
Mushrooms (obviously, stick to known edible varieties only!)	Leathery
Okra	Very brittle
Onions	Brittle
Parsley	Brittle, hard
Peas	Wrinkled, green
Peppers and pimientos	Leathery to brittle
Potatoes	Brittle
Spinach and other greens (kale, chard, mustard)	Crisp
Hubbard squash	Tough to brittle
Summer squash	Leathery to brittle
Tomatoes, for stewing	Leathery
Tomatoes, sliced	Leathery to brittle

Testing for dryness by mathematical calculation

In most cases, you want to dry fruits to 80% and vegetables to 90% of their dry weight. This sounds confusing... but for best results for both plumpness and safety, you can calculate the percent solids in the dried product to determine if the product is adequately dry. Here's how:

1.  Weigh the container that will be used for the food on the scale. (Tray Weight.) If your scales allows you to set a "Tare weight" , do so, and adjust it so that the container weight equals zero.
2.  Weigh the raw (undried) produce in the container (this is the Product and Tray combined weight.)
3.  Calculate the Raw Product Weight. (Raw Weight.), which is
    Product plus Tray Weight. minus Tray Weight equals the Raw Weight.
4.  Calculate the desired final Weight of the dry product using the following formulae:
   
   For Fruits:
   (Raw Weight from step3 above ) times (Solids percent from Table 3 below) = Desired Dry Weight
                                           80%
   
   For vegetables:
    (Raw Weight from step3 above ) times (Solids percent from Table 3 below) = Desired Dry Weight.
                                           90%
    

* 90% solids is a good value to use for vegetables. Fruits are moister if 80% is used for calculation purposes. Do not use a lower percent value for solids.

Example

Let's say we want to dry sour cherries to 80% solids (which means 20% water).

Looking in Table 3 below, we see the solids in raw cherries are 14%

Let's say we weigh our container and find it weighs 5 oz.

And we weight the raw cherries in our container and it is 45 oz.

So, then the weight of our raw cherries is 45 - 5, which equals 40 oz. 

Our desired dry weight should be:

 (40 oz. times 14%) divided by 80% = 7 oz. final dry weight

 

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