3.2 Dehydration


  • To apply the principles of dehydration to home methods of drying.
  • To properly store dehydrated food.
  • To rehydrate or otherwise prepare dehydrated food for consumption.

Laboratory Problems

  • Pretreat, dry, store and serve some commonly dehydrated fruits and vegetables.
  • Observe the characteristics of various dried fruits.

General Laboratory Directions

This lesson is divided into two laboratory periods several weeks apart, with short assignments during the week following the first laboratory.

Preparation Day

Pretreat assigned fruit or vegetable according to specific directions below to control enzymatic deterioration.

Carrots or Onions

Wash and trim.  Cut into ⅛-inch slices, then pretreat if directed.  Steam blanch by spreading vegetable in a thin layer in steamer.  Steam until hot in center, approximately 3 to 3 ½ minutes.

    1. no treatment.
    2. steam blanching.


Wash, peel, core, and cut into ⅛-inch rings.  Immediately drop into assigned pretreatment solution and soak for 10 to 15 minutes.

    1. no treatment.
    2. 1 tsp. salt in 1 pint water.
    3. 2 tsp. ascorbic acid in 1 pint water.


No treatment.

  1. Drain and dry fruits and vegetables. Spread one layer of cheesecloth on dehydrator racks.  Spread food in a single layer on racks.  Set temperature of  dehydrator at 140o-150oF.  Dry until vegetable slices are brittle (3-6 hours) and fruit slices are leathery and pliable (6-8 hours).

Label a Ziploc bag for each dehydrated sample as follows:

    • Name of Product, treatment used, section number, and student initials
  1. Let food stand in a large loosely covered container for a week, stirring each day, to allow moisture to equilibrate.
  2. Place in small air-tight containers and store in a cool place.


Evaluation Day

Prepare food according to specific directions.  Record your observations on the chart.


Rehydrate by soaking for 20 minutes or more in enough water to cover.  Add more water if necessary to keep carrots covered.  Cook carrots as if they were fresh in a small amount of soaking water.


Dehydrated apple slices may be eaten as they are, or they may be rehydrated and cooked.  Add enough water to cover fruit and soak for 1 hour or more.  Add more water if necessary to keep fruit covered.  Simmer fruit in soaking water until tender.

Observations and Explanations

Type of Treatment Before Drying Appearance Texture Flavor
Carrots, No Pre-treatment
Carrots, Steam-Blanched
Apples, No Pre-treatment
Apples, Salt
Apples, Ascorbic Acid


Observe the characteristics of various dried fruits:

Dried Fruits Appearance Texture Flavor


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Basic Scientific Food Preparation Lab Manual Copyright © 2023 by Iowa State University Department of Food Science and Human Nutrition is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.