Science project

Starches as Thickening Agents

If you put a tablespoon of starch into a cup of cold water, nothing will happen because the granules do not dissolve. However, if the water is hot, the heat disrupts the granules and causes hydrogen bonds to form between the water and the starch. Harold McGee describes this best. In his book “Food and Cooking,” he notes that “the granules lose all organized structure and become amorphous networks of starch and water.” The presence of meat drippings, herbs and spices transforms what McGee calls an “amorphous network” into a properly thickened sauce.


How do different starches act as thickening agents in food?


  • Corn starch, potato starch, tapioca, arrowroot
  • Tablespoon for stirring
  • Measuring cup
  • Water
  • Saucepan
  • Book
  • Cookie sheet
  • Small dessert dishes or small bowls for mixing starches
  • Stopwatch
  • Thermometer 


Dissolving the Starch
  1. Measure one cup of water. Add two tablespoons of this water to two tablespoons of starch. Stir until dissolved. Keep adding water, one tablespoon at a time, until the starch dissolves. Continue doing this until the consistency is roughly that of yogurt.
  2. Put the unused water into a saucepan and heat it until it is approximately 150 degrees. Add the starch-water solution. Stir until it is completely dissolved. Continue stirring over the heat for seven minutes.
Testing the Thickness
  1. Make a ramp by placing the edge of a book with a 1”-2” binding under the short edge of a cookie sheet.
  2. Pour one tablespoon of your flour solution onto the high end of the ramp.
  3. Start your stopwatch and measure how fast the thickened solution flows to the bottom of the ramp. Thicker solutions will flow more slowly. 

Repeat both procedures for every starch you are working with. Make a data sheet, noting the time it takes for the starch to flow to the bottom of the ramp.

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