Starches as Thickening Agents

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Updated on Sep 04, 2013

The great French chef and teacher August Escoffier claimed that sauces were responsible for the preeminence of French cuisine. Escoffier was usually right, but here he failed to lay all the credit where it belonged. The great French sauces of which Escoffier spoke are inconceivable without different types of starches to thicken them. Starches such as corn starch and flour are obtained from the seeds of a plant. Other starches, such as potato starch and arrowroot, are obtained from the roots of a plant.

Chemically, starches are little more than chains of sugar molecules strung together. This is a convenient way for a plant to store energy. It is no accident that these are stored in seeds and roots, because these are where energy is most needed. Starches in seeds supply the energy for germination; they continue supplying energy until the first leaves emerge and photosynthesis begins. Likewise, energy is needed in the roots for the roots to grow and transport fluids. Plants generally have a mixture of two different types of starches. Amylose is a straight chain of sugar molecules. Amylose pectin is a branched chain of sugar molecules. When you look at a starch, you are really seeing millions of these molecules packed together in discrete granules. The proportion of these different molecules in a plant differs in different species.

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.

Cy Ashley Webb is a science writer. In addition to having worked as a bench scientist and patent agent, she judges science fairs in the San Francisco bay area. She loves working with kids and inspiring them to explore the world through science.

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