Starch and Gluten 101: The composition and behavior of wheat flour

Often times as a cook, wheat flour has remained on of those elusive ingredients, the understanding of which is left to depraved genius bakers and pastry chefs.  They live in an elevated state, at least in my mind.

What is it though that makes flour so temperamental?

After a horrific failed attempt at making hand pulled noodles, this question was eating me alive, so I had to do a little research.  What are the major chemical components of flour, and what are their roles in its behavior?

Flour is one of nature’s incredible storage machines.  In it’s natural state, it is composed of starches and proteins, along with vitamins and other nutrients.

So what is starch?  Starch is an incredible complex carbohydrate (a polysaccharide) that is found in all plants to store as much glucose (one of three natural simple sugars, or monosaccharide) as possible in a compact granule.  Glucose by itself loves water (it is hydrophilic).  So, to maximize storage potential when glucose is bonded together into starch granules it is not water soluble in cold water (it becomes hydrophobic).

When starch is added to warm water, however, the magic starts to happen.  Starch is composed of two smaller polysaccharides, about 20-30% amylose and 70-80% amylopectin.  Amylose is hydrophobic and bonds with itself and other molecules in flour, acting as a gelling agent.  Its partner, amylopectin is hydrophillic and acts as a thickening or stabilizing agent. Amylopectin provides more pliability (think Play-Doh), while amylose provides more structure or spring-back (think Jello).  As these two components of starch break down and restructure themselves into a slurry of gel and paste the magical process is called retrogradation.

As this retrograded starch starts to cool off, a process called syneresis occurs in which water is expelled causing separation of the thickened gel/paste and water.  You see an example syneresis in everyday life as a layer of water forms on top of yogurt or sour cream.  This process is also partially to blame for bread becoming stale.

The other important component of wheat flour is protein.  The average protein content of grain is 10-18% and of this protein, 80% is gluten.  Gluten, much like starch, is a storage molecule but in this case it provides storage of amino acids.  There are two primary structures that compose gluten: gliadin and glutelin.  These structures are called prolamines and are essentially large amounts of amino acids that are bonded together into one molecule.

The most important role of gluten in bread is the elasticity it allows during the baking process, allowing bread to rise.  Now, here is where some of my confusion originated when attempting to make hand pulled noodles.  When I say gluten elasticity, do not think rubber band elasticity.  Think blowing soap bubbles elasticity.  Try to pull soap water into a noodle shape.  I promise that you will become very frustrated and punch your ball of dough in exasperation, just to see it bounce back to it’s original shape and not even give you the gratification of leaving the indent of your fist.

Here is chart to give you an idea of what happens to your bread with different levels of gluten and starch:

Composition	Flour type	Protein content	Examples
High Gluten (High elasticity) High Starch (Crumbly)	Gluten Flour	45%	Bagels, challah, pizza dough, pullman loaf Pie crust, cake, filo dough, short bread
	High-gluten	14-15%
	Bread Flour	12.5-14%
	AP Flour	10-12%
	Pastry Flour	~9-10%
	Cake Flour	7-9