Types of starch

Grain starches have some common characteristics:

• granules are medium sized
• contain significant amounts of lipids and protein
• have increased structureal stability and thus require higher temperatures to gelate
• have distinct "cereal" flavor
• contain a high proportion of moderately long amylose, so they thicken and congeal quickly

Examples:

• Wheat flour is only 75% starch, which makes it a less efficient thickener than cornstarch or potatoe starch. It adds a distinct wheat flavor to the sauce. Common rule of thumb is to add 1.5 times as much flour as starch.
• Cornstarch is practically pure starch. It is an efficient thickener, but it absorbs odors and develops flavors during processing.
• Rice starch have the smallest granule size and produce a fine texture. It is seldom available in Western markets.  

Tuber and root starches come from moist underground storage organs and have the following characteristics:

• larger granules that retain more water molecules
• cook faster
• release starch at lower temperatures
• contain less amylose, but the amylose chains are four times longer than cereal starches
• readily gelate
• do not require precooking to improve flavor

Examples:

• Potato starch has very large granules and very long amylose chains. Stringiness and initial graininess in the sauces are notable. However, the granules are fragile and fragment easily. It is unusual in that it contains a large number of phosphate groups that carry a weak electric charge and cause the chains to repel each other. This repulsion keeps starch chains evenly dispersed in a sauce and prevents them from congealing when cool.
• Tapioca is derived from the tropical plant casava (aka manioc). It does not develop any strong aromas and it is prized for its neutral flavor. It is mostly used in puddings.
• Arrowroot starch has smaller granules than potato or tapioca starches. Its gelation temperature is higher, more comparable to that of cornstarch.

There are also a number of modified starches available. Plant breeders have developed "waxy" varieties of corn that contain little or no amylose and nearly all amylopectin. Waxy starches make sauces and gels that resist congealing. Manufacturers have also used physical and chemical treatments to produce starches that readily absorb cold water or disperse in liquids without cooking. They have also added cross-linking chains, made them fat-soluble, and have given them other qualities that make them more effective emulsion stabilizers. Such starches are listed as "modified starch."