Why is starch insoluble in ethanol?
Due to the fact that starch (amylum) is a polysaccharide , a long chain compound consisting of glucose monomers it has poor solubilty in most solvents. 

Some starches are water soluble because of the hydroxyl groups involved in the polysaccharide chain, some like the branched form amylopectin are more insoluble. 

Starches form granules in solution with cold water, the granules break down as the water is heated and can be solubilized.

When ethanol is added, which is less polar than water, it lowers the solubility and potential hydrogen bonds of the starch , because the water is more attracted to the alcohol than the starch, the starch is dehydrated by the alcohol and precipitates. 

So while polarity and temperature are variables to starches poor solubility, the critical variable in this case is the starches ability to hydrogen bond with the solvent.