Starch can be converted to ethyl alcohol by?

Starch is broken down by enzymes to glucose. Yeast enzymes then convert glucose into ethanol and carbon (IV) oxide by fermentation.

This is how local drinks such as burukutu and ogogoro start from starchy foods like guinea corn.

Distillation only separates ethanol from the mixture afterwards. Cracking breaks large hydrocarbons. Isomerisation changes the structure but not the formula.