To fully understand and observe the laws and customs of Pesach we must know first what Chametz is.
To be very precise:
1. Chametz is any fermented substance coming exclusively from one of the following five cereal grains: wheat, barley, oats, rye and spelt.
2. Chimutz (the forbidden fermentation) only takes place when one of these elements gets in contact with water and after passing eighteen minutes.
Some common examples of Chametz are: Bread, pasta, crackers, cookies, candies, noodles, some baby foods, dietary supplements (usually drinks) containing fibers, soup powders, whiskey and beer.
Many other alcoholic drinks contain grain alcohol. Years ago Vodka, for example, was made exclusively from potato, but lately, most brands of Vodka use cereal grain alcohol, which of course renders them absolutely forbidden for Pesach. (See http://www.britannica.com/EBchecked/topic/631781/vodka )
Rice, corn and their derivatives, like corn starch or corn syrup (these last two elements are extensively used in the pharmaceutical and food industry) and any other seeds which are not one of the five mentioned grains, are not considered Chametz, even if they are fermented.
And you thought you've heard it all.....
Rabbi Yosef Bitton. YMJC | 130 Steamboat Rd. | Great Neck | NY | 11024