Rice, corn and any seed, legume or grain which is not one of the five grains (wheat, rye, spelt, barley and oats) are not Hamets and do not become Hamets even if they undergo a fermentation process.
The Ashkenazi custom, however, is to forbid the consumption of legumes and grains like rice or corn during Pesah (qitniyot). Let us analyze the case of rice. Obviously, the Ashkenazi tradition does not consider that rice or any other grain besides the five above mentioned grains is Hamets. The reason for the abstention from rice on Pesah is that it was common to find grains of wheat mixed with grains of rice. Either because the fields where rice was grown were usually nearby or within the same fields where wheat was grown, and/or because whole rice-grains and wheat-grains look alike. In the market, it was not uncommon to find grains of wheat within bags of rice or other grains and legumes. And, as we will later explain, the prohibition of Hamets during Pesah is so severe that even one grain of wheat would render a whole food e forbidden for Pesah.
The stringency of refraining from rice is not an exclusive Ashkenazi tradition. Sephardic Jews are divided on the issue of rice. Moroccan Jews and other Jews from North Africa also avoid eating rice during Pesah, while Persian, Syrian and other Middle East Jews consume rice during Pesah. However, to avoid the possibility of the accidental presence of a grain of wheat in the rice, the Persian and Syrian custom is to check the rice three times before using it for Pesah.
Information about rice, Rabbi Eliyahu Ben Hayim.
1. "As per phone conversations with rice importers and receipt of confirmation letters from them, Rabbi Eliyahu Ben Haim has confirmed that the following brands of rice are 100% pure, not enriched, and have no additives or preservatives. Therefore, they are suitable for use on Pesah. The brands are as follows: Lalquila, Shahzadeh, Pari, Royal, Zebra, Deer, Empire, and Gold & Quilla. Even though these rices are 100% pure, our custom is to clean the rice and check it three times before using it for Pesah."
2. Information about enriched rice from Rabbi Yehuda Boroosan, Mashgiach from OU, Atlanta, GA.
"Rice is a primary staple food for many people. When rice is processed into white rice, the fiber and nutrient rich outer bran is stripped first, leaving behind the germ and endosperm. In many cases, the nutritious germ is lost as well during the polishing process. As a result, white rice is not terribly nutritious, naturally. Therefore, the U.S. Food and Drug Administration (FDA) requires that any rice labeled "enriched", regardless of its point of origin - whether domestically grown or imported - must contain at least the minimum level of thiamin, niacin, iron and folic acid as specified in the Code of Federal Regulations. "Organic Rice' on the other hand may not contain other nutrients, in compliance with the regulations set forth by the International Federation of Organic Agriculture Movements (IFOAM). Although the USDA does not require any import permit to import processed "Natural Rice" such as Basmati, Jasmine, etc., without enrichment, for food consumption to the US, in some countries abroad the trend has become to enrich their natural rice that is intended for import purposes.
Niacin (Vitamin B3) - is produced through synthetic process. Although the production process is synthetic, it does rely on enzymatic process. The enzymes used in the process are not of any chametz concern.
Iron ferrous sulfate) - is an inorganic chemical and is not of any chametz concern.
Folic Acid (Vitamin B9) - is an innocuous ingredient and presents no issues for Pesach.
Thiamin (Vitamin B1) - is a vitamin that is made through reaction of ethanol with formic acid to produce ethyl formate that is used to make Vitamin B1. Ethanol variously made either from wheat, sugar cane, sweet potato or corn depending on its price in the market. Presently, there is no definitive assurance that the ratio of Ethanol is less than 1/60 of the total mix that is utilized to produce the final product. However considering the fact that all four vitamins are blended together along with a carrier and then only 3/10 of a pound of enrichment is added to every one thousand pounds (0.03%) of rice, the enrichment is considered null & void. Hence, if you purchase enriched rice DURING Pesach, it will be preferable to rinse it before cooking to remove vitamins. Rice purchased before Pesach could be used as it is.