Another interesting Pesach point is the much maligned Chumra of Kitniyos. Around 800 years ago some Ashkenazi communities began to refrain from the consumption of legumes and similar products, and over the next century of two it became the accepted custom of all Ashkenazi Jewry. A number of motives are cited for this prohibition, primary among them the likelihood of some kernels of grain becoming mixed in with the beans. However, this is not the sole concern; also mentioned is the ability to make flour, and by extension dough and bread-like baked goods, from legumes. The concern arose that if someone would be observed eating bread or cake on Pesach it would appear that he was consuming Chometz. Furthermore, the restriction was extended to most seeds that grow in a pod due to their similarity to peas and beans, including mustard and flaxseed. Additionally, abstention from corn/maize and rice are included in this Minhag.
Interestingly, some Sefardi communities adopted this practice as well. Many Moroccans abstain from Kitniyos for the duration of Pesach, and Iraqis typically do not eat rice. The Pri Chadash writes that their initial Minhag was to examine the grains of rice one-by-one three times before cooking it, but once he discovered a grain of wheat after the third check and never again ate rice on Pesach.
It is generally accepted that the prohibition against legumes includes their byproducts, rendering soybean and canola oils off-limits to Ashkenazim as well. Some Poskim were lenient on the derivatives of species of questionable Kitniyos status; however today with the plethora of Kosher-for-Pesach products this is unnecessary.
Other accepted leniencies due to Kitniyos’ status as a Minhag relate to the quantity required for Bitul. While forbidden foods generally require 60 times their volume to render them insignificant, Kitniyos is permitted by a mere majority. Furthermore, there is no concern regarding the pots used to cook Kitniyos. Additionally, an infant or someone who is ill may be permitted to consume products containing legumes. Many people tend to be Machmir on these issues, and as with all practical Shailos one’s Rav should be consulted.
Some Poskim have proposed that the Chumra should only apply to species that were included in the original injunction, and since the Americas had not yet been discovered at the time, species native to the New World would not be prohibited. While it Is not generally accepted to exempt peanuts from the axe due to their classification as legumes, this is one of the reasons why potatoes were spared. While the Chaye Adam forbids potatoes due to their ability to produce a flour that can be used to bake pastries, this was not accepted. Furthermore, quinoa, while not technically a legume exhibits some of the characteristics of Kitniyos. The OU does not certify quinoa for Pesach because they do not consider it incontrovertibly permitted; however, other Poskim such as Rav Heinemann do permit it.
It should be observed that any permitted product still requires reliable supervision. As without a Pesach Hashgacha, a real risk of Chometz exists.
A Sefardi Rav I am friendly with who is very active in Kashrus once related to me that the motives for the original enactment are by no means outdated and they remain very relevant today. He once visited a factory that produces soybean oil with an eye towards certifying it for Pesach use for Sefardim. Upon a thorough examination of numerous large sacks of soybeans, he found every single one to contain numerous grains of wheat. He exclaimed to me that soybean oil is not merely Kitniyos, it is a Chometz product.