Chametz is any food product made of wheat, barley, rye, oats, spelt, or their derivatives, which has leavened (risen) or fermented. Our sages have determined that flour from any of these five grains that comes in contact with water or moisture will leaven unless fully baked within eighteen minutes.
Quinoa is not one of these grains, nor is it related to any of these grains, and is therefore not chametz.
However, there are two factors that must be considered with regards to consuming quinoa on Passover:
1) Due to the gravity of the prohibition against chametz, the medieval Ashkenazi rabbis forbade the consumption of kitniyot
(legumes) on Passover, as they can be confused with forbidden grains. This includes (but is not limited to): rice, corn, soy beans, string beans, peas, lentils, peanuts, mustard, sesame and poppy seeds.
There are some Halachic authorities who consider quinoa to be kitniyot, while others rule that quinoa, a member of the "goose foot" family (which includes beets and spinach), is not included in the prohibition against kitniyot.
2) The processing of quinoa is generally done in the same locations where wheat is processed. There is very high likelihood that the machines are not adequately cleaned between the processing of the wheat products and the quinoa, which would lead to a reasonable risk of chametz traces being transferred to the quinoa.
In light of the above, if you are an Ashkenazi Jew, you should ask your community rabbi whether he considers quinoa to be kitniyot. And whether you are Ashkenazi or Sephardic, any quinoa would require Kosher for Passover certification to ensure that the plant where it was processed was properly cleaned and purged of any traces of grain products before the processing of the quinoa.
In 2007 and 2008 the CRC (Chicago Rabbinical Council), a widely accepted Kashrut authority, wrote in their Passover products list:
Ancient Harvest brand, made by Quinoa Corp., Gardena, California, only deals with pure quinoa, however, only the “whole grain” quinoa may be used. They also produce a red quinoa called “Inca Red,” under the same label, which is also permissible. Other products such as pasta and flour made from quinoa should not be used for Passover, as they are made in other facilities that do indeed contain Chometz.
However, as production and processing lines constantly change, before buying quinoa for
any given Passover one must verify that the brand(s) is still acceptable. (The
yearly updated Kosher for Passover lists provided by many Kashrut agencies
should be of use in this area.)
Have a happy and kosher Pesach!
Rabbi Baruch S. Davidson