Gemara

(Mishnah): One is Yotzei with Matzah of wheat, barley, Kusmin, Shiboles Shu'al or Shifon.

Inference: One is not Yotzei with rice or millet.

(Reish Lakish): "Lo Sochal Alav Chametz Shiv'as Yomim Tochal Alav Matzos" - Matzah must be made from something that can become Chametz. Rice and millet cannot become Chametz. They merely decay.

Our Mishnah is unlike R. Yochanan ben Nuri;

(Beraisa - R. Yochanan ben Nuri): Rice is a grain. If it became Chametz one is Chayav Kares for eating it on Pesach. One may be Yotzei with rice Matzah.

Rishonim

Maharil (Ma'achalos Asuros b'Pesach 8): One may not use [nut] oil even if it was made now, for they crush it in a mortar in which they soak barley for Lesisah (to pound it afterwards to remove the bran), and it becomes Chametz. Even though zealous people (Kohanim) can do Lesisah during Pesach, others may not, for they delay and it becomes Chametz.

Maharil (9): One should not light in the candlesticks or lamp one uses the entire year. One should not light even olive oil on the table, for one must put it in lamps that absorbed Chametz. Even though we clean them for Pesach, this is only externally. It does not help for what is [absorbed] inside, since it is considered a Kli Rishon. It becomes hot due to the flame, and emits Chametz that it absorbed. One who wants to use it during Pesach must hang the lamp far from the table, so surely no oil will drip onto the table.

Question (R. Akiva Eiger on OC 453:1): This is a third-level Nosen Ta'am of Heter! The mortar absorbed from the barley, the oil absorbed from the mortar, the candlesticks absorbed from the oil, and the oil [he uses now] absorbs from the candlesticks. We permit this above [even regarding Chametz - Magen Avraham 452:1]!

Maharil (9): The same applies to the lamp to illuminate the house for one's needs. He should hang it in a corner and not touch it. Libun (making it glowing hot) does not help for earthenware. The absorptions never leave, unless one returns it to the kiln. It is good to buy a new lamp for Pesach, and hide away the old one. It is a good custom to make twined wax candles to read the Hagadah from their light, and to avoid lighting oil.

Magen Avraham (453:2): Darchei Moshe says that we do not forbid regarding other oils even b'Di'eved, even if it is known that they were ground in a mortar used to soak barley. Even if Mashehu was absorbed, it was Batel in 60 parts of Heter before Pesach. Do not say that the oil absorbed the taste of Chametz from the mortar. Only sharp foods absorb through pressure [of a knife - YD 96:1]. Maharil connotes that one may eat olive oil [during Pesach].

Kaf ha'Chayim (31): Also Chak Yosef and Chemdas Moshe derived that one may eat olive oil during Pesach. Dagul me'Revavah disagrees, for olives are sharp, and they absorb from the mortar. Perhaps the mortar was used for Chametz! Machatzis ha'Shekel says that they have separate mortars for olive oil. They do not use the same one used for barley. The Chida said similarly, for olive oil is made in the olivepress! Shulchan Gavoha brings from R. Yerucham that oil is permitted.

Poskim

Shulchan Aruch (OC 453:1): Kitniyos do not become Chametz. One may make a cooked food from them.

Rema: The custom in Ashkenaz is to be stringent. Surely we do not forbid b'Di'eved if they fell into a Tavshil.

Gra (DH Mihu): We do not decree about this, and there is no custom [to forbid].

Sha'arei Teshuvah (1): Tuv Ayin (of the Chida, 9:6) says that a Gadol was stringent about coffee, even though it is Vadai a fruit of a tree. It seems that he was stringent because the masses did not know what it is. It seemed to them that it is a kind of Kitniyos, and [if it were permitted,] they would permit all Kitniyos and breach the Rishonim's fence. Even in places where they accepted this stringency even for coffee, if it was scorched before Pesach one should be lenient (Shevus Yakov 2:5, unlike Chak Yosef). Here, we clearly permit coffee. Even so, zealous people scorch it before Pesach, and also peruse it before buying it to separate any mixture of rice or other species, to be free from any stringency of Pesach. They will be blessed.

Kaf ha'Chayim (22): Ikarei ha'Dat says that the custom is to permit even if it was not scorched before Pesach.

Sha'arei Teshuvah (1): Shevus Yakov says that many refrain from tea due to concern for swindlers, who use tea [leaves] and dry them out and sell them. Perhaps they were used with Chametz! I heard so from great people. One who guards his soul will be careful. Pesach demands extra distancing. In any case one need not be concerned for Kelim in which tea was cooked, or if tea spilled into food. The custom is to permit tea from merchants in big cities. Also, experts testify that it is Kosher for Pesach, for they can tell through the appearance, taste and smell. Tea that was used and dried is unlike tea the way it grew and was never cooked.

Kaf ha'Chayim (23): Ikarei ha'Dat says that some are careful not to buy tea from stores if the Kelim in which it was brought from Ulandia (Holland?) was opened. They permit if it is closed. We are concerned only for merchants here, but not for merchants of Ulandia. One merchant admitted that he takes cooked tea leaves from parties and mixes them [with raw leaves], for if not, he would not profit. One who guards his soul will not buy tea without investigation.

Rema (ibid.): One may burn oil made from them, and they do not forbid if they fell into a Tavshil.

Birkei Yosef (14): The Pri Chodosh says "Chozer v'Ni'ur is not only when we know that Chametz became mixed. Rather, even when it is common for Chametz to become mixed, e.g. sesame oil, which often has wheat kernels, one may not eat it during Pesach. Our custom is to cook only with olive oil. This is proper." Meticulous people are stringent also about olive oil. We found that every day the Nochri workers, while eating, dip their loaves in the oil. Sha'arei Yeshu'ah says that based on what R. Natrunai Ga'on wrote regarding raisin wine, one should have to eradicate sesame oil from the house. I never heard of anyone in Eretz Yisrael do so, even though most are stringent for Chozer v'Ni'ur. The Pri Chodosh said not to eat it. He did not mention Bi'ur, even though the custom in Yerushalayim is to buy sesame oil [at once] for the entire year, even though he holds like R. Natrunai Ga'on for several laws. Perhaps here is different, for sesame oil does not Vadai contain wheat. It is only common. Alternatively, since most of Yisrael eat sesame oil during Pesach, it suffices to be concerned for Chozer v'Ni'ur and not eat it. To burn it is astounding. This would establish Yisre'elim [elsewhere] to eat real Chametz. It is improper to do so.

Mishnah Berurah (10): One need not be meticulous to hang the oil lamp far from the table, lest the oil drip onto food, for even if it would drip, we do not forbid b'Di'eved. Even if the sesame was crushed in a mortar in which Chametz is crushed, there is no problem. Even if Mashehu was mixed in, it was Batel before Pesach. It does not receive the taste of Chametz, for what is cold does not absorb or emit. However, olives are sharp. If olives were crushed in a Kli used for Lesisah [of grain], surely they absorbed taste. Therefore, one may not hang a lamp of olive oil close to the table.

Kaf ha'Chayim (30): In Eretz Yisrael, the custom is to light with sesame oil, even though they do not drink it. However, I wrote (447:10) that perhaps those who are concerned for Chozer v'Ni'ur should eradicate sesame oil before Pesach. If so, it is better to light with olive oil that was strained well.

Kaf ha'Chayim (32): One may eat oils not made from Kitniyos.

Kaf ha'Chayim (33): The Rema repeated "they do not forbid even if they fell into a Tavshil" to permit even if Lesisah is done to the seeds before making oil, and it is likely that they fermented.