There appears to be a great deal of confusion about Kitniyos for Pesach use. Here are the main questions and answers.
What is the definition of Kitniyos?
We do not have a working definition. In fact one great authority was inclined to prohibit potatoes as Kitniyos and the ShaArey Teshuvah [453:1] records that some considered coffee to be Kitniyos. For all intents and purposes, potatoes and coffee are absolutely acceptable for Passover use.
Are Kitniyos prohibited as is Chomets?
No. Chomets is prohibited by Torah Law. Kitniyos are prohibited by custom of the Ashkenasim. This custom emerged to protect from errors and substitutions between items that can produce flour like compounds.
Are Kitniyos ever permitted on Pesach?
Yes, for those who are not well and for those who do not have this tradition. Also if the Kitniyos are a non visible minority of a food despite the fact that in such proportions they are certainly discernible to the palate. See Mishneh Berurah 453:8 & 9
Do Kitniyos prohibit a food even if they are just a minor component of that food?
No, unless they are visibly discernible, in which case they must be removed; the remaining food however may be consumed. However Kitniyos added in defiance of the known custom, will attract a penalty. This penalty prohibits the food for those who added the Kitniyot and for whom the food was prepared. [implied in the Rema and M"B] It is permitted however, to others for whom it was not prepared. In short it can be offered as a gift to friends. It can even be sold to neighbours as long as it was not manufactured with that purpose in mind.
May I eat during Pesach, foods containing Kitniyos?
Yes. For example, regular chocolate may be eaten during Pesach. Many mistakenly believe that regular chocolate may not be used on Pesach since it contains Lecithin. [used as an emulsifier (just a fancy word meaning it helps all the ingredients stay together as a very smooth paste - if you make your own mayonnaise, you add egg yolk as an emulsifier to make a smooth emulsion (a cream; oil and water do not readily combine) which may be produced from what some consider to be Kitniyos] As per the Mishneh Berurah 453:8 & 9, even if it is Kitniyos it is permitted since:
Its proportion is small enough to be Halachically insignificant,
It is certainly not visibly discernible, and
It has been manufactured for the non-Jewish or the Jewish non-Passover market.
May an Ashkenasi add such proportions to foods being prepared for Pesach, before or during Pesach?
Not during Pesach. Before Pesach some permit and others prohibit it.
Read the following very carefully, "Chocolate certified for Pesach uses no lecithin." ORIGINAL Note, the author is careful to say what is done but does not discuss the Halacha.
Here is another published article to consider: Government regulations dictate that minute amounts of Vitamin D, and Vitamin A be added to milk. These are often derived from Chometz or Kitniyos, and since mixtures of even small amounts of Chometz on Pesach are not “batel” (annulled), we must be cautious concerning milk which contains these additives. Additionally, chocolate milk, may well contain malt, which is made from grain and is Chamets. All milk processed on that equipment might be Chamets. Therefore milk for Pesach must not be processed on chocolate-milk contaminated machinery.
One is tempted to ask, if the vitamins can be considered Halachically insignificant and therefore the milk is Kosher for Pesach, why may the chocolate milk which might contain malt, in proportions that are equally insignificant, also not be considered Kosher for Pesach?