Dear Rabbi Simon
As Pinny (age 5) is allergic to peanuts, I can look forward to Pesach with confidence, knowing that all kosher Ashkenazi homes will be kitniyot free and therefore peanut free – but to my surprise it seems very unclear and I show a few sources below to this effect:
South African Beth Din:
Are peanuts considered Kitniyot?
Halachic Authorities differ on the matter of whether or not peanuts should be considered Kitniyot. Peanuts were not known in Ashkenazic countries at the time when the prohibition was instituted, and as such were not included in this prohibition according to a long standing policy of the Beth Din. See also Igrot Moshe 3:63 where Rabbi Moshe Feinstein too, is lenient on this. Obviously peanut derivatives (e.g. peanut butter and peanut oil), under Beth Din supervision with a Pesach Hechsher, are certainly permitted according to this policy. Once again products containing such ingredients are clearly labelled or mentioned in the guide in consideration for those who prefer to follow stricter opinions.
OK [Chabad-influenced Kashruth authority based in Brooklyn, USA]: An earlier version of their website included the following (see http://www.ok.org/kosherspirit/spring-2009/know-thy-beans-2/ for their current take on the subject):
With reference to peanut oil, I wish to reprint the responsum of Hagaon Rabbi Moshe Feinstein:
“Concerning peanuts, which were called stashkes in Europe—they have been accepted as being permitted on Pesach and are not considered kitniyos (legumes that are forbidden on Pesach) because all the reasons for the prohibition of kitniyos do not apply to peanuts. Peanuts are not sown in fields (with grain), and even if they were there is no fear that grain would be mixed together with the peanuts; bread is not baked from peanuts; and generally speaking though they are vegetables they have the appearance of nuts rather than kitniyos. And even though I have heard that in some places they were considered kitniyos, peanuts should not be forbidden in places where it is not known for certain what the custom had been in their city, because, with reference to kitniyos, when in doubt one should be lenient.
Therefore you may give certification for peanuts and the oil derived from them, and they will be permissible to the majority of persons. Those who know for certain that the custom of their city was not to eat peanuts on Passover should not eat them; others are permitted to eat them.
London Beth Din
I couldn’t find any info on this.
Bottom line – Can we or can’t we?
The answer is that contemporary practice in Ashkenazi homes is to eschew (rather than chew) peanuts on Pesach, despite Rav Moshe’s lenient ruling. The Israeli kashrut authorities, the OU in the USA, and LBD in the UK all decline to supervise peanut products for Pesach. Notwithstanding the citation from the (generally reliable) OK website (transcribing an essay written in 1974), peanut oil for Pesach has long gone out of style. Rav Moshe’s responsum refers to those communities that did (do) have the custom of regarding peanuts as kitniyot, although he asserts that most do not. It may be that the SAf Beth Din retains the established custom (perhaps common in Lithuania too?) to be lenient in this regard.
The “bottom line” is that peanuts should preferably be avoided on Pesach (not only by Pinny), as this has become the general custom in the UK (and many other places). I would add as an aside, however, that the South American pseudo-cereal quinoa was unknown in Jewish communities until very recently, and therefore has never been subject to either the original (medieval) custom of kitniyot, nor a subsequent communal practice to avoid it. Some have nevertheless sought to ban it today, but I do not share that view. See https://kesher.org.uk/knowledge-base/pesach-questions/ for my Q&A on the subject. For more info visit https://www.star-k.org/articles/articles/seasonal/pesach/1864/
Rabbi Rashi Simon