Geo wrote:That's interesting spiny, tnx. I guess that would rule out potato flour too, eh? Be tough on latkes, tho'!!
Geo
Actually, no. The prohibition is not on things that can be called "flour" (potato "flour" isn't really a flour), the prohibition is on the grains, seeds, legumes (peas, garbanzos, beans of all kinds) themselves. Adding further confusion, you can take matzoh and grind it and then use that "flour" to add body to baked goods (the idea being that its leavening powers have been arrested during the initial baking step - although others won't use it if it's re-purposed in this manner, which is sometimes referred to as "gebrokts"). So vegetables that are acceptable for Passover use are acceptable in any form.
The origins of these prohibitions were that certain prohibited foods had an ability to "bloom" or leaven in flour form and thus were considered to be in violation of the prohibition against using leavening agents or leavened products. It went a bit far afield in that seeds like cumin and mustard are prohibited but quinoa is somewhat accepted (this takes us down a different path to foodstuffs that were not within the contemplation of the authorities of the day "way back when" - i.e. no Jes in South America until fairly recently so when stuff when on the bad list, quinoa couldn't be included).
The rules are, to be polite, somewhat arbitrary. For example, 30-40 years ago, the prevalent Passover oil in stores was peanut oil, this was acceptable even though peanuts were not. The current rules eliminate peanut oil entirely.
There are literally volumes of text on the "how" and "what" of Passover observance (with very little "why?" offered in explanation - but that's why they call it "faith.")