From an article by Rabbi Rosen of the Star-K:
“Kitniyos are popularly defined as legumes. But what are legumes? The Shulchan Aruch, Orach Chaim 453, defines kitniyos as those products that can be cooked and baked in a fashion similar to chometz grains, yet are not halachically considered in the same category as chometz. Some examples are rice, corn, peas, mustard seed, and all varieties of beans (i.e., kidney, lima, garbanzo, etc.). The Torah term for the fermentation of barley, rye, oats, wheat, and spelt is “chimutz;” the term given for fermentation of kitniyos is “sirchan.””
zd: yeast may be a fungus but certain yeasts are chometz. Also you wrote “The OU doesnt think Quinoa is Kiniyot”. Actually there was a long standing machlokes between two of their poskim (Rabbi Belsky tzatzal and y’bdlc Rabbi Hershel Schacter) which caused the OU not to give a hechsher on Quinoa for a number of years. Two years ago the opinion of R’ Schacter prevailed after the OU mashgichim actually inspected the fields where the Quinoa was grown.
Avram: Is it the potato starch that make them fluffy or the whipped egg whites?