Note: Due to current confusion and misconception, we must stress that rice or potato matzah is not acceptable for the seder. Matzah for the seder must contain one of the grains mentioned below.
On Passover eve we are commanded to eat matzah, a thin cracker-like bread, in remembrance of the matzah that our forefathers ate when they left Egypt. While this matzah can be made out of flour from any of the five grains (wheat, barley, spelt, rye and oats), the famed codifier of Jewish law, Rabbi Moshe Isserles, writes that the custom is to specifically use wheat flour for the matzah.
(Note: Baking Kosher for Passover matzah at home would be extremely complicated, expensive and time-consuming. Before proceeding, one should consult a rabbinical authority knowledgeable in these laws. For this reason, there are few families who would venture to baking them at home.)
According to most opinions, the reason behind the custom is that wheat is considered to be the most special of the five grains, since the majority of people prefer it. However, if wheat cannot be used, then one should make matzah out of one of the other four types of grain.
Others, however, maintain that the reason for the preference of wheat matzah has to do with the fact that other grains have a different leavening process and become chametz, leavened bread, faster; nevertheless, they would agree that in a situation where wheat flour cannot be eaten, one of the other four grains can be used.
In light of the above, if one has an issue specifically with the consumption of wheat, one should preferably use spelt matzah, as spelt is considered a species of wheat. However, if someone has a problem with gluten in general, things get a bit more complicated.
(Note: It is best to use shmurah matzah, which contains wheat and flour that has been watched from the time it is harvested so that no water would come in contact with it. If it is difficult to obtain shmurah matzah for the entire Passover, you should make every effort to at least have it for the first two nights of Passover.)
Of the five grains suitable for making matzah, oats by far have the lowest gluten content. Because of this, in recent years some have started making matzah out of oat flour. To make these matzahs, they cultivated special breeds of oats that were known to be particularly low in gluten. At one point a small patch of gluten-free oats was found in Scotland, and they cultivated them to make “gluten-free matzah.”
The issue with oats is that, unlike the other four grains, in order to store them, the oats have to be treated with heat. When one of the five grains is treated with heat, it can no longer become leaven, which is problematic in terms of fulfilling the requirement to eat matzah (see footnote at length).
In light of this, contemporary rabbinic authorities rule that in a situation where using one of the other grains poses a serious health risk, one should only use oat matzah that was treated with heat before it was stored. Therefore, it is important to ascertain whether someone’s issue is simply gluten intolerance, celiac disease, or a true allergy, as these conditions vary significantly.
However, recently on the market are gluten-free oat shmurah matzahs. Instead of storing and treating the oats with heat, they bake the matzah immediately after harvesting the oats. It would seem then that these matzahs are free from the above-mentioned concern that the mixture would not be susceptible to become leaven. However, it is still preferable to use wheat flour when possible.