Millions of Jewish families all over the globe are prepping for Passover — an eight-day religious festival that, once a year, turns matzo into one of the most popular commodities at certain grocery stores.

This year, Passover starts the evening of Friday, March 30 and ends at sundown on Saturday, April 7. Those observing Passover will celebrate by eating matzo and holding Seder meals, while sticking to common kosher practices — which means they’ll be avoiding certain foods, specifically leavened breads. But what does keeping kosher even mean — and do foods like rice, corn and oatmeal count as unleavened bread?

Keeping kosher requires that observers — among following other religious practices — refrain from eating pork or shellfish and to only eat meat that has been slaughtered according to specific rules, which includes a rabbi supervising to make sure the meat is kosher. Kosher food rules also extend to the way foods are prepared and served — for example, those who keep kosher can’t eat dairy and meat at the same time.

But during Passover, there’s an additional rule — for those who keep kosher and those just observing the annual Jewish holiday. For eight days, observers are basically on a gluten-free diet as well and have to avoid all unleavened breads. It can be tough to tell which foods are and aren’t kosher for Passover, especially common items like rice, corn, beans and oatmeal. And it turns out the answers vary, and typically depend on a person’s Jewish ancestry.

Ashkenazi Jews, who are of European descent, have historically avoided rice, beans, corn and other foods like lentils and edamame at Passover. The tradition goes back to the 13th century, when custom dictated a prohibition against wheat, barley, oats, rice, rye and spelt, Rabbi Amy Levin said on NPR in 2016. Because rice and legumes were sometimes mixed with wheat — which is avoided during Passover unless it’s in its unleavened form, matzo — those items were avoided, too, according to the Times of Israel.

The kosher food rules have been controversial for about as long as Passover has existed, Levin said, “simply because the custom prohibits foods that are, according to Torah law, which is like the Jewish Constitution, permitted to be eaten.” According to the rabbi, the rule was “geographically limited.”

But the kosher food rules have since changed. In 2015, the Rabbinical Assembly, a global group of Conservative Jewish rabbis, ruled that rice, corn, beans, popcorn and other similar items that were previously prohibited would be allowed at Passover Seders, NPR reported.

These new kosher foods have always been a part of the diet of Sephardic Jews, whose ancestry goes back to the Middle East, North Africa and other areas around the Mediterranean Sea. Legumes and grains are considered kosher, and rice, bean and lentil dishes have long been served at Passover.

So, if you’re hosting a Seder dinner this year, feel free to add a rice and beans dish to the table.

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Write to Mahita Gajanan at mahita.gajanan@time.com.