Editor's note, April 7, 2020: As Jews worldwide observe the Passover holiday under the auspicies of the COVID-19 pandemic, with virtual seders and quarantine-driven riffs on annual traditions, here's a look at the dietary rules and customs that make the eight days special.

The Torah couldn’t make things any clearer. From Exodus 12:14 and 15 : “This day shall be for you a memorial day, and you shall keep it as a feast to the LORD; throughout your generations, as statute forever, you shall keep it as a feast. Seven days you shall eat unleavened bread. On the first day you shall remove leaven out of your houses, for if anyone eats what is leavened, from the first day until the seventh day, that person shall be cut off from Israel.”

But in the centuries since, food has gotten a lot more complicated, and the Jews who fled Egypt were fruitful and multiplied, melding their own traditions with regional customs. Today the rules governing keeping kosher for Passover aren’t as clear as they were in ancient Judea. Erik’s explainer on the Lenten fast taught me much about the Catholic tradition, so I’ll repay the favor with this guide for my Gentile friends on how American Jews keep kosher for Passover. I should preface this section by saying that even among the most observant Jews, disagreements over what is and what is not kosher for Passover persist. Many foods, like jellies or butter, should be considered allowable given their ingredients, but the equipment used to produce them is not cleaned and inspected by rabbinic observers. This is why you may see specially wrapped or branded products of everyday goods for those Jews who look for that extra degree of precaution. Consider this a brief slice of a very complicated discussion.

The Obvious No-Nos:

Wheat, spelt, barley, oats and rye . Known collectively as chometz, these grains are universally left out of diets during Passover week. This means no Apple Jacks, bagels , biscuits, cakes , cookies, danishes, empanadas, ficelles, gyros, hoagies, Italian bread, jelly donuts , knishes, lefse , muffins, naan, oatmeal, pasta, pizza, quiches , rugelach, strombolis, tacos, upside-down cake, Viennese wafers, waffles, yeast or zwieback.

Unfortunately, these rules also mean that all beer and most liquor is forbidden. The only alcohol allowed is wine, of which there are kosher-for-Passover varieties .

It is customary to clean all the chometz out of one’s house. Some totally cleanse the house, others board up closets, others sell the grains to their non-Jewish neighbors (you can help next year!) and buy it back at the end of the holiday, others sell their chometz on the Internet to a stranger and buy it back even though the food never moves.

The Generally Assumed No-Nos:

Rice and beans. The realm of kitniyot (legumes) is among the grayest of areas. Joan Nathan is the Barefoot Contessa of Jewish cooking and she says it best in her book Quiches, Kugels, and Couscous: My Search for Jewish Cooking in France :

In the Middle Ages, rice, lentils, chickpeas, and fava beans were all ground into flour, which in that state could be confused with the true grains. The list continued to grow after corn and beans came to the Old World from the New. In France, where mustard seeds grow, mustard was added to the list, because the seeds could be intertwined and confused with other plants.

The confusion principle is largely the reason why many American Jews abstained from eating any corn or rice products on Passover for decades. According to Nathan, a biblical ruling was made in the 12th and 13th centuries that “any grain that can be cooked and baked like matzo confused with the biblical grains.” Therefore, not kosher for Passover.... until last year, when, as reported by Danny Lewis for Smithsonian.com , the Conservative movement declared that kitinyot were now rabinically approved for consumption during Passover. Whether this changed the ingrained habits of observant Jews remains to be seen, but the shift was noteworthy nonetheless.

The anti-legume tradition has been mostly maintained by Ashkenazic Jews, or those whose ancestors come from eastern Europe. Pre-Inquisition Jews from Spain never followed these rules, and thus Sephardim, who by definition are Jews descended from those who escaped Spain but also include those who are from South America, Asia, the Middle East and Africa, do not either. The vast majority of American Jews, 95 percent or more , are Ashkenazic.

Even now in an era of detailed FDA-mandated labeling, where the confusion Nathan wrote about is nigh impossible, the tradition continues. This is why you see the fabled “Mexican Coke” make an appearance each spring. Made with cane sugar and not high-fructose corn syrup, the imported soda is good to go. ( Relatedly, what tastes better? Regular Coke or Kosher for Passover Coke? The New Republic did a taste test. )

Matzo. For reasons that are unknown to most Jews, some people willingly eat matzo at other times of the year. These matzo boxes are labeled “not kosher for Passover” and should not be eaten as a part of observing the holiday. The difference? Rabbinic supervision to ensure that any matzo made for Passover is untainted by any leavening agents. There is also a debate over whether egg matzo is allowed. While clearly being verboten for the Passover seder (another Torah passage states that only the flour and water version may be used during the ritual), eating egg matzo during the rest of the week is left up to the observant.

Quinoa . The New York Times had a good wrap-up of the quinoa loophole, which is rather ingenious. Since the grain is a relative newcomer to Western diets, the grain wholly bypassed not only the Talmudic scholars but the “confusion principle” as explained above. Ashkenazic rabbis never had the chance to exclude it from the holiday, and so by default it became kosher for Passover. Now concerns are being raised over whether the manufacturing process is clean of any of the banned grains. The Orthodox Union, the authority on such matters, has declared quinoa allowable for consumption during the holiday. The story of how they came to that decision, from NPR:

"This rabbi went all the way to Bolivia and Peru," Elefant reports. "He saw that quinoa grows near the top of the mountain and grain grows near the bottom of the mountain." Thus, there was no chance for the intermingling that might happen with crops planted near wheat. Another plus for quinoa, says Elefant: "Many rabbis are of the opinion that anything that wasn't part of the original custom is not included in the custom."

All that was left for the rabbis was inspection of factories that package quinoa to see if forbidden grains are processed on the same equipment that processes it. And some passed. Those factories that got the all-clear now produce quinoa that will bear the OU-P symbol, meaning they're kosher for Passover.

Fair Game :

Most everything else. All in all, keeping kosher for Passover isn’t all that difficult, especially if you have experience with the Atkins or Paleo diets. I find myself eating more healthy meals this week than usual, as I am forced to cook at home and use copious fruits and vegetables to fill out my diet. If I’m cooking meat, I make my own marinades or sauces, and if I’m eating a salad, my own dressings. Don’t put shrimp salad or a bacon cheeseburger on your matzo—the normal kosher laws still pertain: no shellfish, pork products or mixing of meat and cheese is allowed.

Cigarettes: According to the Associated Press, a rabbinic group in Israel has, for the first time, declared certain cigarettes as Kosher for Passover.

One last note:

If you re-read the passage from Exodus, you’ll notice that it declares that the holiday should be observed for seven days, as is done in modern day Israel, and not the eight customarily observed by American Jews. In the era before standardized calendars, Jews in the Diaspora (any area outside of Israel) added an extra day to ensure that their holiday overlapped with the official celebration. This is also why American Jews have two nights of seders, where in Israel they only have one.