According to Exodus, Jews shall "eat [only] unleavened bread" for seven days each year — and "seven days shall there be no leaven found in your houses."

Matzo, on the other hand, is "the poor man's bread," and eating it symbolizes "getting rid of money, possessions, ego — you're starting out like you just got out of Egypt," says Burg.

In time, Jews developed several procedures for ridding themselves of chametz — which also includes medicines, dietary supplements and household cleaners — by the morning of Passover eve, which falls on the 14th day of Nisan, the first month of the Jewish calendar.

One was to consume it all. Another was to incinerate it, a tradition local Jews observe in an annual community ceremony, the Burning of the Bread ritual at Pimlico Race Course.

But those procedures were born long before the days of modern food storage, including freezing and refrigeration, which allow consumers to keep more chametz on hand than they can reasonably be expected to eat or drink — or so much that burning it would constitute a financial hardship.

By the late 18th century, historians say, Jews had entered the liquor trade and so had to store chametz in quantity. Rabbinical scholars then helped these merchants find legitimate spiritual means not to sacrifice the stuff.

"There's a concept in the Babylonian Talmud that says, basically, 'God has concern for the money of his people,'" Shapiro says. "It's an interesting concept. One option for religions is to think, 'Who cares about what happens to your money? Just do what the text says.' But there's an idea in Judaism that the Torah shouldn't lead you to tremendous financial loss."

That was when Jewish elders revived mechiras chametz, which is spelled out in Scripture but had rarely been invoked.

Today, Shapiro and Burg agree, while few Reform or Reconstructionist congregations offer the practice, the vast majority of Orthodox and most Conservative synagogues do.

Jews taking part, in effect, sell the rights to all chametz in their possession — including the cracker crumbs in someone's purse and the cookie bits under the sofa — to a specific non-Jew for the duration of Passover.

They do this by signing a formal contract that grants their rabbi the legal right to sell those foodstuffs on their behalf.

The rabbi, acting as an agent, or shaliach, collects the contracts and, in a formal ceremony the day before Passover, transfers them in a single sale to the buyer.

From that moment until the end of Pesach eight days later, that individual fully and formally owns all the contracted chametz, be it blueberry muffins, Domino's leftovers or bottles of Jack Daniels.

"From a halakhic point of view, it's a binding sale, a transaction that is taken very seriously," says Bergman. "That's why a competent rabbinic figure does it."

Within the tradition, those who sell the banned food rarely remove it from their homes, though most gather up as much as they can find and store it in a remote cupboard or corner of the basement. Sometimes they will go so far as to tape cabinet doors shut to lessen temptation or will post written warnings to prevent guests from stumbling on it.

The buyer — be it a synagogue staffer, a friend of the rabbi or the minister of a nearby church — makes the purchase as an act of goodwill, Burg says, rarely with any intention of claiming it, even though it would be his or her full right to do so.

Burg, who calls his congregation of 500 families "probably less observant" than many Conservative synagogues, usually ends up selling about 20 contracts. Shapiro said he expected to sell more than 150.

By this year's Jewish calendar, the faithful are to have rid themselves of chametz by about 11 a.m. Monday. Passover begins at sundown that day and continues through next Tuesday, when those who have kept kosher throughout will binge in happy "carbfests," as Shapiro's congregant Reed puts it.

Not that she minds the interim. Reed says she relishes the process, from gathering the chametz to signing the contract to carrying out the noticeable, if comparatively minor, eight-day sacrifice.

"We [Jews] were actually slaves," she says. "That's amazing. We really couldn't bake, and we really have had to run. These physical acts are great reminders. They get me ready for the holiday."

Baltimore Sun reporter Nayana Davis contributed to this article.