A proper kosher Passover matzah must take, from start to finish, no more than 18 minutes. Any longer and the leavening begins. Any longer and it becomes chametz, unfit for the eight-day Jewish spring festival that begins this year at sundown on April 10. Unfit even to be in sight during the holiday.

In many big cities worldwide, it is a tradition for Jewish children to tour a traditional matzah bakery and watch as bakers hand-make the unleavened bread.

But in the Twin Cities, there is no traditional matzah bakery and so, like his father before him, Rabbi Mordechai Grossbaum of the Minneapolis Chabad Lubavitch teaches the tradition to Jewish children here through words, songs and lessons.

The makeshift Model Matzah Bakery was open to the public Sunday at the Sabes Jewish Community Center in St. Louis Park. About 100 people came to learn.

The children (with a little help) took the shafts of wheat and separated the grain from the chaff, making a happy mess on long, paper-covered tables. Each small pile of grain went to the wheat grinders, which turned it into flour.

Noah Altman, 3½, was helped by his mom, Jordana, while dad, Adam, watched.

“We came out today to support the Chabad Lubavitch,” Adam Altman said. “And to give my son the experience of baking matzah.”

Altman explained that matzah is the “bread of affliction.” When the Israelites fled slavery in ancient Egypt and walked into the desert, the sun baked the dough they carried before it had time to rise.

The festival of Passover commemorates that exodus and is observed by avoiding leavened breads, drinking four cups of wine, eating matzah and bitter herbs and retelling the story of the Jews’ flight.

The flour ground by the children Sunday wasn’t used for the matzah — there simply wasn’t enough to go around.

The children sat with Grossbaum and talked about Passover traditions. “The first thing we need is flour,” the rabbi said. “How do you say flour in Hebrew?”

The questions, answers and songs went on as Grossbaum kneaded the flour and water together. He gave small lumps of dough to each child and rolling pins, instructing them to roll it as thinly as possible.

Some children found that difficult. Some used the rolling pins as jabbing sticks. Others rolled it paper-thin.

The sheets of dough were brought to a table to be scored with holes, then slid into a brick oven for just minutes before they emerged crispy and brown.

Jason Bass brought his 3½-year-old twins Charlotte and Hannah to the bakery.

“They’re very proud of their Jewish heritage,” he said. “We like to take any opportunity to expand on that.”