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If one of the five species of grain (wheat, oats, rye, barley, spelt) comes into contact with water after the stalks have been cut off the ground, i.e., if they become fermented, they become chametz. According to our Rabbinic authorities, this fermentation takes 18 minutes. Therefore, in order to be kosher l'pesach, matzoh must take less than 18 minutes to prepare from the time the water and flour are first mixed to the time the matzoh comes out of the oven.
The term chametz is applied not only to foodstuffs, but also to dishes and utensils in which foods that are chametz have been prepared during the year.
Beans, rice, corn, and peas are not among the grains that can become chametz, yet they are also forbidden during Pesach. This prohibition stems from the fact that flour can be made from these foods and it might be confusing. The rabbis felt that people might be tempted to use regular flour if they were allowed to use, for example, rice flour. To avoid such confusion, the rabbis decided that these foods (known as kitniot) not be used at all during Pesach. These additional foods are prohibited only by Ashkenazic Jews whose ancestors come from Eastern Europe. Sephardic Jews, whose ancestry is Middle Eastern, permit these foods during Pesach.
At Beit HaChatulim, removing chametz means getting out of our possession all flour, cereal, pasta, legumes, cookies, crackers, tofu and tofu products (soybeans are legumes!), rice and rice products, breads, brownie and pancake mixes, dry beans and peas, anything with corn sweeteners, baking powder, yeast, grain alcohol (not just the rum, the vanilla extract, too), popcorn, tortillas, and so on. It is a massive undertaking. We generally list all the food in the house and assign each item to one of the following categories:
On a more spiritual note, chametz can stand for other things in our lives that we would like to get rid of. Leaven symbolizes the impurity that causes grains to "puff up" and change. The removal of impurities in ourselves can keep us from "puffing up" and moving away from G-d.
We love the search for chametz. We often eat out the night before Pesach begins, then come home after dark. The kids giggle while they are each given a flashlight and a bag. The candle is lit (a parent holds it); we say the blessing and then they are off.
We move from one room to the next, each child searching one or more rooms. The others stand in the hall and play with their flashlights while the chosen child and the parent with the candle look all around the room for chametz. Since a parent hides about 10 things around the room before we leave, the search is usually successful and we move on to the next room.
Afterwards, there is another blessing to recite, and a formula which states that if we missed anything, it was unintentional and that the overlooked chametz is now "as the dust of the earth". (We don't eat dust, do we?) Then the collected chametz is set aside to be disposed of in the morning.
Odd things have happened to our family during the B'dikat Chametz. One year when Miriam was our only searcher, Aren had hidden 10 fairly large pieces of chametz. When Miriam hunted, she only found 9. We searched everywhere for that last piece of chametz, which happened to be a leftover piece of cornbread. We finally gave up and put our daughter to bed. Some time later, one of us happened to go down to our basement - to find the missing cornstick being happily consumed by our cat Woolly Bear!
There have been years when we found chametz during the search that we had not hidden. There was one famous year when little teddy-bear cookies kept turning up on the floor - "More dust of the earth!" we exclaimed as we reached for the broom. Both of these incidents can tell you either that we're not the world's best house cleaners, or that our cats are wonderfully inventive about stealing and hiding baked goods. Both explanations are just about equally applicable.
And soon.... I'll add the story of what happened to us one year while we were burning chametz in our back yard.