Thanks for the answer Rabbi. I am aware of the general idea of how wheat flour becomes chametz by getting in contact with moisture or water. My question was more specific than that though: (1) Do whole grains (not in the form of flour) become chametz when put in water? (2) Since matzah is not chametz and is made from wheat flour by mixing with water - with the only difference being the time limit for being in contact with water before it is baked, how is cooking bulgur for say just 3 minutes different in that respect? Thanks for your patience.

Shalom, Thank you for your question. Normally the leavening process of water mixing with flour, is stopped by the extreme heat of the baking oven. This is why matzah is kosher for Pessach. But, if one wets grains, and does not bake them, they will continue to leaven, until they become chametz. There are two issues that relate to your question. 1) Letitah – this is the process of washing the whole grains before they are ground into flour. This process does not cause the grains to become chametz, because firstly, it is a quick process, and secondly, the grains are moved constantly during this washing, which also stops the leavening process. (Then the grains are dried.) However, this is not true of every grain. For example, barley grains are softer, and they do become chametz in the letitah process. For many generations we have ruled that we are not knowledgeable enough to determine how and where to apply this process – and we rule today that all letitah is forbidden, and the grains would be chametz. This relates to part of your question. 2) Chalitah – this is the process of putting grains into boiling water. They boil and cook very quickly, and so they do not become chametz. In the Gaonic period, they already forbade this process, worrying that we are not familiar with the details of how to perform this process. We worry today that even after the boiling of the grains, they will continue to leaven even after the boiling stops – this does not happen when thin matzah is baked in an oven at a very high heat. This also relates to your question. So, in answer to your question. Theoretically, had completely dry grains (that had never been washed) and then baked them in a very hot oven, they would be kosher for pessach. So too, theoretically, the leavening process could be stopped by a very quick hard boil. However, practically, unless one has grains that were supervised for Pessach (as is the flour we use for matzah) to ensure that it never became wet, and then after (carefully) quickly kneading it with water, and baking it in a very hot oven – all other grain products will be either chametz (or at very least, suspect of being chametz). This is why the process of making matzah is so carefully Rabbinically supervised. I hope this is of some help to you – Blessings.