The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) discusses the custom observed by some communities not to eat Masa on Pesah if had come in contact with any liquid – which the Ashkenazim call "Gebrukst." People who observe this custom do not cook Masa or Masa meal with water or eggs, and do not put any Masa in cereal or soup. The reason for this custom is the concern that some dough in the Masa might not have been fully baked, and if unbaked dough comes in contact with liquid, it will become Hametz.
The Mishna Berura writes that although one should not deride those who observe this custom, in truth it does not have any Halachic basis. He comments, "Ahazukeh Issur Lo Mehazkinan," which means that we do not suspect that products are forbidden unless there is good reason for such a suspicion. If the Masa was baked in a factory according to the proper Halachic procedures and under supervision, then there is no reason to suspect that it contains unbaked dough. This is especially so regarding the Masot baked nowadays, which are hard like crackers and many of them are almost burnt. It is highly unlikely that today’s Masa has some dough which not sufficiently baked. Years ago, the Masa was thicker and softer, and there was, perhaps, some room for concern. Nowadays, however, this concern is certainly unfounded, and therefore it is indeed the custom of our community (among others) to eat "Gebrukst," and one may dip or cook his Masa in liquid as he pleases. Of course, one must ensure that the Masa he eats was baked under reliable supervision and is accurately marked "Kosher for Passover."
On the first two nights of Pesah, one must eat Masa that is not only kosher for Pesah, but also is marked "Shemura Mi’she’at Kesira." This means that the entire process, from the time the wheat was harvested, was done for the sake of the Misva and under supervision. Strictly speaking, the requirement to use specifically "Masa Shemura" applies only on the first two nights of Pesah. However, the Vilna Gaon (Rabbi Eliyahu of Vilna, 1720-1797) is cited as maintaining that eating "Masa Shemura" throughout the holiday of Pesah constitutes a Misva De’orayta (a Misva from the Torah). There are therefore some people who make a point of eating only "Masa Shemura" throughout Pesah so they can observe this Misva in accordance with the view of the Vilna Gaon. Rav Aharon Kotler, the renowned founder and Rosh Yeshiva of the Lakewood Yeshiva, insisted on serving only "Masa Shemura" to the students in the yeshiva throughout Pesah, despite the extra expense entailed. He felt that if the Vilna Gaon considered it a "Misva De’orayta" to eat "Masa Shemura" throughout Pesah, then it is worthwhile to follow this practice.
Therefore, it is an admirable practice to eat only "Masa Shemura" throughout Pesah, however, as mentioned, this is not required according to the strict Halacha.
Summary: Although some communities have the custom on Pesah not to eat Masa that had come in contact with liquid ("Gebrukst"), it is permissible according to Halacha. On the first two nights of Pesah, one must eat Masa that is reliably certified "Shemura Mi’she’at Kesira." Some people have the custom to eat only "Masa Shemura" throughout the entire holiday of Pesah.
