Hafrashas Challah - Oat and Rice Combination

QUESTION: I made gluten-free bread dough with 1 lb. of oat flour and 4 lbs. of rice flour. Must I separate challah for this bread? Also, how much of this bread must I eat to recite Birkas Hamazon?

ANSWER: In a previous Halacha Yomis, we learned that wheat and rice flour combine to create a shiur for the mitzvah of challah, provided the taste of wheat is discernible in the bread. Does this apply to rice flour blended with flour of the other four grains? The Yerushalmi (beginning of Maseches Challah) cites the ruling of Rebbi Hila in the name of Reish Lakish that rice combines only with wheat. This is also the position of Ramban and most Rishonim. However, the Tur (OC 453) writes that all five grains combine with rice. Rav Chaim Kanievsky (Derech Emunah – Bikurim 6:80) writes that normative Halacha is to follow the Ramban, such that rice combines only with wheat flour and not with any of the other four species.

Birkas Hamazon is only recited if one eats a k’zayis (half the volume of an egg) of bread. What is the status of oat and rice mixtures with respect to satisfying the requirement of eating a k’zayis for Birkas Hamazon?

The same dispute between the Tur and the Ramban regarding challah would apply to Birkas Hamazon as well. According to the Tur, if one ate a single k’zayis (half the volume of an egg) of a rice and oat bread, the two flours would combine and Birkas Hamazon would be required. In contrast, according to the view of the Ramban, which is the accepted view, the rice does not count towards the k’zayis when mixed with other grains. Shulchan Aruch (OC 208:9) writes in a similar case that one is not obligated to recite Birkas Hamazon unless a full k’zayis of oat flour is consumed. In the above scenario, in order to eat a k’zayis of oat flour, one would have to eat five k’zaysim of this bread and it would need to be eaten within a timeframe of k’dei achilas pras (3-7 minutes).

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