Halacha Orach Chaim 168

There are times one is required to wash on cake and cookies. We will be discussing this in greater detail in future posts, but the general reasoning and guidelines are as follows.

Mezonos is recited on cakes and cookies. Although they are products made with flour and water, and should therefore require Hamotzei, they are not generally used like bread. The Bracha of Hamotzei is designated for flour products that are usually used during a meal.
Someone that eats enough cake and cookies that it is considered a meal, must wash and recite Grace After Meals. In addition, if cake or cookies are used in place of bread in a meal, it will also require washing and Bentching.

There is a difference of opinion how much cake must be consumed in order to require washing, when being eaten without other foods.

According to some, the amount is equal to the size of three or four eggs. This is learned out from Hilchos Eruv. The eggs used for calculating this measurement is also not clear, as the average size of an egg today is different from the size of an average egg in the times of the Talmud. According to the calculations of Reb Chaim Naeh, the amount of four eggs comes to around 230 grams.

Practically speaking, Reduced Fat Oreo cookies have 34 grams per three cookies. Based on this information, one would need to eat a bit more than 22 cookies in order to require washing. Yum.

According to others, one is required to eat enough cake equal to half the size of the Manna in the desert. This is equal to 21.5 eggs. According to the calculations of Reb Chaim Naeh, this comes to about 1236 grams.

Practically speaking, Reduced Fat Oreo cookies have 34 grams per three cookies. Based on this information, one would need to eat a bit less than 110 cookies in order to require washing. Ouch.

Mishna Berura recommends that one should be careful to never eat the amount of cake products exceeding the volume of 4 eggs. The reason for this is because the halacha regarding this matter is inconclusive as to whether the proper amount is 4 eggs or 21.5 eggs.

It is important to note that there are many opinions how to calculate the volume of eggs today. Some are substantially less than the numbers given above.