In this question, I learned that one measures the amount of flour used to determine whether challah separation is necessary. Here I learned that there is a difference of opinion between (some) Sefardim and Ashkenazim whether a K'zayit is measured by weight or volume.
My question now is, can one use the amount of ingredients in a recipe to calculate how much of the prepared food is a K'zayit? This would be useful when determining how much is needed to eat to make a blessing over the hand washing, and say the Grace After Meals.
Here's an example which focuses on the volume, but the same question would apply to weight if the igredients were weighed instead of measured by volume. For the sake of simplicity we'll assume that all parts get distributed equally:
- 2 cups of flour (473.1764725 Cubic Centimeters)
- a dash of baking powder
- 1/2 a cup of oil (118.29411812499998 Cubic Centimeters)
- 3/4 of a cup of water (177.4411771875 Cubic Centimeters)
According to this article, R' Avraham Chaim Na'eh holds that the stricter definition of a K'zayit is 27 cubic centimeters, while the Chazon Ish holds that it is 47.5 cubic centimeters.
So my question now is, can I add up all the cubic centimeters used in the recipe, divide by 8 and use that information to determine how much of the tortilla is a K'zayit? If I add it all up, the recipe calls for a total of 768.911768 cubic centimeters. This means that each tortilla uses 96.113971 cubic centimeters of ingredients.
Can I therefore say that one tortilla is 2 K'zaytim according to the Chazon Ish, and 3.5 K'zaytim according to R' Avraham Chaim Na'eh? Is this a valid halachic way to determine the volume of a food item, or are there other factors that must be taken into account?