Originally Posted by Michael in FtW
OVERVIEW of PROBLEM: Converting flour weight to volume in a bread recipe
ASSUMPTIONS: We need to make a few assumptions here to try to avoid me leading someone off in the wrong direction this time.
1. We are using US standard weights and measures ... 1 Cup = 16 Tablespoons
4. The "serving size" information on the side of the bag is correct for US measurements (cups, spoons) and only an approximate for the metric weight conversion due to rounding errors.
You have a bread recipe that lists volumes for everything but the bread and wheat flour - and those are given in pounds and ounces .. and you don't have any scales. What to do?
The recipe calls for
1-lb 1-oz Bread flour
1-lb 2-oz Wheat flour
...you read the information on the side of each bag.
BREAD FLOUR: A serving size is 1/4 cup (30g)
WHEAT FLOUR: A serving size is 3-Tablespoons (31g)
Rounded to the nearest quarter-cup - how many cups of bread flour and wheat flour do you need?
BONUS POINTS: How did you calculate your answer?
As a mathematically challenged little old lady, here's what I came up with. I think you will need
: ~16 1/4-cup units OR ~4 cups
: ~12 1/4-cup units OR ~3 cups
Here's how I arrived at my answer...
The key points from Michael's post are
> The "serving size" information on the side of the bag is correct for US measurements (cups, spoons) and only an approximate for the metric weight conversion
> the premise that 1 Cup = 16 TBS and therefore that 1/4 cup = 4 TBS (this is correct for liquids but not necessarily for solids like flour)
step 1: convert flour measurements to oz
REQUIRED AMOUNT IN OZ
Bread flour 17.00 oz (1 lb + 1 oz)
Wheat flour 18.00 oz (1 lb + 2 oz)
step 2: calculate what % of the total 5-lb flour sack is required, given the sack weight (80oz) and the required recipe amounts in oz
REQUIRED AMOUNT AS % OF 5LB FLOUR SACK
Bread flour 21.25% (17 / 80)
Wheat flour 22.50% (18 / 80)
Michael wants the answer in 1/4-cup units (rounded) so I can calculate the answer easily for bread flour
since the serving size is in 1/4 cup units, there are a total of 75 servings in the sack and I need 21.25% (by weight) of the sack for the 17oz of bread flour called for in the recipe.
REQUIRED AMOUNT IN 1/4-CUP SERVING SIZE UNITS
Bread flour 15.94 1/4-cup units (75 * .2125)
is more complicated, since the serving size is 3TBS
and Michael says to assume that there are 4TBS per 1/4 cup of flour
There are a total of 72 servings in the sack and I need 22.50% (by weight) of the sack for the 18oz of wheat flour called for in the recipe.
REQUIRED AMOUNT IN 3 TBS SERVING SIZE UNITS
Wheat flour 16.2 3-TBS units (72 * .225)
But now I have to get my units from the 3-TBS serving size on the sack to the 1/4 cup (4 TBS) measuring unit that Michael wants.
First, I'll calculate how much wheat flour I need using TBS as the unit of the measure. I get total of 48.6 TBS (16.2 * 3) TBS.
Next, I'll divide 48.6 TBS by 4 since we assume that it takes 4 TBS flour to get 1/4 cup flour. This gives me
REQUIRED AMOUNT IN 1/4 CUP SERVING SIZE UNITS
Wheat flour 12.15 1/4-cup units (48.6 / 4)
======= COMMENTS =======
In baking, flour (and other solids) really should be weighed, not measured. For example, when I measure flour using level TBS into a 1/4 measure, it only takes me 3 TBS to make 1/4 cup, not 4 TBS.
The purchase of a "plain vanilla" digital scale (about $30) would eliminate a lot of the head scratching that went on here (including mine!).
cheers to all =