Scales Trump Sifters
I know that by weighing flour, as opposed to measuring it out, I can achieve more consistent results in my bread machine. My dilemma is that I have seen widely varying weights quoted for 1 cup of flour. Moreover, some references give different weights for different kinds of flour, while some, such as King Arthur, seem to say that all flours weigh the same. I'd like to find a list that has some solid, empirical testing behind it. Do you know of any reliable tables of weight vs. volume for solid ingredients?
Your predicament is undoubtedly shared by home bakers everywhere. I have seen everything from 99 to 160 grams quoted in various sources for the weight of a cup of so-called "all-purpose" flour.
I myself don't like to bake. My mother told me not to play in the mud, and to this day I feel uneasy about mixing milk, egg and flour batters (mud pies?) or kneading sticky dough with my hands.
But here's the crux of the problem: It all depends on what you mean by a "cup of flour." Cups can be filled in many ways, but weight is the only true indication of the amount of any substance.
Different types of flour do have different weights. Whole wheat flour is heavier than white flour, and bread flour is heavier still. That should come as no surprise, King Arthur to the contrary notwithstanding.
Home bakers can measure their cups of flour in different ways, but only two cupping rituals are commanded in the bible -- Rose Levy Beranbaum's "Cake Bible" (William Morrow, 1988): "spooning" and "dip-and-sweep." These two methods capture different amounts of flour, so of course the weights also will differ.
Her "Bible" defines spooning as removing spoonfuls of flour from its container and over-filling an opaque metal or plastic (either way, solid) measuring cup, followed by scraping a straight-edged spatula or knife blade across the cup's rim to remove the excess flour.
In the dip-and-sweep method, the measuring cup itself is dipped into the flour supply to remove a heaping cupful, after which a spatula is scraped across the rim.
So why can't the weights be measured once and for all for each method, so cooks can use whichever weight corresponds to the method they prefer?
Well, it isn't that simple.
Flour is a powder, and powders are notorious for settling down gravitationally into different densities -- that is, packing down to different degrees of compactness. For flour, the number of grams per cup depends on many factors, including the particle size, the shape -- not just the size -- of the measuring cup and even the humidity. Your "cupful" will weigh more if the flour is very fine (sand will settle more tightly than pebbles, which leave big air spaces), if the measuring cup is wide (settling will be more compact than it would be in a tall, narrow container) or if the humidity is high (moisture has weight).
And how do you fill the cup? In dipping and sweeping, do you dip the cup into a densely packed, supermarket five-pound bag (you'll get more weight per cupful) or a loosely filled, kitchen-counter canister (you'll get less weight)? Do you sift the flour (less weight) or not (more weight)? In spooning, do you sprinkle the flour gently from the spoon into the cup (less weight) or dump it in (more weight)? And do you tap the cup with the spatula to settle the flour (more weight) or not (less weight)?