White Flour and Wheat Flour — A Discussion
I’ve been spending a lot of time lately trying to understand the chemistry of baking. Here’s my current project: understanding the effect of substituting whole wheat flour for white flour in bread recipes.
I decided to be scientific about this. I found 12 highly-rated bread recipes (from allrecipes.com and other sources): 6 white bread recipes and 6 that substituted some or all of the flour with whole wheat flour. All used only 6 ingredients: water, oil, sugar, salt, flour, and yeast.† I scaled each recipe so that they were comparable, and I averaged the amounts of the ingredients.
I found some interesting things — some surprising, some not.
First, more water is needed in whole wheat bread, because the bran and germ absorb more water. The “ideal” flour/water ratio is 2.8:1 (by volume) for white flour and (based on some calculations) about 2.5:1 for whole wheat flour. So, if you have 1 cup of white flour and you replace it with 1 cup of wheat flour, you need to add about 2 tsp more water.
Second, a loaf of wheat bread uses less oil — about 1 Tbsp instead of 2 Tbsp. At first, I thought this was because the whole wheat flour contains the fat-rich germ of the wheat. But I’m not sure this is the answer. Three cups of whole wheat flour contains 6 g more fat than white flour, which is closer to a teaspoon than a tablespoon. It might also be that the longer rising time (more on this below) means that less oil is needed to lubricate the gluten strands as they form the structure of the bread. (Just a guess.)
Or — and this is a recurring problem in trying to understand the whys wherefores of baking — this could just be based on custom. After all, recipes are memes. They get random mutations, and various selective factors determine which recipes are successful and replicate. One mutation in an influential recipe for whole wheat bread — even if based in nothing scientific — could affect lots of “downstream” recipes.
The biggest difference was in the yeast. A bread with 3 cups of white flour calls for about 2.5 t of yeast. Replacing half of that with wheat flour reduced the yeast to 1.5 t. This is a huge change, and for a few minutes, it really stumped me.
At first, I thought this might be because people add more sugar to whole wheat bread, to make it more palatable, and the yeast created that much more CO2. But that didn’t seem to be the answer. The “average” wheat bread upped the sugar from 3 Tbsp to 4 Tbsp. But individual recipes ranged from 2 Tbsp to 5 Tbsp for wheat bread and 1.5 Tbsp to 5 Tbsp for white bread. Clearly, bread is not as sensitive to the sugar content as you might think.
But then it hit me: rising time. Whole wheat breads require much more rising time. In my bread machine, for example, a white bread cycle has 95 minutes of rising time. The wheat cycle has 125 minutes of rising time.
Why is this? I found the best answer on the amusingly-named “breaducation” website.
The bran flakes and germ in whole wheat flour act like tiny little razor blades that shred these strands, inhibiting gluten development. The more whole wheat flour you use the more bran and germ there is in the dough and the more the gluten gets shredded. This is why as you increase whole wheat flour you usually must expect a decrease in loaf volume.
To allow for proper gluten formation, you need to let the bread rise longer. Much longer. But if you put the same amount of yeast into the recipe, your bread would have erupted out the top of your bread machine by the time the gluten network had formed. So, less yeast for wheat bread.
So, that’s my first foray into food chemistry. If you liked it, please lick the heart button below to recommend it to others!
† Actually, this is not entirely true. Many of them used honey. But this is just a matter of conversion. If you assume that honey is effectively sugar and water, 1 Tbsp of honey has roughly 17 g of sugar and 4 g of water. This comes out to roughly 4 tsp of sugar and 1 tsp of water.
