Q: Bread recipes always say that the amount of flour needed may vary depending on humidity and moisture content, but my automatic bread machine does quite well using the same amount of flour each time. How can that be?

The idea that the amount of flour required in a bread recipe will vary because of humidity is actually a kitchen myth.  I spoke about that a bit in the earlier post KitchenSavvy Kitchen Science .  The variation actually comes from the protein content of the flour, which changes from region to region and year to year, even within the same variety of wheat, depending on rainfall, temperature, and other factors.

In baking, the proteins glutenin and gliadin in the flour bond with the water and with each other to form long strands and sheets of what we know as gluten.  The gluten acts like small balloons that fill with gases which make bread rise and give the characteristic texture, called the crumb.

Flours used for different applications have different protein levels.  Bread flour has about 12% protein by weight, all-purpose about 10% to 11%, and cake flour as low as 8%.  These are general numbers and may differ from region to region.  Also, unbleached all-purpose flour usually has a higher protein level than bleached.  To see the effect of protein content, try making a mixture of flour and water using a ratio of about two units of flour to one unit of water, by volume, using different types of flour.  The lower the protein level, the wetter the result.

In earlier times, the amount of protein was less tightly controlled than it is now.  Flours were milled directly from the available wheat regardless of protein content.  That meant that the consumer had little or no ability to control how their flour performed.  Lacking a better explanation, the common belief was that the humidity was affecting the amount of water absorbed.

Nowadays, millers can separate out and recombine the various components of flour to produce very consistent results.  The same flour from the same mill will behave pretty much the same from batch to batch, so bread making and other baking has become much more consistent and controllable.

This is why your bread machine produces consistent results.  If the instruction book for your machine is anything like mine, it has some reliable general recipes and a troubleshooting guide.  The guide tells you how to adjust the levels of the various ingredients to get a satisfactory loaf.  You will notice that the recommended variations in the amount of flour are small, one or two tablespoons in a three cup loaf, rather than the cup, more or less, in cookbook recipes.  The bread machine counts on the consistency of the protein in your flour and helps you to adjust for regional differences.

So, bread machines have helped to dispel a common kitchen myth by defying popular wisdom.