Leavened breads are those lifted by tiny bubbles. Most of the bread we eat today is leavened, with a few exceptions for items such as tortillas or other flat breads. The lift is provided by chemical, mechanical, or biological reactions. Chemical reactions provide the lift for quick breads, which are your typical muffins, banana bread, and other goods such as pancakes. Mechanical leavening involves beating air into the batter which is quickly baked to set the dough. Finally steam can be utilized, as seen with popovers and English puddings.
In our bread making series we are concentrating on the lift provided by biological reactions. Specifically that of yeast. If I become quite brave, I may experiment with salt rising bread, which creates a different environment more suitable to the growth of a specific bacteria as opposed to yeast.
Our first forays into bread making will use store bought yeast as described in the introduction to yeast. Later in the series we will cover wild yeast which requires longer rise times, a little more patience, and a willingness to experiment. (Currently I’m working on creating a successful starter for sourdough).
So how does yeast give bread its lift? The yeast cells digest the sugars and starches provided and give off carbon dioxide. The proteins in the dough trap the gas like tiny balloons. If the flour has not been worked enough, through kneading, the gluten proteins are too stiff and the carbon dioxide cannot provide lift for the bread. It’s like trying to blow up one of those long balloons used for shaping or blowing bubbles with a brand new piece of gum. If the dough has been overworked, many of the strands of protein have been broken and the bubbles cannot trap the air – imagine trying to blow bubbles with peanut butter. Use the window test as you near the indicated time frame for kneading.
For the window test, take a golf ball size piece of dough and stretch it into a square using your thumbs and index fingers. The dough should stretch far enough to allow light to pass through before the fibers break. If the strands snap too soon, the dough needs more work.
In addition to proper kneading, time, temperature, and humidity all play a factor in creating loft. Warmer temperatures increase the activity of the yeast creating carbon dioxide faster, be careful, if you get too warm, the little boogers will die off. I like to turn my oven on for one or two minutes, and place the bread inside to rise. Always cover the dough, in drier climates use a damp towel or place a shallow dish of warm water on the lower rack of the oven. Some recipes will suggest an overnight rise in the fridge. The cool temperatures keep the growth of the yeast in check, while allowing additional flavor development.