Bulk fermentation is a process in which wild yeast and bacteria performs the process of fermentation on the flour and water to create sourdough dough. Bulk fermentation plays a crucial role in sourdough in the development of the flavor and structure of the final sourdough bread. Bulk fermentation works because the wild yeast that live in the sourdough starter create carbon dioxide gas, which becomes trapped within the gluten structure of the flour to create the rise of the sourdough bread.
If bulk fermentation is managed correctly, the resulting sourdough bread will be fluffy with an open crumb structure and pleasant taste. If bulk fermentation isnt managed correctly, the sourdough bread may develop a flat structure or a gummy texture. Bulk fermentation require the use of an active sourdough starter.
How to Do Bulk Fermentation for Sourdough
The sourdough starter should be at it’s peak activity prior to bulk fermentation begins. A sourdough starter is at peak activity when it have doubled in size, developed a domed top, and passes the float test in water. To prepare the sourdough starter, feed it four to twelve hours prior to bulk fermentation begins, and ensure that it is stored at a warm room temperature to encourage the activity of the yeast and acids within the starter.
An autolyse process, which involve mixing flour and water for thirty minutes, can be performed prior to bulk fermentation to allow the flour to hydrate and initiate the formation of a gluten structure within the sourdough. After you complete the autolyse process, add the active sourdough starter and salt to the mixture, aiming for a temperature of 75 degrees Fahrenheit. Bulk fermentation’s primary factor that influence the process is temperature.
If the temperature of the sourdough starter is 65 degrees Fahrenheit during bulk fermentation, bulk fermentation will take ten hours or more to complete, and if the bulk fermentation is performed at cooler temperatures, sourdough starter will produce acetic acid, leading to the sour flavor of sourdough. If the temperature of the sourdough starter is 75 degrees Fahrenheit during bulk fermentation, bulk fermentation will take between four and six hours to complete, and 75 degrees Fahrenheit will produce a mild flavor in the sourdough starter due to the production of lactic acid. If the temperature of the sourdough starter is 80 degrees Fahrenheit during bulk fermentation, bulk fermentation will take between three and four and a half hours to complete, but requiring closer monitoring of the sourdough starter due to the potential for overproofing of the sourdough.
Because temperature affects bulk fermentation’s speed, it is essential to use a digital thermometer to monitor sourdough starter during bulk fermentation. Bulk fermentation requires the performance of stretch and folds to create tension within the sourdough dough. Stretch-and-folds help to align the gluten within the sourdough.
Four sets of stretch-and-folds should be performed in thirty to sixty minute interval. The dough will start to become slack after thirty minutes of bulk fermentation, but will eventually become elastic with more stretch-and-folds. After bulk fermentation has begun, you can observe the dough for visual cues to indicate the progress of bulk fermentation.
During bulk fermentation, the dough will develop small bubbles on its surface, and will increase in volume. When the sourdough dough has increased to 50 to 75% of its final volume, and begins to jiggle and develop bubbles on the surface, bulk fermentation is nearly complete. Another way to determine when bulk fermentation is complete is the poke test.
The poke test involve lightly poking the dough with the fingertip. If the dough springs back almost instantly, bulk fermentation is not complete yet. If the dough returns to its original shape with partial elasticity, bulk fermentation is complete, and the sourdough can be pre-shaped.
If the dough does not spring back when poked, bulk fermentation has gone on too long, and the sourdough should be shaped immediately. The type of flour that is used will impact the bulk fermentation process; whole wheat flour will bulk ferment more faster than white flour due to the enzymes present in the whole wheat flour. If bulk fermentation has not occurred correctly, the sourdough will be underfermented.
Underfermented sourdough is tight to the touch, will not contain bubbles, and will form gummy bread. If bulk fermentation occurred too long, the sourdough will be sticky, collapse after being shaped, and produce flat bread. To avoid bulk fermentation issues, use an active sourdough starter and rely upon visual cues to monitor bulk fermentation rather than a timer.
Once bulk fermentation is complete, preshape the sourdough into a round shape and allow it to rest prior to final shaping. Finally, place the shaped sourdough into the refrigerator to perform a cold retard process overnight, which will enhance the flavor of the sourdough bread.