What is Fermentation?
Fermentation in baking is a process where yeasted dough rises, developing volume and flavor. It occurs when yeast converts sugars present in flour into carbon dioxide and ethyl alcohol.1 CO2 gas is trapped by the gluten network in the dough which causes the dough to rise. Fermentation produces the leavening action which results in a light and airy crumb in bread products.
The use of fermentation to make bread rise can be traced to the Egyptians in 3000 BC. In 1854, the French chemist Louis Pasteur determined that it is caused by yeast.2 In 1907, a German chemist named Eduard Buchner received the Nobel prize for showing that enzymes in yeast cells cause fermentation.2 Two decades later, Arthur Harden and Hans Euler-Chelpint determined exactly how yeast enzymes cause this process. They won the Nobel Prize for their work in 1929.2
Fermentation influences product volume, shape, crust color, and crumb cell structure.4
The yeast used for bread manufacturing, Saccharomyces cerevisiae, converts the fermentable sugars present in the dough into carbon dioxide and ethanol as the main products. The intensity depends on the form of the yeast and the availability of fermentable sugars in the flour, including glucose, sucrose, and maltose produced by starch hydrolysis.3
Industrially produced wheat bread is often made from dough with a high concentration of yeast and the dough is fermented at a high temperature in order to decrease the production time. However, longer fermentation time results in bread with a more pleasant aroma. Aroma development in bread crumb has been found to be dependent on yeast concentration, mixing stage and time.3
35 °C is the recommended temperature for commercial production of bread dough. Some studies have suggested to ferment the dough at a low temperature (5°C) with high concentration of yeast (60 g/kg flour) in order to develop bread with a relatively short production time combined with a high concentration of esters (characterized as having a fruity and pleasant aroma) and a low concentration of hexanal and heptanal (characterized as off-flavors).3
Aroma compounds identified in fermented bread crumb are mainly derived from the metabolism of yeast and from the oxidation of flour lipids, whereas the aroma compounds in the crust originates from Maillard reactions occurring at high temperatures and low water activity between reducing sugars and amino acids.3
Commercial dough fermentation may include the following steps: bulk fermentation, intermediate proofing, and final proofing.
Bulk fermentation is the period in which the dough is maturing just after the dough has been mixed. The dough is still in its bulk form prior to dividing into unit pieces for processing, proofing, and baking.4 The length of time can vary from 0-15 minutes (a no-time dough) to 4-5 hours (traditional baguettes or sourdough). An optional process of pre-ferment, in which a certain fraction of flour and water are combined and fermented before the final dough is mixed, is sometimes used to shorten the time.
Intermediate proof is the period between dough division and loaf shaping, which is usually 15-30 minutes.
Final proof is the period after shaping in which the loaves are able to double in size before they are placed in the oven, which is about 45-90 minutes. However, the final proof could be 3-5 hours for some artisan-style bread or sourdough varieties. There is a remaining period of fermentation called oven spring in the first 5-10 minutes of baking before the yeast dies from exposure to the rapidly increasing loaf temperature.
- Ali, Akbar, et al. Yeast, its types and role in fermentation during bread making process-a review. Pakistan Journal of Food Sciences, vol. 22, no. 3, 2012, pp. 171–179. http://psfst.com/__jpd_fstr/63f9e07b9aa310709ce11c70ac9bf266.pdf. Accessed 10 August 2017.
- History of fermentation. Cell process and energy. Pearson Prentice Hall, 2012, pp 87.
- Birch, Anja N., Mikael A. Petersen, and Åse S. Hansen. The aroma profile of wheat bread crumb influenced by yeast concentration and fermentation temperature. LWT – Food Science and Technology 50.2 (2013): 480-488.
- Cauvain S.P. Baking Problems Solved, 1st ed., Woodhead, 2001, pp.147, 194–195.