03 Dec Which mechanisms impact the volume?
Volume is a decisive quality criterion in many bakery goods. Two factors are responsible for that volume: firstly, the volume of gases produced during the final proofing under the effect of fermentation; secondly, the gas retention capacity, not just during final proofing, but also during the first few minutes of baking, during which time the dough mass will swell and stabilise at its final volume (Inra, 1994). This article takes a look at the mechanisms responsible for gas retention in bread dough.
The role of gluten in improving gas retention in dough
While the carbohydrates in flour, in their capacity as substrates for fermentation, play a major role in the production of the gases required for obtaining volume, (see. Short text The gas volume resulting from CO2 production), it is the wheat proteins that will ensure their retention in the dough.
The glutenins and gliadins in dough are what helps to produce the visco-elastic protein network known as gluten. The gluten is formed through the hydration of the flour during mixing. Many types of bonds exist between gliadins and glutenins, of which the most robust are the disulfide bridges (covalent bonds). These play a key role in ensuring the network’s cohesion.
How is the gluten network formed in breadmaking?
The mixing process is organised into several stages during which the gluten network is gradually formed (Le Blanc, 2007):
- the basic mixing stage consists in mixing the basic ingredients together. In the process, water is dispersed throughout the flour particles and absorbed by the gluten proteins and starch;
- intensive or high-speed mixing consists in subjecting the dough in the mixer to all kinds of mechanical actions, such as shearing, stretching and compression, as well as beating (during which air is incorporated). It is during this last phase that the gluten network is formed and imprisons the starch grains. The air trapped in the dough during the beating phase forms micro air-holes, which will serve as niches for the CO2 produced as a result of fermentation. A correctly structured gluten network will result in optimum gas retention, which in turn improves dough development.
Softening of gluten
Some especially strong flours can give rise to the development of short gluten that is lacking extensibility, for which there are three technical remedies:
- An intermediate autolytic stage, added between the basic and intensive/high-speed mixing phases can improve the end result. This technique consists in making a dough from flour and water alone, and leaving it to rest for 15 minutes to several hours after basic mixing, or after a few minutes of intensive mixing. During this time, the gluten proteins undergo hydrolysis through the action of the proteases in the flour. This helps to relax the gluten network and increase its extensibility, thus resulting in increased volume and consistency in the end products (the extensibility of the dough reduces the resistance to gas thrust).
- Yeast-based pre-fermentation techniques, which consist in making a sponge from a mixture of water, flour and baker’s yeast and which have the same effect in terms of softening the gluten.
- Addition of deactivated yeast, which limits the formation of disulfide bridges between the gluten filaments. The protein chains slide in and out of each other more readily, thus promoting volume and reducing shrinkage in the dough balls.