Dough Aeration Research Articles

The kneading process: A systematic review of the effects on dough rheology and resulting bread characteristics, including improvement strategies

BackgroundWorldwide, bread and other baked products are considered to be essential for human nutrition. Current research is focused on technological and nutritional improvements to products, via the application of innovative strategies. The kneading process is influenced by several parameters, notably kneading time, dough temperature, kneading speed, dough aeration, water temperature, and total water content. The correct management of the kneading process, and the application of improvement strategies, can significantly enhance dough rheology and resulting bread characteristics. Scope and approachThe aim is to provide a strong base on the current knowledge related to the kneading process, and its effects on dough rheology and resulting bread characteristics, in order to suggest specific strategies to improve the current process of bread making, thereby increasing its effectiveness, efficiency, and the quality of the final product. Key findings and conclusionsGood progress will be made only via the thorough understanding of the key parameters governing the kneading phase, and their importance and effects on the final products. These parameters should be managed by a dedicated, real-time control system that can determine the end of the process. Finally, the optimal improvement strategy should be applied as a function of production needs. The systematic development of innovations, and their implementation, will have positive effects not only on doughs and resulting bread products, but also on the productivity and profitability of manufacturing companies, and of the entire production chain.

Evaluation of bread dough aeration during kneading by an air-jet impulse system

This paper presents a novel system able to determine in touchless conditions some rheological properties of bread dough, by application of a force driven by a short air-jet impulse, and the concomitant surface displacement measurement by a laser interferometer. In this work, it is shown that in the FPD (Food Puff Device) is based on the displacement measurement due to an air jet by a laser interferometer test, a “softening” of the bread dough along the kneading process is observed, although it is well known that the bread dough gets strengthened by the kneading. This paradox is explained by the fact that, during the kneading, not only the dough become smooth and elastic, but a certain air amount is incorporated in the form of small air bubbles. FPD provides an empirical short time rheology test exciting the time scales linked to the air bubbles entrapped in the dough, so that the surface displacement is mainly due to the dough aeration. Demonstrating a good sensitivity to the air content, the FPD test seems a relevant method to follow the kneading process, in the aim of developing a tractable and efficient supervision tool. The bulk properties of the dough are also measured by a conventional creep recovery test in a rotational rheometer. An attempt of modelling the viscoelastic behavior in FPD treated like a creep-recovery test is proposed here, to provide some insights in the baking monitoring.

Effect of supplementation of wheat bran on dough aeration and final bread volume

One of the best ways to increase the fiber content in the diet is supplementing wheat bran in bread. Wheat bran is known to affect the cellular structure of the dough, resulting in lower final bread volume. The present study was focused on analyzing the effect of wheat bran in throughout the bread making process; the results were compared with the recipe without bran. Wheat bran at different level viz., 0%, 8%, 16% and 24% w/w on flour basis was added into the wheat flour for the preparation of sandwich bread. Results showed that wheat bran significantly (p<0.05) affected the dough kneading parameters. Dough properties like stickiness and extensibility decreased with respect to increase in bran quantity. Unexpectedly, wheat bran enhanced the aeration of dough during mixing and the expansion rate of dough during fermentation. However, wheat bran decreased the specific volume of bread upto 10.81%, which was confirmed using 2D image analysis method where it was observed as the wheat bran alters the pore size distribution in bread crumb.

Investigation of the influence of bakery enzymes on non-yeasted dough properties during mixing

Understanding the influence of bakery enzymes on dough properties during the early stages of the breadmaking process can help optimize the design of enzymes for the bakery industry. The objectives of this study were to determine whether bakery enzymes affected dough aeration during mixing and whether outcomes differed according to flour strength. Doughs were prepared from a strong breadmaking flour and a cookie flour to which various bakery enzymes were added. Dough density was measured, and the ultrasonic phase velocity and attenuation coefficient in the resonance frequency region for bubbles in dough were evaluated. Dough properties differed according to the enzyme and a significant interaction between enzyme type and flour strength was observed. For strong breadmaking wheat flour doughs, the greatest changes were observed for glucose oxidase, followed by xylanase and then cellulose. For the weak flour doughs, the largest changes were observed for doughs containing lipase and xylanase, with the effect of glucose oxidase being much less pronounced. The enzyme-dependent changes in acoustic signatures and in dough density demonstrate that some bakery enzymes influence bread crumb structure as early as at the mixing stage.

Impact on dough aeration of pressure change during mixing

This study aimed to provide a better understanding of the impact on dough aeration of pressure change during dough mixing with a spiral dough mixer with the possibility of controlling the temperature and the overhead pressure from −960 mbar to +500 mbar during mixing. The objectives were to understand the effect of pressure on dough during kneading in order to optimize dough kneading conditions. The well-known experimental strategy was to knead with overpressure to incorporate gas into the dough and maximize dough aeration then to subdivide the gas bubbles introduced in the previous step by applying a vacuum in the mixer's overhead. The results showed that dough aeration was proportional to the number of rotations of the spiral. The time to reach equilibrium was longer for a larger pressure drop. The kinetics of disentrainment were slower with the highest pressure drop.

Effect of sugar on bread dough aeration during mixing

The aim of this study was to understand better dough aeration and in particular to determine how aeration during mixing differs between sugar containing and non-sugar containing dough through modelling and X-ray tomography. Batches of non-yeasted bread dough were mixed using both ‘plain’ and ‘strong’ flours with systematically varying granulated caster sugar formulations. A modified Tweedy 1-type mixer was used and mixer headspace pressure was controlled at various constant values to determine steady state dough aeration conditions. Pressure step-change experiments were used to determine aeration dynamics. A population balance model was fitted to the data to enable quantitative determination of the gas entrainment rate and disentrainment coefficient. X-ray computed tomography studies and uniaxial extensibility tests were also conducted to explore further the results of the aeration studies. This method enabled the model to be fitted to the aeration step-change response using only one parameter. The main effects of granulated sugar in dough were to increase the disentrainment coefficient and, to a lesser extent, to increase the entrainment rate. The combined effect of these was a reduction in dough gas content as granulated sugar content increased.

Volume and texture improvement of gluten-free bread using quinoa white flour

Patients suffering from coeliac disease have to avoid traditional cereals-based products and depend on the availability of gluten-free alternatives. The gluten-free bread matrix and its foam stability are strongly affected by the choice of ingredients. In this study, the impact of quinoa white flour on bread quality parameters, in particular volume, has been investigated. The pseudocereal proved to be a suitable substrate for dough aeration using yeast, since considerably more glucose and a higher activity of α-glucosidase were found in comparison to rice and corn flour. Consequently, quinoa white flour was used to replace 40–100% of the rice and corn flour in a gluten-free control recipe. As a result, quinoa white flour enhanced the specific volume by 33%, which was related to the absence of bran components and the increased α-glucosidase activity. The significance of the latter was proven by separately adding sucrose and fungal amyloglucosidase to the control recipe. Moreover, the crumb featured homogeneous and finely distributed gas bubbles and the taste was not compromised. Thus, it was possible to improve the quality of gluten-free bread by using quinoa white flour, which might be a relief for coeliac patients.

Bread dough aeration dynamics during pressure step-change mixing: Studies by X-ray tomography, dough density and population balance modelling

Industrial bread dough mixing often involves a period of mixing under high headspace pressure to enhance oxygen availability, followed by a period of partial vacuum to favourably manipulate the final bubble size distribution. This paper presents the results of a study using X-ray tomography to measure the gas bubble size distribution in dough samples over the course of a pressure step-change mix. The first objective of the current work was to measure bubble size distributions at points throughout a pressure-step dough mixing process using a non-synchrotron X-ray source. The second objective was to fit a simplified population balance model to the measured size distributions. The third objective was to use the data set and fitted model to explore the validity of the assumptions within the simplified model and to consolidate understanding of underlying aeration and mixing phenomena and the resultant process dynamics. It was found that the dynamic changes in the bubble size distribution of a bread dough during pressure-step mixing could be accurately measured using a laboratory X-ray source. The response of the cumulative dough voidage to a pressure-step change during mixing could be reproduced very well using the simplified population balance model (which assumes: all entrained bubbles are the same size, no bubble break-up or coalescence, and likelihood of bubble disentrainment is proportional to bubble volume). The measured response of the bubble number density and mean volume agreed reasonably well with that predicted by the simplified model (with parameters fitted to only cumulative voidage data). It is demonstrated that the decrease in number density following a pressure step-decrease is much more short-lived than the decrease in size which is permanent.

Aeration of bread dough influenced by different way of processing

The effect of steady shearing versus z-blade mixing on mechanical aeration and gas retaining ability of the dough during processing and subsequent proofing and bread baking stages was investigated. Reduction in moisture content led to reduction in both static and dynamic densities of z-blade mixed dough. At low moisture content, dough had higher consistency and tended to physically entrap more air bubbles upon processing, leading to a higher dough volume and, thereby a low density. The results showed that both processes led to similar mechanical aeration as measured by static dough density immediately after processing. Shearing at a low rotational speed, led to similar proofing dough volume as z-blade mixing did. Nevertheless, both dough expansion test and breadmaking trials showed a significant reduction in gas retaining ability of sheared dough, especially at higher rotational speeds. This is explained by the fact that higher shear rates could break up the gluten network and negatively influence gas retaining ability. The results revealed the influence of processing conditions; e.g. the type of deformation flow on dough aeration. Furthermore, it was shown that rotational speed in the shearing system influences the aeration and gas holding ability of the dough during proofing and baking processes.

Effect of fat level, mixing pressure and temperature on dough expansion capacity during proving

In this work the effect of fat content on dough aeration during proving was investigated using dynamic dough density measurements. Doughs of three different fat levels (0%, 0.04% and 0.2% flour basis) were mixed under various pressures using a Tweedy mixer and proved at five different temperatures (30, 35, 40, 45 and 50 °C) in the dynamic dough density system. The dough expansion capacity and the time of the gas loss of each dough sample were measured and related to fat level, mixing pressure and proving temperature. The time of gas loss decreased with increasing proving temperature for all fat levels, as expected due to increasing yeast activity and reduced carbon dioxide solubility. The final gas capacity of dough is affected by the mixing pressure and the temperature. Fat content had no significant effect on the time of the loss of gas retention or the dough's final expansion capacity. However, fat affected the pattern of gas loss towards the end of proving; thus in doughs with fat, the gas loss rate occurred smoothly and gradually, in contrast to the doughs with no fat that exhibited sudden gas loss. The findings demonstrated that the dynamic dough density method is a sensitive, straightforward technique for the investigation of factors affecting gas retention in bread doughs.

Dough aeration and rheology: Part 3. Effect of the presence of gas bubbles in bread dough on measured bulk rheology and work input rate

AbstractThe effects of dough aeration on measured bulk rheology of dough were investigated by preparing doughs with various gas contents and assessing their rheology under large deformation biaxial extension using the SMS Dough Inflation System. Doughs were mixed to various gas contents using a laboratory‐scale mixer, the Tweedy 1, at various mixer headspace pressures. In order to consider the effect of oxidation processes, doughs were mixed in air, in nitrogen and in a controlled oxygen‐nitrogen atmosphere in which the partial pressure of oxygen was kept constant. In the latter two cases a flow rate of gas through the mixer was maintained, while the doughs mixed in air had a static headspace. Dough aeration was quantified using density measurements. The dough rheology tests were performed under two different modes: constant volumetric air flow rate; and constant strain rate at two levels, 0.1 and 0.05 s−1. Analysis of the stress–strain data of an inflating dough bubble using an exponential model enabled the strain hardening index, failure strain and failure stress to be determined. The strain hardening index, failure strain and failure stress decreased with gas content, indicating that gas bubbles in dough disrupt the integrity of dough structure. The faster strain rate tended to give higher values of all parameters and to be more discriminating, while testing at a constant volumetric air flow rate gave lower values. Doughs mixed under a constant partial pressure of oxygen resulted in the strain hardening index being minimally affected by the gas content, although failure strain and failure stress decreased with increasing gas content in the dough. The flow of gas through the mixer appeared to affect dough aeration and rheology, and the rate of work input was found to increase with increasing mixer headspace pressures. These suggest that dough aeration not only affects the rheology of static dough through the physical presence of gas bubbles following mixing, it also affects the development of its rheological properties within the mixer, through the physical presence of the bubbles affecting the rate of work input that develops the doughs, and also through the turnover of air that supplies oxygen to facilitate this development. Copyright © 2005 Society of Chemical Industry

Dough aeration and rheology: Part 1. Effects of mixing speed and headspace pressure on mechanical development of bread dough

AbstractA laboratory‐scale Tweedy‐type mechanical dough development mixer was modified to monitor work inputs of dough during mixing through a computerised data acquisition system. Recorded torque showed a curve that increased to a peak about midway through mixing. Using this system, the effects of mixing speed and pressure on the development of doughs made from strong and weak flours mixed to a work input of 40 kJ kg−1 were studied. Mixing was characterized in terms of peak torque and torque at the end of mixing (end torque), and in terms of the number of blade revolutions at these two reference points. The peak torque and the end torque both increased with increasing mixing speed. The peak torque increased with increasing mixer headspace pressure, but the end torque did not. The number of blade revolutions to both the point of peak torque and to the end of mixing decreased with increasing mixing speed for both flours, implying dough development at higher speeds was more efficient. Increasing headspace pressure reduced the number of revolutions to the peak, but not to the end of mixing. These results provide evidence that achieving dough development is not independent of mixing speed in Tweedy‐type mixers, and that dough aeration, as affected by mixer headspace pressure, affects dough rheology and hence development in the mixer. Copyright © 2005 Society of Chemical Industry

Dough aeration and rheology: Part 2. Effects of flour type, mixing speed and total work input on aeration and rheology of bread dough

AbstractThe aeration and rheological properties of bread doughs prepared from strong and weak flours at various mixing speeds and work inputs in a high‐speed laboratory‐scale mixer were investigated. Dough aeration was quantified in terms of gas‐free dough density and gas void fraction using density measurements, while dough rheology was characterized in terms of the strain hardening index, failure strain and failure stress under large biaxial extensional deformation using the SMS Dough Inflation System. Increasing mixing speed had little effect on the gas‐free dough density but increased the void fraction of gas occluded in dough. As mixing progressed, the gas‐free dough density initially increased, more dramatically for the weak than the strong flour, before reaching a plateau at approximately 30 kJ kg−1 energy input. The gas content tended to increase over the range of work inputs tested. For both flours, the strain hardening index, failure strain and failure stress increased with work input initially, followed by a decrease. The absolute values were all higher for the strong flour, while maximum values and the work input at which the maximum occurred depended on the mixing speed. These results show that both aeration and rheological characteristics of dough are dependent on both the total work input and the work input rate. The results also demonstrate the facility of the Dough Inflation System to describe the mechanical development of dough rheology over the course of high‐speed mixing. Copyright © 2005 Society of Chemical Industry

Aeration During Bread Dough Mixing: I. Effect of Direction and Size of a Pressure Step-change During Mixing on the Turnover of Gas

The aeration of bread dough during mixing has previously been modelled as a balance between gas entrainment and disentrainment into and out of the dough, from which the gas turnover time was determined. This paper tests this model by mixing dough in a high-speed Tweedy-type mixer which undergoes a pressure step-change midway through mixing. The volume of gas entrained in the dough following the pressure change was calculated from its density. The volume of gas entrained was found to reach a steady state much more quickly following a pressure step-decrease than an increase, appearing to signify gas turnover rates over twice as large. Thus, gas disentrainment was found to be enhanced following a pressure step-decrease in a manner not incorporated into the model. The size of the pressure step-decrease did not appear to affect the gas turnover time, but increasing the pressure step-increase size decreased the gas turnover times. The weak flour doughs exhibited higher gas turnover rates during mixing than the strong flour doughs, in both pressure stepchange directions and at all step-sizes.

Aeration During Bread Dough Mixing: II. A Population Balance Model of Aeration

A novel model for the aeration of dough during mixing is presented. A population balance model was used to model bubble entrainment, break-up and disentrainment over the whole duration of a mix. Following a series of simplifying assumptions, including that all bubbles are entrained with the same volume, the model parameters were fitted to original and previously published experimental dough voidage profiles over the duration of a mix involving a pressure step-change. The assumption that no bubble breakup occurred during mixing enabled a simple model to be derived which quantitatively represented the experimental data, for both a pressure step-up and down midway through mixing, with two mixing parameters: the volumetric entrainment rate and the disentrainment coefficient. Assuming that instantaneous bubble break-up occurred enabled a model to be derived which, with the same two parameters, could qualitatively represent experimental bubble number densities calculated through measurements of dough bubble size distributions.

Measurement of Dynamic Dough Density and Effect of Surfactants and Flour Type on Aeration During Mixing and Gas Retention During Proofing

ABSTRACTA new method for measuring dough densities is presented, based on weighing small dough samples in air and immersed in xylene. The method can be used to evaluate the air content of low‐density doughs and to follow the changing density of a proofing dough sample. The method is applied to evaluate the effect of flour strength and surfactant addition on dough aeration and subsequent proofing. Doughs were mixed in a high‐speed mixer from two flours, a strong breadmaking flour and a weak flour. Surfactants sodium stearoyl lactylate (SSL) and diacetyl tartrate esters of monoglyceride (DATEM) were added at three levels, and the air content, proofing dynamics, and baked loaf quality were evaluated. The air content of dough was proportional to headspace pressure in the mixer, while the strong flour occluded less air than the weak flour. Surfactants greatly improved the volume of baked loaves but appeared to have no significant effect on air incorporation during mixing. The addition of surfactants appeared to increase the rate of growth of the dough piece during proofing, possibly due to increased bubble breakup during mixing or to increased rates of mass transfer of CO2 into bubbles during proofing.