Grant M. Campbell

Creation and characterisation of aerated food products

A diverse range of foods are aerated, using a similarly varied assortment of processing methods. Aerated foods are generally poorly understood, but are of increasing importance as manufacturers seek to exploit the novelty and versatility of bubbles as food ingredients. Food aeration is one of the fastest growing unit operations, while many ingredients achieve their functionality through their effects at bubble interfaces. This paper reviews the range of aerated foods, and attempts to bring some structure to their diversity by examining different bases for classification. Experimental approaches for characterising aerated foods are discussed. Although food foam chemistry is reasonably well understood, the physical behaviour of bubbles in food systems is less well appreciated. Models describing the dynamic behaviour of bubbles as physical entities are reviewed.

On predicting roller milling performance - Part II. The breakage function

The mathematical relationship (breakage equation) between the inlet and outlet particle-size distributions of a roller milling operation is described, and the breakage function linking the two is defined. The forms of the breakage equation and the breakage function are different for roller milling than for other comminution operations, such as hammer milling or ball milling. The breakage equation is discretised to give a matrix form, from which it is demonstrated that during roller milling of wheat, particles break independently of one another. This is an important assumption of breakage equations for many comminution operations and experimental results are presented, which confirm its applicability to the roller milling of wheat grains. Breakage matrices are successfully used to predict the outlet particle-size distributions from First Break milling of wheat. Later papers in this series consider the form of the breakage function.

Discrete particle motion on sieves - A numerical study using the DEM simulation

This paper presents a mathematical investigation of particulate motion on an inclined screening chute using the Discrete Element Method (DEM). Special attention has been paid to the implementation of an apertured boundary and the algorithm for allowing particles to pass through apertures or to rebound when approaching the screen surface. Computational experiments have been conducted to examine the undersize particle motion across the material layer and through the apertures for bimodal mixtures comprising two different sizes of spherical polyethylene pellets. Discrete particle motion at different regions along the screen has been discussed in relation to the physical mechanisms inherent in the solids separation process and their determinative role on screening efficiency. Simulations have demonstrated the negative effect of near-mesh size particles and the positive role of relatively large particles on screening operations and the crucial effect of particle segregation in material layers. Comparison of screening rate along the screen with experiments has demonstrated adequate agreement. This computational study has shown the advantages of using DEM to understand the complex solids separation process. Further works are envisaged to focus on the development of advanced experimental techniques and the implementation of DEM for sieving processes involving moving screens.

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

ABSTRACT A 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 ...

Proving of Bread Dough I: Modelling the Evolution of the Bubble Size Distribution

Models for the growth of bubbles are reviewed. A model of the growth of bubbles during proving of bread dough is then presented, based on diffusive mass transfer of carbon dioxide gas into a population of bubbles. The model incorporates the rate of gas production by yeast and the bubble size distribution, and is solved to simulate the dynamic growth of these bubbles. The effects of the number and size of bubbles and the proving temperature and yeast concentration on the growth of the dough piece are simulated. A greater number of bubbles in the dough, which would be achieved by mixing at higher pressures, results in an initially more rapid transfer of gas into the bubbles. Consequently there is a slower increase in carbon dioxide concentration in the liquid dough phase, such that later during proving the rate of bubble growth slows. Increasing yeast level increases the rate of gas production and hence the growth of the dough piece. Increasing temperature similarly increases the rate of growth of bubbles, partly due to the increased rate of gas production, but also as a result of the decreased gas solubility at higher temperatures.

Proving of bread dough: Modelling the growth of individual bubbles.

Proving of bread dough was modelled using classical one-component diffusion theory, to describe the rate of growth of bubbles surrounded by liquid dough containing dissolved carbon dioxide. The resulting differential equation was integrated numerically to predict the effect of initial bubble size and system parameters (carbon dioxide concentration, surface tension at the bubble interface, temperature) on bubble growth. Two situations exist, potentially; the dough could be either supersaturated or subsaturated with carbon dioxide. When the dough is supersaturated, the model predicts a critical bubble size above which bubbles grow indefinitely,while belowthe critical bubble size bubbles reach a limiting size and stop growing. The critical bubble size decreases with increasing carbon dioxide concentration and increases with increasing surface tension.Below saturation, all bubbles reach an upper size limit proportional to their initial size. The final bubble size increases with carbon dioxide concentration and decreases with increasing surface tension. Higher temperatures increase the rate of bubble growth and reduce the critical bubble size for supersaturated doughs, by increasing the value of Henry’ s Law constant. Higher temperatures also increase the final bubble size for subsaturated systems. The model could be extended to include yeast kinetics and entire bubble size distributions, to develop a full simulation of the proving operation.

Proving of Bread Dough II: Measurement of Gas Production and Retention

Dynamic dough density measurements were applied to monitor the rate of production of carbon dioxide gas during proving and its partitioning between the liquid phase and the bubbles in bread dough. The effects of yeast concentration, temperature, mixing speed, headspace pressure and sugar level were investigated. Increasing yeast level increased the rate of carbon dioxide production, as did increasing temperature up to 40°C, beyond which the production rate decreased. Mixing at low pressures resulted in fewer bubbles in the dough and a smaller interfacial area for mass transfer into bubbles; consequently the carbon dioxide concentration in the dough increased rapidly initially. This was followed by rapid growth of the few bubbles present, as a result of the high carbon dioxide concentration in the liquid phase, and sudden and rapid decrease of the dough density. Mixing at higher speeds increased the air content, but gave slightly slower rates of growth of the dough piece. The apparent drop in the rate of carbon dioxide production as proving proceeded was not caused by depletion of sugars, but rather by loss of gas from the dough piece. The results were compared with simulations of proving of bread doughs, giving good qualitative agreement; however, loss of gas from the dough pieces caused the rate of carbon dioxide production to be underestimated and resulted in deviations from the simulations.

A numerical simulation of separation of crop seeds by screening: Effect of particle bed depth

Effective separation and grading of cereal grains and crop seeds are of importance in the production of quality cereal foods. This paper presents a two-dimensional numerical study of the separation process of crop seeds by screening, using the Discrete Element Method (DEM) modelling technique. Computational experiments have been conducted for the separation of two common crop seeds, soybeans and mustard seeds, using a vibrating screen. The screening rate and the required screen length at different feeding rates are discussed in relation to the discrete particle motion on the screen. This study has demonstrated the crucial effect of particle bed depth on screening efficiency. For a screening system involving granular materials, the critical feeding rate for the most effective screening operation can be determined via conducting the DEM simulation.

Effect of Roll Fluting Disposition and Roll Gap on Breakage of Wheat Kernels During First-Break Roller Milling

ABSTRACT Breakage of wheat kernels during first-break roller milling depends on many factors, including the disposition of the fluted rolls: sharp-to-sharp, sharp-to-dull, dull-to-sharp, or dull-to-dull. Wheat kernel breakage under different dispositions during milling was studied using high-speed video imaging. The results show significant slippage between kernels and the flutes when a dull working angle is used, especially when the dull angle is on the fast roll. Experiments were conducted to compare the size distributions resulting from the four dispositions. Representative hard and soft wheat cultivars were milled using fluted rolls at five different roll gaps, and the resulting size distribution of the milled stocks was measured by sieve analysis. A sharp-to-sharp disposition gave a relatively uniform or straight line size distribution over the particle size range of 212–2,000 μm. By contrast, a dull-to-dull disposition gave a U-shaped distribution with more larger and smaller particles and fewer in ...

Stress-Strain Analysis and Visual Observation of Wheat Kernel Breakage During Roller Milling Using Fluted Rolls

The endosperm and bran of a wheat grain have different mechanical properties and break differently under the same stresses. Stress-strain analysis was used to model the factors affecting wheat kernel breakage during milling using fluted rolls. The planes of principal compressive and tensile stress and the maximum shear stresses, along which the kernel is most likely to be broken, were calculated for a sharp-to-sharp roll disposition. With the occurrence of compressive stress in the horizontal direction and shear stress in the vertical direction, a kernel tends to break along a principal tensile stress plane because the tensile strength of the endosperm is much smaller than its compressive strength. The model presented quantifies the mathematical relationship of three design and operational factors affecting the principal stresses and the maximum shear stresses: roll gap, differential, and roll diameter. High-speed video was used to observe wheat breakage events during milling; the results show consistency with the theoretical analysis.