P.J. Fryer

The Effect of Adding Minerals on Fouling from Whey Protein Concentrate: Development of a Model Fouling Fluid for a Plate Heat Exchanger

Deposits formed on the surface of heat treatment equipment in the dairy industry compromise product quality and process efficiency. Whey protein concentrate (WPC) solutions have been used by a number of researchers to investigate the fouling mechanism and to understand cleaning, in an attempt to optimize thermal treatment processes of milk. However, differences in the fouling from milk and WPC have been found at high temperatures, possibly as a result of the mineral content of the two solutions. The effect of adding minerals (calcium and phosphorus) on fouling and cleaning behaviour of WPC has been investigated. Solutions of differing mineral content were tested; deposits formed in each temperature region of the PHE were analysed for chemical compositions. Increasing the mineral content decreased the extent of fouling and altered the deposit composition closer to that of milk. Overall cleaning times and cleaning rates, under standard conditions, were found to be dependant on the deposit composition and cleaning chemical concentration. Alternation of the cleaning chemical with water at different time intervals throughout the cleaning process elucidated the balance between hydraulic (physical) and chemical effects during cleaning.

Concentric flow regime of solid-liquid food suspensions: theory and experiment

Abstract Continuous food-sterilisation processes involve the flow of solid–liquid mixtures in pipes. Prediction of particle passage times in the system is required for ensuring sterility and optimising product quality. It is important to be able to predict both the minimum and maximum passage times of particles in the heating and holding sections of the system, and ideally the whole distribution of passage times (PTD) should be known. A Positron Emission Particle Tracking (PEPT) technique was used to determine the trajectories of almost neutrally-buoyant 5– 10 mm alginate spheres in viscous non-Newtonian solutions. Particle passage times were measured by Hall effect sensors or visual tracers. A wide range of experimental conditions were investigated including solids fractions from 16 to 55 vol % and mean mixture velocities from 20 to 230 mm s −1 . Thus, the mean apparent viscosity of the carrier fluid ranged from 20 to 510 mPas corresponding to tube Reynolds numbers of 2.1–381. Experimental results revealed the existence of four different PTD forms depending on the flow pattern present. A theoretical two-region flow model is presented which gives good predictions of the PTD forms, the minimum and maximum particle passage times.

Visualisation of three-dimensional flows in rotating cans using positron emission particle tracking (PEPT)

Abstract The flow of foods in cans is critical in determining process times and thus product quality. The flow of liquids has been followed in axially rotated metal food cans using positron emission particle tracking. The technique involved placing a small (≈600 μm) isokinetic radioactive tracer into a container and following its movement with a positron sensitive camera. The small size of the tracer, as well as the ability of the emitted gamma rays to penetrate both opaque fluids and considerable thicknesses metal (≈10 cm) make the method ideal for studying fluid flows inside real equipment. The method enables a spatial resolution of close to one millimetre and a time resolution of a millisecond. Flows have been studied in axially rotated cans filled with Newtonian liquids of differing viscosities and a varying amount of headspace. The inclusion of a headspace in a can caused the flow within the two-phase system of a viscous solution to become inherently three-dimensional with a regular period of circulation and flow trajectory.

The spouted-bed roasting of barley: development of a predictive model for moisture and temperature

Roasting of barley is currently an artisan process. As regulations and customer specifications become more precise, and experienced operators retire, a new approach to roast barley production is needed. To improve the quality of product greater understanding of the process is required. To enable automatic control methods to be implemented a model of the roasting process has been developed and tested on a spouted-bed roaster. The model uses parameters measured by other workers in fields such as grain drying and allows the change in temperature and moisture content of the barley to be predicted throughout the roasting period: a good fit between theory and experiment is obtained without recourse to any fitted parameters. This will enable changes in product characteristics to be modelled as a function of roasting control parameters such as temperature and time.

Heat Transfer to a Model Dough Product During Mixed Regime Thermal Processing

A number of food processes involve mixed regime (combination of conductive, convective, and radiant) heating. The behaviour of foods under these conditions is complex and requires on-line measurements. A laboratory-scale study has been undertaken to relate the heat transfer characteristics of a domestic oven to a dough product and the changes in food properties. Experiments were designed to isolate each of the heat transfer modes from the mixed regime process using metal discs with different surfaces. The convective heat transfer coefficient was determined at various oven settings, and this result used to prove the method by comparing the heat capacity of a known system to a published value. A dough product was heated in a process similar to an industrial heating process and the contributions of conduction, convection, and radiation were established. The heat capacity profile (Cpf) of the dough product was measured in the rig and compared to results obtained from a differential scanning calorimeter (DSC). The results suggest that the relative contribution of the various heat transfer mechanisms in an industrial processing environment could be manipulated to achieve a desired quality in the final product.

Assessment of the Effects of Agitation on Mashing for Beer Production in a Small Scale Vessel

Mashing is the brewhouse operation concerned with producing the fermentable sugars necessary for the successful fermentation of wort into beer. The process involves adding grist to water and heating to promote the enzymic conversion of malt starch into sugars. The conversion process depends on several factors including raw materials, the final product specifications and on the equipment used downstream in the subsequent unit operations to recover and stabilize the wort. Although the biochemistry of the process is well understood, the interactions between operating parameters and mash quality are less so, despite the fact that this information holds the key to process improvements in the brewing industry. A study of the effects of agitation in mashing has been carried out, to examine the impact of this parameter on mash quality and to investigate agitation as a possible process intensification route for brewing. Experiments have been carried out in small-scale agitated vessels with well characterized geometry. Results of the studies suggest that for the materials studied here the conversion of starch into fermentable sugars is independent of the agitation conditions. Agitation does not provide a viable route for process intensification. The primary effect of increasing agitation speed is to increase the number of fine particles formed, which may compromise the efficiency of downstream recovery operations through reduced filtration rates. Under agitation conditions encountered in industrial mash tuns, solubilization of β-glucan from the grist and the proposed consequent increase in viscosity is unlikely to be the reason for the increased separation times reported. Likewise, processing conditions are such that the viscosity of the mash itself cannot be considered to present a challenge to the agitation requirements of the process.

THE RATE AND EXTENT OF FOULING IN A SINGLE-TUBE WORT BOILING SYSTEM

Wort is the fermentation feedstock that provides all the necessary sugars and nutrients required for successful brewing. It is boiled to stabilize its composition prior to fermentation, a process that leads to the coagulation and subsequent flocculation of proteins and tannins, and fouling of the heat transfer surfaces. Fouling by commercially-supplied wort was studied in a single-tube (15 mm × 0.2 mm wall thickness, with wall temperature control) model wort boiling system, at wall temperatures of 130, 150 and 170°C and flow velocities of 0.07, 0.14 and 0.18 ms –1 , with the overall objective being to identify modes of operation which prolong operating times. Heat transfer was quantified in terms of the amounts of heat transferred to the liquid and vapour phases. The influence of operating conditions on the fouling process was determined by calculating the decrease in heat transfer coefficient with the increasing number of batches of wort processed. The work quantified the influence of wall temperature, wort velocity (and hence circulation time) and the duration of the boil. Fouling showed little temperature dependence as for all wall temperatures, a constant rate of fouling (d R f / dt ) was determined; d R f /d t = 1 × 10 –5 m 2 kW –1 h –1 , in the absence of vapour condensation and d R f /d t = 2 × 10 –5 m 2 kW –1 h –1 , with vapour condensation. The rate of fouling in the system was more affected by wort velocity, particularly under conditions where vapour was condensed. Under these conditions, curves obtained for velocities 0.07 and 0.14 ms –1 showed an initial, more rapid rate of fouling, which then continued at a reduced rate. The initial rate of fouling doubled as the wort velocity halved (at wort velocity 0.07 ms –1 initially d R f /d t = 4 x 10 –5 m 2 kW –1 h –1 compared to d R f /dt = 2 × 10 –5 m 2 kW –1 h –1 at velocity 0.14 ms –1 ), whereas the final rate was the same at both velocities (d R f / dt = 8 × 10 –6 m 2 kW –1 h –1 ).

Mechanical properties of maltodextrin gels: Small and large deformation

As part of a study of the large deformation behaviour of mixtures of maltodextrin with other biopolymers, pure maltodextrin gels have been thoroughly characterised. Whilst such studies have been made in the past1, the current work highlights some aspects of maltodextrin gel behaviour not previously reported.