MODELING OF THICKNESS FOR SEMISOLID FOODS

We investigated the relationship between orally perceived thickness and calculated shear stress on the tongue for mayonnaise and custard. To this end, the applicability of the models of Kokini et al. (1977), describing the mechanical breakdown in the mouth, have been tested. Within a limited range of shear stresses (mayonnaise < 150 Pa; custard < 30 Pa), there was a linear relationship between shear stress and thickness, in accordance with the work of Kokini et al. (1977). Beyond this range, the linear relationship breaks down and the thickness levels off with shear stress for both mayonnaise and custard. The relationship over the entire range of shear stresses used in this paper can be satisfactorily described by a semilogarithmic (Fechner) relation. For both types of products, the quality of the thickness prediction by the decreasing‐height model and the constant‐height model of Kokini et al. (1977) is similar. For most mayonnaises, the contribution of the lateral movement of the tongue to the shear stress in the decreasing‐height model of Kokini et al. (1977) is orders of magnitude larger than the contribution of the squeezing or compression movement of the tongue towards the palate. This difference in magnitude is affected by the low value measured for the compression force and by the high values for material consistency K. The values for K are high because yield‐stress behavior has been neglected when the flow curves were analyzed. For custard, the models of Kokini et al. (1977) are found to be less adequate. It is proposed that this is because the models ignore interactions with saliva. Several routes to improve the modeling by incorporating viscoelastic behavior were unsuccessful. Elongational stress and yield stress were neglected in all tested models.     

Application of turbulent pulsating flows to the bacterial removal during a cleaning in place procedure. Part 1: Experimental analysis of wall shear stress in a cylindrical pipe

The effects of pulsating turbulent flows on wall shear stress components were investigated in a straight pipe using the non-intrusive electrochemical method. Experiments were made using a new pulsation generator system which allows high amplitude pulsations in addition to a perfect stability of the installation. Maximum pulsation frequency equal to 2.86 Hz is used, above which fluid inertia dominates over most part of the flow field.Analysis showed that pulsating flows induce an increase of local velocity gradient at the wall pipe. This result is explained by the periodic renewal of the boundary layers. Spectral analysis showed high increasing rates of the fluctuation energy for the different pulsating conditions in comparison with a steady flow. The tested condition involving a recirculation flow induced a modification in the energy dissipation cascade, which can be explained by the redistribution of eddies size near the wall.     

SPINNING DISC MEASUREMENT OF TWO-STAGE CLEANING OF HEAT TRANSFER FOULING DEPOSITS OF MILK

The efficient and effective cleaning of milk protein – based deposits from heat transfer equipment is essential in the dairy industry. The aim of this study was to evaluate the effectiveness of two‐stage cleaning using acid and caustic. Stainless steel discs were fouled during heat transfer by skimmed milk and whey protein. The discs were then cleaned with acid and sodium hydroxide solutions under controlled mass transfer conditions using spinning disc techniques. The use of 0.5% nitric acid, and a commercial acid known as Triplex, as a rinse before caustic cleaning increased the cleaning rate by 2.5 times. The foulant was found to swell about 40% and calcium was leached out within 5 min after exposure to acid. The acid treatment is believed to cause a reduction in the viscosity, and hence an increase in dissolution, of the gel layer formed when caustic cleaning takes place.     

APPLICATION OF AN IN-LINE RHEOLOGICAL CHARACTERIZATION METHOD TO CHEMICALLY MODIFIED AND NATIVE CORN STARCH

The application of an in‐line ultrasonics‐based rheological characterization method for measuring the rheological properties of 6% (w/v) acid‐thinned and native corn starch suspensions and gels was studied. The measurements were performed in steady, laminar pipe flow using a 5 MHz frequency transducer to determine the radial shear rate distribution. Two pressure transducers were used to measure the pressure drop allowing the shear stress distribution to be calculated through the conservation of linear momentum. It was possible to obtain shear viscosity over a range of shear rates, 1–50 1/s, from a single velocity profile. A comparison of the shear viscosity function at different flow rates showed that this method could be a valid method of process rheometry during the manufacturing of starch‐based products. Both ultrasonics and rotational rheometry results showed that acid‐thinned and native corn starch suspensions exhibited Newtonian behavior before heat treatment and non‐Newtonian behavior after heating. Power law consistency index and flow behavior index of the acid‐thinned corn starch gel at 39°C were 0.60 Pa.s ^0.68 and 0.68, respectively; whereas those of the native corn starch were 5.90 Pa.s ^0.37 and 0.37 at 38C. Their consistency index increased and flow behavior index decreased with cooling and a thermoreversible change in the flow behavior index was observed in the native corn starch after storage.     

COMPARISON OF IN-LINE CONSISTENCY MEASUREMENT OF TOMATO CONCENTRATES USING ULTRASONICS AND CAPILLARY METHODS

This study focuses on the development of a noninvasive, in‐line rheometer using ultrasonics and its comparison with data from a traditional capillary viscometer. The ultrasonic based pointwise viscosity measurement technique combines a measurement of the velocity profile and the pressure drop to determine the shear rate and the shear stress distributions, respectively in a pipe. The experiments were carried out using tomato concentrates at 8.75%, 12.75%, and 17.10% total solids content. The flow system consisted of a 53.2 mm diameter acrylic tube, a positive displacement pump and two pressure transducers. Multiple shear viscosity‐shear rate data were recorded under actual pipeline conditions from a single combined measurement of the velocity profiles using ultrasonics and the pressure gradient, using the pressure transducers. The samples showed shear thinning behavior and a yield stress. Power law and Casson models were used to fit the data and both obtained R² values higher than 0.99. The yield stress was also directly determined from the velocity profiles. Shear viscosity versus shear rate data of the 12.75% total solids sample were obtained by capillary rheometry at four different flow rates. These showed very‐good agreement with those obtained using the velocity profile technique.     

PREDICTING CLEANING OF EQUIPMENT USING COMPUTATIONAL FLUID DYNAMICS

In the food industry, production lines are ideally run for very long time periods without the need for cleaning. A prerequisite is that the equipment and the line are hygienically designed. This means that there are no stagnant areas, crevices or other parts of the flow domain that may cause entrapment of the product that can subsequently lead to bacterial growth. However, unhygienic geometries such as those described are frequently encountered in practice, and more frequent cleaning is a necessity. This article reported modeling results validated with experimental work. Computational fluid dynamics was used to assess the cleanability of a T‐junction. Electrical conductivity measurements of a salt solution of known concentration before and after the T‐junction is cleaned using deionized water were reported. This comparison gives an acceptable qualitative agreement with finite volume‐based calculations that involve both steady‐state and transient operations. This approach is a necessary prerequisite for the development of models that will ultimately include bacterial growth and deactivation kinetics under processing conditions.     

IN-LINE MONITORING OF TOMATO CONCENTRATE PHYSICAL PROPERTIES DURING EVAPORATION

This work continues the development of an ultrasonic sensor system for in‐line measurement of the physical properties of fluid foods. The test system was a semi‐batch evaporator in which juice from three varieties of processing tomatoes was concentrated from 5 to 24 Brix. The physical properties of the tomato concentrates were measured and correlated to ultrasound properties. Speed of sound was linearly correlated with density, soluble solids content and total solids content of the tomato concentrates. Shear viscosity of the tomato concentrates flowing in viscometric pipe flow was evaluated using ultrasonic Doppler velocimetry (UDV). The UDV technique combines a fluid velocity profile and a simultaneous pressure drop to create a rheogram. Simple shear viscosity was modeled as power law behavior for tomato concentrates as a function of solids content for the three processing varieties. Off‐line measurements of apparent viscosity were well correlated to the in‐line measurements.     

AN APPROACH to STUDY and MODEL the HYDRODYNAMIC CLEANING EFFECT

A sensor has been developed for continuous measurements of the removal of deposit. the sensor, which was based on heat transfer measurements, was also able to measure the wall shear stress. The device was used to study the mechanical effect during cleaning. It was found that the removal rate of deposits, at a surface, could be scaled by the mean wall shear stress. Measurements were performed under both laminar and turbulent flow conditions. the turbulent fluctuations did not influence the removal rate.     

REMOVAL KINETICS OF BACILLUS CEREUS SPORES FROM STAINLESS STEEL PIPES UNDER CIP PROCEDURE: INFLUENCE OF SOILING AND CLEANING CONDITIONS

Cleaning efficiency is of prime importance for food industries to ensure both the quality and safety of the products. The removal kinetics of Bacillus cereus spores adhering to unheated stainless steel pipes was studied under turbulent flow conditions (Reynolds’number of 77500 and 116300) in order to be close to those encountered in industrial practice. The experimental data was fitted using a hyperbolic tangent model. Variance analysis was then performed to underline any potential effects on the kinetics of the processing parameters, such as soiling conditions, soiling media and mean walls shear stress during cleaning. A significant influence of the adhesion medium (milk or saline) is shown at the level of spore removal (P < 0.001). This trend could probably be explained by the change in the surface properties of spores and stainless steel surfaces when covered by milk macromolecules. After milk soiling in turbulent flow conditions, removal efficiency was enhanced by a factor of 2.5 to remove 50% of the initial spore contamination and by a factor of 2 for the remaining spores after 30 min of cleaning. No effect of the two mean wall shear stresses (9.4 and 19.1 Pa) has been identified. The removal kinetic model proposed here could now permit the effect on the cleaning efficiency of a wide range of CIP conditions to be tested.     

Modelling and simulation of bottle rinsing

This study describes newly developed mathematical models of bottle rinsing. Our approach is based on 3D‐CFD models of turbulent two‐phase flow (water and air), which have been implemented based on the freely available open source software OpenFOAM. The models are validated using data obtained with a standard injection nozzle and then used to evaluate the performance of two fictitious modified nozzle types w.r.t. cleaning efficiency, water consumption and water drainage. Maps of the interior walls of the bottles showing the distribution of important parameters such as wall shear stresses or water coverage were derived from the simulations. The simulations suggest that rotating or pulsating injection nozzles may perform better than standard nozzle configurations.     

INTERNATIONAL INTER-LABORATORY TRIALS TO DETERMINE THE FACTORS AFFECTING THE MEASUREMENT OF CHOCOLATE VISCOSITY

The working group of the International Office of Cocoa, Chocolate and Sugar Confectionery (IOCCC) performed a sequence of five ring tests to improve the agreement of the standard method for measuring viscosity of chocolate between laboratories. Reporting shear stress measurements instead of using the Casson equation improved the agreement, as did standardising the method of cleaning the concentric cylinder and calibrating the viscometers. In the revised method, the standard deviation for shear stress measurement at shear rates greater than 5 s⁻¹ from 23 laboratories was less than 8%. However, the Casson yield values had a seven-fold range and the Casson plastic viscosity a two-fold range, which was unacceptably high. A new method (IOCCC 2000) has been published as a result of this work and is available from CAOBISCO in Bruxelles, Belgium.     

MECHANICAL CLEANING EFFECT AND PRESSURE DROP OF AIR-WATER-FLOW IN HORIZONTAL GLASS TUBES (VACUUM DAIRY PIPELINES)

Mathematical models are presented which make it possible to calculate pressure drop and mechanical cleaning effect for plant design of vacuum dairy milking pipes. Experimentally, air-water mixtures were sent through a test plant, consisting of glass pipes 0.034 m in diameter and 60 m in length (93 m in some experiments), where a soiled piece of pipe could be inserted without disturbing the flow. The soiling was milk-based and dried on application. Light absorption of the soiled glass tube was measured before and after the cleaning operation, which was performed for 45 s with plain water at room temperature. To calculate the pressure drop, the so-called Dukler constant-slip-method was used. A holdup correlation according to Hughmark was improved to fit the pipe system used. Through linear regression analysis an equation was obtained, describing the cleaning effect as influenced by the Reynold number and the liquid fraction of the air-water mixture.     

The impact of pipe geometry variations on hygiene and success of orbital welding of brewing industry equipment

Brewery industry processing plants are made‐up of tanks, heat exchangers and columns, which are factory‐built, interconnected by thin‐walled pipes and bends, assembled together on‐site. However, pipes are inaccessible from inside so onsite welding is more difficult to control, leading to poor or inadequate welded joints that can compromise product quality for correctly designed plants. One factor leading to poor welds is pipe geometry as pipes are manufactured to outer diameter (OD), wall thickness and ovality tolerances that affect the alignment of pipe ends. A mathematical algorithm was developed to assess interconnecting pipes and bends from a brewery fabrication site to achieve a minimum of 80% area overlap around the pipe circumference. The 80% was simply a reference point based on a 90% overlap ±10%. 316 L stainless steel pipes of different OD were tested together with 53 mm OD 90° elbows. It was discovered that well‐performing welds were difficult to achieve with random orientation of pipes. Better results were achieved by aligning major axes of pipes as there was an increase from 51 to 91% after major axis alignment on welds for straight pipes. There was an increase from 22 to 59% and from 58 to 85% for manufacturers 1 and 2, respectively, for straight pipes‐to‐bends welds. The higher chances of success for manufacturer 2 were attributed to better OD, wall thickness and ovality control. Whilst the welder is unable to control manufacturer tolerances, they are able to manage orientation of pipes to achieve better welds. Copyright © 2017 The Institute of Brewing & Distilling     

Characterization of the flow behaviour of sausage emulsions with a simple tube viscometer

A specially designed tube viscometer was used to measure apparent viscosity during flow of Bologna type sausage emulsions moving through a pipe. Emulsions varied in fat content (from 21.8 to 44.3%) and in moisture/protein ratio (from 3.7 to 5.6), and the effects of added sodium chloride, sodium diphosphate, starch and blood plasma were investigated in a 36% fat, 3.7 moisture/protein emulsion.
The shear stresses determined as a function of shear rate were fitted by a power law. Yield stress of the emulsions was negligible relative to the applied stress. However, inspection of the flow profiles indicated that considerable slip of the sausage emulsion occurred at the pipe wall. Both emulsion flow and slip contribute to overall flow behaviour, so a kind of effective viscosity is determined. Intrinsic rheological properties and wall slip will both be affected by the composition of the sausage emulsion.     

Application of turbulent pulsating flows to the bacterial removal during a cleaning in place procedure. Part 2: Effects on cleaning efficiency

Pulsating turbulent flows effects on cleaning in place procedure of straight pipes were investigated for various pulsations parameters (frequency and amplitude) and mean velocities of the flow. Pulsations generation was made with a new system which allows high amplitude of pulsations. Experiments showed the contribution of the different pulsation parameters, in the removal of adhered bacterial spores, in addition to the effect of the mean velocity of the flow. A high level of the cleaning rate is observed despite the reduction of the magnitude of the mean velocity. This result can be explained by the effect of the two pulsations parameters (amplitude and frequency) which ensure a high wall shear rate. The study of the cleaning kinetics has shown the increase of the removal constant rate of spores using pulsed flow in comparison with the use of a steady turbulent flow.     

A systematic study of the residence time of flour in a vibrating apparatus used for thermal processing

The dry heat treatment of flour is well established for the production of cake flour for high ratio cakes. This study investigates a new tubular apparatus in which flour is conveyed by vibrations through a helical pipe. Residence time distributions (RTDs) of flour were characterised for various processing conditions and the development of the residence time in extended operation was analysed.A method was developed to accurately determine the RTDs, which could be approximated by normal distributions. The width of the distributions is a critical factor for the accuracy of a thermal process and was identified for different processing conditions. The distributions were narrow, with variations of ± 1% at most.In some cases, the residence time increased over 3.5 h of machine run-time by 7.7%–13.9%. To explain this phenomenon, several hypotheses have been tested. The machine performance was constant with time and no influence of ambient temperature or humidity could be found. It was furthermore shown that changes in the bulk material passing through the apparatus were not the cause of the increase. However, electrostatic charging of the material was observed.Two things led to a reduction in residence time: i) cleaning the pipe with a cleaning pig and water and ii) time, during which the machine is not running. It was suggested that a thin layer of particles inside the pipe in combination with electrostatics effects could be the reason for the residence time increase. Frequent cleaning can therefore allow relatively uniform behaviour and control of residence time.Industrial relevanceThis work investigates the potential application of a novel, vibrating device for the dry heat treatment of flour as a replacement for chlorination in the production of cake flour. Since chlorination was banned in the EU in the year 2000, there is an industrial interest for alternative treatments and equipment to produce flour for high ratio cakes.     

SLIT RHEOMETER STUDIES OF WHEAT FLOUR DOUGH1

Rheological properties of bread dough having different levels of added gluten (0, 2.5, 5.0 and 7.5%) were measured. The dough was forced through a slit die attached to a cylindrical container. The material functions of interest included steady shear viscosity, first normal stress coefficient in steady shear flow derived from hole pressure measurements and planar extensional viscosity as estimated from entrance pressure drop measurements. These rheological properties were correlated to the loaf volume of the baked bread. Results indicate that the first normal stress coefficient and planar extensional viscosity were affected by the gluten content of the dough and correlated well with the loaf volume. The entrance pressure drop increased with increasing apparent shear rate but entrance correction was found to decrease with apparent shear rate. Water had a greater effect on the rheological properties than gluten content. The Trouton ratio was rather large and ranged between 850 to 2000 at a strain rate of 1s^-1 and decreased with increasing extension rate for most cases.     

Simulation of the Flow Conditions in Different Types of Bar Structures of Disc Refiner

Disc refiner is a critical equipment in the pulping and papermaking industry, pulp is refined in the refining zone, and different bar structures of refining disc constitute the different refining zones. With the use of the 3D modeling software SOLIDWORKS, five different refining discs that are commonly used in low consistency pulping, were built. The five refining discs were simulated and analyzed using the Computational Fluid Dynamics(CFD)software. The distribution of pulp velocity and surface shear stress, which is displayed between the bar and groove structures, can indirectly show the stress conditions on the refining discs. This paper provides a theoretical basis for research on the bar and groove failure of the refining discs.     

RHEOLOGY OF YOGURT DURING PIPE FLOW AS CHARACTERIZED BY MAGNETIC RESONANCE IMAGING

Flow behavior of yogurt during pipe flow was investigated using a magnetic resonance imaging (MRI) viscometer. The technique utilizes a velocity profile and independent pressure drop measurement to evaluate rheological parameters. The yield stress and slip velocity were obtained directly from the MR images; the Herschel-Bulkley consistency index, K, and the flow behavior index, n, were obtained through curve fitting procedures for product temperatures of 25C and 35C, over a shear rate range of 0.5 - 40 s⁻¹. At 25C, the average value of the yield stress was 14 Pa; the values of K and n were 5.6 Pa sⁿ and 0.36, respectively. As the wall stress increased from 15 to 42 Pa, the slip velocity increased linearly from 13 to 54 mm s⁻¹. At 35C, the average value of the yield stress was 10 Pa; the values of K and n were 1.1 Pa sⁿ and 0.88, respectively. As the wall stress increased from 12 to 31 Pa, the slip velocity increased linearly from 14 to 59 mm s⁻¹. These rheological parameters and slip velocities are relevant to the postfermentation cooling process performed in a continuous heat exchanger.