Food Mixing Techniques and Principles

Mixing

• A key process in food production where two or more components are combined to form a uniform mixture.
• Used for achieving desired functional or sensory characteristics like texture development in dough or aeration in butters.
• Does not preserve food.
• Essential for processing, meeting product standards and developing desirable product characteristics.
• Multicomponent systems contain ingredients with differing physical properties and quantities.
• Involves either high-viscosity or non-Newtonian fluids.
• Mixing patterns influence final product characteristics.

Criteria for Successful Mixing

• Sensory properties (taste, texture)
• Functionality (mix consistency, aeration)
• Homogeneity (even distribution of ingredients)
• Particulate integrity (no damage to fragile components)
• Safety and hygienic design
• Compliance with legal standards
• Process efficiency and flexibility

Theory of Solid Mixing

• Particle size, shape, and density as well as moisture content are important factors.
• Surface and flow characteristics, tendency to aggregate and mixer efficiency also influence the process.
• More uniform mixing is achieved when materials have similar shape, size, and density.
• Difference in material properties can cause unmixing, leading to temporary uniformity.
• Overmixing can cause separation.

Theory of Liquid Mixing

• Key velocities in liquid mixing include:
  • Longitudinal velocity (parallel to the mixer shaft).
  • Rotational velocity (tangential to the mixer shaft).
  • Radial velocity (perpendicular to the mixer shaft).
• Effective mixing technique uses baffles or angled blades to maximize radial and longitudinal velocities.
• Avoid vortex formation as it leads to ineffective mixing.

Mixing High-Viscosity Liquids

• Mixing in viscous materials includes methods like Kneading, Folding, and Shearing.
• Challenges include:
  • Non-Newtonian liquids require special attention to mixer design.
  • Pseudoplastic: Exhibit decreasing viscosity under increased shear rate, becoming thinner and flowing easier when stirred vigorously.
  • Dilatant: Exhibit increasing viscosity as the shear rate increases, becoming thicker and more resistant to flow under sudden high shear stresses.
  • Viscoelastic: Exhibit both elastic and viscous properties, showing viscous (deformation) and elastic (recovery) response under stress.

Mixing Indices

• Monitor and compare the extent of mixing with different equipment.
• Used for approximately equal masses of components at low mixing rates (M1).
• Used for small quantities mixed into larger bulk at higher rates (M2).
• Used for liquids or solids in similar manner to M1 (M3).

Timing and Equilibrium in Mixing

• Accurate timing is crucial to prevent unmixing.
• Uniformity of the final product depends on the balance between mixing and unmixing.
• Influenced by the type of mixer, operating conditions, and component properties.

Measuring Mixing Progress

• Samples initially contain mostly one component.
• As mixing progresses, samples become more uniform and approach the average composition.
• To track change in composition, standard deviation of each sample’s composition is calculated.
• Lower values indicate greater uniformity.

Rate of Mixing

• The rate of mixing depends on the viscosity of the fluid being mixed.
• Baffled mixers are used to reduce the viscosity of fluids.
• The density of the mixtures also plays a role in the rate of mixing.

Equipment

• Different types of mixers are used for various applications.
• Dry powder or particulate solids
• Low- or medium-viscosity liquids
• High-viscosity liquids and pastes
• Dispersion of powders in liquids.

Bread Moulder

• Has three stages:
  • Sheeting: Dough is passed through rollers that decrease the gap size, turning it into thin sheets.
  • Curling: The sheeted dough is curled into a cylindrical shape.
  • Rolling-Sealing: A revolving drum seals the dough by pressing it against a pressure plate, removing trapped air.
• Moisture content increases at the trailing end of the dough, and moulder designs vary to ensure the moist part is at the center.

Dough Encasing Equipment

• Uses a co-extrusion process where inner and outer materials are co-extruded and shaped using 'encrusting discs'.
• Thickness control is achieved by adjusting the flow rates of each material, providing flexibility in product design.

Forming

• The process of shaping raw materials into specific forms or sizes.
• Improves food quality, consistency, and appeal.

Applications of Forming

• Rice dough and bean paste cakes
• Sweetbreads with jam
• Doughnuts, meat pies
• Hamburgers with cheese
• Fish with vegetable fillings

Pie Formers

• Dough is pressed into shapes using a die, forming the pie casing.
• Filling is added into the casing.
• A continuous sheet of dough is laid on top to cover the filling.
• Reciprocating blades cut the dough sheet to form the pie lid.

Biscuit Formers

• Biscuit Formation Methods
  • Rotary Moulder: Dough is pressed into shaped cavities in a metal moulding roller.
  • Moulding Rollers: Shapes are cut from a sheet of dough using a cutting roller.

Effects on Food

• Mixer action has no direct effect on nutritional quality or shelf life.
• There can be indirect effect by allowing components to react together.

Metal Moulds with Ejector Pins

• For hard confectionery (e.g., butterscotch).
• A piece of dough is placed into aluminum foil containers or reusable pie moulds.
• Ejection by mechanical deformation.

Flexible PVC Moulds

• Used for soft confectionery (e.g., toffee, fudge, jellies, caramel, fondant, chocolate).
• Filling is added into the dough casing.

Polytetrafluoroethylene-Coated Aluminum Moulds

• With compressed-air ejection, used for jellies, gums, fondant, crèmes.

Extrusion and Shaping

• Sugar confectionery can be extruded into a ‘rope,’ shaped by rollers and dies.

Microprocessor-Controlled Depositors

• Used for cake mixes and high-viscosity liquids.
• Can store sizes, shapes, and weights for up to 100 products.
• Food can be deposited as single type, layered, or center-filled.
• Food is cooled in a cooling tunnel, then ejected once solidified.

This quiz explores the essential processes involved in food mixing, including criteria for successful mixing and the theory of solid mixing. Understand the importance of achieving homogeneity, sensory properties, and compliance with standards in food production. Test your knowledge on how mixing affects final product characteristics.