1. Theory of liquids mixing
1.1. Mixer in low viscosity liquids (Figure 5.1) (Page: 335)
1.1.1. G Longitudinal velocity (parallel to the mixer shaft)
1.1.2. Rotational velocity (tangential to the mixer shaft)
1.1.3. Radial velocity that acts in a direction perpendicular to the mixer shaft.
1.1.4. impeller, turbine, propeller agitators
1.2. To achieve successful mixing
1.2.1. the radial and longitudinal velocities imparted to the liquid are maximized by baffles
1.2.2. off-center or angled mixer shafts
1.2.3. angled blades
1.2.3.1. (Fig. 5.2)
1.3. Most liquid foods are non-Newtonian
1.3.1. the viscosity changes with rate of shear
1.4. Pseudoplastic foods such as sauces
1.4.1. the viscosity decreases with increasing shear rate
1.4.2. form a zone of thinned material around a small agitator
1.4.3. the bulk of the food does not move
1.4.4. Other food examples: syrups, brines, tomato paste for sauces
1.5. Dilatant foods such as corn flour and chocolate
1.5.1. the viscosity increases with shear rate, should be mixed with great care
1.6. Thixotropic foods, such as yoghurt
1.6.1. the structure breaks down and viscosity decreases with increasing shear rate
1.6.2. exhibit both a shear-thinning viscosity
1.6.3. time-dependent thixotropic effect
1.7. Viscoelastic foods, such as bread dough
1.7.1. exhibit viscous and elastic properties
1.7.1.1. The design of equipment should enable thorough mixing without overloading the motor or reducing the mixing efficiency
1.7.2. including stress relaxation, creep and recoil
1.7.2.1. These require a folding and stretching action to shear the material
1.7.2.2. Suitable equipment includes twin-shaft mixers and planetary mixers with intermeshing blades
1.8. The rate of mixing is characterized by a mixing index
1.8.1. Formula: 5.7 (Pg. 336)
1.9. Liquid flow is defined by a series of dimensionless numbers
1.9.1. the Reynolds number, Re (Eq. 5.8) (Pg. 336)
1.9.2. the Froude number, Fr (Eq. 5.9) (Pg. 336)
1.9.3. the Power number, Po (Eq. 5.10) (Pg. 336)
1.9.4. Related formula (Eq. 511) (Pg. 336)
1.10. The density of a mixture is found by adding the component densities of the continuous and dispersed phases:
1.10.1. Formula (Eq. 512) (Pg. 336)
1.10.2. The viscosity of a mixture is found using the following equations for baffled mixers and for unbaffled mixers
1.10.2.1. Formula (Eq. 13) (Pg.337)
1.10.2.2. Formula (Eq. 14) (Pg. 337)
1.10.2.3. Figure 5.3 (Pg. 337)
1.10.2.4. Sample 5.2 Problem (Pg. 337-338)
2. Coating
2.1. Enrober Equipment
2.1.1. Second type (unnamed)
2.1.1.1. Food passes through beneath a single or double curtain of hot liquid coating.
2.1.2. Submerger type
2.1.2.1. Food passes through the coating on a stainless conveyor belt.
2.2. Operational steps
2.2.1. pre-bottoming: when centers (peanuts) are passed on a wire belt through the upper surface of tempered chocolate.
2.2.1.1. specifically for chocolate with fillings (ex: chocolate bark with hazelnut or peanut m&m's)
2.2.1.2. first step: pre-bottomed chocolate passes over cooling plate to partially set chocolate.
2.2.1.3. 2nd: chocolate passes through enrober curtain
2.2.1.4. 3rd: chocolate is cooled in cooling tunnel to prevent fat crystals from melting.
2.2.1.5. 4th: products are held at 22*C for 48 hours to allow for crystallization.
2.2.2. 6 types of coating and 1 type of breading - equipment: hopper fitted with a mesh base located over a conveyer
2.2.2.1. 1. breading
2.2.2.1.1. 1st: foods are coated with a thin batter pass on a stainless steel wire belt through a bed of breadcrumbs to coat base and then thru a curtain of crumbs to coat the upper surface.
2.2.2.1.2. 2nd: excess material is removed by air knives.
2.2.2.1.3. 3rd: food is gently pressed between tamping rollers to drive and absorb batter into material to create a strong bond.
2.2.2.1.4. 4th: final product is frozen or fried and then chilled.
2.2.2.2. 1. (regular) coating
2.2.2.2.1. rotating stainless steel drum is fitted internally with angled flights or to tumble the food gently and coat all surfaces with powder or seasoning.
2.2.2.2.2. 1st: flavors and salt are blown directly on to drum with compressed air (spraying mechanism).
2.2.2.3. 2. pan coating
2.2.2.3.1. panning: build up thin layers of sugar or chocolate on to additional filling components.
2.2.2.3.2. equipment: tilted elliptical mixer, typically rotates at 15-35rpm.
2.2.2.3.3. after food passes thru tilted elliptical mixer, rapid drying occurs with (35-65*C) to remove unwanted particles. This is done thru an automated control system to reduce batch-to-batch variation.
2.2.2.4. 3. hard coating: centers must be coated with sweet solution or gum arabic for adhesive purposes thru an erober.
2.2.2.4.1. chocolate coating is similar to this
2.2.2.5. 4. soft coating: glucose or crystalline sucrose are prepared for the centers.
2.2.2.5.1. this includes multiple heating and cooling steps with drying time. ex: jelly beans
2.2.2.6. 5. chocolate coating: when pans rotate around 20rpm and held at 16*C for plain chocolate and 14*C for milk chocolate.
2.2.2.7. 6. Microencapsulation: when each small droplet or particle is coated with thin film of edible encapsulating material (typically used for spices or flavorings)
2.2.2.7.1. four main processes
2.2.3. liposomes: hollow spheres ranging in size from a few nanometers to a few microns
2.2.3.1. typically used in the nutraceutical industry
2.2.3.2. popular application: beta-galactosidase added to milk for lactose intolerant people.
2.2.4. nanoparticles
3. Mixing
3.1. develop desirable product characteristics
3.2. multicomponent
3.2.1. involving ingredients of different physical properties and quantities
3.3. high-viscosity or non-Newtonian liquids
3.3.1. Examples: sugar pastes, chewing gum, marzipan
3.3.2. multiple-paddle agiators, orbital mixers, Z-blade mixer
3.4. Some are intended primarily to mix liquids or powders
3.4.1. Others have been developed for mixing viscous materials
3.4.2. Examples: blending flavors, spices, cake mixes, dried soup mixes
3.5. successful mixing is to achieve an acceptable product quality
3.5.1. sensory properties
3.5.2. functionality
3.5.3. homogeneity with adequate safety
3.5.4. hygiene and legality
3.5.4.1. Compositional standards for some foods
3.6. Mixers should
3.6.1. be energy-efficient and flexible to accommodate changes in processing
3.6.2. increasing demand for continuous
3.7. Rotor-Stator Mixers
3.7.1. Stage 1: high speed rotor blades build low-pressure to draw material up to stator head.
3.7.2. Stage 2: centrifugal force, hydraulic/mechanical shearing between blades and inner wall of stator.
3.7.3. Stage 3: material out at high velocity through holes/slots in stator. Mixing & size reduction.
3.7.4. Stage 4: material expelled from head & projected radially at high speed.
3.7.5. Figure 5.14 (A-D) shows operation.
3.8. Static/Motionless Mixers
3.8.1. 1. Radial Mixing
3.8.2. 2. Flow Division
3.8.3. 3. Transient Mixing
3.9. 5.1.4 Effect on foods/microorganisms
3.9.1. Substantial effect on sensory qualities/functional properties
3.9.2. Main effect of mixing is to increase uniformity by evenly distributing ingredients throughout bulk
3.9.3. Nutritional value changes depend on amount/type of ingredient not mixing action.
3.9.4. Mixing has no effect on shelf life. Indirect effect by intimately mixing other components that can cause reactions.
3.9.5. Not much information on effect of mixing operations on microorganisms in foods.
3.9.5.1. Sometimes temperature is allowed to rise during mixing which may increase microorganisms from greater availability of nutrients.
4. Forming
4.1. is a size enlargement operation in which foods
4.1.1. high viscosity
4.1.2. dough-like texture
4.1.3. are molded into a variety of shapes and sizes,
4.1.4. immediately after a mixing operation
4.1.4.1. 5. Panner deposits the dough into baking tins.
4.2. 5.2.1 Bread Moulders
4.2.1. 1. Divider cuts dough in pieces. Check weighers ensures consistency.
4.2.2. 2. Conical rounder/cylindrical moulder forms dough into shapes.
4.2.3. 3. Moulder panner shapes dough into cylinders. Preshaping and 2-4 pairs of sheet rollers.
4.2.4. 4. Control software compensates for dough variations to main even pressure.
4.3. 5.2.2 Pie, Tart, Biscuit Formers
4.3.1. 1. After mixing, pastry dough goes through 2-3 pairs of polished chilled “sheeting” and “gauge” rollers.
4.3.2. 2. Casings are formed by putting pieces in aluminum foil containers, tins, or reusable moulds.
4.3.3. 3. The “blocking unit” presses the dough into shape and filling is added after.
4.3.4. 4. Reciprocating blades cuts and lays a sheet of dough over top
4.4. 5.2.3 Confectionary Moulders & Depositors
4.4.1. High Boiled Sweets
4.4.1.1. brittles, humbugs, butterscotch, Edinburgh rock and sugar mice. Boiled sweets have varied centers like fudge, effervescent, sherbet powder, chocolate, liquorice, caramel, or pastes from hazelnut, fruits, spearmint, coconut, almond, etc. in stripes, layers, or random patterns.
4.4.2. Soft Confectionery
4.4.2.1. toffees, caramels, fudges, fondants, chews, gums, liquorice, pastilles, jellies, marshmallow, nougats, chewing/bubble gum.
4.4.3. Chocolate Products
4.4.3.1. solid bars, coins, buttons, chips, multicolored, marbled chocolate. Fondant crème-filled chocolate, sold chocolate with inclusions like fruit, nut, biscuit, or puffed rice, hollow goods (Easter eggs) and aerated products
5. Theory of solids mixing
5.1. materials that are similar in size, shape and density can form a more uniform mixture than are dissimilar materials
5.2. In a mixing operation
5.2.1. differences in these properties can cause
5.2.1.1. unmixing of the component parts
5.3. In some mixtures
5.3.1. uniformity is achieved after a given period
5.3.1.1. unmixing begins
5.4. The uniformity of the final product depends on the equilibrium achieved
5.4.1. mechanisms of mixing and unmixing
5.4.1.1. related to the type of mixer
5.4.1.1.1. rotating vessels, screw -type mixer
5.4.1.2. operating conditions and the component foods
5.5. Formulas
5.5.1. (5.1, 5.2, 5.3, 5.4, 5.5, 5.6)
5.5.1.1. (pg. 331)
5.5.2. demonstrates how to use the formulas in a problem
5.5.2.1. Sample problem 5.1
5.5.2.2. (pg. 332-334)