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Rheology

of food materials

2

Food products: life cycle

Food products Rheological characterization

Formulation-- Composition, additives and stabilizers

Viscosity and flow behavior of formulation

Production Flow behavior, viscosity, elasticity

Storage Sedimentation stability, thermal stability

Application (usage) Flow behavior under shear conditions, Thixotropy

3

Rheology roadRheology road and measuring system

4

- Measuring systems for rotational and oscillatory rheometers- Flow and viscosity curves in a wide shear rate range

Examples: Water; Polymer solutions (polysaccharide); Emulsions; Binder solutions- Special measuring systems: measuring with the ball measuring system

Examples: Marmalade, Bolognese sauce with meat chunks- Yield point in flow curves (via rotational tests)

Examples: Creams; Ketchups- Yield point as the limiting value of the linear-elastic deformation range (via rotational tests)

Example: Ketchup- Structure at rest as G’ value (via oscillatory tests: amplitude and frequency sweeps)

Examples: 1) Butter; 2) Starch gels; 3) Pudding; 4) Milk drinks; 5) Emulsions- Structure regeneration of coatings, leveling, sagging behavior and layer thickness- Step tests (oscillatory and rotational tests)

Example: Ketchup- Temperature-dependent behavior during heating, softening, melting, cooling, solidification, crystallization (using rotational and oscillatory tests)

Examples: Chocolate; Ice creams; Spreading cheese and melting cheese- Gel formation (using time-dependent and temperature-dependent rotational and oscillatory tests)

Examples: Corn starch; Gelatin

Overview

5

Typical shear rates

         

Process Shear rate range [s-1] Examples of application

Sedimentation (fine particles in a suspension)

10-6 to 10-4 Salad dressing, fruit juice

Leveling - due to surface tension

10-2 to 10-1 Coatings, printing inks, lacquers, chocolate

Dip coating 1 to 100

Chewing, swallowingPouring from a bottle

10 to 100 Cheese, yogurt, chocolate

Transport in tubes, pipe flow, pumping, filling into containers

1 to 104 Blood, crude oils, paints, juices

Mixing, stirring 10 to 104 Emulsion, plastisol, polymer blends

Brushing, painting, spraying, blade coating

100 to 104 Brush coating, tooth paste, butter

6

Materials Shear viscosity

Gases / air 0.01 to 0.02 / 0.018 mPas

Water at 20°C(at 0 / 40 / 60 / 80 / 100°C)

1.0 mPas(1.8 / 0.65 / 0.47 / 0.35 / 0.28 mPas)

Milk, coffee creams 2 to 10 mPas

Olive oil approx. 100 mPas

Glycerin 1480 mPas

Polymer melts (T=+100 to +200°C and at shear rates of 10 to 1000 1/s)

10 to 10 000 Pas

Polymer melts (zero-shear viscosity) 1 kPas to 1MPas

Bitumen (T = +80 / +60 / +40 / +20 / +0°C)

200 Pas / 1 kPas / 20 kPas / 0.5 MPas / 1 MPas

Viscosity values

7

Typically used measuring systems Cone - plate and plate - plate systems

Use sandblasted or profiled measuring systems for oily and fatty substances !

Viscoelastic, high viscous, caution to particles and structures sizesPaste like, sticky and almost not flowing

Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas)(larger particles or super structures )

Low viscosity

CP75-0,5

CP50-1

PP50

CP25-1, CP25-2, CP25-2

PP25

Gel-like samples G‘ > G‘‘ and temperature testsProfiled geometries for mozarrella type of cheeses, sandblasted for cream cheese

Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas)Flowing liquid but larger super-structures (CP50-2)

8

Cone with truncation:

CPxx: Cone & PlateCone truncation

+ Shear rate and shear strain constant+ Easy to clean- Measurement of friction if particles are below the tip of the cone

Standards: ISO 3219, DIN53019, DIN53018

Crash!!

Name Cone Truncation- [µm]CP25-1 50CP25-2 105CP25-3 170CP35-3 240CP50-0.5 50CP50-1 100CP50-2 210CP50-3 345CP60-0.5 60CP60-1 120CP60-2 250CP75-1 150CP75-2 315

cone truncation=

measuring gap

9

Double Cone BI-C60-1°Applications: Food, Cosmetics, Pharma

modularBi-conefor inset-Peltier

precise determination of melting and crystallization temperature homogenous heating and cooling low temperature measurements without condensation (inert, dry) no evaporation of water or solvents

Peltier basis-control by conduction

Peltier-hood heating & coolingby convectionand radiation

N2

10

PTD – Peltier Temperature DeviceExcellent temperature control from the bottom to the top

unique combination of radiation, convection (frost protection) & conductive heating & cooling

homogenous heating and cooling low temperature measurement without having

- condensation (inert, dry)- frost formation

Peltier-Hood Heating / Coolingby Convectionand Radiation

Peltier Basis Temp.-Control by Conduction

optional evaporation blocker

11

Sealing the Gap: PP & CP Applications: Food, cosmetics, coatings

2 - guard ring

oil (10 mPas Si-Oil)

evaporation of solvent / water ? skin formation ?

12

Sealing the Gap: PP & CPApplications: Food, cosmetics, coatings

evaporation of solvent / water ? skin formation ?

1a - solvent trap

sample

solvent

13

Typically used measuring systems Concentric cylinders systems

Standards: ISO 3219, DIN53019, DIN53018

Easy to prevent sample from drying-out (oil film on top of sample) No trimming Good solution for all kind of liquids in rotational mode CC: not recommended for oscillation; DG: also recommended for oscillation CC: Helical groove if phase separation or vertical profiling to prevent slippage

Above 10mPas and below 100mPas with super-structures DG27 (same dimensions like CC27), gap size = 1mm

Above 1000mPas (100mPas) CC27

Above 10mPas and below 1000mPas CC39

Below 10mPas und homogenous, small structure DG26.7, gap size = 0.4mm

14

0.1

1

10

mPas

0.01

0.1

1

10

1000

mPa

1 10 100s-1

DG 42(double gap MS)

T = +20°C

Double-gap measuring systems are special systems designed for low - viscosity liquids.

constant viscosity

water

lg h lg t

lg

Flow Behavior: ideally viscous behavior

15

A special measuring system for:E.g. natural yoghurt

Natural Food ProductsMeasure natural product without destroying the initial structure by cutting into the sample structure

Advantages: allows measurement of brittle, natural materials excellent penetration characteristics dimensions similar to standard CC27 alternative: combination with flexible cup holder - >

ST22-4V-40 measuring system aluminum cup or stainless steel cup

16

Coarse disperse materials

Building materials Slurries Food (Yoghurt)

Special GeometriesCC with Surface Treatment or Vanes, Stirrers, Propellers

Better grip No slip

More Stirrers on request:

- User defined

- Brookfield Spindels

- Krebs Stormer Spindels

- ...

17

All these stirrers are relative measuring systems

Special Geometries (Relative Values)

Helix 1 Helix 2

Stirrer forBuilding Materials

StarchStirrer

Blade Anchor

Ball Measuring System

18

Rheometry with special Geometries Ball Measuring System (BMS)

for dispersions containing coarse-grained particles(showing a diameter up to 10mm)

Example: Marmaladecontaining fruit pieces

19

Rheometry with special Geometries

Ball Measuring System (BMS)

1

10

100

1,000

Pa

1

10

100

1,000

Pa·s

0.1 1 10 1001/s

Shear Rate .

Flow- and Viscosity Curves of Jams at 23 °CMeasured with the Ball Measuring System

Anton Paar GmbH

blueberry

KMS-3 /Q1; d=0 mm

Shear Stress

Viscosity

lemon

KMS-3 /Q1; d=0 mm

Shear Stress

Viscosity

Flow and Viscosity Curves of two Marmalade Preparations

20

Rheometry with special Geometries Ball Measuring System (BMS)

Flow and Viscosity Curves of a

Sauce Bolognese

10 0

10 1

10 2

10 3

Pa

10 0

10 1

10 2

10 3

10 4

Pa·s

10 -4

10 -3

10 -2

10 -1

10 0

10 1

10 2

1/s

Shear rate .

Copyright (C) 1999 Physica Meßtechnik GmbH

meat sauce

KMS - 1M

shear stress

viscosity

meat sauce (new sample)

KMS - 1M

shear stress

viscosity

Spaghetti Sauce containing meat pieces(testing reproducibility)

21

Further measuring systems/ temperature control systems

Starch (pressure) measuring cell

Tribology cell

Penetration measurements

Interfacial rheology (IRS)

Sentmanat extensional rheology(SER)

Flexible Toolholder

Rheo-Microscopy

22

Flow Behavior

Rheo - Microscopy

Size and shapeof the dropletsare dependingon shear rate

and “shear history”.

water / oil emulsiondispersions

lg

23

Shear-Thinning flow Behavior

Suspension 1:Orientation of particles(needle shaped)

Suspension 2:Agglomerated particlesBreak-up of agglomerates

Emulsion:Deformation and break-up of droplets

high viscosity low viscosity

rest high shear rates

24

Shear-Thickening flow Behavior

At low shear load:The rod inclines slowly.

Low viscosity

At high shear load:Solidification of the liquid due to shear

thickening.High viscosity

25

Suspensions shear - thickening of suspensions at - high solid concentrations- high shear loads

Flow BehaviorShear-thickening Behavior

1

f ... volume fraction of solid particles

dispersions

26

Flow Curves on a linear scale

Yield Point as a limiting value of the shear stress

1 without a yield point2 having a yield point y

2

1

ty

Flow Behavior

Yield Point

Break of the structure - at - rest.Super - structure by a chemical - physical

network via interactive forces.

The applied force is higher than the structural force

Low stress…no movement

High stress…sample starts moving

t1

t2

Examples: Pastes, concentrated dispersions, suspensions, ketchups, mayonnaises, chocolate melts, butter, gels

27

0

500

1000

1500

2000

2500

Pa

t

0 200 400 600 1000s-1

shear rate

Ketchup

t shear stress

Yield point can hardly be read-off

Flow curveshowing a yield point(on a linear scale)

Flow behavior: yield point

28

10

100

1000

104

Pa

1 10 100 1000s-1

Ketchup

Flowcurveshowing a Yield Point(on a logarithmic scale)

yield point y = 48 Pa

food

Flow BehaviorYield Point, comparison lin / log diagrams (2)

lg t

lg

29

Flow curves on a logarithmic scale

ty

Flow behavior: yield point

Yield point analysis in the low-shear range,

e.g. read off at = 0.01 s-1

ty

Yield point analysis in the low-shear range,

e.g. read off on the - axis

30

Mathematical curve fitting for flow curves on a linear scale (approximation, "regression")

other often used models: - Cassonblood, food - Herschel / Bulkleymaterials with a yieldstress and shear thinning or shear thickening behavior

Flow behavior: yield point

Bingham: flow curve of a material with a yield stress and a constant viscosity(food or cosmetics)

B - “yield point acc. to Bingham“B - “Bingham viscosity“

Windhab:chocolate and other cocoa products

0 - yield point

1 - linear yield point

- “high-shear viscosity“

examples: models

according to

31

0

200

400

600

800

1,200

Pa

0 50 1001/s

Cream 1

Shear Stress

Cream 2

Shear Stress

Cream 1 Herschel-Bulkley

tau0 = 705.01 Pa; b = 11.503; p = 0.84742

Shear Stress

Cream 2 Herschel-Bulkley

tau0 = 31.224 Pa; b = 4.7648; p = 0.94538

Shear Stress

Analysis using Approximation Functions for Flow Curveshere: according to Casson (OICC 1973), and Windhab (IOCCC 2001 / ICA)

0

50

100

150

200

250

300Pa

0 10 20 30 40 501/s

Scherrate .

Anton Paar GmbH

Zartbitter 2

Schubspannung

Weiße 1; A4...A4

Schubspannung

Vollmilch; A4...A4

Schubspannung

ChocolateMelts(T = +40°C)

Bitter

White

Whole Milk

Analysis Casson Windhab 0 (Pa) 0 (Pa)

Bitter 15 18 White 19 25Whole Milk 21 23

shear rate

food

Summary:

Yield Points are not material constants,since they are depending on the measuring method and on the analysis method.

Flow BehaviorYield Point

32

Viscoelastic Behavior

Yield Point (using a / - Diagram)

Testing with controlled shear stress

Yield point as the limiting value of the shear stress:

The sample starts to flownot before the externalforces are exceeding thenetwork-of-forces of the internal structure.

Below the yield pointthere is elastic deformation.

yield point y using the best fit straight line (“ tangent“) in the linear-elastic deformation range

yield point y using the „tangent crossover“ method

lg

lg lg

lg

33

10-2

100

102

104

106

%

lg g

0.1 1 10 100 1000Pa

shear stress lg t

without binderyield point 13.5 Pa

with binderyield point 114 Pa

Comparison of two Ketchups

deformation

food

Viscoelastic Behavior

Yield Point (using a / - Diagram)

34

IntroductionViscoelastic Behavior

liquid - likestructure

„at the gel point“

gel - like structure

G'' >> G' G'' > G' G'' = G' G' > G'' G' >> G''

tand>> 1

tand> 1

tand= 1 tand< 1

tand<< 1

0

with

tand= G'' / G'

viscous

viscoelastic elastic

35

ApplicationShear Modulus

Material Stiffness and Shear Moduli

Example: different types of cheese

cheese type

example shear modulus(around)

1 cream Philadelphia 1 kPa

2 soft French Camembert

10 kPa

3 semi-hard Holland Gouda (young)

0.1 MPa

4 hard Swiss Emmentaler

0.5 MPa

5 extra hard Italian Parmigiano

1 MPa

5

1

2

4

36

100

1000

10,000

Pa

1

0.1 1 10 100%

Gel Strength, Dependence on the Binder - Concentration

15 w-%

10 w-%

7.5 w-%

5% w-%

0.1

10

Viscoelastic Behavior Amplitude Sweeps

ω = 10 rad/sT = +23°Closs factortan = G‘‘ / G‘

Starch Gel (in water)

Summary: Gel strengthis dependent on the binderconcentration

First check in the LVE range:tan < 1 for all samples ( = gel structure) ? Yes !

food

lg tand

lg G'

strain lg g

37

0.01

0.1

1

10

MPa

0.01 0.1 1 10%

ω = 10 rad/s

Temperature Dependence of Butter

Viscoelastic BehaviorAmplitude Sweeps

Summary:cold butter shows

brittle break,hence

poor spreadability

T = +10°C

T = +23°C

food

lg G'

lg G''

strain lg g

38

102

103

104

105

Pa

G'

G''

100

101

102

103

Pa

0,001 0,01 0,1 1 10 100%

Deformation

am03014

Margarine css

CP 50-2; d=0,05 mm

G' Speichermodul

G'' Verlustmodul

Schubspannung

102

103

104

105

Pa

G'

G''

10-1

100

101

103

Pa

0,001 0,01 0,1 1 10 100%

Deformation

am03014

Margarine CSD

CP 50-2; d=0,05 mm

G' Speichermodul

G'' Verlustmodul

Schubspannung

Amplitude Sweep /CSD /CSSMargarine as semi-solid material with flow point

CSD

CSS

39

ApplicationSedimentation, Long-term Storage Stability

in the beginning

Stability of DispersionsExample: Salad Dressings

after 15min

Behavior in the low-shear range or at rest, respectively

dispersions

40

Frequency SweepStability of suspensions

t = 1 / omega

Time dependent structural strength G’ decreasing

- Long term behavior = Fluid -like- Strength of the structure G’ decreases- Good flow

characteristics - Low stability

G’ constant, light decreasing - Long time structural strength G‘ - Bad flow characteristics - High stability

11 2

=1/w Time

G‘‘

2

G‘

1

2

41

Milk: Geometry DG26.7*

Pure milk Chocolate Milk Plus Chocolate Milk Budget Ca enriched Mill

Mechanical storage stability

Amplitude SweepSedimentation-Stability

42

Amplitude Sweep Structural strength G´ as function of stress

TAULVE = Yield stress = External force to overcome the structure at rest

Shear stress t

*) Strain-Test, plottet as function of strain

10-4

10-3

10-2

10-1

Pa

G'

0,0001 0,001 0,01 0,1Pa

Pure Milk (no G‘ )

tLVE tLVE tLVE

CA MilkCHOC budget CHOC plus

43

Measurement of structural strength at rest or mechanical stability of milk

Frequency SweepSedimentation Stability

10-4

10-3

10-2

10-1

100

Pa

G'

0,1 1 10 1001/s

w

Pure milk

DG 26.7

G'

Choc milk, plus

DG 26.7

G'

Choc milk, Std.

DG 26.7

G'

CA-Milk

DG 26.7

G'

44

Spread cheese Temperature behavior Flow point = Spreadability as crossover point at G‘ = G“

Spread cheese 5°CG'G''

Spread cheese 20°CG'G''

Spread cheese 36°CG'G''

103

104

105

Pa

G'

G''

102

103

104

Pa t

5°C20°C

36°C

Amplitude Sweep Representation as function of stress to determine the flow points

45

Penetration measurementsSoft cheese

Presetting 0.3N contact pressure Temperature 60°C Temperature of cheese before test ca. 25°C

0

2

4

6

10

mm

d

0

10

20

30

40

60

°C

T

0 2 4 6 8 10 12 14minZeit t

Penetration Test

Anton Paar GmbH

Start

End

Depth

Time

46

-1

-0,5

0

0,5

1

2

N

FN

-2.000

-1.500

-1.000

-500

0

500

1.000

2.000

µm/s

v

0 5 10 15 20 25sZeit t

Penetration measurement Margarine

Presetting: Penetration velocity down/up = 2000µm/s Alternatively: Normal force controlled testing

stop

up

down

Time

47

Flow Behavior

Temperature - dependent Behavior

softening and melting, or solidification and crystallization

preset: constant shear conditions (shear rate or shear stress)

result: viscosity / temperature curve with steadily decreasing or increasing viscosity values, respectively

gel formation and curing

preset: constant shear conditions (shear rate or shear stress)

result: viscosity / temperature curve showing a viscosity minimum

T

T

min

48

0

2

4

6

8

10

Pas

h

20 25 30 35 40°C

temperature T

Chocolate Melt

Flow Behavior

Temperature - dependent Behavior

Cooling process:Crystallization Temperature

of Cocoa Butter

food

crystallization

49

Starch gelling

Electrical heated cellWatercoolingFast heating and cooling

rateStirrer acts against

sedimentation of particles

50

melting or crystallization process

preset: constant shear conditions (amplitude and frequency)(with an amplitude in the LVE-range, and mostly with ω = 10 rad/s)

Tk ... crystallization temperature

result:steep decrease or increase, resp.,in a narrow temperature range

Viscoelastic Behavior

Temperature - dependent Behavior

51

preset:

g= 0.02 % ω = 10 rad/s T = T(t)

Viscoelastic BehaviorTemperature - dependent Behavior

food

melting

102

103

104

105

106

108

Pa

-20 -15 -10 -5 0 5 10°C

temperature T

Advantages of icecream 2:1) better separable at –20°C2) less cold - feel when melting3) creamier feel at molten state

lg G' lg G''

1

2

Comparison of two Ice Creams

1 Old Freezer2 New Freezer

52

10-1

100

101

102

Pa

G'

G''

30

35

40

45

50

55

60

65

70

75

°C

T

0 20 40 60 80 100minTime t

Anton Paar GmbH

Vegetable Fat 10%

G' Storage Modulus

G'' Loss Modulus

T Temperature

=1 % =10 1/s

Crystallization of a Vegetable FatRheo-Microscopy

53

Different Behavior of two Ketchup Samples

fast structure recovery

slowstructure recovery

Viscoelastic BehaviorTime - dependent Structure Recovery

for coatings: high wet-layer thickness, good film stability

for coatings:small wet-layer thickness, good levelling

54

Viscoelastic BehaviorTime - dependent Structure Recovery

preset:1 low - shear conditions

(strain in the LVE-range, oscillation)2 high - shear conditions (rotation)3 low - shear conditions

(strain in the LVE-range, oscillation)

measuring result:1 state of rest2 structure decomposition3 structure regeneration

Step test with 3 intervals, as oscillation / rotation / oscillation (measuring „thixotropic behavior“)

2nd test interval:liquid, at high shear rates

1st & 3rd test interval:G‘ > G‘‘ („gel-like structure“ at rest)

www.anton-paar.com

10

100

1000

Pa

G'

G''

0.4

0.6

0.8

1.0

Pas

h

0 50 100 150 200 250s

time t

Ketchup

G'

G''

h

g1 = g3 = 0.3 %

ω = 10 rad/s

=100 s-1 T = +23°C

Step test: oscillation / rotation / oscillation

Viscoelastic behavior: time - dependent structure recovery

56

Interfacial Rheology System (IRS)

MCR Rheometer + Interfacial Rheology System (IRS)

H1 = 22,5 mm

H2 = 45 mm

R = 40 mmR2 = 34,14 mm

2 = 10°

~~~~~~~~ ~~~~~~~~

~~~~~~~~~~~~~~~~~~~~

Air

Liquid 2

Liquid 2

Liquid 1 R2

R

z = H2

z = H1

z = 0

MotorTransducers

P. Erni et. al. J.Rev.Sci.Instr., 74(11), 4916-4924 (2003)

57

IRS: Film Formation of a Coffee Sample at different Concentrations

0.1% strain, frequency 1Hz 0.05g, 0.15g, and 0.3g coffee powder / 114ml double distilled water

10-6

10-5

10-4

10-3

10-2

100

Pa·m

Gi'

Gi''

0 200 400 600 800minTime t

Gi´= 3*10-5 Pa*m