Flow and Filtration: The Flow and Filtration: The Physics of BrewingPhysics of Brewing

Dr. Alex Speers

Department of Food Science and Technology

<Alex.Speers@dal.ca>

OutlineOutline

Introduction– Brewing gums– shearing

Methods– Rheometry– Filtration

Summary

Why study -glucans?

Cause processing problems in brewing:

• Under-modification of barley endosperm

• High viscosity of wort and beer

• Slow runoff of wort and beer

• Haze formation in packaged beer

• Clogging of membranes

• Increased production cost

Localization of barley -glucans

Structure of a barley kernel

Brewer Product Type B-Glucan Arabinoxylan

A/USA Popular Priced Lager(PPL)

29.4 1968

B/USA 23.6 1031C/USA 20.4 1684A/USA Premium Lager (PL) 24.2 1657B/USA 23.6 2094B/USA 32.7 1292D/USA 0.4 1386E/USA 149.7 2368F/USA 79.9 3347G/Germany 247.7 2598H/Germany 145.1 3131B/USA Light 0.3 514F/USA Wheat 29.3 3103H/Germany 21.4 4211G/Germany 57.2 3174LSD 4.5 524

Beta-Glucan and Arabinoxylan Content of Selected Beers (ug / ml)

Chemical structure of barley -glucans

Unbranched chains of -D-glucopyranose residues

-(14)- linkage -(13)- linkage

O OO

OO O

Chemical structure of arabinoxylans

Localization of gums

• Deposited mainly in in endosperm cell walls

• Barley endosperm cell walls contain

20% arabinoxylans

70% -glucans

• Barley aleurone cell walls contain

65-67% arabinoxylans

26-29% -glucans

• Beta-glucan content

barley: 0.14 - 8.9 %

wort/beer: 12 - 940 mg/L

Non-Fermentable Brewing Gums

Defined as Non Starch Polysaccharides Gums - warm water extractable

Tend to viscosify wort and beerThus, add body/foam stabilityIn the distant past - not ‘a problem’With advent of membrane filters, tight

production schedules & lighter beerPose problems in some breweries some

times

Beta-Glucan fringed micelles

A

D

>70°C20°C

C

B

Micelle-like Aggregation

MethodsMethods

Rheological DefinitionsRheological Definitions

Science of deformation and flow Three important terms are shear rate (), shear

stress () and viscosity () - note different symbols used.

h={

V, F

V/h, = F/A

Calculation ExampleCalculation Example

Shear rate if dV= 1 cm/s and h = 1 cm? Shear rate = 1cm/s ÷ 1 cm =1 /s Shear rate units /s or s-1

Shear stress if F= 0.001 N and A= 1 m2 ? Shear stress = 0.001 N/ m2 = 1 mPa

Viscosity = 1 mPa s

Shear stress/shear rate Shear stress/shear rate measurement: rotationalmeasurement: rotational

RPM -> shear rate Torque -> shear stress Viscosity = shear stress/shear rate

Rheometry

Cone and plate and coaxial fixtures

Shear stress/shear rate Shear stress/shear rate measurement: pipe flowmeasurement: pipe flow

Flow rate -> shear rate Pressure loss -> shear stress Viscosity = shear stress/shear rate

Best suited for measuring Newtonian flow behaviour.

Rheometry

Capillary viscometer

Rheometry

Viscomat

Viscosity Dependence Viscosity Dependence

Temperature = A e E/RT

Concentration (gums,oP, Etoh)

Shear rate

Shear history

Shear effectsShear effectsShear effectsShear effects

Newtonian Flow

0

500

1000

1500

2000

2500

0 500 1000 1500

Shear Rate (/s)

Sh

ear

Str

ess

(mP

a)

Shear effectsShear effectsShear effectsShear effects

Newtonian Flow

0

0.5

1

1.5

2

2.5

0 500 1000 1500

Shear Rate (/s)

Vis

cosi

ty (

mP

a.s)

Non-Newtonian FlowNon-Newtonian FlowNon-Newtonian FlowNon-Newtonian Flow

Found at high gum concentrations

Pseudoplastic Flow

020406080

100120

0 500 1000 1500

Shear Rate (/s)

Vis

cosi

ty (

mP

a.s)

Rheological NotesRheological Notes

Normally viscosity properly defined as apparent viscosity - mPa s (= cP),

Kinematic viscosity is apparent viscosity divided by density (Stokes)

– (Misleading terms in literature),

1 mPa s is = 1 cP ~ viscosity of water at 20oC,

Apparent viscosty depends on density, temperature, shear rate and shear history.

Rheological NotesRheological Notes

Intrinsic Viscosity [

Based on extrapolated Specific viscosity (/ s -1)/c ->0

Can be used to determine shape of polymer based on molecular weight:

[

Determination of C* with 327 kDa -glucan in a control buffer

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10

-glucan concentration (g/L)

C*= 3.11 g/L

1/

log

(

rel

)

Effect of ConcentrationEffect of Concentration

Early ResultsEarly Results

Using 327 kDa -glucan at 50 g/L, ethanol (0-7%), maltose (0-15%) and pH (3.6-5.2)

Viscosities were significantly different (P<0.05).

Variation of [] and C* of -glucan solutions

High ethanol 4.1 0.5 6.0 464 6.47

Low ethanol 4.1 0.5 4.0 812 2.72

Control 4.1 0.5 5.0 815 3.11

High maltose 4.1 0.8 5.0 806 2.13

Low maltose 4.1 0.1 5.0 862 3.05

Low pH 3.6 0.5 5.0 741 3.95

High pH 4.5 0.5 5.0 827 3.05

Treatment pH maltose ethanol [] C* (%) (%) (mL/g) (g/L)

Why Sporadic?

Depends on crop year

Stressed plant tends to more -glucan (Kendall)

Why Some Breweries?

Depends plant equipment

Depends on process

Possibly due to differences in shearing of wort & beer

Brewing Shear Rates?

Turbulent or laminar?

NRE =V L/

= density, V = velocity L= diameter = viscosity

Average shear rate in turbulence

= [(/)3 / ]1/4

= average power dissipation per unit mass

Brewing Shear Rates?

Turbulent or laminar? Turbulent flow cascades to

laminar flow at small distance scales

Brewing Shear Rates

Defined by Reynolds number of 2000-3000

Note Re= DV/ Also note V is the average pipe velocity

Generally get turbulent flow

Brewing Shear Rates

Shear in Kettle 8600 s-1

– (Speers et al. 2002) Shear in Fermenter 20-60 s-1

(Speers & Ritcey, 1995) Shear in Yeast brink tank <15 s-1

(Kawamura et al. 1999) Average shear rate in pipe flow

– High 915 s-1

– Mean 500 s -1

– Low 175 s -1

Membrane filtration

Theory developed in 30’sBased on capillary plugging due to gradual

restriction in diameter

Surdarmana et al. 1996 Tech Quarterly

t/V = t/Vmax + 1/Qinit

Vmax maximum filtrate volume

Qinit intial flow rate

Membrane filtration

Theory developed in 30’sBased on capillary plugging due to gradual

restriction in diameter

Surdarmana et al. 1996 Tech Quarterly

t/V = t/Vmax + 1/Qinit

Vmax maximum filtrate volume

Qinit intial flow rate

Filtration Filtration ApparatusApparatus

Example Sudarmana TransformExample Sudarmana Transform

Medium viscosity arabinoxlyan in model beer

Relation of Intrinsic Viscosity Relation of Intrinsic Viscosity and Filtrationand Filtration

1/Vmax [] for membrane test

Filterability negatively correlated with [] for commercial (DE) filtration

Membrane filtration more suited for detection of -glucan problems

ConclusionsConclusions

Ethanol, pH and maltose effect viscosityShear strong effect on filtration

Shear within brewery typically turbulent average 40-1250 s-1

Sudarmana fit ‘works’ (Tech. Quart 33:63)

Students !NSERC

Labatt Brewing R&D

NSDAMWestcan MaltingCanada MaltingPfeuffer GmbH and Profamo Inc

(Viscomat automated capillary rheometer)

Acknowledgments