Transcript Brewing Physical Chemistry: Beta

Flow and Filtration: The
Physics of Brewing
Dr. Alex Speers
Department of Food Science and Technology
<[email protected]>
Outline

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
Scutellum
Acrospire
Aleurone layer
Husk
Embryo axis
Rootlets
Pericarp/testa
Endosperm
Beta-Glucan and Arabinoxylan Content
of Selected Beers (ug / ml)
Brew er
Product Type
B-Glucan
A/USA
Popular Priced L ager
(PPL)
29.4
1968
23.6
20.4
24.2
23.6
32.7
0.4
149.7
79.9
247.7
145.1
0.3
29.3
21.4
57.2
4.5
1031
1684
1657
2094
1292
1386
2368
3347
2598
3131
514
3103
4211
3174
524
B/US A
C/USA
A/USA
B/US A
B/US A
D/USA
E/US A
F/US A
G/Ge rmany
H/Ge rmany
B/US A
F/US A
H/Ge rmany
G/Ge rmany
LSD
Premium La ge r (PL)
Light
Whe at
Arabinoxyla n
Chemical structure of barley glucans
Unbranched chains of -D-glucopyranose
residues
O
O
O
O
-(14)- linkage
O
-(13)- linkage
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 beer
 Thus, add body/foam stability
 In the distant past - not ‘a problem’
 With advent of membrane filters, tight
production schedules & lighter beer
 Pose problems in some breweries some
times

Beta-Glucan fringed micelles
C
A
B
20°C
>70°C
D
Micelle-like Aggregation
Methods
Rheological Definitions


Science of deformation and flow
Three important terms are shear rate (), shear
stress () and viscosity () - note different symbols
used.

h={
 V/h,
 = F/A

V, F
Calculation Example
Shear rate if dV= 1 cm/s and h = 1 cm?
 Shear rate = 1cm/s ÷ 1 cm =1 /s
-1
 Shear rate units /s or s
2
 Shear stress if F= 0.001 N and A= 1 m ?
2
 Shear stress = 0.001 N/ m = 1 mPa


Viscosity = 1 mPa s
Shear stress/shear rate
measurement: rotational
RPM -> shear rate
 Torque -> shear stress
 Viscosity = shear stress/shear rate

Rheometry

Cone and plate and coaxial fixtures
Shear stress/shear rate
measurement: 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

Temperature  = A e DE/RT

Concentration (gums,oP, Etoh)

Shear rate

Shear history
Shear effects
Shear Stress (mPa)
Newtonian Flow
2500
2000
1500
1000
500
0
0
500
1000
Shear Rate (/s)
1500
Shear effects
Viscosity (mPa.s)
Newtonian Flow
2.5
2
1.5
1
0.5
0
0
500
1000
Shear Rate (/s)
1500
Non-Newtonian Flow
 Found
at high gum concentrations
Viscosity (mPa.s)
Pseudoplastic Flow
120
100
80
60
40
20
0
0
500
1000
Shear Rate (/s)
1500
Rheological 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 Notes

Intrinsic Viscosity []

Based on extrapolated Specific viscosity (/  s -1)/c ->0

Can be used to determine shape of polymer based on
molecular weight:

[]KMa
Effect of Concentration
3
1/ log ( rel )
2.5
2
1.5
1
0.5
C*= 3.11 g/L
0
0
2
4
6
8
-glucan concentration (g/L)
10
Determination of C* with 327 kDa -glucan in a control buffer
Early 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
TreatmentpH
maltose ethanol []
C*
(%)
(%)
(mL/g) (g/L)
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
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 20003000

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
– Mean
– Low
915 s-1
500 s -1
175 s -1
Membrane filtration
Theory developed in 30’s
 Based 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’s
 Based 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
Apparatus
Example Sudarmana Transform

Medium viscosity arabinoxlyan in model
beer
Relation of Intrinsic Viscosity
and Filtration

1/Vmax a [] for membrane test

Filterability negatively correlated with
[] for commercial (DE) filtration

Membrane filtration more suited for
detection of -glucan problems
Conclusions
Ethanol, pH and maltose effect viscosity
 Shear strong effect on filtration


Shear within brewery typically turbulent
average 40-1250 s-1

Sudarmana fit ‘works’ (Tech. Quart 33:63)
Acknowledgments
Students !
 NSERC


Labatt Brewing R&D
NSDAM
 Westcan Malting
 Canada Malting
 Pfeuffer GmbH and Profamo Inc

(Viscomat automated capillary rheometer)