Flow and Filtration: The Physics of Brewing

1. Flow and Filtration: The Physics of Brewing Dr. Alex Speers Department of Food Science and Technology <Alex.Speers@dal.ca>

2. Outline • Introduction • Brewing gums • shearing • Methods • Rheometry • Filtration • Summary

3. 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

4. Localization of barley -glucans Structure of a barley kernel

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

6. Chemical structure of barley -glucans Unbranched chains of -D-glucopyranose residues O O O O O O -(14)- linkage -(13)- linkage

7. Chemical structure of arabinoxylans

8. 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

9. 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

10. Beta-Glucan fringed micelles

11. Micelle-like Aggregation

12. Methods

13. Rheological Definitions • Science of deformation and flow • Three important terms are shear rate (), shear stress () and viscosity () - note different symbols used.  V, F h={  V/h,  = F/A 

14. Calculation 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

15. Shear stress/shear rate measurement: rotational • RPM -> shear rate • Torque -> shear stress • Viscosity = shear stress/shear rate

16. Rheometry • Cone and plate and coaxial fixtures

17. 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.

18. Rheometry • Capillary viscometer

19. Rheometry • Viscomat

20. Viscosity Dependence • Temperature h = A e DE/RT • Concentration (gums,oP, Etoh) • Shear rate • Shear history

21. Shear effects

22. Shear effects

23. Non-Newtonian Flow • Found at high gum concentrations

24. 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.

25. Rheological Notes • Intrinsic Viscosity [h] • Based on extrapolated Specific viscosity (h/ hs -1)/c ->0 • Can be used to determine shape of polymer based on molecular weight: • [h] = K M a

26. 3 2.5 2 1/ log (h rel ) 1.5 1 0.5 C*= 3.11 g/L 0 0 2 4 6 8 10 b-glucan concentration (g/L) Effect of Concentration Determination of C* with 327 kDa b-glucan in a control buffer

27. Early Results • Using 327 kDa b-glucan at 50 g/L, ethanol (0-7%), maltose (0-15%) and pH (3.6-5.2) • Viscosities were significantly different (P<0.05).

28. Variation of [h] and C* of b-glucan solutions Treatment pH maltose ethanol [h] 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

29. Why Sporadic? • Depends on crop year • Stressed plant tends to more b-glucan (Kendall)

30. Why Some Breweries? • Depends plant equipment • Depends on process • Possibly due to differences in shearing of wort & beer

31. 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

32. Brewing Shear Rates? • Turbulent or laminar? • Turbulent flow cascades to laminar flow at small distance scales

33. Brewing Shear Rates • Defined by Reynolds number of 2000-3000 • Note Re= DVr/h Also note V is the average pipe velocity • Generally get turbulent flow

34. 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

35. 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

36. 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

37. Filtration Apparatus

38. Example Sudarmana Transform • Medium viscosity arabinoxlyan in model beer

39. Relation of Intrinsic Viscosity and Filtration • 1/Vmaxa [h] for membrane test • Filterability negatively correlated with [h] for commercial (DE) filtration • Membrane filtration more suited for detection of b-glucan problems

40. 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)

41. Acknowledgments • Students ! • NSERC • Labatt Brewing R&D • NSDAM • Westcan Malting • Canada Malting • Pfeuffer GmbH and Profamo Inc (Viscomat automated capillary rheometer)