Rheological characterisation of cake batters generated by planetary mixing:
Elastic versus viscous effects
A.K.S. Chesterton
a
, B.E. Meza
a,b
, G.D. Moggridge
a
, P.A. Sadd
c
, D.I. Wilson
a,
⇑
a
Department of Chemical Engineering and Biotechnology, New Museums Site, Cambridge CB2 3RA, UK
b
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET),
Universidad Nacional del Litoral (UNL), Güemes 3450, 3000 Santa Fe, Argentina
c
Premier Foods, High Wycombe HP12 3QR, UK
article info
Article history:
Received 23 November 2010
Received in revised form 14 February 2011
Accepted 20 February 2011
Available online 24 February 2011
Keywords:
Cake batter
Kenwood
Hobart
Planetary mixer
Rheology
Shear rate
Elastic
abstract
Studies of cake batter rheology have focused on viscous behaviour. We demonstrate that elastic effects
dominate at the shear rates used in commercial mixers. The development of batter structure was inves-
tigated for two flour types using two bench-scale planetary mixers with known shear rate profiles (Ken-
wood-KM250, maximum 100 s
À1
; Hobart-N50, 500 s
À1
). These wet foams (air volume fraction 0.39–0.45)
showed shear-thinning behaviour at low shear rates (0.1–10 s
À1
), with apparent viscosity dependent on
air volume fraction. Simple shear thinning behaviour ceased, for foams, above 10–20 s
À1
: for slurries (air
volume fraction, 0.11–0.15) the limit approached 100 s
À1
. Elastic effects, predominantly arising from the
bubble phase, therefore dominate cake batter behaviour at the shear rates experienced in commercial
mixers. Filament thinning extensional rheometry confirmed the VE behaviour of batters. These results
indicate that visco-elastic analyses are likely to be the most appropriate probe of microstructure in cake
batters.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Many foodstuffs are examples of soft solids whose microstruc-
ture (and therefore properties and behaviour) are dictated by their
ingredients, formulation, and processing conditions. The latter
grouping can include the type of process unit (and its mode of ac-
tion) as well as the operating parameters. Cake batter is a prime
example of a structured, soft solid. Commercially, batter is gener-
ated by the aeration of a water-based mixture, typically containing
wheat flour, sugar, egg, fat, leavening agents, salt, water and milk
powder in varying proportions (Mizukoshi et al., 1979). Fat may
be added prior to, or following, the aeration process yielding a
three-phase fluid, of (i) air bubbles; (ii) suspended insoluble mat-
ter; and (iii) a fat–water emulsion as the continuous phase. The
air bubble volume fraction is typically 0.25–0.45, so the batter is
considered as a wet foam. At these gas volume fractions the foam
behaves as a bubbly liquid, rather than a rigid foam. On heating,
the foam sets to form a stable structured food product, the micro-
structure of which is directly determined by the batter from which
it is baked. The physical properties of cakes, such as the volume,
shape, texture, porosity and colour, depend on many factors,
including the processing conditions (Baixauli et al., 2007; Cauvain
and Cyster, 1996; Edoura-Gaena et al., 2007; Massey et al., 2001).
Knowledge of the impact of processing on product structure is
essential for process improvement. Inclusion of air is a key aspect
of batter preparation, not only in determining the structure of the
baked product but also its effect on the batter rheology which gov-
erns the expansion of the material before the continuous phase
sets. Foam rheology is a key product attribute and likely to be sen-
sitive to shear history. Knowledge of the relationships between
process units, processing conditions and formulation is important
for comparing laboratory results with different mixers and scaling
these to a bakery scale unit.
This paper is concerned with the generation of cake batters
using planetary mixers, which are ideally suited for small scale
batter preparation in the laboratory and kitchen. They are able to
combine and mix the ingredients sufficiently, achieving a uniform
dispersion of insoluble material, and during the aeration stage, the
entrainment of air (Sumnu and Sahin, 2008). In a companion paper
(Chesterton et al., 2011) we presented a quantitative analysis of
the shear rates generated in two widely used lab scale planetary
mixers, namely a Kenwood-KM250 and a Hobart-N50 device. The
shear rates generated at the wall ranged from 20-100 s
À1
and
100-500 s
À1
, respectively. This paper reports the results of rheo-
metrical studies on the batter as it is prepared in the two devices,
showing shear thinning behaviour described by the Ostwald-de
0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2011.02.043
⇑
Corresponding author. Tel.: +44 1223 334 791; fax: +44 1223 331 796.
E-mail address: ian_wilson@cheng.cam.ac.uk (D.I. Wilson).
Journal of Food Engineering 105 (2011) 332–342
Contents lists available at ScienceDirect
Journal of Food Engineering
journal homepage: www.elsevier.com/locate/jfoodeng