Conventional mixers used in industrial breadmaking are frequently flanked by plants offering latest useful functions for the production of wellhydrated dough with a homogeneous textur

Lunadei, Loredana

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

B
read certainly is Italy’s
favourite food, thanks to
its perfectly balanced mix
of flavours, aromas and
nutritional properties. 
The data on Italian bread
consumption confirm its popularity
on Italian tables: 1.2 million tons of
bread and similar products were
consumed in 2005, worth Euro 2.86B
altogether. The base ingredients used
in bread-making are: flour, water,
yeast, and salt, which may be added
with other substances, such as malt,
fats, eggs, milk, nuts, seeds, etc. 
Thanks to an adequate technological
process, all these ingredients
contribute to the creation of different
types of bread, displayed in the
appealing baskets of bakery shops
and supermarkets, as: baguettes, toast
bread, bread with olives or nuts. 
The sequence of operations
composing this process, and
contributing to the production of
well-aired and porous structures,
includes only a few – although basic
– steps as: mixing, leavening, and
baking. 
The mixing phase
Mixing certainly is one of the most
critical operations in the bread-
making process. Here, in fact, all the
ingredients are added and mixed to
produce a perfectly homogeneous and
hydrated dough, while insoluble
proteins start forming the gluten
assembly, from which depends the
behaviour of the dough during
fermentation and cooking. In this
phase, the critical issues consists in:
selecting top-quality raw materials;
assessing with great care the
mechanical properties of the flour,
also in connection to the properties of
the end-product; and in accurately
monitoring specific parameters.
Among these, temperature is probably
the most important one, as it can
strongly influence the dough’s
chemical, biological and rheological
properties. In order to guarantee an
environment suitable to the
metabolism of yeasts, an optimal
development of gluten is required,
and, hence, in order to guarantee the
top-quality of the final product, the
temperature must be comprised
between 23 and 27°C, according to
the hydration rate. To this purpose,
the heat developed during the process
– resulting from the friction, the
environment, the hydration heat and
the speed of the mixing elements –
must be kept under control.
april 200746
TECHNOLOGY
CALLING UPON...
g by Loredana Lunadei
Latest advancements 
Mixer technology for
bread-making machines
Conventional mixers used
in industrial bread-
making are frequently
flanked by plants offering
latest useful functions for
the production of well-
hydrated dough with a
homogeneous texture
Mixers and their features
In the case of industrial production,
the mixing is performed by mixing
machines, consisting mainly of: an
electric motor, running at one or two
speeds; a base, bearing the mixing
elements; a mixing bowl, in rotary or
stationary version, open or tightly
sealed; mixing arms; and transmission
components transmitting the
movement to the bowl and to the
various tools. Various different types
of mixing machines are available on
the market, offering a variety of
properties and performances, and
mainly characterised by the number,
shape and position of the mixing arms
(generally from one to three, equipped
with beaters, hooks, spirals or rotary
shafts, mounted in vertical, horizontal
or skewed position), the rotation speed
(conventional mixers achieve 25 to 35
r.p.m., with high-speed models
reaching up to 70 to100 r.p.m., the
bowl unloading system (which may be
fixed or mobile, or equipped with
lifting and tilting device for dough
unloading), the volume of dough that
can be mixed (ranging from capacities
of less than 100 l to more than 1000 l),
and, finally, by the type of process they
can achieve ( batch or continuous).
The most popular mixers in Italy for
bread-making processes are of the
“slow” type, i.e.: 
– Fork mixer, mainly used for hard or
medium-hard dough, with a water
content of 32-35% or 45-50%
respectively. Compared to other
models, this kind of mixer is the
slowest, and is characterised by a
longer dough rising and kneading time
for the same volume;
– Double-arm mixer, soft and
medium-hard dough, characterised by
a water content of 50-70%  and 45-
50%, respectively. The double arm
action incorporates lots of air in the
dough, and is excellent for capturing
air and “opening” the dough,
providing for shorter kneading time
and faster rising processes;
furthermore, the resulting volume of
dough – and, hence, of end-product –
is far higher;
– Spiral mixer; here the dough is the
result of compressions from top to
bottom; this unit produces soft and
medium-hard dough. On one side, this
mixer incorporates less air and causes
a higher heating of the mix, but is
characterised by a considerably
shorter mixing time compared to other
types of mixers. 
The problem of excessive temperature
increase in the dough varies according
to the implemented type of mixer, and
according to the friction developed by
moving parts: fork mixers, for
instance, cause the lowest temperature
increase (0°-2°C), followed by double-
arm mixers (4°-6°C), and spiral
april 2007
47
mixers (with an increase of 9°-10°C).
As for energy consumptions, on the
other hand, spiral mixers rank first
(for which, however, a system has
been developed providing for up to
20-25% energy savings), followed by
double-arm mixers and fork mixers.
Next to conventional models, there are
also high-speed mixers, in which the
rest period can be avoided (3-5
minutes required for completing the
hydration and formation of gluten in
conventional mixing systems), since
the high-speed movement brings
about the same effects of the action of
enzymes during the rest time required
for fermentation. This technology,
however, has not found fertile ground
in Italy, whereas it developed itself
mainly in the United Kingdom and
US, because the resulting bread does
not have the typical flavour and
aroma required by Italian consumers,
and also since this kind of process
requires the addition of a considerable
amount of oxidising agents, which doe
not comply with Italian regulations on
this matter. Another type of mixer, the
carousel mixer, launched in the US by
the end of the ’50s, is suitable for
continuous bread-making processes, in
which the whole process is performed
without stops. 
These technologies are not widespread
in Italy for the production of bread
(also due to their high installation and
maintenance costs), and are more
popular in English-speaking countries
or for the production of other kinds of
baked goods.
Innovations on the market 
The mixers conventionally used in
bread-making processes may profit of
innovative technologies
and tools, capable of
improving their
effectiveness, reliability
and efficiency, while
providing for perfect
dough in – often
considerably – shorter
times.
Dough cooling with
liquid nitrogen: the
problem of dough heat
can be generally solved by
implementing one of the following
solutions: using pre-cooled flour and
water, replacing part of the water with
ground ice, blowing carbon dioxide
into the dough, which chills the
dough when the liquid turns into gas,
or by means of a mechanical
refrigerating system, consisting of a
cooling jacket surrounding the mixing
bowl, inside which the coolants (cold
water, solutions of propylene-glycol,
ammonia or halogenated
hydrocarbons) are flowing.
An innovative system has been
recently introduced on the market,
consisting in the addition of liquid
nitrogen directly into the pneumatic
flour conveying pipe, by means of a
series of specifically designed nozzles.
Liquid nitrogen (injected at a
temperature of–196°C) is used to
decrease the flour temperature by
approx. 25°C, which inside the silos
can reach even 35-40°C. The
integration of this injection system
does not require considerable
modifications to the plant, and can be
performed quickly during a periodical
machine standstill. This cooling
system offers a variety of benefits, as:
flexibility and high cooling
effectiveness; homogeneous
temperature; absence of thermal
shock; high cooling speed; automation
of the plant during mixing processes.
Continuous spiral-mixing system: a
new technology has faced in the range
of continuous mixers, combining the
advantages of continuous process to
the quality and flexibility of the spiral
mixing system. Thanks to this
technology, the limitations of
conventional continuous systems can
be avoided. Several advantages are
offered, as: high production; delicate
mixing; low heat; and high production
flexibility. The ingredients fed by
means of “loss in weight feeders” are
blended in a premix chamber and
mixed in a circular channel, in which
a variable number of spiral mixing
tools (depending on the required
production per hour) are machining
small portions of batch. Each spiral
tool has a circular motion around its
axis (responsible of the machining
process) and a planetary motion
around the bowl axis (for conveying
the dough to the outlet area). The
speed of each motion is independent
and adjustable, for an efficient control
april 200748
TECHNOLOGY
CALLING UPON...
of the production both in terms of
quality and quantity. Moreover,
process parameters (including dough
temperature, production data, etc.) are
constantly monitored via a PLC.
Industrial mixing systems with
lubrication-free gearboxes: of recent
construction, these mixers are suitable
for biscuits and industrial baked
products and feature lubrication-free
gearboxes. Planetary mixers derive
their name from the movement of the
mixing tool, which is similar to that of
planets as it turns on itself and at the
same time along the edge of the
mixing bowl. These units are
extremely versatile and are used for
various applications, as sponge cakes
and creams. In particular, the mixers
featuring the new gearbox provide for
higher process hygiene (thanks to
their simple design that allows easy
cleaning and to the total elimination
of oil, which may contaminate food)
and are characterised by sturdy
mechanical construction; there are no
seals and gaskets, and no special
maintenance is required. Furthermore
they provide for excellent use
flexibility, as the gearbox is driven by
two independent motors, providing for
independent rotation of the tools and
of their planetary movement.
New combined mix: a new mixing
system has been combining in a sole
machine the dough concepts and
advantages of spiral and twin-arm
mixers. The dough is the result of
“compressions” between the mixing
tools and the bowl wall, and of the
“stretching” actions between the two
arms, which cross in opposite
directions. This sequence of
compressions and stretching produces
a complete dough “opening” followed
by optimal gluten development. This
mixer perfectly meets the needs of
processing products with an “open
structure”, such as “ciabatta” or
artisan bread, but they are suitable
also for producing other kinds of
products with a high fats content, as
“panettone”, croissants, donuts, puff
pastry etc., as well as of classic
products such as baguette, pizza or
rye bread. 
Compared to conventional mixing
systems, the new mixer offers
improved dough hydration and
increase in water absorption, with
minimum increase in temperature;
excellent gluten development;
shorter mixing time; and improved
mixing of fat matter (butter,
margarine, eggs, etc.).
Latest news on natural yeast
fermentation: recently, a new system
for the quick forming of sour dough
from natural yeast fermentation has
been developed suitable for feeding
processing lines  handling  a variety
of baked goods, including various
types of rye and corn bread, leavened
baked goods such as panettone,
pandoro, colomba. 
Here, the ingredients – flour, salt and
yeast - are fed into the mixing bowl
and then water is added at high
pressure. 
This system provides for an optimal
distribution of water molecules
between flour particles, which are
perfectly hydrated. These particles
glutinize creating a homogeneous
product, ready for use.
april 2007
49
Oxidisers are synthetic inorganic salts
contributing to improve the rheologic properties
of gluten, providing for improved water
absorption and retention of carbon dioxide.
When added to the dough ingredients, they
guarantee the development of perfectly
leavened products with a uniformly open
structure. This effect derives from the peculiarity
of these substances of inhibiting the proteolysis,
i.e. the reaction that, by means of proteases,
separates the proteins of the dough in shorter
peptides, thus reducing the strength of the flour
and weakening the structure of the dough.
Oxidisers, in fact, transform the active part of
proteins present in dough (showing a dominating presence of thiolic groups, -SH-), more sensitive to
the aggression of protease, in the passive part (containing mainly disulphuric groups, -S-S-), less
subject to chemical attack. In several countries, among which Italy, the use many oxidisers such as
potassium bromate and   azodicarbonamide, has been prohibited due to their toxicity. The sole
additive accepted by Italian legislation is l-ascorbic acid  (vitamin C), which may be added to the
dough in one part per million.
The effect of L-ascorbic acid on dough was first noticed in 1935 by Jorgensen. Until that moment,
the reducing action of Vitamin C was known, but practical tests on dough revealed an action similar
to that of the oxidisers studied until that moment. In 1938, the researchers Melville and Shattock
found an explanation to this phenomenon, and discovered that the enzymes present in the flour
contribute to transform the L-ascorbic acid into de-hydroascorbic acid, a powerful oxidiser which, on
its turn, oxidises the thiolic groups of gluten proteins, transforming them into bisulphuric groups.
FLOUR OXIDISING SUBSTANCES:
WHAT’S THEIR USE?


Latest advancements: mixer technology for bread-making machines

Conventional mixers used in industrial breadmaking are frequently flanked by plants offering latest useful functions for
the production of wellhydrated dough with a
homogeneous texture

Latest advancements: mixer technology for bread-making machines

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