Yearbook 2013/2014 - ehedg

European Hygienic Engineering & Design Group
Infection-free preparation of bacterial cultures
The preparation and compounding of freeze-dried bacterial cultures available in powder form
requires extremely high standards of hygiene. If the material is also deep frozen the mixing
equipment must have very good insulation and meet increased strength requirements.
Dipl.-Ing. Ludger Hilleke, amixon GmbH, D-33106 Paderborn, Phone: +49 5251 68 88 88-0, info@amixon.de,
www.amixon.de
Today, fermented specialities enhance nearly all of the most
commonly produced dairy products. Whether in cheese,
curd and yoghurt, or when used for improving meat, they
can be found everywhere. However, the production of these
powdery granular materials is a real challenge, especially in
further processing environments, which demand a high level
of cleanliness, quality of handling, and a granular dust-free
structure.
A determinant of the quality in this process is operation
with the minimum of interruptions; in other words, as nearly
continuously as possible. High-purity bacterial cultures form
by cell division, and for industrial production, the aqueous
suspension of bacteria is continuously diluted with nutrient
solution. After a constant dwell time, the matured suspension
is removed and washing processes follow. The cell division
process does not stop until the extracted cultures are frozen.
To facilitate handling, the cultures also are sometimes freeze
dried, which produces a loose powder or granulate with bulk
densities around 0.1 to 0.4 kg/dm 3 .
In subsequent automated processing of bacterial cultures
there is often a mixing process. Naturally, a quick result is
desirable, with the mixing done in a way that avoids causing
damage and that work efficiently under difficult conditions
(i.e., differing filling degrees, bulk densities, particle sizes,
rotational speeds, etc.). In addition, as a result of the
alternating stresses that result from very high temperature
changes in these processes, mixers must be specially
designed to avoid fatigue cracks.
Meeting all of these challenges of producing powderform
freeze-dried bacterial cultures in a hygienic manner
requires mixers that are designed with hygiene in mind.
A good example is a single-shaft mixer whose mixing
principle is based on a three-dimensional rearrangement,
such as those produced by amixon GmbH (Figure 1). In
such a mixer, the material in the periphery of the mixing
chamber is screwed upwards and then flows downwards
in the centre. The helical mixing tool performs mixing
very gently at circumferential speeds of 0.2 to 0.9 m/s. A
particularly useful feature is that the mixing process takes
place independently of the filling level. In this respect the
emptying process also takes place without segregation,
even when it takes a long time or occurs while pulsating.
The high degree of residue emptying assists in keeping the
mixer highly sanitary.
Figure 1. Example of a single-shaft mixer that can be used in the
manufacture of powder-form freeze-dried bacterial cultures.
Thorough cleaning of a processing plant in which mixing
of powders occurs is also clearly essential. Avoiding
contamination is both a determinant of quality and an
absolute ‘must’ in producing foods free of allergens. One
solution to this challenge is the automation of wet cleaning
and drying of powder mixers. In one patented process, a
clean-in-place (CIP) device is firmly installed on the mixing
chamber and remains there permanently. For wet cleaning,
the sealing plug in the mixing chamber opens and makes
the space available for the motion of a rotating wash lance.
The latter moves into the mixing chamber with translatory
motion. With an applied water pressure of about 3.5 bar,
the head rotates and three nozzles spray the entire mixing
chamber interior. Depending on the size and execution of
the mixer, three, four, or in some cases five, washing heads
are necessary for wetting the entire mixing chamber and all
parts of the mixing tool.
After completion of the wet cleaning, drying is essential.
Bearing in mind that the specific heat capacity of water is
about nine times as great as that of stainless steel, the wet
cleaning with hot water spontaneously heats up the mixer.
This heat assists the steam stripping of the mixer. Additional
hot air entering via an inlet through the main connection of
the CIP device accelerates the drying process.
The entire mixer and the CIP system are dried. Only then
does the rotating lance move out of the mixing chamber and
the sealing plug closes the container, gas-tight and liquidtight.