pH is one of the key parameters in food production.
adjusted pH value determines the degree of enzyme activity.
Endopeptidase, which is responsible for decomposing protein in
mash when brewing beer, requires a pH environment of pH5.
which thickens milk in cheese production, requires a value of
In the production of acidified milk products, the pH must
be maintained precisely to ensure the quality of the final
In the production of yoghurt, the pH must not drop below
4 - 4.2.
Therefore, the product is rapidly cooled down at a pH of
4.4 - 4.6 during yoghurt maturation to prevent
Although the pH value in food processing is
an important control parameter, it is usually measured in the
laboratory and not in-line in the process.
measurements are firstly expensive, and secondly inefficient
compared with an in-line pH control system, which can display the
current product pH values and start or stop process steps
It could also create documentation of pH curves for an
entire bottled product batch.
Of course, the issues relating to
cleanability of the sensors and assemblies integrated in the
process are extremely high.
Contrary to laboratory measurements,
a glass electrode is subjected to various continuous stresses in
Chemical influences as well as cold acids
and alkalis occurring during CIP cleaning dehydrate the
pH-sensitive coating on the glass membrane.
during steam sterilisation age the glass prematurely and lead to
a loss of slope.
On the reference side, the diaphragms (mainly
made of ceramic) can become blocked by fat and proteins.
lead to seriously false measured variables.
If the electrode
connectors and cable connections are not spraywater-proof, it can
lead to repeated faults.
Modern pH process electrodes, such as
the gel-filled Orbisint or the Ceraliquid filled with liquid KCl,
have a pH-sensitive process glass membrane which supply excellent
measurement results in cold, weak-acid and acid pH ranges of the
product (eg, beer: pH4.4 at 0C).
Attack by acids and alkalis in
CIP systems on the glass membrane is negligible, ie, the acid or
alkaline error after CIP cleaning is max.
glass recipe ensures long life, even when exposed to extremely
differing process conditions.
Of course, these electrodes can be
sterilised in steam and in autoclaves.
Orbisint, a gel-filled pH
combination electrode, is equipped with a large-area ring
diaphragm made of special sintered PTFE.
PTFE is dirt-repellent
and prevents the deposit of fats and proteins on the diaphragms.
The enormous increase in area also ensures long-term defect-free
function of the reference system.
Not always is the gel-filled
electrode the best solution for the process.
liquid-filled electrode is better suited to fast-changing pH
jumps or media containing high levels of protein or fat.
Ceraliquid, the liquid-filled combination electrode, is fitted
with a zirconium dioxide diaphragm which has a constant pore size
due to a patented production process.
It therefore ensures a
constant KCl flow rate (0.65ml/d).
This flow rate is vital since
it rinses the diaphragm free and allows a drift-free pH
The escaping electrolyte, 3-molar KCL, poses no risk
of contamination for the foodstuff produced since its
concentration is high and the volume used is low.
is provided with a diagram which shows the pressure settings to
obtain the optimal electrolyte flow through the diaphragm at
various process pressures and temperatures.
In order to determine
the pH value in the process with absolute accuracy, it is vital
to measure the temperature and perform temperature compensation
with the currently measured value at the same time.
This is why
Orbisint and Ceraliquid electrodes have an integrated Pt100
temperature sensor which is located directly at the tip of the
electrode behind the pH-sensitive glass.
The advantage here is
that the actual temperature is detected both in measurement and
calibration mode, thus ensuring precise measurement and
Moisture bridges immediately lead to short circuits
in the high-impedance pH measurement.
THe measuring systems in
breweries and dairies are constantly sprayed with water by the
TOP68 is a pH electrode plug-in system that is
protected to IP68 and is therefore more than just spraywater
An O-ring on the electrode head forms the radial seal
with the coupling.
The plug and the coupling are made of rigid,
highly resistant PPS.
The insulator, in which two, four, or six
contact pins are embedded, is made of soft, hydrophobic
(water-repellent) PFA plastic.
The contacts can thus be embedded
without gaps and the electrode can then be cleaned in an
autoclave in open state.
Since PFA repels water and only
microfine droplet traces remain on the surface, there are no
moisture bridges if the plug is wetted during assembly or
The electrode need only be wiped to make it
immediately functional again.
Retractable assemblies are used to
immerse pH sensors in the process.
These assemblies can be
cleaned during the process, immersed in water during idle times,
retracted during CIP phases or the pH sensor can be automatically
cleaned and calibrated.
The Probfit CPA 465pH retractable
assembly is made of polished stainless steel and is designed to
fit all process adapters typically used in the food industry,
such as the DN 50 sanitary tube union, 2" clamp adapter, APV
or the Varivent adapter.
The electrode is inserted in a metal
tube and sealed with an O-ring.
The pH-sensitive glass membrane
is additionally protected against mechanical forcess and damage
by fours webs.
For cleaning or calibration, the electrode guide
together with the electrode are retracted from the process
pneumatically and a shaped seal wipes off any product rests still
adhering to the electrode.
The shaped seals made of EPDM are
integrated in the assembly with no undercuts and have much
greater strength than other O-rings normally used.
have much longer service intervals than O-rings.
If the seal is
damaged, it is immediately signalled by a leak detector.
USA, the Probfit CPA 465 is approved as 3-A Sanitary Equipment;
in the Netherlands, the TNO has granted its approval for steam
sterilisation according to the regulations fo the European
Hygienic Equipment Design Group (EHEDG).
The pH transmitters of
the Mycom and Liquisys series designed for the food industry are
fitted with several functions which allow easier and more
reliable pH measurements: Simple two-point calibration with
The measuring point is calibrated by only
pressing one button on the instrument and involves no complicated
menu navigation; Safety functions provided by sensor and process
check systems such as sensor life check alarm which checks
continuously whether the sensor signal is a live measuring
signal; Sensor check system for the pH glass detects hairline
cracks and glass breakage; Sensor check system for the reference
system detects soiling and blockages in the reference electrode.
This can also trigger sensor cleaning; All instruments are
available with Profibus-PA protocol as well as the conventional 4
- 20mA output signal for the pH and temperature measured
Finally, two different examples of quality monitoring
with pH in-line systems: Before bottling, liquid mustard must not
exceed a pH range of 3.5 - 3.7, otherwise quality is drastically
Therefore, for safety reasons, a pH measuring system is
installed comprising a gel-filled electrode, a CPA 465
retractable assembly fitted with pneumatic manual control and a
transmitter with limits.
The system is cleaned manually after
every bottling operation and is calibrated once a week.
solution gives the user a high degree of measuring reliability,
allows simple cleaning and minimises maintenance costs.
milk acceptance point, milk collected from various farms is
transferred from the tanker to the dairy.
The key criterion is
that the pH value of the incoming milk should not be less than
6.65 or more than 6.85.
To ensure high measuring accuracy, a
pressurised, liquid-filled Ceraliquid pH electrode is installed.
The retractable assembly is controlled by a CPC 200/210 automatic
calibration and cleaning system.
This system controls all the
cleaning and calibration processes, and moves the wetted assembly
to standby position during service breaks.
takes place ten times a day with water and a special cleaning
Calibration takes place once a day.