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Fifteen organisations from nine countries have collaborated
in certifying a standard wheat flour (denoted CRM 563). The flour
is characterised by 17 properties measured from eight standard test
procedures. Samples of the flour are now available to food manufacturers
and laboratories who wish to calibrate their measuring apparatus to
common European standards.
A bag of flour in the supermarket may look
like any other but, as every bread maker knows, no two batches of
flour are the same. Even flours milled from identical varieties
of wheat will vary according to the soil in which they were grown,
weather conditions, cultivation methods and so on. No farmer can
undertake to grow identical wheat two years running, and flour mills
cannot guarantee that the properties of their flour will remain
the same from one batch to the next.
These differences do not matter much provided that industrial users
of flour, such as bakers and other food manufacturers, can check
the properties of the flour they buy to maintain good quality control.
Some of these properties, such as moisture content, are relatively
straightforward to measure, others, such as the 'rheological' properties
are concerned with consistency and strength of doughs and require
specialised apparatus. While the methods used are agreed by international
standards, there can be considerable differences between measurements
made in different laboratories. Such differences can have serious
financial consequences where large quantities of flour are concerned
and may require costly duplication of effort if re-testing is required.
Ideally, laboratories should have access to a 'certified reference
flour', whose properties are precisely known. The reference flour
can then be used to calibrate the measuring equipment to ensure
that tests are compatible between different laboratories. Until
now no such flour has been available. This project was set up by
the European food industry to remedy that deficiency.
Testing the flour
An ordinary, commercially milled flour was selected by the project's
Scientific Steering Group on the basis of its physical and chemical
properties. A 400-kg batch was blended and then packed into 1000
vacuum-sealed laminated sachets each containing about 360 g; 50
kg of the batch was blended with a different flour to produce control
samples with slightly different properties. In order to ensure stability
of the flour characteristics, all the sachets were stored at a temperature
of minus 20°C.
The partners decided to test the flour for 17 properties measured
from eight standard procedures. The work was carried out by 14 different
laboratories in nine countries which were sent coded samples of
both the flour and the controls.
Apart from standard tests for moisture, protein and ash content,
and more specialised industry tests (falling number, Zeleny sedimentation
volume), empirical some were in nature. The rheological tests required
several different countries to test samples under defined conditions
within a short period of time. This provided a wide base of independent
tests whose values could then be compared.
The rheological tests were based on three specialised measuring
machines used in the food industry:
• The Brabender Farinograph records the resistance of a dough to
mixing (known as consistency) as it is formed from flour and water.
The features of the resulting 'mixing curve' are a guide to the
strength of the flour in relation to its water absorption.
• A sample from the Farinograph is then moulded into a standard
shape. After a fixed period of time the dough is stretched on the
Brabender Extensograph and a curve is drawn recording the resistance
of the dough to stretching. The size and shape of the curve are
a guide to the baking characteristics of the flour.
• Another specialised machine, the Chopin Alveograph, records the
pressure developed in a dough bubble during inflation. The resulting
graph describes the resistance to stretching and the extensibility
of the dough. As with the Extensograph, the length and shape of
the curve can be related to the baking characteristics of the flour.
Strict protocols
Each participating laboratory agreed to perform a certain range
of measurements, depending upon its expertise. In order to reduce
as much as possible any variation between laboratories, the tests
had to be carried out to a strict protocol over a two-week period.
Where the protocol was not followed, the results from that laboratory
were rejected. All the results were subject to rigorous statistical
evaluation to guard against systematic error.
Certified values were found for each of the 17 properties. Full
details are published in the EU Community Bureau of Reference report
EUR 16478 EN.
The greatest technical problem was that the partners were working
with biological material, where it is much more difficult to achieve
consistent results than with a non-biological product.
The project has had two major benefits. First, the partners have
produced a common reference material (now denoted CRM 563) which
will find applications in a very large commercial market. This is
the first time that a suitable reference flour has been available
for this range of rheological properties. Although the reference
flour is used only on a limited scale at present, its use among
European food laboratories and bakeries should eventually become
routine.
Secondly, the project has established a very strong network of laboratories
across Europe which are now all working to a common set of standards.
The result of a test on a food which contains flour in one country
will also be valid for any other country in Europe.
(Samples of the flour may be obtained at the Institute for Reference
Materials and Measurements, IRMM, Retiescweg, B 2240 Geel, Belgium)
When the samples of CRM 563 are used up, the partners plan to certify
another batch of flour in the same way to maintain common standards
throughout the European food industry.
It should be noted that this project is not an attempt to force
European bakeries to standardise the type of flours they use in
their products, but only to ensure that their measuring equipment
is calibrated to common standards.
The potential market for the product is very large as there are
thousands of laboratories, bakeries and food manufacturers in Europe.
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