ISO 27971:2015

INTERNATIONAL ISO
STANDARD 27971
Second edition
2015-06-01
Cereals and cereal products —
Common wheat (Triticum
aestivum L.) — Determination of
alveograph properties of dough at
constant hydration from commercial
or test flours and test milling
methodology
Céréales et produits céréaliers — Blé tendre (Triticum aestivum
L.) — Détermination des propriétés alvéographiques d’une
pâte à hydratation constante de farine industrielle ou d’essai et
méthodologie pour la mouture d’essai
Reference number
ISO 27971:2015(E)
©
ISO 2015

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ISO 27971:2015(E)

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© ISO 2015, Published in Switzerland
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ISO 27971:2015(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 1
5 Apparatus . 2
6 Sampling . 9
7 Preparation of the wheat for laboratory milling. .10
7.1 Cleaning the laboratory sample .10
7.2 Test portion .10
7.3 Wheat moisture content determination .10
7.4 Wheat preparation.10
7.4.1 General.10
7.4.2 Wheat with initial moisture content between 13 % and 15 % (one-
stage moistening) .10
7.4.3 Wheat with a moisture content less than 13 % (two-stage moistening) . .10
7.4.4 Wheat with a moisture content greater than 15 % (preliminary drying
followed by moistening, as described above) .11
8 Laboratory milling .11
8.1 General .11
8.2 Milling procedure .11
8.2.1 Breaking .11
8.2.2 Reduction .11
8.2.3 Flour homogenization .12
8.2.4 Storage of the flour.12
8.3 Expression of milling results.12
9 Preparation and alveograph test .13
9.1 Preliminary checks .13
9.2 Preliminary operations .14
9.3 Kneading .15
9.4 Preparation of dough test pieces .16
9.5 Alveograph test .20
9.5.1 Initial preparation.20
9.5.2 First operation: Adjusting the dough test piece .21
9.5.3 Second operation: biaxial extension .22
9.6 Expression of alveograph test results .23
9.6.1 General.23
9.6.2 Maximum pressure parameter, P . 23
9.6.3 Mean abscissa at rupture, L . 23
9.6.4 Swelling index, G . 24
9.6.5 Elasticity index .24
9.6.6 Curve configuration ratio, P/L . 24
9.6.7 Deformation work, W . 24
10 Precision .24
10.1 Interlaboratory tests .24
10.2 Repeatability limits .25
10.2.1 Commercial flour: limits established by the interlaboratory test .25
10.2.2 Flour obtained from laboratory milling .25
10.3 Reproducibility limits .25
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10.3.1 Commercial flour: Limits established by the proficiency tests .25
10.3.2 Flour obtained from laboratory milling .26
10.4 Uncertainty .26
11 Test report .26
Annex A (informative) Characteristics of the Chopin-Dubois CD1 mill .27
Annex B (normative) Quantity of water to be added to wheat for conditioning.29
Annex C (informative) Sample milling sheet .31
Annex D (informative) Conversion table from L to G .32
Annex E (informative) Interlaboratory and proficiency test data for commercial flours .34
Annex F (informative) Interlaboratory data for laboratory milled flour .44
Annex G (informative) Routine maintenance instructions for the alveograph .61
Annex H (informative) Assessment of proteolytic activity in wheat (T. aestivum L.) or flour .63
Bibliography .65
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ISO 27971:2015(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 34, Food products, Subcommittee SC 4,
Cereals and pulse.
This second edition cancels and replaces the first edition (ISO 27971:2008), which has been
technically revised.
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ISO 27971:2015(E)

Introduction
The end-use value of wheat is determined by a number of properties that are useful in the manufacture
of baked products such as bread, rusks, and biscuits.
Such properties include the important viscoelastic (rheological) properties of dough formed as a result
of flour hydration and kneading. An alveograph is used to study the main parameters by subjecting a
dough test piece to biaxial extension (producing a dough bubble) by inflating it with air, which is similar
to the deformation to which it is subjected during panary fermentation.
Recording the pressure generated inside the bubble throughout the deformation of the dough test piece
until it ruptures provides information on the following:
a) the resistance of the dough to deformation, or its strength. It is expressed by the maximum pressure
parameter, P;
b) the extensibility or the possibility of inflating the dough to form a bubble; It is expressed by the
parameters of extensibility, L, or swelling, G;
c) the elasticity of the dough during biaxial extension. It is expressed by the elasticity index, I ;
e
d) the work required to deform the dough bubble until it ruptures, which is proportional to the area
of the alveogram (sum of the pressures throughout the deformation process). It is expressed by the
parameter, W.
The P/L ratio is a measurement of the balance between strength and extensibility.
Alveographs are commonly used throughout the wheat and flour industry, for the following purposes:
— selecting and assessing different varieties of wheat and marketing batches of wheat;
— blending different batches of wheat or flour to produce a batch with given values for the alveographic
criteria (W, P, and L) complying with the proportional laws of blending.
Alveographs are used both on the upstream side of the industry for marketing, selecting and assessing
the different wheat varieties and on the downstream side throughout the baking industries (see
Bibliography).
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INTERNATIONAL STANDARD ISO 27971:2015(E)
Cereals and cereal products — Common wheat (Triticum
aestivum L.) — Determination of alveograph properties of
dough at constant hydration from commercial or test flours
and test milling methodology
1 Scope
This International Standard specifies a method of determining, using an alveograph, the rheological
properties of different types of dough obtained from common wheat flour (Triticum aestivum L.)
produced by industrial milling or laboratory milling.
It describes the alveograph test and how to use a laboratory mill to produce flour in two stages:
— stage 1: preparation of the wheat grain for milling to make it easier to separate the bran from the
endosperm (see Clause 7);
— stage 2: the milling process, including breaking between three fluted rollers, reduction of particle
size between two smooth rollers and the use of a centrifugal sieving machine to grade the products
(see Clause 8).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 660, Animal and vegetable fats and oils — Determination of acid value and acidity
ISO 712, Cereals and cereal products — Determination of moisture content — Reference method
ISO 12099, Animal feeding stuffs, cereals and milled cereal products — Guidelines for the application of near
infrared spectrometry
3 Principle
The behaviour of dough obtained from a mixture of different types of flour and salt water is evaluated
during deformation. A dough disk is subjected to a constant air flow; at first it withstands the pressure.
Subsequently, it inflates into a bubble, according to its extensibility, and ruptures. The change in the
dough is measured and recorded in the form of a curve called an alveogram.
4 Reagents
Unless otherwise specified, use only reagents of recognized analytical grade, and only distilled or
demineralized water or water of equivalent purity.
4.1 Sodium chloride solution, obtained by dissolving (25 ± 0,2) g of sodium chloride (NaCl) in water
and then making the volume up to 1 000 ml. This solution shall not be stored for more than 15 d and its
temperature shall be (20 ± 2) °C when used.
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4.2 Refined vegetable oil, low in polyunsaturates, such as peanut oil. It is possible to use olive oil if its
acid value is less than 0,4 (determined according to ISO 660). Store in a dark place in a closed container
and replace regularly (at least every three months).
Alternatively, liquid paraffin (also known as “soft petroleum paraffin”), with an acid value of less than
or equal to 0,05 and the lowest possible viscosity [maximum 60 mPa·s (60 cP) at 20 °C].
4.3 Cold degreasing agent, optimum safety.
5 Apparatus
Usual laboratory apparatus and, in particular, the following.
5.1 Mechanical cleaner, fitted with sieves for wheat cleaning, in accordance with the manufacturer’s
instructions.
5.2 Conical or riffle sample divider.
5.3 Analytical balance, accurate to 0,01 g.
5.4 Glass burette, of 50 ml in capacity, graduated in 1 ml divisions.
1)
5.5 Rotary blender , for grain conditioning and flour homogenization, including the following components:
5.5.1 Constant speed stirrer.
5.5.2 Two worm screws integral with the flask, possibly via the stopper (one for wheat preparation,
the other for flour homogenization).
5.5.3 Several wide-necked plastic flasks, 2 l capacity.
5.6 Test mill (laboratory mill), manually or automatically operated (see Annex A).
5.7 Complete alveograph system (see Table 1 for specifications and characteristics of the accessories)
including the following devices:
5.7.1 Kneading machine [for models MA 82, MA 87, and MA 95, see Figure 1 a); for model NG, see label
a in Figure 2 and Figure 3], with accurate temperature control, for dough sample preparation.
2)
5.7.2 Hydraulic manometer or Alveolink [for models MA 82, MA 87, and MA 95, see Figure 1 b); for
model NG, see label b in Figure 2 and Figure 3] for recording the pressure curve.
3)
5.7.3 Alveograph [for models MA 82, MA 87, and MA 95, see Figure 1 c); for model NG, see label
c in Figures 2 and Figure 3] with accurate temperature control, for biaxial deformation of the dough
1) The Chopin MR 2 l rotary blender is an example of a suitable product available commercially. This information
is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO
of this product.
2) Alveolink is an example of a suitable product available commercially. This information is given for the
convenience of users of this International Standard and does not constitute an endorsement by ISO of this product.
3) The methods specified in this International Standard are based on the use of the MA 82, MA 87, MA 95 and NG
models of Chopin alveograph which are examples of suitable products commercially available This information is
given for the convenience of users of this International Standard and does not constitute an endorsement by ISO of
this product.
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ISO 27971:2015(E)

test pieces. It has two rest chambers, each containing five plates on which the dough test pieces can be
arranged prior to deformation.
5.8 Burette with stopcock, supplied with the apparatus, 160 ml capacity, graduated in divisions of
0,1 % of moisture content.
NOTE Throughout this International Standard, “content” is expressed as a “mass fraction” (see ISO 80000-9,
[6]
12 ), i.e. the ratio of the mass of substance in a mixture to the total mass of the mixture.
5.9 Timer, for use with model MA 82 only.
5.10 Planimetric scales, supplied with the apparatus where an Alveolink is not included.
5.11 System for recording the test environment conditions (temperature and relative air humidity)
as specified in 8.1 and 9.1.
5.12 Volumetric flask, 1 000 ml capacity, complying with the requirements of ISO 1042, class A.
5.13 Pipette, 25 ml capacity, graduated in divisions of 0,1 ml, complying with the requirements of
ISO 835, class A.
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ISO 27971:2015(E)

a) Kneading machine
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ISO 27971:2015(E)

b) Manometer
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ISO 27971:2015(E)

c) Alveograph
Key
1 handle A in position 2
2 pump potentiometer
3 micrometric valve for air flow adjustment
Figure 1 — Model MA 82, MA 87, and MA 95 alveograph assemblies
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ISO 27971:2015(E)

Key
1 micrometric valve for air flow adjustment
a
NG kneading machine.
b
NG integrator-recorder.
c
NG alveograph (with NG integrator-recorder).
Figure 2 — NG alveograph assembly with Alveolink integrator-recorder
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ISO 27971:2015(E)

Key
1 micrometric valve for air flow adjustment
a
NG kneading machine.
b
NG recording machine.
c
NG alveograph (with hydraulic recording manometer).
Figure 3 — NG alveograph assembly with hydraulic recording manometer
Table 1 — Specifications and characteristics of the accessories required for the test
Value and toler-
Quantity
ance
Rotational frequency of the kneading machine blade (60 ± 2) Hz
Height of sheeting guides (12,0 ± 0,1) mm
Large diameter of the sheeting roller (40,0 ± 0,1) mm
Small diameter of the sheeting roller (33,3 ± 0,1) mm
Inside diameter of the dough cutter (46,0 ± 0,5) mm
Diameter of the aperture created when the moving plate opens (which determines the
(55,0 ± 0,1) mm
effective diameter of the test piece)
Theoretical distance between the fixed and moving plates after clamping (equal to the
(2,67 ± 0,01) mm
thickness of the test piece before inflation)
a
Volume of air automatically injected to detach the test piece prior to inflating the bubble (18 ± 2) ml
Linear speed of the periphery of the recording drum (5,5 ± 0,1) mm/s
b
Air flow ensuring inflation (96 ± 2) l/h
a
Some older devices are fitted with a pear-shaped rubber bulb for manual injection of the 18 ml required to detach the
test piece.
b
To adjust the flow rate of the air generator used to inflate the bubble, fit the nozzle (Figure 4) to create a specified
pressure drop (and obtain a pressure corresponding to a height of 92 mmH2O(12,3 kPa) on the manometer chart). The air
flow rate is set with the standardized pressure drop to obtain a pressure corresponding to a height of 60 mmH2O(8,0 kPa)
on the manometer chart, i.e.(96 ± 2) l/h (see Figure 4 and Figure 5).
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Table 1 (continued)
Value and toler-
Quantity
ance
Rotation time of the manometer drum (from stop to stop) (55 ± 1) s
a
Some older devices are fitted with a pear-shaped rubber bulb for manual injection of the 18 ml required to detach the
test piece.
b
To adjust the flow rate of the air generator used to inflate the bubble, fit the nozzle (Figure 4) to create a specified
pressure drop (and obtain a pressure corresponding to a height of 92 mmH2O(12,3 kPa) on the manometer chart). The air
flow rate is set with the standardized pressure drop to obtain a pressure corresponding to a height of 60 mmH2O(8,0 kPa)
on the manometer chart, i.e.(96 ± 2) l/h (see Figure 4 and Figure 5).
Key
1 knurled ring
2 nozzle
3 nozzle holder
4 top plate
Figure 4 — Flow control system
6 Sampling
A representative wheat or flour sample should have been sent to the laboratory. It shall not have been
damaged or changed during transport or storage.
Sampling is not part of the method specified in this International Standard. Recommended sampling
[1]
methods are given in ISO 24333.
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7 Preparation of the wheat for laboratory milling.
7.1 Cleaning the laboratory sample
Pass the laboratory sample through a mechanical cleaner (5.1) to ensure that all stones and metal
fragments are removed and to avoid damaging the rollers during milling. A magnetic device may also be
used to remove ferrous metal fragments.
7.2 Test portion
The test portion shall be representative of the initial wheat mass. Use the sample divider (5.2) to
homogenize and divide the laboratory sample until the mass required for laboratory milling plus
moisture content determination is obtained. The minimum wheat mass of the test portion for milling
shall be 800 g.
7.3 Wheat moisture content determination
Determine the moisture content of the test portion as specified in ISO 712, or using a rapid device the
measurement of which does not differ from the reference value by ±0,4 g water per 100 g of sample
(see ISO 7700-1).
7.4 Wheat preparation
7.4.1 General
Preparing the wheat for milling makes it easier to separate the bran from the endosperm. The target
moisture content is (16,0 ± 0,5) %.
7.4.2 Wheat with initial moisture content between 13 % and 15 % (one-stage moistening)
Using the balance (5.3), weigh a test portion (minimum 800 g) to the nearest 1 g of wheat and pour it
into the blender.
Add the required amount of water (see Table B.1) to the grain from the burette (5.4) directly, or after
weighing it to the nearest 0,5 g.
Immediately after adding the water, insert the stopper fitted with the worm screw provided for use with
wheat into the flask, shake vigorously for a few seconds and place on the rotary blender (5.5).
Run the rotary blender for (30 ± 5) min (time required to distribute the water evenly across the surface
of the grains).
Allow it to rest for a period that brings the total time of the moistening, shaking and resting operations
to (24 ± 1) h.
7.4.3 Wheat with a moisture content less than 13 % (two-stage moistening)
As a larger volume of water is required, divide it into two halves and add in two stages during the
preparation period.
Proceed as described in 7.4.2, using only half the total quantity of water required (see Table B.1).
Shake the flask as described in 7.4.2 and allow it to rest for at least 6 h.
th th
Then add the second half of the total quantity of water between the 6 hour and the 7 hour.
After adding the second half, shake the flask again for (30 ± 5) min, then allow it to rest for a period that
brings the total time of the moistening, shaking and resting operations to (24 ± 1) h.
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