ISO 15598:1999

INTERNATIONAL ISO
STANDARD 15598
First edition
1999-06-01
Tea — Determination of crude fibre content
Thé — Détermination de l'indice d'insoluble dit «cellulosique»
A
Reference number
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 15598 was prepared by Technical Committee ISO/TC 34, Agricultural food products,
Subcommittee SC 8, Tea.
Annex A of this International Standard is for information only.
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
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Printed in Switzerland
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INTERNATIONAL STANDARD  © ISO ISO 15598:1999(E)
Tea — Determination of crude fibre content
1 Scope
This International Standard specifies a method for the determination of crude fibre content in tea.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 1573:1980, Tea — Determination of loss in mass at 103 °C.
ISO 3696, Water for analytical laboratory use — Specification and test methods.
3 Term and definition
For the purposes of this International Standard, the following term and definition apply.
3.1
crude fibre content
the whole of the substances which are insoluble and combustible under the operating conditions specified in this
International Standard
NOTE It is expressed as a mass fraction, in percent, of the product on a dry basis [formerly expressed as % (m/m)].
4 Principle
The suitably ground sample is successively treated with boiling sulfuric acid solution and sodium hydroxide solution.
The residue is separated by filtration, washed, dried, weighed and then ashed. The loss in mass resulting from
ashing is called the crude fibre content.
5 Reagents
Use only reagents of recognized analytical grade.
5.1  Water, complying with grade 3 of ISO 3696.
5.2  Sulfuric acid stock solution, c(½H SO ) = 2,040 ± 0,040 mol/l (corresponding to 100 g of sulfuric acid per
2 4
litre of solution).
© ISO
Add 275 ml of concentrated sulfuric acid (r = 1,84 g/ml) to water, cool and dilute to 5 l.
CAUTION — Wear gloves and face protection.
5.3  Sulfuric acid working solution, c(½H SO ) = 0,255 ± 0,005 mol/l (corresponding to 12,5 g of sulfuric acid per
2 4
litre of solution).
Dilute 125 ml of the sulfuric acid stock solution (5.2) to 1 l.
5.4  Sodium hydroxide stock solution, c(NaOH) = 2,504 ± 0,040 mol/l (corresponding to 100 g of sodium
hydroxide per litre of solution).
Dissolve 500 g of sodium hydroxide in water, cool and dilute to 5 l.
CAUTION — Wear gloves and face protection.
5.5  Sodium hydroxide working solution, c(NaOH) = 0,313 ± 0,005 mol/l (corresponding to 12,5 g of sodium
hydroxide per litre of solution).
Dilute 125 ml of the sodium hydroxide stock solution (5.4) to 1 l.
5.6  Octan-1-ol, as antifoaming agent.
5.7  Hydrochloric acid, 1 % solution (volume fraction).
Dilute 10 ml of concentrated hydrochloric acid (r = 1,19 g/ml) to 1 l.
CAUTION — Wear gloves and face protection.
5.8  Ethanol, of minimum purity 95 % (volume fraction).
5.9  Acetone.
6 Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1  Laboratory mill, of hammer or centrifugal type, fitted with a 1 mm screen.
6.2  Conical flasks, of 1 l capacity, with plain neck (or ground glass neck if reflux condensers are to be used).
6.3  Dispenser, capable of dispensing 200 ml of hot liquid.
6.4  Heating unit, equipped for heating a bank of 1 l conical flasks.
6.5  Cold-finger condensers, to fit into the necks of 1 l conical flasks (or reflux condensers if apparatus with
ground glass joints is being used).
6.6  Buchner flasks, with rubber adaptors and fitted with Hartley funnels for 12,5 cm diameter filter paper, plus
adaptor funnels for 70 ml sintered-glass crucibles.
6.7  Sintered-glass crucibles, of porosity No. 1 or P 160 (pore size 100 μm to 160 μm), of 40 mm plate diameter
and 70 ml capacity.
6.8  Oven, fan-assisted, capable of maintaining a temperature of 103 °C ± 2 °C.
© ISO
, capable of maintaining a temperature of 550 °C ± 10 °C.
6.9 Muffle furnace
6.10  Desiccator, containing an efficient desiccant.
6.11  Filter papers, of 12,5 cm diameter, hardened, ashless grade, with a porosity of 20 μm to 25 μm.
1)
NOTE Whatman No. 541 have been found to be suitable.
7 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport and storage.
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 1839.
8 Preparation of test sample
Using the mill (6.1), grind the sample to pass through the 1 mm screen.
9 Procedure
NOTE If it is required to check whether the repeatability limit (11.2) is met, carry out two single determinations in
accordance with 9.1 to 9.3 under repeatability conditions.
9.1 Determination of dry matter content
Calculate the dry matter content (w) from the moisture content
...