This standard specifies the principle, instruments and utensils, operation methods and result calculation methods for the determination of water extracts in tea. This standard is applicable to the determination of water extracts in tea. GB/T 8305-2002 Determination of water extracts in tea GB/T8305-2002 Standard download decompression password: www.bzxz.net

GB/T 8305--2002
This standard is equivalent to ISO9768:1994 "Determination of tea extract" while revising GB/T8305-1987 "Determination of tea extract".
The main difference between this standard and ISO9768:1994 is that boiling water bath heating is used instead of direct heating in an electric furnace to improve the uniformity and stability of the extraction.
The main difference between this standard and G/T8305-1987 is that the difference method of weighing tea residues is used instead of the drying method of weighing tea extract. The reproducibility and reproducibility of GB/T8305-2002 are better than GB/T8305--1987. This standard is proposed by the All-China Federation of Supply and Marketing Cooperatives. This standard is under the jurisdiction of the Hangzhou Tea Research Institute of the All-China Federation of Supply and Marketing Cooperatives. The drafting unit of this standard: Hangzhou Tea Research Institute of the All-China Federation of Supply and Marketing Cooperatives. The main drafters of this standard are Zhou Weilong, Sun Anhua and Zhong Fu. This standard is interpreted by the Hangzhou Tea Research Institute of the China National Federation of Supply and Marketing Cooperatives. 117
GB/T8305—2002
ISO Foreword
ISO (International Organization for Standardization) is an international alliance of national standardization organizations (ISO member groups). Usually, the work of formulating international standards is undertaken by ISO technical committees. Each member group has the right to become a representative of the project committee if it is interested. Official or unofficial international standard organizations associated with ISO also participate in the work. ISO and the International Electrotechnical Commission (IEC) work closely on electrotechnical standard documents.
The draft international standards adopted by the technical committees are submitted to the member groups for voting. The publication of international standards must obtain the approval votes of not less than 75% of the member groups.
International Standard ISO9768 was prepared by ISO/TC34 Technical Committee on Agricultural Products and Food. This second revised edition replaces the original first edition (ISO9768:1990), which has been technically revised. Appendix A of International Standard ISO) 9768:1994 is for reference only. 118
1 Scope
National Standard of the People's Republic of China
Determination of water extracts content of tea
Tea--Determination of water extracts contentGB/T 8305---2002
eqv ISO 9768: 1994
Replaces GB/T8305-1987
This standard specifies the principle, instruments and utensils, operating methods and result calculation methods for the determination of water extracts in tea. This standard is applicable to the determination of water extracts in tea. 2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. The versions shown are valid at the time of publication of this standard. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T83022002 Tea sampling
3 Definitions
This standard adopts the following definitions.
water extracts
Water overflow
Under specified conditions, water-soluble substances in tea leaves are extracted with boiling water. 4 Principle
Water-soluble substances in tea leaves are extracted with boiling water reflux, and then the tea residues after filtration, rinsing, drying and extraction are weighed to calculate the water extract. 5 Instruments and appliances
Conventional laboratory instruments and the following items:
5.1 Blast electric heating constant temperature drying oven: temperature control 120℃ ± 2C. 5.2 Boiling water bath.
5.3 Buchner funnel with suction filtration device.
5.4 Aluminum box: with lid. Inner diameter 75mm~80mm. 5.5 Dryer: Contains effective desiccant.
5.6 Analytical balance: sensitivity 0.001g.
5.7 Conical flask: 500ml.
5.8 Grinder: Made of material that does not absorb water; dead corners as small as possible, easy to clean; equipped with a sieve with an aperture of 3mm. 6 Operation method
6.1 Sampling
According to the provisions of GB/T8302.
6.2 Sample preparation
First grind a small amount of sample with a grinder (5.8), discard it, and then grind the rest. Approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on June 17, 2002, implemented on December 1, 2002www.bzxz.net
6.3 Aluminum box preparation
GB/T 8305--2002
Put the aluminum box (5.4) together with 15 cm qualitative rapid filter paper in a constant temperature drying oven (5.1) at 120℃±2℃, dry for 1 hour, take it out, cool it to room temperature in a desiccator (5.5), and weigh it (precision to 0.001g) 6. 4 Determination steps
Weigh 2g (accurate to 0.001g) of ground sample (6.2) into a 500ml conical flask (5.7) and add 300mL of boiling water. Immediately transfer to a boiling water bath (5.2) and extract for 45min (shake every 10min). Immediately filter under reduced pressure while hot (using filter paper treated in 6.3) after extraction. Wash the tea residue several times with about 150mL of boiling distilled water, transfer the tea residue together with the filter paper of known mass into an aluminum box (6.3), then transfer to a 120℃2C constant overflow drying oven (5.1) and dry for 1h. Cover and take out to cool for 1h and dry for another 1h. Immediately transfer to a desiccator (5.5) and cool to room temperature, and weigh.
7 Calculation of results
7.1 Calculation method
The water extract in tea leaves is expressed as dry mass fraction and calculated according to formula (1): Water extract (%)
Wu Zhong: M. Sample mass, g.
m Mass of dried tea residue, g,
m Dry matter content of sample, %.
If the requirements of repeatability (7.2) are met, take the arithmetic mean of the two measurements as the result, and keep one decimal place. 7.2 Repeatability
The difference between the two measured values ​​of the same sample shall not exceed 0.5g for every 100g of sample. 120
(1)
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