1、BRITISH STANDARD BS 770-2:1976 Methods for Chemical analysis of cheese Part 2: Determination of water content (reference and routine methods) NOTEThis Part should be read in conjunction with Part 1: General introduction, published separately. UDC 637.322:543.812BS770-2:1976 BSI 10-1999 ISBN 0 580 08
2、727 5 A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comp
3、rises a front cover, an inside front cover, pagesi andii, pages1and2 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. D
4、ate CommentsBS770-2:1976 BSI 10-1999 i Contents Page 1 Scope 1 2 References 1 3 Definition 1 4 Principle 1 5 Reference method 1 6 Routine method 2 7 Test report 2ii blankBS770-2:1976 BSI 10-1999 1 1 Scope This Part of BS 770 describes two methods for the determination of the water content of cheese
5、or processed cheese products. One method (clause 5) is a reference method; the other (clause6) is a routine method that yields results in close agreement with the reference method but conveniently allows the drying procedure to proceed overnight. Both methods are applicable to cheese and to processe
6、d cheese products made from cheese with the addition of emulsifying salts only. An International Standard describing a method for determination of the “dry matter” of cheese and processed cheese products is in preparation. It describes a procedure similar to that described in clause5 of this Part, b
7、ut the method of calculation differs. 2 References The following British Standards are referred to in this Part. BS 410, Test sieves. BS 2648, Performance requirements for electrically-heated laboratory drying ovens. 3 Definition For the purposes of this Part the following definition applies. 3.1 wa
8、ter content loss of mass on drying as determined by the procedure described in clause5 or clause6. Water content is expressed as percentage by mass 4 Principle A weighed mass of prepared sample is mixed with sand and dried in an oven, at102 1 C for the reference method and at100 1 C for the routine
9、method. The percentage loss in mass is calculated. 5 Reference method 5.1 Apparatus and materials. Usual laboratory apparatus is required and, in particular, the following. 5.1.1 Dishes, diameter about75mm and depth about25mm, of metal (nickel, aluminium and stainless steel are suitable), flat, suit
10、ably flanged and with readily removable but close-fitting lids. Each dish shall be provided with a short glass stirring rod having a widened flat end and a hooked handle to rest over the edge of the dish. The total length of the rod shall be less than the internal diameter of the dish. 5.1.2 Drying
11、oven, electrically heated, complying with the requirements of BS2648 and capable of maintaining a temperature of102 1 C. 5.1.3 Desiccator, provided with an efficient desiccating agent, e.g. silica gel. 5.1.4 Boiling water bath, of a type in which metal dishes placed on the bath do not come into cont
12、act with copper, e.g. a bath with a stainless steel top, or with porcelain or plastics rings to support the dishes. 5.1.5 Balance, capable of weighing to0.1mg. 5.1.6 Sand. White quartz sand that passes through a mesh of aperture5004m, is retained by a mesh of aperture1804m (sieves complying with the
13、 requirements of BS410 should be used) and that has been prepared as follows. Wash the sand with hot concentrated hydrochloric acid and then wash thoroughly with water. Heat the washed sand at550 C for1h and cool to room temperature. When 20g of the prepared sand is moistened with water, dried on a
14、water bath and then for1h in an oven at102 1 C, then cooled in a desiccator and weighed, the final mass shall not differ from the mass taken by more than1mg. 5.2 Procedure 5.2.1 Carry out in duplicate the procedure described in5.2.2. 5.2.2 Into the oven at102 1 C place a dish, containing approximate
15、ly20g of the sand, alongside the corresponding lid holding the stirring rod. After drying the dish for at least1h, replace the lid (with the rod still on it) on the dish, remove the closed dish from the oven and transfer the dish immediately to a desiccator. Allow the dish to cool to the balance roo
16、m temperature (at least45min will probably be required) then weigh the dish, with lid and rod, rapidly.BS770-2:1976 2 BSI 10-1999 Tilt the sand to one side of the dish, place on the clear space about3g of the sample of cheese prepared as described in Part1 and again weigh rapidly. Add sufficient wat
17、er to saturate the sand, thoroughly mix the wet sand with the cheese by macerating with the glass stirring rod and distribute the mixture over the bottom of the dish. Leave the stirring end of the glass rod in the mixture, the other end resting on the side of the dish. Place the dish on the boiling
18、water bath, stir until the mixture has a crumbly appearance, and then place the stirring rod flat inside the dish. NOTEWith cheeses that form a horn-like mass during the process of drying, it is recommended that the dish should be removed from the water bath as soon as the mixture becomes difficult
19、to stir and that the stirring should be continued until the mass again becomes friable. This process of heating and stirring should be continued until the mixture is apparently dry. After allowing the dish to remain on the water bath for a further20min, dry the bottom of the dish and transfer the di
20、sh and rod, with the lid alongside, to the oven at102 1 C. After 4 h, put the lid on the dish and transfer the closed dish to the desiccator. Allow the dish to cool to balance room temperature, then weigh the dish. Remove the lid and replace the dish and lid in the oven for a further period of1h, th
21、en transfer the dish to the desiccator, cool and weigh again. Repeat this drying, cooling and weighing sequence until the loss of mass between successive weighings does not exceed0.5mg. Note the final mass. 5.3 Expression of result 5.3.1 Calculation. Calculate each duplicate value for the percentage
22、 loss in mass using the following formula: loss in mass =100 (m 2 m 3 )/(m 2 m 1 ) where m 1= mass of the dish, lid, stirring rod and sand after drying; m 2= mass of the dish etc. plus test portion before drying, m 3= mass of the dish etc. plus test portion after drying. 5.3.2 Agreement between dupl
23、icates. The difference between the two values calculated as described in 5.3.1 shall not exceed0.4.If this requirement is not complied with, the result is not valid. 5.3.3 Mean value. Provided that the duplicate values calculated as described in5.3.1 comply with the requirement of5.3.2, calculate th
24、e mean value and express this result, to one decimal place, as the water content (reference method) of the sample. 6 Routine method 6.1 Apparatus and materials. The apparatus and materials required are as listed in5.1 except that the oven (5.1.2) shall be capable of maintaining a temperature of100 1
25、 C. 6.2 Procedure. Proceed as described in5.2.2 but with the oven operating at100 1 C. After removal of the dish from the boiling water bath, place the dish in the oven at100 1 C for18 2h. Then cool the dish in the desiccator and weigh the dish to the nearest0.5mg. 6.3 Expression of result. Calculat
26、e the percentage loss in mass using the formula given in5.3.1. Express this result, to one decimal place, as the water content (routine method) of the sample. 6.4 Repeatability. The difference between the results (calculated as described in6.3) of two determinations carried out simultaneously, or in
27、 rapid succession, by the same analyst should not exceed0.4. 7 Test report See Part 1.blankBS 770-2:1976 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Eu
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