1、BRITISH STANDARD BS1743-4: 1980 Methods for Analysis of dried milk and dried milk products Part4: Determination of the dispersibility and the wetting time of instant dried milk IMPORTANT NOTE. It is essential that this Part be read in conjunction with Part1“General introduction, including preparatio
2、n of laboratory samples”, published separately. UDC 637.143:664.97:543:541.182.6BS1743-4:1980 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was published under the authority ofthe Executive Board and comesinto effect on 30September1980 BSI08-1999
3、 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment79/50641 DC ISBN 0 580 11524 0 Foreword This Part of this British Standard is one of a new series of methods for analysis of dried milk and dried milk products. The two methods described in
4、this Part are technically similar to those described in International Dairy Federation (IDF) Standard87:1979 “Determination of the dispersibility and wettability of instant dried milk”. The UK actively participated in the extensive international collaborative work involved in the development of thes
5、e methods. This Part comprises three sections. Section1 is a general section, section2 specifies a method for the determination of the dispersibility of instant dried milk and section3 specifies a method for the determination of the wetting time of instant dried milk. The methods apply to dried milk
6、 purporting to be “instant”; they permit assessment of the degree to which a dried milk possesses instant characteristics, i.e.the ability to be rapidly dispersed and to be rapidly wetted when added to water. Minimum dispersibility values are provisionally recommended for instant dried skimmed milk,
7、 instant dried partly skimmed milk and instant dried whole milk. 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
8、from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6 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
9、front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS1743-4:1980 BSI 08-1999 i Contents Page Foreword Inside front cover Section 1. General 1 Scope 1 2 References 1 3 Definitions 1 Section 2. Determination of the dispersibility of instant dried milk 4 Introduction 1 5 Pr
10、inciple 1 6 Reagent 1 7 Apparatus 1 8 Procedure 2 9 Calculation of results 3 10 Test report 3 11 Replication and precision 3 12 Interpretation of results 4 Section 3. Determination of the wetting time of instant dried milk 13 Introduction 4 14 Principle 5 15 Reagent 5 16 Apparatus 5 17 Procedure 5 1
11、8 Calculation of results 5 19 Test report 5 20 Replication and precision 5 Appendix A Derivation of formulae for dispersibility 6 Figure 1 Apparatus for the determination of dispersibility and of wetting time 4ii blankBS1743-4:1980 BSI 08-1999 1 Section 1. General 1 Scope Section2 of this Part of th
12、is British Standard specifies a method for the determination of the dispersibility in water of instant dried milk. A provisional recommendation for the interpretation of dispersibility results is given. Section3 specifies a method, for routine use, for the determination of the wetting time in water
13、of instant dried milk. Both methods are applicable to instant dried skimmed milk manufactured either by the “straight-through” or by the “re-wet” process, and also to instant dried partly skimmed milk and instant dried whole milk. 2 References The following standards publications are referred to in
14、this Part of this British Standard. BS410, Specification for test sieves. BS593, Laboratory thermometers. BS1741, Methods for the chemical analysis of liquid milk and cream. BS1743, Methods for analysis of dried milk and dried milk products Part 1 General introduction, including preparation of labor
15、atory samples. BS3978, Water for laboratory use. BS5272, Method for simultaneous routine determination of the water contents of a batch of dried milk samples. BS5497, Precision of test methods Part 1 Guide for the determination of repeatability and reproducibility for a standard test method. 3 Defin
16、itions For the purposes of this Part of this British Standard the following definitions apply. 3.1 dispersibility percentage by mass of the dry matter of the sample that can be distributed uniformly in water, as determined by the procedure specified in this Part of this British Standard 3.2 wetting
17、time time, in seconds, that elapses between placing the sample on the surface of water and all of the sample becoming wetted, i.e.either sinking below the surface or assuming a typical “wet” appearance without sinking, as determined by the procedure specified in this Part of this British Standard Se
18、ction 2. Determination of the dispersibility of instant dried milk 4 Introduction The degree to which a dried milk is “instant” depends on various properties which can be classified as wettability, sinkability, solubility and dispersibility. The first three all affect the last to some extent and hen
19、ce dispersibility, as defined and determined below, is probably the best single indication of the overall “instant” characteristics of a dried milk. 5 Principle A test portion of the sample, of known water content, is evenly spread on the surface of water (water temperature25 C), the mixture is stir
20、red manually for a short time, part of the mixture is filtered through a sieve, and the total solids content of the collected liquid is determined. Dispersibility is calculated from the mass of the test portion, the water content of the test sample and the total solids content of the collected liqui
21、d. 6 Reagent 6.1 Water, distilled or of a purity at least equal to that of distilled water, complying with the requirements of BS3978. 7 Apparatus 7.1 Container, capacity approximately twice the volume of the laboratory sample (see BS1743-1), with air-tight lid. 7.2 Apparatus for determination of wa
22、ter content of dried milk, as specified in BS5272. 7.3 Balance, top-pan, capable of weighing to0.1g. 7.4 Scoop, with smooth surface, suitable for containing the test portion. 7.5 Thermometer, suitable for taking readings at25 C with an accuracy of 0.1 C. Thermometer A40C/100, complying with the requ
23、irements of BS593:1974 and certified in accordance with the requirements of Appendix A of that standard, is suitable. 7.6 Beaker, glass, with spout, capacity600ml, height123mm, diameter88mm, graduated at150ml and250ml, with the rim lying in a horizontal plane parallel to the base. 7.7 Stand and clam
24、p, for holding the glass tubing(7.9). 7.8 Glass plate, 120mm 120mm, thickness approximately2.5mm, with ground edges.BS1743-4:1980 2 BSI 08-1999 7.9 Glass tubing, length65mm, outside diameter80.0 1.8mm, wall thickness2.5 0.3mm, with the ends ground, parallel, and at right angles to the longitudinal a
25、xis. 7.10 Brush, suitable for removing the test portion from the scoop(7.4). 7.11 Spatula, stainless steel, thickness1mm, overall length250mm, length of blade135mm, width of blade25mm, length of handle115mm, width of handle15mm see Figure 1b). These dimensions should be followed as closely as possib
26、le. 7.12 Stop-watch, 60seconds, numbered at intervals of5s, indicating intervals of1s and0.5s (or less). It is helpful to have the dial marked at5s,25s and55s. 7.13 Test sieve, woven metal wire cloth, diameter200mm, nominal size of apertures1504m, with receiver, complying with the requirements of BS
27、410. 7.14 Conical flask, capacity250ml, with stopper. 7.15 Filter funnel, suitable for transferring the contents of the test sieve receiver(7.13) to the conical flask(7.14). 7.16 Apparatus for determination of total solids content of liquid milk, as specified in BS1741. 8 Procedure 8.1 Notes on test
28、 procedure 8.1.1 See clause11 regarding replication of the test(8.4). 8.1.2 It is essential that the test, once started, is completed without delay at any stage and that all timed operations are carried out strictly as specified. 8.1.3 The mass of the test portion(8.4.1) and of the water used for re
29、constitution(8.4.2) are such that the total solids content (% m/m) of the mixture approximates to that of the original liquid product. 8.2 Preparation of the test sample. Before proceeding, ensure that the laboratory sample (see BS1743-1) has been kept at laboratory temperature for at least48h. This
30、 treatment, besides adjusting the sample to an appropriate temperature for all the subsequent operations, eliminates any influence on the dispersibility (and wetting time) of the sample caused by a variation in the physical state of fat present. Gently transfer all the laboratory sample to the conta
31、iner(7.1), immediately close the container, and thoroughly mix the sample by very gently rotating and inverting the container in such a way as to avoid reducing the particle size of the sample; a reduction in particle size is liable to reduce the dispersibility of the sample. 8.3 Determination of wa
32、ter content of the test sample. Use, in duplicate, the method specified in BS5272 to obtain two single test values rounded to the nearest0.01% (m/m) for the water content of the test sample. Record the mean of these values, rounded to the nearest0.1% (m/m), as the water content of the test sample. 8
33、.4 Test procedure 8.4.1 Weigh into the scoop(7.4) a test portion of the test sample(8.2) as follows: 8.4.2 Weigh250.0 0.1g of water(6.1) at25.0 0.1 C into a dry beaker(7.6) taking care that the inside of the beaker above the final water level remains dry. 8.4.3 Place the beaker on the base of the st
34、and(7.7), place the glass plate(7.8) centrally on top of the beaker and place the glass tubing(7.9) on the glass plate, clamping the tubing so that it is centrally located above the beaker and the glass plate is free enough to be withdrawn easily seeFigure 1a). 8.4.4 Transfer all of the test portion
35、(8.4.1) to within the glass tubing, using the brush(7.10) if necessary, and spread the test portion evenly over the glass plate with the spatula(7.11). 8.4.5 Start the stop-watch(7.12) and when, after1min, its main hand again indicates0/60s, withdraw the glass plate with one hand (holding the beaker
36、 with the other hand) so that the test portion progressively falls onto the surface of the water. Withdraw the plate with a gentle continuous movement in approximately2.5s. instant dried skimmed milk: 26.0 0.1g instant dried partly skimmed milk: 34.0 0.1g instant dried whole milk: 34.0 0.1gBS1743-4:
37、1980 BSI 08-1999 3 8.4.6 Immediately remove the beaker from below the glass tubing and, when the main hand of the stop-watch indicates5s, insert the spatula into the beaker (vertically down the side with the full width of the blade facing the centre of the beaker) until it touches the bottom. During
38、 the next5s stir the contents of the beaker with the spatula, making one complete stirring movement per second, i.e.a smooth continuous movement of the spatula centrally across the beaker from one side to the opposite side and back and occupying1s, with the end of the spatula blade in continuous con
39、tact with the bottom of the beaker and slightly tilting the spatula away from the side of the beaker at the end of each half stirring-movement so as to minimize accumulation of unwetted dried milk on the sides of the beaker. Without interruption, continue the stirring for15s in the same manner excep
40、t that the spatula is maintained in a vertical position throughout. While making the20 complete stirring movements in20s, continuously rotate the beaker on its base so that approximately one complete turn(360 ) is achieved during the stirring. 8.4.7 After completion of the stirring allow the content
41、s of the beaker to stand for30s, i.e.until the main hand of the stop-watch indicates55s, and then, without disturbing any sediment, quickly pour off the liquid down to approximately the150ml mark, distributing the decanted liquid as evenly as possible over the test sieve(7.13) below which is fitted
42、its clean, dry receiver. Do not tilt or move the sieve during the sieving. To facilitate the passage of the decanted liquid through the sieve, the sieve is wetted before use by rinsing it with water(6.1). All excess water is removed from the sieve by wiping it with a towel; the top and bottom surfac
43、es of the wire cloth are only superficially wiped. 8.4.8 Thirty seconds after the beginning of the sieving operation, i.e.when the main hand of the stop-watch has returned to the25s position, remove the test sieve from the receiver, transfer the contents of the receiver as completely as possible to
44、the conical flask(7.14) by means of the filter funnel(7.15), and stopper the flask. 8.4.9 Thoroughly mix the liquid in the flask by repeatedly inverting the flask and, using the procedure specified for liquid milk in BS1741, obtain two single test values rounded to the nearest0.01% (m/m) for the tot
45、al solids content of the liquid. Record the mean of these values, rounded to the nearest0.1% (m/m), as the total solids content of the liquid. 9 Calculation of results Calculate the dispersibility of the laboratory sample using the following formulae: NOTEThe derivation of these formulae is given in
46、 Appendix A. Round the dispersibility value obtained to the nearest1% (m/m). 10 Test report The following information shall be included in the test report on a laboratory sample: a) full identification of the sample; b) the dispersibility, in% (m/m), indicating if it is the mean of two single test v
47、alues (see clause11); c) reference to the method of test; d) any observation that indicates that the value may be unreliable; e) sampling date, date received and date tested. 11 Replication and precision Since the repeatability (r) of the test(8.4), as defined in BS5497-1, has been found to be4.1 pe
48、rcentage units, it is recommended that the test is carried out in duplicate with a test sample to obtain a mean value for dispersibility. If the difference between the two single test values obtained within a short time-interval by the same analyst does not exceed4percentageunits (the rounded value
49、for r), report the mean of these values rounded to the nearest1% (m/m) as the dispersibility of the laboratory sample. If the difference between the two single test results exceeds4percentageunits, repeat the test in duplicate until a pair of acceptable single test values is obtained. As experience of the test method is gained, duplication may be considered unnecessary for some purposes. However, for the application of the provisional recommendation for the interpretation of results (clause12), the mean of acceptable duplicate single test values is re
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