The cooking interval starts at a standardized initial temperature of 30° C (86° F) instead of at a haphazard room temperature. The duration of cooking is specified for reference conditions only instead of for each individual test, and the interval is changed from what amounts to 23 minutes 2 minutes to 20.00 minutes 20 seconds (for the reference conditions) and to whatever interval of time results with reliably adjusted apparatus in the individual tests on the unknown samples. The form and arrangement of the burner are definitely specified instead of being left to chance, and means are provided for attaining the precision required. The boiling vessel is covered at the moment the temperature of the mixture reaches 70° C (158° F), with the sugar practically dissolved, before, instead of after, boiling has commenced. The vessel is uncovered at the instant the sirup has attained a temperature of 120° C (248° F) instead of precisely 15 minutes after the heating was started 29. Once the sugar is approximately all dissolved and a temperature of 70° C (158° F) is attained, the thermometer remains fixed in the clasp attached to the vessel throughout the remainder of the cooking interval, with its bulb located at a definite place in the sirup where it is least exposed to direct radiation from the vessel bottom immediately above the flame, and at a place where the sirup is least superheated and least subject to fluctuation of temperature. Hand stirring of the uncovered boiling sirup is omitted.30 No stirring rod is used at any time. The plaques are formed on a water-jacketed metallic slab which is supplied with a steady current of water at a temperature of 25° C (77° F), instead of on a simple sheet of copper which varies in temperature. This augments the uniformity of heat exposure to which the different samples are subjected. For the observation of certain variable properties of the samples, which were not comprehended in the original Hooker candy test, the National Bureau of Standards basic method provides special means. Especially notable among these properties are the varying tendencies of the samples to foam at the initial boiling, to "froth" later, to form colored compounds in the test, and to slump or spread and yield different specific areas in the formation of the plaque. The specifications are planned for systematic modifications in the less critical details to provide for the setting up of specialized procedures meeting the requirements of various types of candy tests not considered in the present discussion. The Hooker procedure was devised for a very limited field of service. (g) UTILITY AND RELIABILITY OF THE CANDY TESTS Barley-sugar tests and the associated observations offer one of the simplest and surest means of evaluating the quality of commercial 29 This specification obviates the possibility that the sirup may become considerably supersaturated while the vessel is still covered; thus it avoids danger of starting crystallization by the shock of uncovering the vessel. Moreover, when tests are operated on different cooking intervals (for which provision will be made in specialized procedures not covered in the present discussion), they are placed on a more nearly uniform basis in respect to the effects of uncovering when uncovering occurs at a uniform temperature instead of at a uniform time from the start of heating [4]. 20 It was shown as long ago as 1913-14 that hand stirring of the boiling sirup is a productive source of variability in the results obtained by different operators of the Hooker procedure [4]. white sugars. The Hooker procedure has proved adequate for verifying the purification of the most highly refined commercial products and for detecting gross faults of purification in products of ordinary quality. Regardless of the classification of the product in trade, a lot of sugar which consistently yields excellent barley sugar in the Hooker test almost certainly will prove adequately refined for practically any manufacturing use. Conversely, a lot which repeatedly yields poor results in this test assuredly contains inexpedient quantities of impurities, either too little of certain favorable kinds or too much of the deleterious kinds. Since impurities of the latter class can impair the keeping qualities of the sugar as seriously as they affect its suitability for manufacturing uses, candy tests have a much broader field of usefulness than is comprised by the needs of the confectionery industry alone. For many years certain progressive producers of refined and direct-consumption sugars have used candy tests of various kinds as a guide to the improvement of their wares, and as a means of routine control in the daily maintenance of the particular quality standards which each producer has set for his output. All too frequently general consumers have overlooked the possibilities of the candy tests, not merely as a means of inspecting their purchases or as an instrument for comparing the different products offered, but also as a basis upon which specifications can be definitely established prior to purchase. Important disputes have arisen over the stability of sugar in storage, as well as in manufacturing operations, which might have been avoided through such specifications. Losses of sugar are suffered by producers themselves, as well as by handlers and consumers, in spoilage which could be forestalled through a more extensive use of candy tests. In the sugar and confectionery industries, two phases of the effects of impurities upon the stability of sugar in candy tests commonly are distinguished as the inversion, or hydrolysis, of sucrose and the caramelization of the resulting mixture of sucrose, the products of hydrolysis and certain other substances which may be present. Caramelization is a phenomenon which comprises numerous complex reactions resulting in the formation of colored compounds and other substances which are deleterious to the quality of candy. 31 The types of reaction which occur, and the velocities of the reactions (hence the extent to which they progress during any individual test), are influenced by the particular regime of conditions which obtains during the operation of the test, not solely by the kinds and the amounts of impurities present. Therefore, the arbitrary schedule of heat expossure of the sample under arbitrary conditions of operation ought to be specified within sufficiently narrow limits of variability to assure that the resulting decomposition shall be practically proportional to the reciprocal of the stability of the material. The quality of the sample 3 finally is judged by an examination of the product of the test. While a visual examination of the plaque may serve the more inexact purposes 32 Involved in both phases of the instability of the material are not only various decompositions and deg. radations of sucrose and the products of hydrolysis, but also reactions comprising several types of chemical synthesis, probably including reversions and polymerizations and possibly chemical combinations between glucose and amino acids or between glucose and proteins in certain instances. The reactions are so numerous and yet so generally interdependent and (with but slight alteration of conditions) so variable that their chemistry and kinetics never have been cleared up, even for a single case. Except those phases of the quality which are indicated by the appearance of the sirup while boiling. Differences of quality are distinguishable by this method in only a limited number of samples. (See "foam number", p. 373.) of a candy test, any quantitative statement of the stability of the sample must depend upon analytical procedure and other physical measurements. Examples are the estimation of sucrose hydrolysis (as by polarimetric or copper-reduction methods), the estimation of caramelization (as by measurements of the color in the solid plaque or in a water solution of the candy), and the estimation of the "slump," or specific area, all as outlined above. Appraisal of the differences in the stability of the various samples, and the separation of the samples accordingly into various classes, is practicable only to the degree that the particular candy-test procedure approximates a reliable reproduction of a constant program of operating conditions each time it is applied. This is to say that the variability among the programs established in numerous individual tests on random samples of the same lot of sugar must result in much smaller differences in decomposition (as distinguished by the chosen methods of examination) than the variations in decomposition arising from the differences in stability of the different lots of sugar that are to be separated on the basis of quality. The tolerances for deviation from a constant program must be smaller the more precise the separations are to be. On the other hand, the minimum tolerances which may be imposed are limited by the character of the candy-test procedure available. The minimum feasible tolerances which may be stipulated for candy tests according to the Hooker procedure are so great that satisfactory separations of samples on a quality basis are impracticable. This is doubly evident where different operators are involved, what with inadequacy of directions as to arrangement of apparatus and what with the inclusion of details of procedure which inherently are subject. to individual variability. No long array of samples could be arranged precisely in the order of minutely graduated differences of stability, nor could the degree of departure of a sample from an established standard of quality be indicated, on the findings of candy tests carried out by different operators by means of the Hooker procedure alone or by means of any of its ordinary modifications. The deviations are great, indeed, that nearly every user of the test has entertained at least transient doubts that the results obtained even by a single operator are valid criteria for any useful separation of samples on a stability basis [11, 12]. The circumstances are complicated by the failure of many users to appreciate the fact that no finer separations should be demanded than definitely will be put to practical use. e so Very pure sucrose in candy tests is distinctly weak but relatively stable in respect to caramelization. The purest commercial products have similar characteristics in both respects. Because of this, certain brands of "first-run" char-refined sugar, as produced for confectioners' use, have been strengthened at the refinery for many years by the addition of small quantities of sodium carbonate or sodium bicarbonate 33 to the water used for washing the crystals [5]. The small amount of impurity thus deliberately introduced has but little influence upon the color of hard candy produced from the sugar, although much excess of the alkali would bring about marked caramelization. 33 In 1897 Wiechmann presented data [1] on experimental suppression of sucrose hydrolysis by the presence of 1 part of calcium oxide, sodium carbonate, or sodium bicarbonate, in 100,000 parts of refined cane sugar during its conversion to barley sugar. Possibly even earlier, Hooker initiated the practice of strengthening confectioners' sugars, in response to the complaints of certain consumers. The treatment was devised and originally controlled through the Hooker candy-test procedure. The stability of refined cane sugar of ordinary quality is inferior to that of the strengthened confectioners' sugars in respect to both hydrolysis and caramelization [5]. On the other hand, beet sugars generally tend to be distinctly stronger than either type of cane sugar but definitely less stable than either as to caramelization. There are notable exceptions to these usual relations of the three types of sugar mentioned. Indeed, the stability gradations of all sorts are so nearly continuous that probably no one would propose to distinguish the types of sugar to which many individual samples belong, solely on the evidence of candy tests. Because such gradations are continually encountered, most users and prospective users of candy tests need a method which is both more reliable and more precise than any of those heretofore available. For selecting or for segregating different lots of sugar according to the requirements of different consumers, without an excessive number of tests, a high degree of reliability is demanded of the individual candy test. For the precise control of quality in sugar production in any plant with relatively little variation of stability in its products, the candy test procedure should have a high degree of reproducibility to permit stipulation of small tolerances of standard deviation. For many other purposes, like precision must be attained. The method and equipment described for the National Bureau of Standards simple barley-sugar test procedure are designed to reduce the standard deviations, as compared with those which prevail in the candy tests heretofore available, (1) by diminishing the variations of practice through more specific directions, (2) by diminishing the influence of the operator's individual technique upon the procedure, and (3) by greatly reducing instrumental variability in several important respects. Providing these specifications are adhered to in detail both as to operation and equipment, this enhancement of precision in candy tests should be realized in fact. With attention to the order of occurrence of stability variations in relation to the usual control and operating data of a plant, as a clue to the presence or to the advent of "assignable causes", manufacturers can make use of the increased precision as a means of bringing the production of sugar more definitely within the field of statistical control as practiced in certain other industries. The dependability and increased convenience of the new procedure, once the equipment is installed, and as compared with what heretofore has been available, should place the candy test on a much surer footing from the viewpoint of the consumer as well as the producer. 3. CONCLUSION After quoting Hooker's directions for candy-test procedure for comparison, directions for a new and greatly improved simple barleysugar test method are presented in detail, together with specifications for the apparatus required for its use. It is proposed not only as a standard method for the inspection of commercial sucrose with respect to stability to heat, but also as a model procedure which with suitable modification can be converted to various other types of candy tests for the examination of all sorts of sugar products. Details of the latter use are reserved for discussion in another place. It is pointed out that the method as used for the examination of commercial sugar is of value both to the producer who wishes to establish a more effective control of the quality of his product, and to the consumer who either purchases sugar on quality specifications or allocates his purchases to different uses according to their quality. The possibility has been suggested of implementing the control of quality in the production of sugar through the introduction of modern statistical methods which make use of the order of occurrence of stability variations as a clue to their assignable causes. 4. REFERENCES [1] F. G. Wiechmann, J. Phys. Chem. 1, 69–74 (1897). [2] S. J. Osborn, The Use of Beet Sugar in Candy-Making (1913), unpublished report of the techincal staff of the Great Western Sugar Co., Denver, Colo. [3] Cir. BS C44 [ed. 2] (1918). [4] Max J. Proffitt, Laboratory Work in Connection with Experiments on the Production of Candy Sugar (1914); Filtration Experiments (1916); unpublished reports of the technical staff of the Great Western Sugar Co., Denver, Colo. [5] Frederick W. Murphy, Candy Mfr. 1, [3] 36–37, 51 (1921). [6] H. S. Paine, M. S. Badollet, and J. C. Keane, Ind. Eng. Chem. 16, 1252-60 (1924). [7] J. A. Ambler, Mfg. Confectioner 7, [1] 17–19, 82 (1927). [8] G. L. Spencer and G. P. Meade, Handbook for Cane Sugar Manufacturers and Their Chemists, p. 189-90 (John Wiley & Sons, New York, N. Y., 1929). [9] J. A. Ambler and S. Byall, Ind. Eng. Chem., Anal. Ed. 7, 168–73 (1935). [10] Otto Windt, Mfg. Confectioner 12, [8] 20–24 (1932). [11] A. B. Kennedy, Mfg. Confectioner 13 [5] 18-23, 51 (1933). [12] E. K. Ventre and S. Byall, Report of Studies on Uniformity of Quality of Sugars, U. S. Dept. Agr. Bur. Chem. Soils (1938). [13] Max J. Proffitt, Unpublished paper on candy test methods. XXV. PREPARATION AND PURIFICATION OF PURE SUGARS 1. DEXTROSE With a view to assisting in the unification of methods of sugar analysis, the National Bureau of Standards issues chemically pure dextrose as one of its standard analyzed samples. This was first issued in 1914. At that time, and for some years thereafter, the method of purification and crystallization was that devised by Jackson [1]. The raw material used was the purest form of commercial dextrose obtainable at that time and was marketed under the trade name of Cerelose.3 It was a brownish-colored granular material containing about 87.2 percent of dextrose, 3.9 percent of nonfermentable sugars, 0.55 percent of ash, and a quantity of dextrins. The method is as follows: 34 The impure material is submitted to a preliminary treatment similar to that described by Bauer [2]. The crude material is digested in a shaking machine with alcohol in order to wash the mother liquor from the crystals. The mass is then poured into a centrifugal machine and drained at high velocity. The drained crystals are then washed repeatedly in the rotating basket with fresh portions of alcohol. The washed substance is dissolved by heating in 40 percent of its weight of water and 140 ml of alcohol added for each 100 g of the washed substance. This mixture is then heated on a steam bath and filtered to remove the precipitated impurities. The filtrate is evaporated in 34 At the present time this name is applied to a highly purified commercial dextrose having the physical appearance of granulated beet or cane sugar. |