Impurities in White Sugars VII. Distribution of Impurities in the Sugar Crystal’ J. C. KEANE,J. A. AMBLER,AND S. BYALL,Bureau of Chemistry and Soils, Washington, D. C.
D
U R I K G the study of considerable part will not be I n the .study of possible means of reducing the possible means of imdisplaced in this manner or even quantity qf the impurities in white sugar, a proving the quality of by the washing liquid because the knowledge of fheir distribution throughout the white sugars by decreaiing the velocity of the latter is too great cryslal mass is obtained by mingling sugar crysquantities of the various mipurito permit it to penetrate comtals of uniform size (screened f r o m samples ties in them, it became important pletely behind and around the to ascertain the distribution of crystals into all of the space collected f r o m various sources) with sugar soluthe nonsugars throughout the between them. Again, as the tions of different densities below saturation, mass of the crystal. In the case wash liquid travels through the so that proportions varying f r o m 4.3 to 30.0 per of raw sugar, practical experience mass of c r y s t a l s , i t becomes cent of the crystal mass are dissolved. Analyses has shown that the major porprogressively more impregnated tion of the impuritie., such a. of the original and resulting sugars show that in with the mother liquor, so that coloring matter, ash, and invert the crystals lying in the outer general over 50 per cent of the ash, suvates, sugar, is located in the film of sections of the whirling mass are chlorides, sodium, potassium, and total nitrogen molasses wrrounding the indiw a s h e d wi t h liquid of lower is located in the outer 5 per cenf of the crystalvidual c r y s t a l s and that the purity than the inner sections i. e., in the surface layer-whereas color, calcium, purity of the sugar is increased and therefore are washed less by washing away thi. adherent and sulfites are more uniformly distributed efficiently. The result is that, film, as in the affiliation of raw a t best, washing in the centrifthroughout the whole crystal. The barley candies sugar. ugals is neither complete nor made f r o m the sugars show a marked improrePaine and Ralch ( I C ) +tudied uniform. The original film of ment in color when the outer layer of the crystal the nonsugar substance- in the mother liquor can be removed has been removed. A possible means of imsugar crystal by dissolring away completely only by suspending one-half and then three-quarters and mingling the crystals in the proving the quality of white sugars is suggested. of the mass of the crystal. They washing liauid. followed bv anfound that the collbidal matter present is fairly uniformly d i v other separation of the crystals in t h i Centrifugals, which was tributed throughout the mystal and that, while the ash is dis- the method employed by Honig (11) in his study of the syntributed throughout the crystal, the greater part of it is located crystallization of nonsugars and sucrose in specially prepared in the outer half, probably in the dried film of mother liquor sugars of high ash content. He repeated the mingling and adhering to the surfaces of the crystal and in occlusions of the centrifugalizing until the saturated, high-purity sucrose solumother liquor between the Furfaces of clustered or multiple tion used as the washing liquid removed no more color from crystals. They point out the difficulties of completely remov- the crystals. Although increasing the purity of the liquor from which the ing the occlusions from the multiple crystals by washing in the centrifugals, since the multiple crystals are not broken sugar is to be crystallized is, of course, the first step in makdown into single crystals to any appreciable extent until the ing sugar as free from impurities and as uniform in quality as possible, there is a limit beyond which, for practical and sugar passes through the granulators. Because of their greater tendency toward matting or close economical reasons, further removal of nonsugars is not packing, small-grained sugars and those containing crystals feasible. Even when the purity of the liquor has been raised of unequal size, including “false grain,” are more difficult to to the highest possible point, the concentration of nonsugars rid of mother liquor by washing in the centrifugals with in the mother liquor continuously increases as the evaporaminimal quantities of water than are sugars of large and uni- tion of water and the growth of sugar crystals proceeds. form grain. Furthermore, the shape of the sugar crystal Therefore, regardless of the original purity of the liquor itself prevents complete and uniform removal of the film from which the sugar was made, the separation of the crystals of mother liquor in the centrifugals. The centrifugal force from the mother liquor must be as complete as possible, and to which the wash liquid is subjected throws it against those the adherent film of mother liquor must be removed in order portions of the crystals nearest the center of rotation, and to obtain the purest sugar possible from a given liquor. The removal of this film must be accomplished, from the such portions of the crystals will be relatively well washed and immediately afterwards will be subjected to the drying standpoint of economy, with as little loss of the purer crystalaction of the current of air which is forced through the whirl- line sugar as is possible. Berg6 (9) claims that the color, ing mass of crystals. But those portions of the crystals fac- especially of raw sugar, is improved by mingling the sugar ing away from the center of rotation are protected from the from the centrifugals with a saturated pure sugar solution direct action of the wash liquid by the mass of the crystal followed by a second separation in the centrifugals, and that itself. Each crystal also shields the adjacent, more remote this improvement merely removes the film of mother liquor crystals from the full action of the wash liquid to a greater or without dissolving any of the crystalline sugar. While this less extent, depending on the relative positions of the crystals treatment does result in an improvement in color (and also in ash content, which Berg6 does not mention), a further proto each other. Some of the mother liquor will be expelled from the inter- nounced improvement in color, purity, and quality of the stices between the crystals by centrifugal force, but a very sugar is obtained when the outer shell of the crystal is also removed (10). I n fact, this is to be expected, since the 1 Parts I t o V I of this series appeared in the Analytical Edition of INDUSexterior layers of the crystal are formed from liquor which is TRIAL A N D ENGINEERINQ CHEMISTRY in 1931 and 1932. 30
January, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
31
becoming progressively of higher nonsugar content, resulting in the absorption of larger quantities of impurities in this portion of the crystalline mass than in the central portions, which grow from the liquor before the concentration of the nonsugars in it has been materially increased. Since the film of mother liquor and the exterior portions of the crystals seem, therefore, to contain a larger proportion of the nonsugars than the interior portion-, it becomes important to know how far into the crystal mass this higher concentration of impurities extend>, in order to ascertain the least amount of the sugar crystal which should be removed in order to effect a substantial decrease in the quantity of the impurities and thus to improve the quality of the sugar. The work described here was performed entirely on white sugars on which the film of mother liquor had becoine dry by passage of the sugars through the granulator.. The study of wet sugars direct from the centrifugals has not yet been undertaken, but, reasoning from the facts already discussed, it ii believed that the results to be derived from such a study will differ from the present results only in degree and will amount chiefly to a further partition of the nonsugar distribution between the adhering film of mother liquor and the outermost layer of the crystal itself. PREPAR.4TION OF SUGAR CRYSTALS
In order to obtain crystals of approximately uniforiii size, the samples of sugar as received from the various sources were screened, and in each case only those crystals which were collected between 30-mesh and 50mesh screens were used. A portion of each of the screened sugars was reserved for analysis. The solvents for removing the outer layers of the crystals were sirups of 60, 63, and 65 per cent sucrose by refractometer, made from a sugar having a n ash content of less than 50 parts per million, and sirups of 63.5 and 66.5 per cent sucrose, made from a misture of white sugars having an average ash content of approximately 300 parts per million. These sirups are indicated in the tables by the numerals 1, 2, 3, 4, and 5, respectively. They were made of different concentrations in order to vary and limit the quantities of sugar which they could dissolve in becoming saturated with sucrose. Sirups 4 and 5, made from the sugar mixture of higher ash content, were prepared for the purpose of comparing the efficiency of higher ash sirups in the method which follows with that of more nearly ash-free sirups. As would be expected, the lower ash sirups were somewhat more effective, but the differences between the results obtained with the two types of sirups were so small that they are negligible from a practical standpoint (cf. Tables I and 111). The samples of screened sugar were thoroughly mingled at room temperature with the sirups in proportions ranging between 10 and 12 parts of sugar to 10 parts by weight of sirup, depending on the percentage loss of sugar desired and the concentration of the sirup used. In the preliminary experiments with sirup No. 1 the mixtures were allowed t o stand at room temperature with occasional thorough stirring until the sirup phase had become saturated with sucrose. In the subsequent experiments with the more concentrated sirups the magmas, which were often very stiff, were stirred continuously at room temperature until saturation of the sirup was complete, The crystals mere then separated from the sirup by means of a laboratory centrifuge. In the preliminary experiments the sirup was displaced from the crystals by wishing in the centrifuge with a 50 per cent solution of low-ash sugar. In all the other experiments the crystals were mashed in the centrifuge with a very small
INDUSTRIAL AND ENGINEERING
32
amount of water. After the crystals had been freed from the sirup and wash liquid as completely as possible, they were dried in the air and analyzed, in so far as the quantity recovered permitted, for color ($), ash (by charring and incineration a t 550” C.), sulfates and sulfites (b), calcium oxide ( 6 ) , sodium oxide (8), potassium oxide (7), chlorine (4), and total nitrogen ( 3 ) . They were then subjected t o the “barley candy” test (1). h A L Y S E S OF SUGA4RS
The data obtained from the analyses of the screened and of the treated sugars are given in Table I. It is evident that there is but little difference in the percentages of nonsugars eliminated, regardless of whether a large or a small percentage of sugar was removed. This is better shown in Table 11, in which the percentage removals are averaged in three groups: Group I includes those experiments in which more than 20 per cent of the sugar was dissolved away; Group 11, those in which more than 10 and less than 20.1 per cent of sugar was removed; and group 111, those in which 10 per cent, or less, sugar was dissolved.
CHEMISTRY
and I T.The former contains the ratios of the percentage nonsugar removals to the percentage sugar removals for each experiment, and the latter the averages of these ratios for the same three groupings as in Table 11. These ratios are indexes of the relation between the concentrations of the nonsugars in the outer layerq of the original crystals and the concentrations of the qanie nonsugar. in the inner portions. Thus, if the nonsugars were uniformly distributed throughout the lvhole crystal, these ratios would a l w a y be unity; this means that, as each unit weight of wgar was dissolved from the crystal, a constant amount of the nonsugar would be dissolved. But since tliese ratios tend to increase as the percentage of sugar dissoll-ed decreaceq, it is strikingly evident that the concentration of the nonsugars is greate*t in the extreme outermost layers of the crystals. TABLEIC. A V E R A G E RATIOS O F PERCENTAGE PU’OSSUGAR REMOVED T O P E R C E S T a G E OF SlJG.4R REMOVED SUOAR
RE-
GROUPMOVED COLOR.hi 603
TABLE11. AVERAGEPERCEXTAGE REMOVALS GROUPSUQARCOLOR.48H
% 14
IIb IIIc
%
%
SOs
SOz
CaO
NazO
KzO
C1
%
%
%
%
%
%
50 0 76.0 71.2
79.0 66.3 63.7
25.0 56.7 78.7 25.9 27.3 1 3 . 4 2015 5 8 . 4 6 3 . 7 2 9 . 5 7 . 0 18.3 59.2 72.8 2 7 . 0 37:6
N
11 I11
%
68.0 88:3 60.9 67.4 6 0 1
Thehe tables reveal: (1) The average percentage removal of each nonsugar studied varies but little in the three groups, indicating that the nonsugars are fairly uniformly distributed in small proportions throughout the outer portions of the crystals, which iz in agreement with the findings of Honig (11) in his syncrystallization study on sugars of higher nonsugar content; (2) the outermost portions of the crystals (the portions dissolved away) have a higher content of nonsugars than the inner portions; and (3) the percentage removals of coloring matter, of sulfites, and of calcium are much less than those of the other nonsugars, indicating a more uniform distribution of these three substances throughout the whole crystal mass. These facts are more strikingly brought out in Tables I11
MINGLINQ SUGAR SIRUPNo. REMOVED
PERCENTAGE
COLOR
ASH
.
SOa
3: 1
.. 2:s
a
22.2 22.0 20.0 15.6 15.4 13.8 12.3 11.5 10.8 10.6 10.5 10.0 10.0 8.5
2
8.2
3 3 3 2 3
7.6 6.7 6.3
5 5 3
5.4 5.0 4.3
~~
;?!
... ... ... ...
...
1.2 2.8 0.6 2.0 0.8 3.3 1.1
...
...
3.8 3.0 2.1 ~~
...
1.8 1.1 4.2 5.6
..
2.6 3.2 2.2 4.7 4.2 4.7 4.9 5.4 5.2 5.7 3.9 6.3 7.1 8.0 5.6 5.6 8.9 10.8 9.8 13.8 8.7 9.4 14.2
25.0 13.4
7.0
i:8
2.8
2.3 4.8 9.0
3.3 4.8 10.8
CaO
Nag0
KzO
1.0
1.1
2.3 4.1
5,s
2.1 6.1 10.9
3.3 5.4 9.9
...
CI
...
6.9 9.9
N 2.8 5.0 9.3
Tables 111 and IT’ also bring out the relatively smaller concentrations of coloring matter, sulfites, and calcium in the outermost layer and consequently the more nearly uniform distribution of these nonsugars throughout the whole crystal. Their gradual accumulation in the mother liquor during the crystallization of the sugar results in an appreciably greater concentration in the surface layers than in the interior of the crystals, but not to the extent indicated in the cases of the other nonsugars. If the quantity of any of these three inipurities in the mother liquor is excessively high, the concentration in the surface layer or in the original film of mother liquor becomes greater, approaching those of the other non.ugars, as was found in the case of sample 0 (Tables I and 111) which contained a very high proportion of calcium. The high percentage removal and ratio for calcium in sugar hA is no doubt due in part to experimental errors. The data derived from the analyses of the “barley candies,” given in Table V, show strikingly the improvement in the
REMOVED REMOVED TO PERCEXTAGE OF SUGAR NONSUGAR
%
1 1 1 1 4 4 2 2 2 2 2 4 1 7
SOz
%
I
From 30 0 t o 20 1% sugar removed b From 20.0 t o 10 1% sugar removed. 10 0% and less suear removed
TABLE111. RATIOSO F
Vol. 2 7 , No. I
sot 0.8 1.0 0.9 1.9
...
3.5
Oa7
2:5 3.7 3.0 3.4 4.1 4.3 4.0
1.1
5.5
4.8 5.5 2.9 2.9
..
z.5 .3 6.6 10.4 9.0 2.6 11.0 13.8 14.1 15.4 14.1
,
14;4
None. or only very small amounts, present in original sugars ( c f . Table I ) .
0.2 0.9
...
1.5 2.0
...
1.6 1.4 1.8 2.3 3.4 3.4 2.0 4.0 3.6 2.2 3.8 2.7 5.2 4.4 5.3 5.9 5.4 4.7
CaO (+0:3) 2.4
.. ..
0.6 2.2 0.0 1.1 1.8 1.8 0.6 2.3 4.6
..
.. .. ..
..
..
4:7
..
.. ..
2: 1 10.6
....
7.4 4.0
..
NalO
Kz0
c1
N
..
.... ..
.. .. .. .. ..
1.9 2.4
,.
.. i :9
.. .. .. .. ..
3:7
.. .. .. ..
2.3
2.8
4:9 5.4 6.2 6.5 7.5 6.5 6.9 5.0 8.6 6.9
4:a 4.5 4.2 4.1 6.1 5.3 9.4 4.9 6.1
..
..
7.1
..
.. .. ..
5:8
..
..
6.4
.. .. .. . t
8.4 7.5
..
16.7
8.9 4.9 6.7 9.4 11.4 10.0 16.9
1.5 11.2 3.3 8.9 6.8 15.2
10.5
7.0
16.5 18.2
0
3.0 9.2 11.9 0.
10.5
9.8 21.4
7.4 23.3
,.
..
1.9 3.5 3.6 2.7 3.8 2.4 3.2 3.5
..
..
..
4:s 5.8 4.8 6.5 4.6
6:7 4.5 6.5 9.1 9.1 8.4 6.7 15.1
..
17,2
TABLEv. COMPARATIVE DATAON BlRLEY CANDIES MADEFROM MINQLI s u SIRUP
SUGAR
No.
SEGAR REMOVED
Original
Treated
2 2 T U
&wX Y Z
AA AB P .\ B AB AC
4 4 2 2 2 2 2 4 3 2
3 3 3 3 2 5 5 3
15.4 13.8 12.3 11.5 10.8 10.6 10.5 10.0 8.5 8.2 7.6 6.7 6.3 6.1 5.5 5.4 5.0 4.3
% 42 57 43 57 47 29 46 57 41 38 50 43 38 54 42 54 54 36
25 33 30 32 29 17 34 32 22 25 27 29 29 35 19 33 34 21
ORIGINAL AND
COLOR Improve- Ratio of yo improve- removed ment merit/%. sugar
% P
33
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1935
2.6 3.0 2.4 3.8 3 5 3.9 2.5 4.4 5.4 4.1
40 42 30 44 38 41 26 44 46 34 46 33 24 35 55 39 37 42
quality of the sugar resulting from the removal of the outer layer of crystals. The improvement in color of the candies of the treated sugars over those of the originals is another inllication that the nonsugars causing the production of color in the candy test have been largely eliminated by the treatment and are therefore located mainly in the outermost shell (of the crystals. It is noteworthy that this improvement in color of the candy is not accompanied by any significant decrease in the "strength" of the sugar as indicated by practically the same invert sugar and sucrose percentages in the candies. ACKNOKLEDGMENT The authors are indebted to R. L. Holmes of the Carbohydrate Division, Bureau of Chemistry and Soils, for many of the analyses in the preliminary experiments with sirup 1.
6.1
4.9 3.8 5.7 10.0 7.2 7.4 9.8
TREATEDSUGARB
INVERTSUQAR Original Treated % % 1.66 1.38 1.73 1.45 1.72 1.20 1.83 1.45 1.44 1.61 2.31 1.44 2.02 1.38 1.69 1.45 1.66 1.36 1.72 1.66 1.82 1.38 1.72 1.48 1.75 1.71 1.65 1.38 1.75 1.38 1.47 1.38 1.55 1.38 1.90 1.25
SUCROSE
Original
Treated
%
%
96.97 96.97 96.51 96.97 96.82 98.82 96.74 96.97 97.12 97.12 96.51 97.27 96.89 97.12 96.97 97.12 97.12 97.04
96.66 96.59 96.74 96.82 96.59 95.30 96.51 96.74 96.44 96.89 96.21 96.81 96.51 96.66 96.59 96.66 96.59 96.14
LITERATURE CITED (1) (2) (3) (4) (5) (6)
(7) (8) (9) (10) (11)
Ambler, Mfg. Confectioner, 7, No. 1, 17-19,82 (1927). Ambler and Byall, IND.ENO.CEIEM.,-4nal. Ed., 3,135 (1931). I b i d . , 4, 34 (1932). Ibid., 4, 379 (1932). -4mbler, Snider, and Byall, Ibid., 3, 339 (1931). ilssoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 3rd ed., pp. 268-9, Sect. XXVI, paragraph 21 (1930). Austerweil and Lemay, Bull. SOC. chim.. 49, 1541 (1931). Barber and Kolthoff, J.A m . Chem. SOC.,50, 1625 (1928). Berg& Julien, U. S. Patent 1,811,169 (June 23, 1931). Fort, C. rl., Bur. Chem. and Soils, unpublished information. Honig, Proc. 3rd Congr. Intern. SOC.Sugar-Cane Tech., Surabaya,
1929, 572-80. (12) Paine and Balch, Facts About Sugar, 21, 566, 575 (1926). RECEIVED October 30, 1934. Presented before the Division of Sugar Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934. This paper is Contribution 131 from the Carbohydrate Division, Bureau of Chemistry and Soils.
Effect of Cold and Freezing Storage on Wine Composition M. A. JOSLYNAND G. L. MARSH,University of California, Berkeley, Calif.
R
EFRIGERATION has been used in wine-making for the purpose of cooling the fermenting must to avoid the undesirable effects of fermentation at high temperatures; of preserving the wine; of aiding the disgorging, charging, or bottling of sparkling wines; of removing excess cream of tartar and other substances that would deposit when untreated wine is exposed to winter temperatures; of aiding aging by precipitation of cream of tartar and by increasing the absorption of oxygen by the wine; and of concentrating wine and increasing its market value by raising its alcohol content ( 1 , 6, 6, 9, 12, 16, 18, 19, 20, 21, ZS, 24). Refrigeration for the rapid clarification of wine by cold is being extensively used in wine-making centers of Europe and has been employed to some extent in California for the treatment of new wines. Although only about twenty of the four hundred odd wineries of the state are clarifying wine by cold, they represent a considerable proportion of the total gallonage. As practiced in California there is a wide divergence in the temperature to which the wine is cooled, the length of time i t is held a t that temperature, and the age and condition of the wine when treated. I n general, the wine is cooled close to its congealing point, held for one day to one month, and filtered cold. I n order to establish the practice on a rational basis, a n investigation of the factors
involved in the clarification of wine by cold was started, and this paper comprises the results of a preliminary survey of the problem together with a review of the more important literature on the subject.
REVIEW OF LITERATURE Although the wine-makers of certain viticultural regions of Europe employed the natural winter cold for clarification of wine for many years (9, 21, 24), the earliest application of artificial cold not only for the concentration of wine but also for clearing was that of Vergnette-Lamotte in 1868 (25). He recommended congelation of Burgundy wines a t -6" C. and even as low as -12" to -15" C., using ice and salt as refrigerant. After cooling to the desired temperature the ice formed was removed and the wine was stored in a cool place for 4 to 6 weeks and then racked. He recognized in the deposit a large proportion of cream of tartar, and a part of the coloring and nitrogenous matters. As a result of concentration by partial freezing, the alcohol content increased by 7.5 to 20.0 per cent of the initial value. Miroir (20) claimed that the first application of artificial refrigeration to the clearing of wine was made by his father in 1903. Carles in 1908 (9) recommended the storage of barreled wine in open air a t a temperature of 5"to 10°C. but stated
