Determination of Malt Sirup Density Application of the Brabender Recording Viscometer to Sirup Densimetry RICHARD H. FOSNOT AND ROBERT W. HAMAK The Wander Company, Ovaltine Laboratories, Villa Park, I l l . The use of the Brabender recording viscometer for the rapid determination of malt sirup densities has been demonstrated. A n extensive application of the viscometer in routine control work has shown an accuracj- comparable to that obtained with the hydrometer and pycnometer. The application of this method to other types of sirup has been indicated.
C
USTOMER specifications for malt siiups often set narrow hiiiits for the range of total solids content, and necessitate accurate determinations of sirup densities. In addition, shipping schedules often require that density data be made available in the shortest possible time. Thus, accuracy and speed are very essential for estimations of malt sirup density. .\loat widely used for determining sirup density are the hydrometer, pycnometer, and refractometer procedures as outlined in the methods of analysis of the Association of Official -4gricultuial Chemists ( 1 ) . The use of hydrometers, calibrated to lead directly in degrees Baume, is probably the most simple and direct method of measuring malt sirup concentration. For “free-flowing” sirups around 42 ’ BE. density, the hydrometer method is satisfactory, but with certain types of sirup, especially those of higher densities, the hydrometer no longer gives reliable readings. The composition of the sirup also has an effect on the accuracy of hydrometer values. As the ratio of nonsugar solids to sugar solids increases, the tendency for the hydrometer to give too high a density reading becomes greater. The time required to obtain an accurate hydrometer reading on an undiluted sirup decreases the value of the procedure as a rapid control method. Malt sirup density may be accurately and reliably determined by means of the specific gravity as obtained with a pycnometer. However, the necessary steps of sirup weighing, dilution, tempering to a standard temperature, volume adjustment, and final weighing require considerable time. The refractometer method is applicable only to sirups containing no undissolved solids. Refined corn siiups fall in this category, but malt sirups containing varying amounts of colloidal protein material cannot be accurately analyzed for solids content by a method dependent upon light tiansmittance. Thus, the methods most widely used for determinations of sirup density do not have the required combination of rapidity and accuracy. The possible use of some other physical property of sirups to determine solids was considered. The most obvious characteristic which might be correlated with density is the consistency or viscosity. Binghani and Jackson ( 2 ) showed the effect of solids content and tempeiature on the viscosity of pure sucrose solutions. Chatoaay (3),followed by Oppen and Schuette 16) developed quantitative relationships between the density and viscosity of honey, and demonstrated that the moisture content of honey could be calculated from viscosity measurements. Miller and Jlench ( 5 ) studied the viscosity-density correlation for corn sirups, and showed the effect of composition bv working with sirups of varying dextrose equivalents. The above workers used very precise instruments and techniques to obtain their viscosity values, as the expression of viscosities in absolute units required extremely accurate control of all variables. Although such procedures are necessary for fundamental research, they are not particularly adaptable to routine control work. Furthermore, the very nature of sirupy material
955
makes instrument cleaning a tedious piocess with viscometers of the Ostwald and Hoeppler types. Consequently, a survey of other viscometers was made, n i t h emphasis on simplicity and ease of operation. The instrument that appeared to meet the desired qualifications was a recording, rotational type of viscometer designed and developed by Kicker and Geddes ( 7 ) in conjunction with the Brabender Corporation, Rochelle Park, K. J., for the specific purpose of measuring paint consistency. T h e ,instrument fills the desired requirements of speed, ease of cleaning, and simplicity of operation. Consequently, the possibility of applying this viscometer to malt sirups was considered. The operating principles of the Brabender viscometer are relatively simple. The sample container is rotated a t constant speed by a revolving platform, imparting a torque to a paddle submerged in, the sample. This torque is opposed by a helical spring, so that the angular displacement of the spring is a measure of the induced torque. By means of a lever arm and inking mechanism, a permanent record of the spring displacement is obtained. The machine may be used to cover a wide range of consistencies, as there are three factors that can be varied. The speed of the platform rotation can be changed by the use of different pulley combinations, the resistance to the torque can be changed by using various sizes of spring wire, and the torque can be varied by changing the size and shape of the submerged paddle. EXPERIMEYTAL METHOD
The proper combination of speed, spring strength, and paddle design had to be determined as the first step in adapting the Brabender instrument to the measurement of malt sirup consistency. Experimental work shelved that the lonest speed on the Model A instrument, 50 r.p.ni., with a pin paddle as shown in Figure 1, in combination u i t h either a light (d = 0.07 em., 0.028 inch) or a heavy ( d = 1.11 mi., 0.444 inch) spring, covers the practical range of malt sirup consistencies. The heavy spring had to be used a t higher densities in order to keep the recorder pen \Tithin the limits of the chart. As two springs were used, a factor was required to convert from one spring reading to the other. This factor was obtained by taking readings with both springs on cei tain sirups of intermediate consistency and calculating a5 follows: Spring factor
=
reading with light spring reading with heavy spring
7‘0
Subsequent correlation experiments with high density sirups proved this factor to be valid.
To obtain a consiatencv reading, a 350-ml. (12-ounce) open end can (outside diameter 6.7 cni., 211:16 inches; height 12 em., 413/1,inches), is filled with the sirup sample and then centered and clamped on the turntable by means of setscrews. The can is locked in position and the table raised until the level of the sirup coincides with the mark on the paddle shaft. The motor switch is then turned on and the torque created causes the pen arm to
ANALYTICAL CHEMISTRY
956
+
describe an arc on the recorder paper. Inasmuch as malt sirups show no thixotropic or rheopectic properties, the pen will draw a vertical line on the graph as the recorder mechanism moves the paper. The paper furnished with the instrument is graduated in "consistency units' from 0 to 1000, so that the position of the recorded line may be numerically evaluated.
log Cr = -2.63 log t 5.95824 (2) shown in Figure 3. An expression combining the three variables, degrees Baum6, consistency, and temperature may now be set up. From Equation 2 the relationship between consistency and temperature a t 20' C. is log Czo' = -2.63 log 20' log
C20e
-2.63 log 20' 6.95824 - 5.95824
By substituting this expression for log C ~ Oin" Equation 1 the desired relation among the three variables is obtained. "Be =
MATHEMATICAL ANALYSIS OF DATA
The coordinate points relating density to consistency appeared to express an exponential function of the general type, Y = blOMX. When such an exponential curve is plotted on semilogarithmic paper, the equation becomes a straight line expressed as log Y = M X + log b. Figure 2 shows the relationship between the logarithms of the consistencies and the respective densities a t 20" c. In order to evaluate the constants M and 6, the regression line was calculated from the experimental values and found to be = 0.413 ( " BC.
+
- log Ct
+ 2.63 logt log C d = -2.63 log 20' + 5.95824 - 5.95824 + 2.63 log + log Ci log Czoo = 2.63 (log t - log 20") + log Cr (4)
In order to determine the relationship between density apd consistency, a series Figure 1. Viscometer Paddle of siruD samdes of varying densities was required. To obtain these, samples of a malt sirup were taken from a plant evaporator a t various stages during the "finishing off" process, giving a density range of 39.5" to 42.5" Be. Densities were determined by the A.O.A.C. pycnometric procedure (diluting 50.0 grams of sirup with an equal weight of water), and consistency readings were taken a t a constant temperature of 20°C. Similarly, to determine the relationship between consistency and temperature, samples of the finished sirup (constant density) were tempered to 20 ', 29.5 O , 35 ', and 40.5 O C. and consistency determinations were made at those temperatures.
C20°
(3)
Subtracting Equation 2 from Equation 3:
The three variables, density, consistency, and temperature, are expressed in the following units: densitv in degrees BauniG (modulus 145), consistency in Brabender "consistency units," and temperature in degrees Centigrade.
log
+ 5.95824
log Cr
+ 2.63 (log t
- log 20") -
0.413
log 20
+ 39
By means of Equation 5 the density of sirups of this particular type may be calculated from the Brabender consistency value at any temperature. To eliminate the calculation of densities from consistency readings, a chart may be constructed as shoun in Figure 4. Each diagonal line represents the relationship between temperature and consistency for a specified BauniB value. For this particular sirup these "iso-Baum6" lines are calculated over a range between 41.5" and 43.0" BB. in steps of 0.1" BB. The density is read from the chart by determining the value of the diagonal line nearest the point of intersection of the coordinate values of temperature and consistency. DISCUSSION
When the consistency-density-temperature relationships were investigated for other types of malt sirup, it was discovered that the composition of the sirup affected these relationships (4). Comparable composition effects have been clearly shown for corn sirups by Miller and Mench (6). Consequently, separate curves must be developed for each type of sirup analyzed. I n the authors' laboratories, this has been done for five different types of sirup. Table I shows average approximate analvses. These typical commercial sirups were produced from masheb varying in composition from all barley malt and no adjunck (Types IV and V) to those containing 40% barley malt and 60% adjunct (Type I). Intermediate sirups were made from mashes
- 39) + log 20
where Y = CZO"= consistency units at 20' C. izI = 0.413 X = "Be. b = 20 (intercept on the Y axis) (The constant, 39, compensates for shifting the intersection of the
X and Y axes from 0' to 39' Be.) By transposition, the above
equation may be expressed:
which permits the calculation of sirup density in degrees BaumC from the Brabender consistency reading made at 20' C. When the temperatureconsistency data were graphed on logarithmic paper, a straight line was obtained, which indicated that the relationshi was that of a power function whose general equation is Y = b3!M or the straight-line form, log Y = M log X log b. The regression line was calculated and the consistencytemperature equation for this particular sirup was found to be:
+
(5)
I 39
41
40
DENSITY
Figure 2.
42
OB(.
Density-Consistency Relationship
9Sl
V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8 Table I.
dirup Type I I1
Density, OBI. 42.1 42.1 42.6 42.5 43.0
I11 IV V
Analyses of Malt Sirups
Total Solids,
%
Protein, %
Ash, 70
79.3 79.3 80.3 80.1 81.1
2.3 3.5 4.3 6.1 4.7
0.8 1.1 1.2 1.5 1.3
Reducing UndeSugars termined as (Dextrins, Crude Gums, Maltose. etc.), % % 9.0 16.6 3.2 2.1 15.5
67.2 58.0 72.1 70.8 59.6
Table 11. Comparison of Density Values Obtained by Consistency and Specific Gravity Methods (Density, ’ BaumB) Specific Gravity Consistency Method Method
Type
I
41.5 42.6 42.2 42.2 42.0 42.3 42.2 42.0 42.8 42.2 43.0 42.4 42.4 42.6 43.1 42.3 43.2 42.5 42.6 43.4
[I
111
IV
V
Difference 0.0 f0.l 0.0 -0.1 0.0 -0.1 -0.1 0.0 -0.1 fO.l 0.0 -0.1 fO.l 0.0 -0.2 0.0 +0.2 +0.1 -0.1 0.0
41.5 42.7 42.2 42.1 42 .O 42.2 42.1 42.0 42.7 42.3 43.0 42.3 42.5 42.6 42.9 42.3 43.4 42.6 42.5 43.4
are listed in Table 11. These values cover the normal range of densities of the five types of sirup mentioned above. The advantages of the consistency method of determining density are: no dilution of sirup required, no weighing involved, no temperinq to standard temperature, no operative skill required, great time saving over other methods, and record of reading obtained for future reference. The use of the consistency method has greatly shortened the time previously used for density determinations. I t has been estimated that the time required for one operator to determine the densities of six sirups by the specific gravity procedure is between 2.5 and 3.0 hours. The same number of determinations require approximately 30 minutes when the Brabender viscometer is used. Density-consistency and temperature-consistency equations have also been developed for corn sirup, molasses, and invert sugar sirup. Because the fundamental equations are of the same form as those developed for malt sirups, the consistency method of density determination should be applicable to sucb sirups.
consisting of 75% barley malt and 25y0 adjunct (Types I1 and 111). The brewing procedures used varied from low temperature diastatic processes (Types I11 and IV) to high temperature nondiastatic processes (Types I1 and V). Although the sirup composition shows great variation among the different types, there are only insignificant changes between batches of the same type, owing to rigid standardization of the mash bills and brewing procedures, Thus, when the temperatureconsistency and density-consistency relationships have been determined for any particular type of sirup, those relationships can then be applied to subsequent batches of the same type of sirup. Daily use of this consistency method for approximately two years has definitely established its reliability and accuracy. To illustrate the degree of correlation between density values obtained by the specific gravity method and those calculated from consistency readings, twenty pairs of Baume determinations
2.
; TEMPERATURE
Figure 4. Temperature-Consistency-Density Relationship
%
ACKNOW LEDGM EYT
\ I
LO
40
TEMPLRATURL
The authors acknowledge their appreciation of the assistance of Beatrice Hjelte in determining the pycnometric densities of all sirup samples used in this investigation. LITERATURE CITED
60
60 lo0
‘c,
Figure 3. Temperature-Consistency Relationship
(1) Assoc. Official 4 g r . Chem., Official and Tentative Methods of Analysis, 6th ed., pp. 557-8, 1945. (2) Bingham, E. C., and Jackson, R. F., Bur. Standards Bull. 14, 59 (1917). (3) Chatoway, H. D., Can. J . Research, 6, 532 (1932). (4) Fosnot, R. H., and Haman, R. W., unpublished data, 1946-47. ( 5 ) Miller, B. S., and Mench, J. W., “Viscosity of Corn Sirups,” Purdue University, September 1946. (6) Oppen, F. C., and Schuette, H. A., IND.ENG.CHEM.,ANAL.ED.. 11, 130-3 (1939). (7) Wicker, C. R., and Geddes, J. A., Am. SOC. Testing Materiala, Bull. 120 (1943).
RECEIVED August 8, 1947.
