1959
TWENTY-SIXTH CONFERENCE
45
THE RELATIONSHIP BETWEEN BRIX AND
VISCOSITY FOR KALAMIA SYRUP AND
MOLASSES
By p. G. ATHERTON
Introduction
At Kalamia a new set of A and B molasses pumps was installed, for the
1958 crushing season. The molasses from the high grade centrifugals is diluted
before entering the inlet to these pumps and in order to ascertain the viscosity of
molasses presented to the pumps under various conditions of dilution, an
investigation into the relationship between brix and viscosity of A and B
molasses was carried out. The results were found to show a high degree of
regularity and the investigation was extended to include syrup and final
molasses.
Apparatus and Procedure
Samples of syrup were taken from the pump outlet to the pan stage, A and
B molasses from the fugal gutters before dilution and the pump delivery after
dilution, and final molasses from the fugal gutters. The samples were carefully
mixed, a portion placed in the viscometer cup and a second portion diluted 1 : 1
and the brix determined by spindle.
The viscosity of the sample was determined without deaeration at a
temperature of 50° c. using a Technico torsion wire viscometer described, by
Kelly and McAntee [2]. This viscometer is fitted with a water- jacketed cup
through which water was circulated by means of a gear pump from a
thermostatically controlled bath. The temperature of 50° c. was chosen as this is
approximately the average temperature at which syrup and molasses are
pumped. The viscosity was determined as soon as temperature conditions were
steady and without any attempt at deaeration as the viscosity of the material
actually being pumped was desired.
The first series of samples was taken early in the 1958 season while a
second smaller series was taken at the end of the season to ascertain any changes
caused by alteration to the nature of the material being handled.
Results and Conclusions
The results are shown in graphical form in Fig. 1, 2 and 3. Figure 1 shows
a graph of viscosity at 50° c vs. brix for the first series of tests. The graph shows
a gradual increase of viscosity with brix up to approximately 80 brix. Between
80 and 90 brix, the rate of increase becomes larger and above 90 brix, viscosity
increases very rapidly with brix. It can be seen from the graph that the brix
values for syrup, A molasses and B molasses overlap blit the viscosity values
still lie on the same smooth curve. Thus it would appear that the viscosities of
these samples, are fairly independent of the purity of the material, at least down
to about 55 apparent purity. This agrees with the work of King [3] on.
1959
TWENTY-SIXTH CONFERENCE
Fig. 2—-Comporison of results at Kalamio and those of King in the Philippines.
Fig. 3—Log viscosity ot 50M C. vs. brix, showing transition points.
41
1959
TWENTY-SIXTH CONFERENCE
49
The theoretical reason for the transition point is another point of interest.
Several possible causes can be considered and discussed, viz.;
1. The existence of grain in the higher brix samples.
2. Increased aeration.
3. The onset of saturation.
4. The natural effect of increased concentration.
1. Samples above and below the transition point were examined
microscopically and apart from a small quantity of large grain, which had
obviously come through the fugal gauze, no appreciable amount of grain was
found in any of the samples.
2. A sudden increase in the viscosity characteristic due to increased
aeration is not likely as it would be expected that any increased tendency to
aeration would be gradual.
3. With regard to the transition point being caused by the concentration
reaching the saturation point, Doss, Gupta and Vishnu fl] state that a break in
the viscosity curve has been found when molasses is cooled through the
saturated condition. If so, this would also be expected when molasses passes
through the saturation point by increasing concentration.- However, neither
Micheli and De Gyulay [4] or Kelly and McAntee [2] working with Australian
molasses, found a transition point when cooling through the saturation point. It
also seems unlikely that this would be the cause of the transition point in this
case as both A and B molasses exhibit the same brix at the transition point while
the sucrose concentrations would be quite different; for example:—
A molasses at 83.5 Bx. and (Ỉ2 purity.
Pol = 51.8. Water = 10.5 approx.
Pol/100 water = 314.
B molasses at 83.5 Bx. and 55 purity.
Pol — 45.9. Water = 16.5 approx. Pol/100 water — 278.
which shows a difference of more than 10 per cent, in concentration.
4. The view that the transition point is a concentration effect caused by
internal cohesion seems more likely. King calibrated his viscometer using pure
invert solutions at different concentrations and found the same type of
viscosity—concentration relationship as has been found for molasses. As the
invert solutions were deaerated and free from crystal, the influence of crystals
and aeration can be discounted and, from the work of Micheli and De Gyulay
and Kelly and McAntec, saturation seems an unlikely reason for the transition
point.
Such semi-log or log-log relationships with transition points are quite
commonly found in experiments with naturally occurring materials and it seems
likely in this case that the transition point is not caused by any heterogeneity of
the material or by the onset of saturation, but is due to an increase in internal
cohesion.
The practical application of the transition point, which marks the onset of
the steep increase in viscosity with brix, can be seen when considering the
pumping of A and B molasses back to the pan stage. Molasses from the
centrifugals is usually diluted before pumping for • purposes of sugar boiling
and this dilution also cases the load on molasses