2009_Book_FoodChemistry

872 19 Sugars, Sugar Alcohols and Honey
and 1−2% of water. It is light yellow to dark
brown in color due to the adhering syrup. Like
the after-product sugar (3−4% of organic and
1.5−2.5% of inorganic nonsugar substances
and 2−3% of water) obtained in the last
crystallization stage, raw sugar is generally
not suitable for direct use. It is processed to
consumer sugar in refineries.
In the refinery, the sugar is mashed into
a magma with a suitable syrup, centrifuged,
and washed with water and steam (affination).
Thus, it directly yields a consumer sugar
called affinated sugar. Another possibility is
to dissolve the sugar and feed the resulting
syrup (liquor) to a crystallization process
which then yields refined sugar, a consumer
sugar of the highest quality.
A simplified crystallization scheme for the
production of white sugar is presented in
Fig. 19.8. After affination and dissolving, the
raw sugar and after-product sugar accumulating
in the course of the process are boiled
down together with the thick syrup, and the
Table 19.6. Production losses a during saccharose recovery
from sugar beet
Processing step 1950 1974
Beet slice extraction 0.4−0.5 0.15−0.25
Sugar extract purification 0.1−0.2 0.02−0.05
Other steps 0.6−0.8 0.25−0.90
Total process 1.1−1.5 0.42−0.60
a
Sugar amount in % based on the processed beet
weight.
main part of the sugar finally crystallizes out
of the supersaturated solution as white sugar.
Centrifugation at 40–45 ◦ C yields not only
crystals of 2−4 mm (first-product sugar), but
also centrifugal syrup (green syrup) which
is subjected to two further crystallization
steps. The last discharge, a highly viscous
brown syrup, is molasses. In the processing
of thick syrup to refined sugar, first raw sugar
is isolated exclusively. It is then dissolved
and fed back into the crystallization process.
In this way, the process is independent of
variations in the quality of the thick syrup.
Processing losses in sucrose recovery from beets
in 1974 were 0.4−0.9% (sugar determined polarimetrically;
and based on processed beet weight)
and, when compared to 1950, represent a significant
improvement of the sucrose yield (Table
19.6). This technological progress is also reflected
in a rise of work productivity (work min/t
beets), which was 130−150 in 1950 but only
12−30 in 1974.
19.1.4.1.3 Production of Cane Sugar
Fig. 19.8. White sugar evaporation and crystallization.
Quotient Q: % saccharose in dry matter
Sugar cane processing starts with squeezing out
the sweet sap from thoroughly washed cane.
For this purpose, the cane moves to a shredding
machine where knives shred the stalks and then
moves to crushing machines where a series of
revolving heavy steel rollers squeeze the cane
under high pressure. After the first roller, more
than 60% of the cane weight is removed in the
form of sap which contains 70% or more of
the cane sucrose content. Repeated squeezing
provides a sucrose yield of 93–97.5%. The
squeezing may be combined with extraction by
mixing the “bagasse” (the pressed cane) with hot