The interior of the drier is fitted with narrow shelves (parallel to its axis) so that as the drum rotates, the sugar is repeatedly carried upwards on the shelves and then dropped, whilst a current of hot air is drawn through the drum by means of a fan (shown on the right). On reaching the lower extremity of the drum, the sugar becomes dry and contains about 99.9% of sucrose. It gravi tates to the revolving sifter below, Plate, fig. 3, which is made in three sections, each section having wire-gauze of different mesh.
The crystals are thus sorted into three sizes or grades :—fine, medium and coarse which fall into three cone-shaped hoppers be low. Any lumps (accidentally produced) pass beyond the sieve and fall into a fourth hopper. The sifted sugar next gravitates from these hoppers to automatic weighing machines from which bags are suspended (Plate, fig. 3). The attendant opens a shutter which allows the sugar to flow into a bag, and, when the correct weight has entered, the machine automatically closes the shutter. The attendant then unfastens a strap holding the bag to the ma chine and the filled bag drops a few inches upon a band-conveyor which carries it to a sewing machine by which it is stitched up.
Cube sugar, sometimes called loaf sugar, is made by two alter native methods which can only be very briefly described here. Method (a). The production of rectangular slabs of white sugar, measuring about 20"X io" X 4", these being then cut up into single cubes by machirkery. This method includes the Scheibler process (now little used) and the more modern Adant and Hubner processes. In the Adant process, the hot massecuite is run into a number of rectangular metal moulds, where it sets during partial cooling. The filled moulds are then transferred to a centrifugal
machine of special construction, the mother-liquor separated by spinning, and the slabs of sugar washed with pure syrup entering at the centre of the machine. The latter is then stopped, the moulds removed, and the slabs of white sugar dried and cut up into small cubes (see Plate, fig. 4). The Hubner process is a modi fication of Adant's, and, whilst it economizes time, and labour, gives a slightly reduced yield.
Method (b). The sugar is moulded directly into cubes instead of into slabs. The massecuite discharged from the vacuum pan is spun in the ordinary type of centrifugal (Plate, fig. 5 [bottom] ). The crystals are washed white and discharged into a mixer where they are thoroughly mixed with white sugar-liquor to form a magma. This flows into rows of small cubical pockets on the surface of a slowly rotating horizontal drum.
During every half-revolution of this drum, the magma is compressed inside each pocket forming single cubes, and rows of these cubes are ejected from the drum when the pockets reach their lowest positions. The empty pockets are refilled with magma on further rotation to their highest positions. The cubes fall from the drum upon a travelling band which carries them slowly through a drying chamber to the packing cases without any handling.
Icing sugar and the finest grade of caster sugar are made from some of the foregoing grades by grinding in mills.