The physical characters which serve to show that a beet-root is of good
quality, are its being firm, brittle, emitting a creaking noise when
cut, and being perfectly sound within; the degree of sweetness is also a
good indication. The 45th degree of latitude appears to be the southern
limit of the successful growth of beet in reference to the extraction of
sugar.
_Extraction of Sugar from the Beet._--The first manipulations to which
the beets are exposed, are intended to clear them from the adhering
earth and stones, as well as the fibrous roots and portions of the neck.
It is desirable to expose the roots, after this operation, to the action
of a cylinder washing-machine.
The parenchyma of the beet is a spongy mass, whose cells are filled with
juice. The cellular tissue itself, which forms usually only a twentieth
or twenty-fifth of the whole weight, consists of ligneous fibre.
Compression alone, however powerful, is inadequate to force out all the
liquor which this tissue contains. To effect this object, the roots must
be subjected to the action of an instrument which will tear and open up
the greatest possible number of these cells. Experiments have, indeed,
proved, that by the most considerable pressure, not more than 40 or 50
per cent. in juice from the beet can be obtained; whilst the pulp
procured by the action of a grater produces from 75 to 80 per cent.
[Illustration: 1098 1099]
The beet-root rasp of Moulfarine is represented in _figs._ 1098, 1099.
_a_, _a_, is the frame-work of the machine; _b_, the feed-plate made of
cast iron, divided by a ridge into two parts; _c_, the hollow drum; _d_,
its shaft, upon either side of whose periphery nuts are screwed for
securing the saw blades _e_, _e_, which are packed tight against each
other by means of laths of wood; _f_, is a pinion upon the shaft of the
drum, into which the wheel _g_ works, and which is keyed upon the shaft
_h_; _i_, is the driving rigger; _k_, pillar of support; _l_, blocks of
wood, with which the workman pushes the beet-roots against the
revolving-rasp; _m_, the chest for receiving the beet-pap; _n_, the
wooden cover of the drum, lined with sheet iron. The drum should make
500 or 600 turns in the minute.
A few years ago, M. Dombasle introduced a process of extracting the
juice from the beet without either rasping or hydraulic pressure. The
beets were cut into thin slices, by a proper rotatory blade-machine;
these slices were put into a macerating cistern, with about their own
bulk of water, at a temperature of 212° F. After half an hour’s
maceration, the liquor was said to have a density of 2° B., when it was
run off into a second similar cistern, upon other beet-roots; from the
second, it was let into a third, and so on to a fifth; by which time,
its density having risen to 5-1/2°, it was ready for the process of
defecation. Juice procured in this way is transparent, and requires
little lime for its purification; but it is apt to ferment, or to have
its granulating power impaired by the watery dilution. The process has
been accordingly abandoned in most establishments.
I have seen the following operations successfully executed in a
beet-root factory near Lille, and have since verified their propriety in
my own laboratory upon white beets, grown near Mitcham in Surrey. My
product was nearly 5 per cent.; it was very fair, and large grained,
like the vacuum-pan sugar of Demerara, but without its clamminess.
The roots were washed by a rotatory movement upon a grating made like an
Archimedes’ screw, formed round the axis of a squirrel-cage cylinder,
which was laid horizontally beneath the surface of water in an oblong
trough. It was turned by hand rapidly, with the intervention of a
toothed wheel and pinion. The roots, after being sufficiently agitated
in the water, were tossed out by the rotation at the end of the cylinder
furthest from the winch. They were next hoisted in a basket up through a
trap hole into the floor above, by means of a cord and pulley moved by
mechanical power; a six-horse steam engine, upon Woolfe’s expansive
principle, being employed to do all the heavy work. They were here
subjected to the mechanical grater (_rape mécanique_), see _fig._ 1098,
1099., which had, upon its sloping feed-table, two square holes for
receiving at least two beets at a time, which were pushed forwards by a
square block of wood held in the workman’s hand by means of a strap. The
rasp was a drum, having rows of straight saws placed half an inch apart
round its periphery, _parallel to the axis_, with teeth projecting about
1/8 of an inch. The space between each pair of saws was filled with a
wedge of wood. The steel slips, or saw plates, were half an inch broad,
twelve inches long, and serrated on both their longitudinal edges, so
that when the one line of teeth was blunted, the other could be turned
out. The drum made 750 turns per minute.
The pulp from the rasp fell into a flat trough placed beneath, whence it
was shovelled into small bags. Each bag had its mouth folded over, was
laid upon a wicker plate, and spread flat with a rolling-pin. The bags
and hurdles were then piled in the hydraulic press. There were three
presses, of which the two allotted to the first pressure were charged
alternately, and the third was reserved for a final and more durable
pressure of the _marc_. See PRESS, HYDRAULIC, and STEARINE PRESS.
The juice flowed over the edges of the wicker plates, and fell into the
sill-plate of the press, which was furnished with upright borders, like
a tray, through whose front side a pipe issued, that terminated in a
leathern hose, for conducting the juice into an elevated cistern in the
boiling-house. Here one pound of slaked lime was mixed with every four
hectolitres (about 88 gallons imp.) of juice. The mixture was made to
boil for a little while in a round pan alongside, whence it was decanted
into oblong flat filters, of blanket stuff. The filtered liquor, which
had in general a spec. gravity of 15° Baumé, (about double that of the
fresh juice), was now briskly concentrated by boiling, in an oblong pan,
till it acquired the density of 28° B. The fire being damped with raw
coal, the syrup was run off rapidly by a stopcock into a large basin
with a swing handle, and immediately replaced by fresh defecated liquor.
The basin was carried by two men to the opposite side of the
boiling-house, and emptied into a cistern set on a high platform, whose
horizontal discharge-pipe was provided with a series (five) of
stopcocks, placed respectively over five copper chests (inverted
truncated pyramids), containing a thick bed of granular bone black,
covered with a perforated copper plate. The hot syrup thus filtered had
a pale straw-colour, and was subsequently evaporated in swing pans,
_figs._ 1096, 1097., over a brisk fire, in quantities equivalent to half
a cwt. of sugar, or four hectolitres of average juice.