Part 11 (2/2)
A battery of horizontal grinding mills, by which the cacao nibs are ground to paste (Messrs. Cadbury Bros., Bournville.)]
The sh.e.l.l, the only waste material of any importance produced in a chocolate factory, goes straight into sacks ready for sale. The pure cacao nibs (once an important article of commerce) proceed to the blenders and thence to the grinding mill.
(_g_) _Blending._
We have seen that the beans are roasted separately according to their kind and country so as to develop in each its characteristic flavour.
The pure nib is now blended in proportions which are carefully chosen to attain the result desired.
(_h_) _Grinding the Cacao Nibs to Produce Ma.s.s._
In this process, by the mere act of grinding, the miracle is performed of converting the brittle fragments of the cacao bean into a chocolate-coloured fluid. Half of the cacao bean is fat, and the grinding breaks up the cells and liberates the fat, which at blood heat melts to an oil. Any of the various machines used in the industries for grinding might be used, but a special type of mill has been devised for the purpose.
In the grinding room of a cocoa factory one becomes almost hypnotised by a hundred of these circular mill-stones that rotate incessantly day and night. In Messrs. Fry's factory the ”giddy motion of the whirling mill”
is very much increased by a number of magnificent horizontal driving wheels, each some 20 feet in diameter, which form, as it were, a revolving ceiling to the room. Your fascinated gaze beholds ”two or three vast circles, that have their revolving satellites like moons, each on its own axis, and each governed by master wheels. Watch them for any length of time and you might find yourself presently going round and round with them until you whirled yourself out of existence, like the gyrating maiden in the fairy tale.”
In this type of grinding machine one mill stone rotates on a fixed stone. The cacao nib falls from a hopper through a hole in the centre of the upper stone and, owing to the manner in which grooves are cut in the two surfaces in contact, is gradually dragged between the stones. The grooves are so cut in the two stones that they point in opposite directions, and as the one stone revolves on the other, a slicing or shearing action is produced. The friction, due to the slicing and shearing of the nib, keeps the stones hot, and they become sufficiently warm to melt the fat in the ground nib, so that there oozes from the outer edge of the bottom or fixed stone a more or less viscous liquid or paste. This finely ground nib is known as ”ma.s.s.” It is simply liquified cacao bean, and solidifies on cooling to a chocolate coloured block.
[Ill.u.s.tration: SECTION THROUGH GRINDING STONES.]
This ”ma.s.s” may be used for the production of either cocoa or chocolate.
When part of the fat (cacao b.u.t.ter) is _taken away_ the residue may be made to yield cocoa. When sugar and cacao b.u.t.ter are _added_ it yields eating chocolate. Thus the two industries are seen to be inter-dependent, the cacao b.u.t.ter which is pressed out of the ma.s.s in the manufacture of cocoa being used up in the production of chocolate.
The manufacture of cocoa will first be considered.
(_i_) _Pressing out the excess of b.u.t.ter._
The liquified cacao bean or ”ma.s.s,” simply mixed with sugar and cooled until it becomes a hard cake, has been used by the British Navy for a hundred years or more for the preparation of Jack's cup of cocoa. It produces a fine rich drink much appreciated by our hardy seamen, but it is somewhat too fatty to mix evenly with water, and too rich to be suitable for those with delicate digestions. Hence for the ordinary cocoa of commerce it is usual to remove a portion of this fat.
[Ill.u.s.tration: A CACAO PRESS.
Reproduced by permission of Messrs. Lake, Orr & Co., Ltd.]
If ”ma.s.s” be put into a cloth and pressed, a golden oil (melted cacao b.u.t.ter) oozes through the cloth. In practice this extraction of the b.u.t.ter is done in various types of presses. In one of the most frequently used types, the ma.s.s is poured into circular steel pots, the top and bottom of which are loose perforated plates lined with felt pads. A number of such pots are placed one above another, and then rammed together by a powerful hydraulic ram. They look like the parts of a slowly collapsing telescope. The ”ma.s.s” is only gently pressed at first, but as the b.u.t.ter flows away and the material in the pot becomes stiffer, it is subjected to a gradually increasing pressure. The ram, being under pressure supplied by pumps, pushes up with enormous force.
The steel pots have to be sufficiently strong to bear a great strain, as the ram often exerts a pressure of 6,000 pounds per square inch. When the required amount of b.u.t.ter has been pressed out, the pot is found to contain not a paste, but a hard dry cake of compressed cocoa. The liquified cacao bean put into the pots contains 54 to 55 per cent. of b.u.t.ter, whilst the cocoa press-cake taken out usually contains only 25 to 30 per cent. The expressed b.u.t.ter flows away and is filtered and solidified (see page 158). All that it is necessary to do to obtain cocoa from the press cake is to powder it.
[Ill.u.s.tration: SECTION THROUGH CACAO PRESS-POT AND RAM-PLATE.]
(_j_) _Breaking Down the Press Cake to Cocoa Powder._
The slabs of press-cake are so hard and tough that if one were banged on a man's head it would probably stun him. They are broken down in a crus.h.i.+ng mill, the inside of which is as full of terrible teeth as a giant's mouth, until the fragments are small enough to grind on steel rollers.
(_k_) _Sieving._
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