Lime oil & juice
Practical Action
Screw-press
Screw-presses are generally made of stainless steel or bronze and do more 'work' on the limes
than roller-crushers. The skins emerge from the screw-press in a shredded state. As a result the
raw juice contains more fine pulp, after sieving, than juice from a roller mill and therefore takes
longer to settle. Also, the settled juice from a screw-press is rarely as clear as that obtained from
a roller mill. However, this need not be a drawback if a filter press is used to clarify the settled
juice. Higher yields of raw juice are obtainable from the screw-press and this may be of
particular advantage where distilled lime oil is to be the main or only product. The screw-press
is a smaller piece of equipment and easy to strip down and adjust, but requires adjustment at
regular intervals if its crushing efficiency is to be maintained. It is possible with a screw-press to
apply too much pressure and to produce a raw juice which will not settle properly under gravity
no matter how long it is left to stand.
As indicated, a triple roller mill of the size described should be capable of crushing 100 tons of
fruit in a week. In order to obtain an efficient separation of top pulp from the clear juice, it is
inadvisable to add to one vat, more than four consecutive days production of 'raw juice' from
crushing. Generally, the volume of this juice approximates 40-45% of the fresh fruit, thus 1 ton
of fruit should yield about 100 gallons of expressed fluids. The roller mill should produce 5 to 6
thousand gallons of 'raw juice' over 4 days and 4 or 5 vats of this capacity would be required to
cope with this level of production.
Processing for both lime oil and lime juice
The juice extracted by the crusher should pass through screens for the removal of coarse pulp
and pips. The waste skins can be removed either by a suitably placed conveyor, or by a
removable waste box. The former is preferable, particularly when working at maximum
throughput of the machine.
In the West Indies, the raw juice is usually collected in wooden boxes (coated with paraffin wax),
or a stainless steel box in one case, placed under the mill. The raw juice is screened through
stainless steel mesh (16 mesh and 32 mesh). Screening is often done by hand brushing,
although a rotary stainless steel screen is used in one factory.
Crusher and screens must be kept scrupulously clean and scrubbed down thoroughly after each
days crushing.
Settling vats
Settling vats are normally wooden and cylindrical with removable covers on the top so that they
can be closed and sealed when raw juice is settling.
Vats may be constructed of any wood which will not taint the lime juice and oil. White oak has
been used in the West Indies and is thought to have a life of about 7 years. After that time wood
borers will have made white oak vats unreliable. Harder woods such as wallaba and greenheart
have been used with more success but both are more expensive and difficult to work. However,
in the long-run they are probably to be recommended.
Lime setting vats are not usually coated on the inside although the outside may be painted. One
company has been experimenting with an epoxy resin based paint on the inside of setting vats
but the results of these tests are not known.
The cleanliness of lime settling vats is of paramount importance in the production of high quality
lime products. Vats should be scrubbed out and steamed at regular intervals. When not in use
for settling they should be kept full of water to which potassium (or sodium) metabisulphite has
been added and the lids tightly closed.
Raw juice is fed into the settling vats by gravity or is pumped. It is worth remembering that if
electricity is unreliable a manual and/or mechanical juice pump is essential.
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