If tank water is being collected the boiling is done by steam jacket on the box; if not, by direct application of free live steam. In either case stir contents freely.
Pressing Tankage.
—As soon as the operation of the skimming of the vat has been thoroughly accomplished the contents are in the proper condition to be pressed and should be handled while still hot. The water is mostly drained off. In building the cakes, a portable car is run under the surface box. By the use of a quick opening lever gate the contents are dropped in quantity desired upon a press cloth; between each cheese is placed a rack—the process being thus, a rack made of 1 × ¹⁄₄ inch material, usually elm, thoroughly nailed together, is first laid on the press head; next a frame of the size and depth required to handle the product is used. This frame should not exceed two inches in depth. The press cloth is then spread over them and the material drawn onto the press. Well spread out, the cloth is carefully folded over the top of it. The form is then lifted off the press, another press rack is put on top of the cheese already made, and the process repeated. Ten or twelve plates are usually used to a press.
After the car is filled it is placed in the hydraulic press and pressure applied. This should be done slowly at first, giving the water ample time to run out of the press. If the pressure is applied too rapidly the tendency is for the material to slide out on one side or the other, but if the water is pressed out slowly the material adheres better or gets a good “bond,” so that it will not slip.
After the press has run until the cakes are about one-half of their original thickness spray with hot water, thoroughly washing off the sides of the press, turn on more pressure until this reaches about 300 tons on a 5 × 5 foot plate. It will be found that it is the last pressing which brings out the grease.
Where tankage is properly handled it should run from six to eight per cent of residual grease on a dry basis. Where improperly handled it will oftentimes run from eighteen to twenty per cent, the excess being lard or tallow which should have been saved, but worthless if left in tankage.
Treatment of Lard and Tallow.
—As the oils are being withdrawn from the rendering tanks the same should be passed through a small over-flow type of catch tank arranged so that the oils pass through a straining system to remove fibre or floaters. From the above basin the oils should be passed to the receivers or coolers preparatory to settling.
In the judgment of the writer these tanks should preferably be in a department or room separated from the rendering department, to avoid possibility of contact and absorbing odors. The receivers or reservoirs should be circular in form with a coil of heating pipe arranged, supported from the sides of the kettles. The pipe should be sufficiently spread to allow perfect cleaning.
The cones on the bottom should be at an angle of 45° so as to collect the sediment, water or scrap that may deposit in small volume. The scrap should be settled out and removed daily. Tallow and lard should be allowed to cool to a tiercing temperature and kept in as large volume as conditions permit, so as to obtain uniformity in cooler.