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PRESERVATION BY METHOD II.

While the method outlined in the preceding pages gives very satisfactory results, it is time-consuming and laborious. The juice must be twice pasteurized; it must have storage space where the temperature is under some degree of control during the period of clarification, which necessitates keeping on hand a large number of containers; and there is a considerable proportion of loss due to fermentation and to repeated handling and consequent breakage. For these reasons considerable effort has been devoted to devising methods of treatment of unfermented fruit juices which will eliminate as much of the labor of preparation as possible without sacrificing the quality or palatability of the product. A method developed in the laboratories of the Bureau of Plant Industry is regarded as combining several highly desirable features. It makes the entire process of preparation of a juice, from pressing the fruit to the pasteurization of the juice in the final containers, a practically continuous process, eliminates the necessity of pasteurizing the juice and holding it in storage containers for clearing, lessens the loss from breakage and the cost of production. by reducing the handling necessary, and enables the maker to put the finished product on the market within a few days after pressing begins. At the same time it produces a clear sediment-free product without the use of costly special equipment and without the loss of the characteristic flavor and beverage quality of the juice.

The steps in the treatment of the juice by the new method are as follows: The juice is pressed, allowed to stand for 12 hours or overnight to settle, decanted from the sediment, and blended if necessary. It is then mixed with diatomaceous earth (also called infusorial earth, kieselguhr, and diatomite) at the rate of 6 to 8 pounds per hundred gallons, thoroughly stirred, and immediately filtered through a thin layer of diatomaceous earth supported by a closely woven cloth. The clear juice is placed in the final containers as it comes from the filter, sealed, and pasteurized, which completes the work. The details of the process will now be stated.

MIXING THE JUICE WITH DIATOMACEOUS EARTH.

In pressing, sedimenting, siphoning off, and blending, the juice is handled precisely as in Method I. Instead of placing the blended juice in storage containers for pasteurization and storage, as in that method, the juice in the blending tank or other good-sized open tank is treated with diatomaceous earth. The dry earth, previously prepared for use by the method outlined in a subsequent paragraph, is weighed out and slowly shaken into the juice, which is vigorously stirred meanwhile. It is essential that the earth be added to the juice in a finely divided condition, avoiding lumps, in order that it be equally distributed through the tank. An ordinary flour sifter is

an excellent device from which to add the earth. If the plant is equipped with power, a small power stirrer may advantageously be used to agitate the liquid; if power is not available, the liquid should be very thoroughly stirred by hand, and the stirring should be repeated two or three times before filtration begins. As the efficiency of this treatment depends upon bringing the particles of the earth into contact with the floating matter of the juice, which becomes attached to the surfaces of the earth particles, repeated and vigorous stirring of the mixture is not a process to be omitted or carelessly performed. From 10 to 15 minutes should be allowed for this stage of the work, after which the juice is ready for filtration.

FILTERING THE TREATED JUICE.

The treated juice now has suspended in it innumerable fine particles of the earth, each more or less completely covered with a layer of gummy or slimy material derived from the juice. These particles are. for the most part, extremely thin, slightly curved, saucer-shaped or boat-shaped bits of silica, with a small percentage of smaller irregu larly shaped fragments produced by the crushing of the larger pieces. The next step in the process is to pass the juice through a filter capable of holding back these fine particles, which will retain all the suspended matter and give a perfectly clear liquid.

Suction or gravity pulp filters of the usual type, such as were described in connection with Method I, do not give satisfactory results with juices which have been treated with earth. The reason is that the finer particles of earth at first pass through the pulp, giving a cloudy filtrate. They then gradually choke up the openings in the pulp and build up on the surface a slimy, gummy layer which almost entirely stops the passage of liquid; consequently, the filtration is extremely slow and soon stops entirely.

The most effective method of filtration for such juices is to pass them through a thin layer of earth supported on rather closely woven cloth. The particles of earth form a meshwork having excessively fine openings through which the juice must pass, and any floating particles which enter these passages become attached to the surface of the earth particles and are held there.

The plate and frame type of filter press is ideally adapted to filtering by this method, as the filter cloths can be coated with a thin layer of earth by pumping a suspension of earth in water through the press before the treated juice is turned in. Deposition of earth from the juice constantly builds up a fresh surface, so that filtration goes on at a fairly rapid rate until the chambers of the press are completely filled with the cake. Where large volumes of juice are to be handled a wood-frame press of this type should be installed, as the rather high initial cost will be offset by the rapidity of filtration. Such a filter

press should be so constructed as to permit cleaning by back flushing, that is, by forcing water through the press in the reverse direction, as much time is thereby saved.

A pulp filter of the suction type can be so modified as to do very satisfactory work by replacing the layer of pulp with a closely woven cloth. A piece of heavy nickel or bronze wire screen should be fastened permanently in place in the bottom of the filter tub, to serve as a support for the filter cloth. The cloth, which should be a moderately heavy, closely woven denim, is laid upon the screen and fastened by placing the aluminum ring supplied with the filter upon it and packing the space between the ring and the wall with filter pulp. Then pour a suspension of prepared diatomaceous earth in water upon the cloth, start the suction, and wash with water until the water comes through free of earth. The flow of juice is then started.

Care must be taken to agitate the juice in the supply tank from time to time in order that constant deposition of earth from the liquid over the surface of the filter may occur. If this is not done, the larger particles of earth will settle in the supply tank, leaving in suspension very fine fragments which tend to form a slimy layer over the top of the filter, causing clogging. It is also a good plan to scrape the surface of the filter slightly from time to time, to remove a portion of the deposited earth, but care must be taken not to cut through the cake and expose the cloth.

Some types of the multiple-disk pulp filters discussed under Method I are so constructed that it is a simple matter to replace pulp disks with cloths and to coat the cloths with earth by running a sus pension in water through the press. In a filter of this type very good capacity is obtained by placing the supply tank 15 to 20 feet above the filter so as to obtain a gravity pressure of 7 to 9 pounds per square inch. Greater capacity is, of course, obtained by employing a force pump capable of giving 15 to 20 pounds pressure. By cutting off the juice supply when the filter becomes clogged and connecting a hose from a water faucet with the juice outlet of the filter, it is possible to clean the cloths by back flushing in much less time than would be required to open the press and to wash and replace the cloths.

When only small quantities are to be handled very satisfactory results can be obtained with a bag filter. The bag filter should be made of closely woven denim or flannel and should have the form of a rather tall cone. The seam should be double, to guard against leakage. To make it ready for use, the bag is thoroughly wetted, suspended by the top from supports, and filled with a fairly thick suspension of diatomaceous earth in water. As the water drains through, it leaves the inner wall of the bag covered by a thin layer of the earth. Water is run through until any particles of earth

which may have found a way through the cloth are washed off. The filtering of the juice may then be begun. As the only force driving the liquid through the filter is the weight of the juice in the bag, filtration is, of course, rather slow, and it is well to make the bag a tall narrow cone and to keep it full of liquid in order to hasten the filtration as much as possible.

The juice which passes through a properly prepared diatomaceousearth filter is perfectly transparent and without murkiness or cloudiness, and it remains so after bottling and pasteurizing. Samples prepared in this way have been kept for more than two years without developing haziness or throwing a sediment. When a freshly prepared filter is started up, the first liquid coming through usually is not clear, as fine particles wash through the cloth. The filtrate should, therefore, be returned to the filter until it comes through entirely clear. The color of the filtered juice is not affected by the treatment, as properly prepared diatomaceous earth does not remove the dissolved coloring matters. The color consequently depends upon the varieties of apples used and the length of exposure of the juice to the air.

The juice should be bottled, sealed, and pasteurized as rapidly as it is filtered. The details of these processes have already been dis cussed and need not be repeated here.

HEATING THE JUICE TO AID FILTRATION.

Heating the juice before filtering and passing it through the filter while hot has the advantage that the filtration is much more rapid than with cold juices. In the case of small quantities the juice may be heated in enameled vessels over a stove after the addition of the earth, stirring occasionally to keep the earth in suspension and make the heating uniform. If the filter is being fed from a supply tank, a small steam coil placed in the tank will serve the purpose. In whatever way the heating is accomplished it is extremely important that the temperature be known and under control, as the juice can not be raised to a temperature much greater than 140° F. in open vessels without undergoing some alteration in flavor, probably owing to the driving off of some volatile flavoring constituents by the heat. In experiments with a large number of apple juices no such change was found to occur when the temperature was held below 135° F. unless the juice was kept at this temperature in an open vessel for several hours. Consequently, the operator who heats the juice should control the process closely with the aid of a good thermometer and should also guard against keeping a tank of juice hot for a long period while filtration is stopped.

PREPARATION OF DIATOMACEOUS EARTH FOR USE.

Diatomaceous or siliceous earth consists of the cell walls of microscopic 1-celled plants, diatoms, which exist in a great variety of forms in both fresh and salt water and in damp soils. The wall about each individual consists of two parts, which fit together like the top and the bottom of a pill box, and is made of silica. Extensive deposits of this earth are found in various parts of the United States. A number of these deposits are being worked, as the earth has many industrial uses, the principal ones being as an abrasive and metal polisher, as an insulating and sound-deadening material, as an absorbent for nitroglycerin in the manufacture of dynamite, and as a clarifying agent in the manufacture of cane sugar.

The earth comes upon the market under various names; among these may be mentioned kieselguhr, infusorial earth, infusorial silica, fossil flour, diatomite, tripolite, and tripoli powder. The material as found on the market has been subjected to grinding and screening, hence can be obtained in various grades of fineness from the manufacturers and from chemical and agricultural supply houses. In experiments conducted in the Bureau of Plant Industry it has been found that the grades of fineness known as 150 mesh and 200 mesh, which means material which has passed through screens having, respectively, 150 and 200 openings to the inch, are most suitable. Most companies manufacturing diatomaceous earths make special grades intended for use in filtration. These should be employed rather than the coarser grades intended for use as abrasive or insulating materials.

Some of the earths on the market instead of consisting of silica contain varying quantities of calcium carbonate. Such earths are unfit for use with apple juice, as the lime salt reacts with the acids of the apple juice so as to neutralize it partially. Therefore it is well to test a sample of earth for the presence of lime carbonate by putting a few drops of dilute hydrochloric acid upon it. Pure silica is wetted by the acid just as it would be by water, without reaction, while the presence of carbonates of lime is shown by the release of carbon dioxid. Any earth which fails to pass this test should be rejected. As obtained from manufacturers and dealers, diatomaceous earths contain some organic matter which will give a disagreeable foreign or "earthy" flavor to the juices unless it is removed. The usual method recommended by manufacturers is to place the earth in a large wooden or other vessel, pour boiling water over it, stir, allow it to settle, pour off the water, and repeat the treatment once or twice, after which the earth must be allowed to dry before it is used. This method is not only troublesome and time-consuming but fails to remove wholly the substances which give the foreign flavor, even when six to twelve changes of water are used.

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