Rack and frame press

A rack and frame press uses heavy nylon cloth positioned in a wooden frame inside a rack. A measured amount of apple or other fmit mash is added from a hopper above the frame. The mash is leveled with a hand trowel and the edges of the nylon cloth are folded over the mash to encase it and create a cheese. The frame is removed, and a second rack is placed on top of the first cheese the process is repeated until a stack of cheeses is prepared. A hydrauhc ram then appHes gradually increa sing pressure on the stack and expresses the juice. A high yield of juice (80%) is obtained and no press aid is required. Because this process is labor intensive (17), it is mostly used for small farm and pilot-plant operations. 

Use of ultrafiltration (UF) membranes is becoming increasingly popular for clarification of apple juice. AH particulate matter and cloud is removed, but enzymes pass through the membrane as part of the clarified juice. Thus pasteurization before UF treatment to inactivate enzymes prevents haze formation from enzymatic activity. Retention of flavor volatiles is lower than that using a rack-and-frame press, but higher than that using rotary vacuum precoat-filtration (21). 

Pectin in the musts of native and hybrid varieties has caused problems, primarily in the hot pressing of red varieties. In years past when the Eastern grape juice and wine industries were using the hydraulic rack and frame press for pressing Concords and other native varieties, prob-... 

The rack and frame press is a further development of the basket press. Rack and frame presses are commonly used on farms that process apples and pears. They are particularly suitable for mashes that are difficult to press. They give high yields and good juice quality with little suspended... 

In terms of their design they are fairly small in size, but the output is high. The biggest disadvantage of the rack and frame press is the high labour requirements. Other disadvantages are the severe oxidation of the juice produced and the irregular flow of juice. 

Sheli-and-leaf filters. For filtering under higher pressures than are possible in a plate-and-frame press, to economize on labor, or where more effectivv washing of tlie cake is necessary, a shell-and-leaf filter may be used. In the horizontal-tank design shown in Fig. 30.6 a set of vertical leaves is held on a retractable rack. The... 

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