Pressing expression

Presses are of two basic types hydraulic batch presses and screw presses. Hydraulic presses are used for extracting fruit juices, and screw presses for dewatering materials such as paper pulp, rubbish and manure. The equipment used is described in the handbooks Perry et al. (1997). 

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Kim, J.H., M.E. Sherman, EC. Curreiro, F.P. Guengerich, P.T. Strickland, and T.R. Sutter (2004, in press). Expression of cytochromes P450 1Al and IBl in human lung from smokers, non-smokers, and ex-smokers. Toxicol. Appl. Pharmacol. 

Essential oil components are often found in the glands or intercellular spaces in plant tissue. They may exist in all parts of the plant but are often concentrated in the seeds or flowers. Many components of essential oils are steam-volatile and can be isolated by steam distillation. Other methods of isolating essential oils include solvent extraction and pressing (expression) methods. Esters (see the essay "Esters-Flavors and Fragrances") are frequently responsible for the characteristic odors and flavors of fruits and flowers, but other types of substances may also be important components of odor or flavor principles. Besides the esters, the ingredients of essential oils may be complex mixtures of hydrocarbons, alcohols, and carbonyl compounds. These other components usually belong to one of the two groups of natural products called terpenes or phenylpropanoids. 

Multi-element candle Multi-element leaf Plate frame press Precoat Nutsche and multielement leaf Precoat plate frame press Recessed plate filter press Sheet filter Single leaf Nutsche Bag Cartridge Dead-end membrane Fibre bed Low shear crossflow Sand bed Simplex strainer Belt press Duplex strainer High shear crossflow Rotary disc Rotary drum Sand bed Tower press Diaphragm filter press Expression (screw) press Horizontal element tube press Vertical diaphragm filter press Vertical element tube press... 

The Data Analysis module of FDS facilitates the interactive analysis of constant pressure and constant flow filtration, jar sedimentation and piston press (expression) tests the procedures are computer software implementations of the analysis techniques described in Chapter 4. Data obtained at the laboratory, pilot and even full scale can be analysed in a consistent manner... 

Pradhan, R.C., Meda, V, Rout, P.K., Naik, S. and Dalai, A.K. 2010. Supercritical COj extraction of fatty oil from flaxseed and comparison with screw press expression and solvent extraction processes, J. Food Eng. 98 393-397. 

The automation of filter presses has affected several other advantages and developments. Plate shifting mechanisms have been developed, allowing the cloths to be vibrated filter cloth washing, on both sides, has been incorporated to counteract clogging from the expression and downtimes have been reduced with automation, thus increasing capacities. 

Fold. Strength of concentrated flavoring materials. The concentration is expressed as a multiple of a standard, eg, citms oil is compared to cold pressed oil. In the case of vanilla, folded flavors are compared to a standard extract with minimum bean content. 

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. 

Natural Products. Various methods have been and continue to be employed to obtain useful materials from various parts of plants. Essences from plants are obtained by distillation (often with steam), direct expression (pressing), collection of exudates, enfleurage (extraction with fats or oils), and solvent extraction. Solvents used include typical chemical solvents such as alcohols and hydrocarbons. Liquid (supercritical) carbon dioxide has come into commercial use in the 1990s as an extractant to produce perfume materials. The principal forms of natural perfume ingredients are defined as follows the methods used to prepare them are described in somewhat general terms because they vary for each product and suppHer. This is a part of the industry that is governed as much by art as by science. 

In the older method, still used in some CIS and East European tar refineries, the naphthalene oil is cooled to ambient temperatures in pans, the residual oil is separated from the crystals, and the cmde drained naphthalene is macerated and centrifuged. The so-called whizzed naphthalene crystallizes at ca 72—76°C. This product is subjected to 35 MPa (350 atm) at 60—70°C for several minutes in a mechanical press. The lower melting layers of the crystals ate expressed as Hquid, giving a product crystallizing at 78—78.5°C (95.5—96.5% pure). This grade, satisfactory for oxidation to phthaHc anhydride, is referred to as hot-pressed or phthaHc-grade naphthalene. 

Significant improvements were made in the 1980s and early 1990s in high capacity, automated variable volume filters that incorporate automatic pressure filtration, expression, washing, and air displacement. Some of the large plate-and-frame automatic presses can operate at up to 2 MPa (ca 285 psig), with up to 100 chambers (25,26). 

Expression Dewaterings of Fibrous Materials. Fibrous materials are frequently dewatered in belt-filter, screw, disk, and roU presses and in batch pot and cage presses. Table 1 Hsts appHcations of screw, roU, and pot presses. Screw and high pressure belt presses are continuous and have replaced batch pot and cage presses in most appHcations. Traditionally, however, batch presses have been used for squee2ing cocoa butter from cocoa beans, which require pressures up to 41 MPa (6000 psi) (39). A description of many types of batch presses is included in Reference 40. 

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