Coffee solid extraction

Both solvent-extracted and expelled coffee oils can be sprayed directly onto soluble coffee solids. The oil is adsorbed without degradation, provided moisture and oxygen are absent. However, the most volatile compounds do tend to leave the coffee powder and fill the head space of the container. 

One or more components of sucli mixture are removed (extracted) by exposing the mixture to the action of a solvent in which the component to be removed is soluble. If the mixture consists of two or more solids, extraction is performed by percolation of an appropriate solvent through it This procedure is also called leaching, especially if the solvent is water coffee making is and example. Synthetic fuels can be made from coal by extraction with a coal-derived solvent followed by hydrogenation. 

Because of its low cost, nonhazardous chemical nature, and low critical temperature, carbon dioxide has been used in many applications. A commercial process to remove caffeine from coffee, using supercritical C02 as the solvent, is shown in Fig. 17. While actually a liquid-solid extraction process, it demonstrates principles involved in SCFE. A commercial SCFE process has been reported for recovery of hydrocarbon liquid from heavy oil. As compared with conventional propane deasphalting, this SCFE process can reduce capital and energy costs. 

Extraction - making a cup of coffee involves extraction of the flavour chemicals and caffeine from the insoluble vegetable matter using hot water and is an example of liquid-solid extraction. 

This publication provides several examples of the use of solid-phase extractions for separating analytes from their matrices. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analytes maybe determined quantitatively by gas (GC) or liquid chromatography (LG). 

Inorganic compounds Monosodium phosphate mixed with boric acid and ethyl carbonate, disodium phosphate sodium aliiminate, bentonite and other solids Distillation instant coffee boiler feedwater sugar extraction... 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

In some cases, the solids themselves are subjected to extraction by a solvent. For example, in one process used to decaffeinate coffee, the coffee beans are mixed with activated charcoal and a high-pressure stream of supercritical carbon dioxide (carbon dioxide at high pressure and above its critical temperature) is passed over them at approximately 90°C. A supercritical solvent is a highly mobile fluid with a very low viscosity. The carbon dioxide removes the soluble caffeine preferentially without extracting the flavoring agents and evaporates without leaving a harmful residue. 

Figure 1.9. Modelling concepts for the packed bed solid-liquid extraction. Process of coffee percolation.

In outline, a percolation process is used to produce an aqueous coffee extract, which in turn is dehydrated to yield water-soluble solids. Instant and soluble coffees are synonymous for these water-soluble coffee extract solids. Usually some of the volatile aroma and flavor compounds, which are lost during the processing, are added back immediately before packaging. 

One of the most widely used spray-drying techniques for coffee extract involves spraying percolated coffee extract at 40°F into the top of a baffled tower of hot air at 480°F initially. The cooler wet air is removed toward the bottom of the tower and finally a powder of the coffee extract solids leaves the tower at about 90°F. These solids are in the form of hollow beads and contain 3% moisture. 

Fig. 1.53. Freezing and thawing plot of coffee extract with 25 % solids. UFW (g H20/g solids) as a function of temperature (Fig. 2 from [ 1.37])-I, Subcooling 2, collapse temperature.

If the material is granulated, e. g. frozen and granulated coffee extract, having a solid content perhaps of 40 % and a density of 0.6 g/cm3 (Fig. 1.61), Eq. 12 is still applicable, but the product data are different. The heat transfer is through the dried product with a Atr = 8.37 10 2 kJ/m h °C. To make the results better comparable, d = 0.7 cm and rtot have been retained from the earlier example, even if Ttol were normally higher, e. g. 100 °C. 

The freeze drying of coffee extracts has been, and still is, the most frequent application of this process in the food industry. For economic reasons it is best to start with 40 % solid content in the extract. The final product is judged by the following criteria ... 

Bicchi, C., loti, C., Rubiolo, P. and Sandra, P. (2002) Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE) and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew. J.Agric. Food Chem. 50, 449-459. 

The vegetable soup preparation is a solid-liquid extraction. So is coffee making. You extract some component(s) of a solid directly into the solvent. You might do a solid-liquid extraction in lab as a separate experiment liquid - liquid extractions are routine. They are so common that if you are told to do an extraction or a washing, it is assumed, you will use two liquids—two INSOLUBLE liquids—and a separatory funnel. The separatory funnel, called a sep funnel by those in the know, is a special funnel that you can separate liquids in. You might look at the section on separatory funnels (later in this chapter) right now, then come back later. 

Much of the interest in SFE has been focused on using carbon dioxide to extract different natural products from solid materials. Examples of large industrial processes in this area are decalfeinating coffee beans and hop extraction. 

Solid — Liquid Extracting. This is not done too often, but if you have ever made tea or coffee you should be able to do this, as it is basically the same thing. 

Typical lengths of cycles for food stuffs are 5-10 hr, for bacterial pellets 2-20 hr, and for biological fluids 20-50 hr. A production unit with capacity of 500 L may have 75 kW for refrigeration and 50 kW for heating. Conditions for the preparation of freeze dried coffee are preparation of an extract with 20-25% solids, freezing at —25—43°C, sublimation at approx. 200Torr to a final final moisture content of 1-3%, total batch processing time of 6-8 hrs. 

Clarification of extracts can be accomplished with Carrez reagents (44). Purification has been performed by solid phase or partition. Wu et al. (47) absorbed saccharin onto ODS-4 cartridges and then eluted with methanol phosphate buffer. Puttemans et al. (28,50) extracted saccharin from soft drinks and yogurt by ion-pair extraction with tri-n-octylamine and back-extraction to an aqueous phase with perchlorate. Tereda and Sakabe (48) used cetrimide and Sep-Pak Cl8 in the cleanup of saccharin in coffee drink. The column was preconditioned with methanol, water, and 5 mM cetrimide. The sample, diluted in phosphate buffer pH 3.0 containing cetrimide was poured into the cartridge, washed with water, and eluted with acetonitrile water (1 1, v/v). Moriyasu et al. (40) added n-propylammonium bromide to the extract, passed it through a Bond Elut Cl 8 column, and eluted the sweetener with a mixture of methanol-water (4 6, v/v). The eluate was passed through a Bond Elut SAX column and washed with 0.5% phosphoric acid and water, and the sweetener was eluted with 0.3 N hydrochloric acid. 

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