Patent GB-663254-A (GB)
Title: Process of preparing dried coffee extract
Inventor: SCHWARZ HUGH WALTER
IPC: A23F5/26
Filed: 1949-10-04
Abstract: 663,254. Coffee. NATIONAL RESEARCH CORPORATION. Oct. 4, 1949, No. 25462/49. Class 129 To prepare dry coffee extract the water content of a hot water extract and a steam extract is reduced to less than 4 per cent. by heating them for 4 to 30 minutes at 110‹ to 200‹F. under a total pressure of less than 10 mm. Hg, the steam extract having been previously purified and concentrated to a soluble solids content approaching that of the hot water extract. Ground, roasted coffee having been packed in a plurality of steam-heated columns 10, pure water is forced by a pump 12 through a heat exchange 14 and thence through the columns in sequence. As each column becomes exhausted it is cut out of the water system by valves, and steam at about 100 p.s.i.g. enters the column via line 15, water initially being drained from the column through line 17 until the coffee is surrounded by steam. When the column is completely drained the valve in the line 17 is closed and the steaming is continued for about one hour. The valve in the line 16 is then opened, and the steam extract passes via a manifold line 18 and a tank 19 where it is mixed with a coagulant, e.g. egg albumin, entering through a line 20. The contents of the tank 19 are heated to cause agglomeration of the colloids in the extract, these and other impurities being removed, after cooling of the extract, by a filter press 22. The water content of the filtrate is reduced to about 65 per cent. in.an evaporator 23, and this concentrated steam extract is combined with the water extract at 21. This combined extract passes to a deaerator 24, connected at 25 to a vacuum pumping system, and is exposed to a moderate vacuum. After degassing, the extract is forced by a pump 26 to a heated vacuum drier 27 connected at 28 to a vacuum pumping system evacuated to a free air pressure not exceeding 200 microns, preferably about 1 micron, so that the bulk of the pressure during drying is due to the evaporating moisture. An endless belt 29 in the drier 27 is heated to a temperature between 110‹ and 200‹F., and the extract is sprayed on to it at the left hand side at a rate such that a thin liquid film between 0À002 and 0À012 inches thick is formed over the belt. The heat of the belt penetrates the film rapidly, keeping it above its freezing point and causing it to become highly viscous and to swell considerably due to bubbles of trapped moisture vapour and gas; as drying proceeds the film solidifies, by moisture loss, in this frothed condition and is scraped from the belt at 30. It falls into a hopper 31, passes to an air lock 32 and is removed from the vacuum system through said lock. The water vapour evaporating from the extract passes via the connection 28 to a vapour pumping system which maintains the total pressure (free air plus evaporating moisture) in the drier 27 no higher than 10 mm., preferably about 1 mm. The system comprises an absorption column 34 into which a constant supply of liquid dessicant solution flows from a line 35. Aqueous solutions of lithium halide salts, e.g. lithium chloride or lithium bromide, are suitable dessicants when refrigerated. The vapours from the drier 27 flow up from the base of the column 34 and are absorbed, so that only the non-condensable gases pass through a line 36 to the vacuum pumping system 38. The dessicant solution and absorbed moisture pass to a regenerating system 40, which includes a heat exchanger through which the cold solution flows before passing to an evaporation and thence to a refrigerating system.