Chemical Treatment
pp. 59-65 · Read in the full issue
of Coffee Beans
IHE so-called washed coffee of . commerce is prepared by first passing the mature coffee erries through a machine which moves the outermost pulp (peri rp), leaving the seed in a parch mt covering with a pectinaceous rer called the mucilage, rhe seeds are then stored for un 12 to 90 hours to ferment the icilage so that it can be removed washing. The washed seeds are ied and may be then sold as rchment coffee or they may be lied to remove the parchment and d as clean coffee for roasting. )ver a period of 20 years several 'estigators have reported the use alkalis to remove the mucilage
■veral months ago PIM gave brief details i coffee processing invention which is the It of research carried out by two United es Government technicians, Merriam A. s, and Edgar de L. Davies, and called by i the Cafepro. The men were engaged in S International Co-operation Administration i aiding the Guatemala coffee industry. e have now received from Mr. Louis Franke, :tor of the ICA in Guatemala, full details he Cafepro contained in a paper written rterriam A. Jones and J. Joaquin Bayer S.
Jones is deputy director and Senor Bayer ical engineer of the ICA team in Guatemala we are indebted to them for the details his article.
n the freshly pulped coffee. ie, sodium hydroxide, potassium roxide, and wood-ash have all i used, in tanks with little or agitation. i 1953, Messrs. Davies and Jones Bloped an agitator machine in :h a stream of pulped coffee is could be treated with alkali emove the mucilage and, in 1954, srs. Jones and Bayer modified machine, and it has now been her modified to become the ?pro Model-C. le machine described below is en at about 40 rpm and requires hp motor. It processes pulped from 5,700 lbs of coffee cherries hour. It calls for a 2 per cent, li solution at the rate of 2 ms per minute. Ash or lime be used separately, or they may nixed and then extracted with t in a separate container and extract filtered through a screen passed into the feed-tank, dium hydroxide is usually more ily available and simpler to lie, but it is more expensive, though simpler is more danger to handle. ben the alkaline strength of an lime extract is obtained from a ometer reading referring to a me gravity table for potassium oxide, the strength thus found wut twice the actual strength, efore, if a 2 per cent, solution Jsired, the hydrometer reading
should correspond to 4 per cent.
If sodium hydroxide is used the solid may be suspended in a per forated basket just below the water level in the tank; then as the solid dissolves the heavy solution sinks Only a little stirring is needed to ensure a uniform solution.
Approximately one pound of clean coffee is obtained per pound of solid hydroxide used.
The advantages of the alkali pro cess are simplification of construc tion of processing plant by elimina tion of fermentation tanks; the process becomes continuous from cherry to dried bean stage; the pos sibility of over-fermentation and damage is eliminated; the mucilage is readily recovered; and, most im portant, there is less weight-loss in the final beans. (Over)
The Cafepro Model-C is essenti ly a stand on which is mounted 3/32 in. sheet-metal trough 72 . long and about 2 ft in diameter, is formed of one piece of metal such a way that the lower part semi-circular in cross-section, th vertical 6 in. sides and a II in. irizontal turnover at each upper ge for the mounting of lid hinges id fastenings. There are end ues of the same cross-section, th circular holes 2 in. in diameter.
At the discharge end one upper arter of the endplate has been cut ray, so that the discharge can erflow into a down-sloping dis arge chute attached to this end ite. In line with this end ite hole there is another 2 in. hole -ough the side of the chute. There a water-seal at this hole and at ; hole at the other end of the ugh. The trough is supported each end by metal stands on ich are mounted suitable bear s to support the 2 in. shaft which ends sufficiently far for a driving ley at one end. :he trough is divided into two lal parts by a semi-circular plate ending to the height of the shaft treline, and across which the .tents overflow from the first into second compartment.
'here is a 3/32 in. metal cover or
lid of arc cross-section, of sufficient height to clear the agitator blades mounted on the shaft. The lid has a II in. horizontal turnover for at tachment of hinges and fastenings At the extreme end of this lid at the end away from the trough’s dis charge chute, there is a hole about 4 in. in diameter, or square if pre fered, fitted with an intake hopper Alternatively this intake hole may be on the intake end of the trough itself, towards the upper edge thus reducing the overall height of the machine.
There are 21 in. plug holes in the bottom of each compartment for draining and cleaning. Such plugs must be recessed clear of the agitators.
At intervals of 41 in., centre to centre, there are mounted on the shaft steel agitators. The end of •* s cu PP ec * slightly, convex in the direction of rotation, and pitched alternately to propel the coffee with or against the direction of flow from intake to outlet end.
The alternate beaters which propel the coffee forwards towards the outlet are pitched 30 degrees from parallel with the shaft The other beaters are pitched in the opposite direction but only 20 degrees. The result is an overall forward movement of the contents.
h * S e beater s or agitators may be secured to the shaft by any suit 2j?ie means ; 0 he y are about 3 in. nSSJ and of 3/32 irL sheet steel > and a^ e sev . en pairs spaced in each .. A P air consists of th? in lHi e at 180 degrees on Si h f; Alternate pairs are at ™ degrees angular dif °n x£ he , shaft - Their ends SI olear bottom of the trough nw i?*’ a ? d . there must be u in aSh? C '% be l we^ n , the end plate and beater in compartment
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A, and the centre plate and the first beater in compartment B.
Within half an inch of the centre plate in compartment A, and within half an inch of the end plate in compartment B there are mounted on the shaft radially split discs of such diameter that they clear the bottom by I in. Each disc has U in. pitch in such a direction as to propel the coffee over the centre plate and end plate re spectively, towards the outlet. They also regulate the overall rate of flow of material through the machine. These discs simply consist of circular metal plates of radius i in. less than the radius of the trough, with 2 in. centre holes, with a straight cut from perimeter to centre, and a means of clamping to the shaft so that they are given the correct pitch.
Their edges along the straight cut are bent at about 45 degrees for an inch or so, so that they will betjter scoop in and expel the contents of the tank. (The degree of bending probably has to be adjusted in actual operation in the first in stance) .
Above the Cafepro and adjacent to it is the alkali tank. The quantity of fluid per pound of beans can be
calculated from the information given earlier. Alkali and beans can be fed into the Cafepro together.
A photo and constructional diagram of the Cafepro were pro vided by the inventors but these are unsuitable for reproduction in PIM. However, the description of
the machine has been altered meet these circumstances as the o tails here given should be amix clear to any mechanically-mino person.
The report emphasises that * haustive tests have shown tH; there is no difference in flavour t
een alkali-processed beans and * naturally-fermented product.
Che report also mentions that in ad of the alkali treatment fol red by washing, freshly pulped fee beans may be bathed in a pension of lime in calcium oride solution, after which no shing is necessary; the treated duct is dried immediately. The ility of the product of this water ing process is the same as that fermented coffee beans.