Page 8 



BETTER FRUIT 



August, 1921 



doubtless be reduced still further by en- 

 larging the ventilators and thus allowing 

 a larger portion of the air capable of being 

 taken into the drier to pass out. In a com- 

 parison of this type drier it has been ob- 

 served that the height of the heating 

 chambers varies from 7 to 1 6 feet, and that 

 the higher chambers are usually accom- 

 panied by shorter drying periods. 



The tunnels of one drier of the Oregon 

 type were found to be inclined at a pitch 

 of 3.5 inches to the foot, this being the 

 greatest pitch of any drier visited. The air 

 movement was tested by an anemometer and 

 found to be 700 linear feet per minute at 

 the point of intake. The drying time was 

 stated as 20 to 24 hours. 



Another drier depending upon natural 

 draft is the stack type. This drier is used 

 to some e.xtent in this vicinity, but has been 

 largely replaced by the tunnel drier. The 

 drying chamber of the stack drier is usually 

 divided into cabinets with cleats nailed to 

 the sides which permits the use of trays for 

 holding the fruit during drying. The 

 heated air passes through the slatted floor, 

 through the trays within the cabinets, and 

 out through the ventilator at the top. 



A FEW mechanical draft driers of the 

 ■'-^ tunnel type are in use for the exclus- 

 ive drying of prunes, but the forced draft 

 driers are not generally considered econ- 

 omical of construction in this vicinity unless 

 there are a variety of crops in the locality 

 which lends themselves to drying. The 

 reason for this is that a prune drier is used 

 for only a very short period (18 to 25 days) 

 in each year and the interest on the invest- 

 ment is too large for economic results. 



A mechanical draft drier located in the 

 southern part of Oregon, and reported to 

 give excellent results, is a modified Oregon 

 tunnel. Vento heaters are placed on the 

 lower floor through which the air is cir- 

 culated by a 40-inch Sirocco fan. The 

 heated air passes through the openings in 

 the floor into the tunnels, being distri- 

 buted by dampers placed even with the 

 floor, which permit regulation. The used 

 air passes out at the top through a ventilator 

 as in the standard Oregon type drier except 

 that arrangements are made for recirculat- 

 ing any portion of the air desired. Usually 

 about 60 per cent of the air is recirculated. 



Great differences of opinion are ex- 

 pressed among the growers concerning the 

 question of dipping previous to drying. 

 Some of the prunes are dipped in hot lye 

 solution, some in boiling water, others in 

 cold water, and some are dried without 

 previous treatment of any kind. All of 

 these prunes, however, are marketed at stan- 

 dard prices. The percentage of lye where 

 used varies between 0.5 per cent and 1.5 

 per cent. The dipping is done in vats by 

 hand methods in the smaller driers and 

 by machines in plants handling considerable 

 tonnage. The method of spraying the 

 boiling lye solution onto the prunes is 

 used to some extent with favorable results. 

 In all cases where lye dipping is practiced, 



this is followed by washing; in the smaller 

 plants by means of wire baskets, and by 

 means of chain conveyors passing through 

 a t.ink of water, or by spraying in the larger 

 plants. 



The spraying of the lye solution fol- 

 lowed by a spray washing seems to give 

 more uniform results because all the prunes 

 are subjected to equal treatment. Undoubt- 

 edly, if the prunes were graded before 

 the treatment with lye, the value of the 

 :-pray methods for lye treatment and wash- 

 ing would prove far superior to other prac- 

 tices in use at the present. 



In some instances the prunes are run 



through a tank containing boiling water 



which is claimed by the operators of this 



- »".^rli; to give results equal to lye dip- 



MHTMOJI OF STAGGF.Kl.VG TRAVS 0\F.R 

 AIR INLET OR DRIER 



ping, without the disadvantages. In some 

 cases the prunes are merely run through 

 cold water on a chain conveyor, or dipped 

 into cold water by wire baskets, the operators 

 of this system claiming that no advantage 

 is to be gained by the use of lye or boiling 

 water. In a few instances the prunes are not 

 dipped into any solution previous to drying, 

 but it can be said that these instances are 

 few. 



The cost per pound to dry prunes in the 

 Oregon type drier varies considerably as the 

 figures are presented by different plants. 

 The range of costs as given lies between 

 one-half and two and one-half cents per 

 pound. A great deal of variation may be 

 accounted for in the factory methods of 

 handling, the kind of fuel used, and the 

 construction of drier and heating chamber. 

 The average figure taken from actual ob- 

 servations, where satisfactory factory 

 methods are employed, is 1J4 to 1^ 



cents per dry pound exclusive of invest- 

 ment and depreciation. 



The fuel used in this vicinity is almost 

 entirely wood since this may be obtained 

 nearby in sufficient quantities and at a 

 price which makes its use less expensive than 

 coal. The price per cord varies with the 

 kind of wood, ranging between 5 and 8 

 dollars per cord for the year 1920. It is 

 estimated that between one and two cords 

 of wood are required to dry one dry ton 

 of prunes, with the drying time averaging 

 from 20 to 25 hours. 



The degree of heat employed to dry 

 prunes is another factor of wide variation. 

 Temperature from 150 degrees Farenheit 

 to 195 degrees have been observed. Those 

 using the lower temperature claim the 

 prunes will scorch above 155 degrees, while 

 those using the higher temperature claim 

 no scorching at the higher temperatures. 

 Probably not over 170 degrees as the high- 

 est limit should be used for prune drying, 

 and 160 degrees of heat would be a safer 

 margin in order to prevent scorching or 

 caramelization of the sugars. 



Observations of humidities proved that 

 in all driers of the Oregon type that were 

 tested, the relative humidity was always 

 below 1 per cent at the intake, and from 

 11 to 27 per cent at the ventilator. In the 

 Oregon type drier installed at the Oregon 

 Agricultural College, an attempt was made 

 to increase the initial humidity of the in- 

 coming air by cementing off about one- 

 fourth of the floor of the heating chamber 

 by a wall six inches high, and filling this 

 space with water. Although the water 

 evaporated rapidly, the relative humidity 

 was not raised above 10 per cent. 



From these observations it would appear 

 desir.ible: 



( 1 ) To change the design of the driers 

 in order to give more rapid circulation of 

 air by enlarging the size of the ventilators 

 and increasing the pitch of the tunnel from 

 2-3 inches to the foot. 



(2) To secure greater circulation and 

 greater heat transmission by (a) increasing 

 the height of the furnace chamber and (b) 

 increasing the radiating surfaces within the 

 furnace chamber. The latter may be done 

 bv supplying more lengths of flue pipe 

 within the chamber in order to remove a 

 greater amount of the heat from the flue 

 gases before passing out at the stack. 



(3) To aid circulation by increasing the 

 number of holes around the furnace cham- 

 ber. This will necessitate increasing the 

 fire correspondingly in order to heat the 

 greater volume of admitted air to the de- 

 sired temperature. 



(4) To adrnit air on all four sides of the 

 furnace chamber in order to obtain equal 

 distribution of air within the tunnels. This 

 practice is followed in single unit driers 

 and m.iy be followed in multiple unit 

 driers by constructing the heating chambers 

 with a space between them of about one 

 foot, in order to provide for the necessary 



{Concluded on fage 21) 



