1922. ! 



CULTIVATION OK THK 11<>!' CltOI'. 



L48 



or slightly above which drying finishes, the maximum content of 

 water vapour is as much as 15 oz. of water vapour in 10 cub. yd. 

 That is to say the rate of drying of hops in a current of dry air 

 at 150° F. may be nearly 5 times as fast as in dry air at 

 100° P. and m arly 20 times as fast as in dry air at 50° F. 



If, therefore, hop drying merely consisted of evaporating 

 water it is clear that the use of air at a high temperature would 

 be both more expeditious and more economical, hut another 

 factor is involved : the passage of the air through a depth of 

 10 in. or so of hops spread over a wide floor is necessarily slow ; 

 contact at the beginning of drying between the cold hops and the 

 air, as well as the evaporation of the water into it. cools the 

 air so thai as the warm air passes up through the hops its 

 moisture content becomes greater and greater and its tempera- 

 ture lower and lower. If these two processes reach the point at 

 which the air becomes saturated with water vapour, then if cool- 

 ing proceeds further moisture is deposited upon the hops which 

 are consequently " reeked " and spoilt. The initial temperature 

 of drying must therefore be adjusted so that with the draught 

 available the air can pass through the layer of cold hops without 

 the deposition of any " reek.'' It is obvious that this initial 

 temperature is not necessarily a constant : it may be varied 

 somewhat with the draught available, the initial temperature of 

 the green hops, the depth of the hops and other factors. 



Temperature. — In the previous paragraphs upon evaporation 

 emphasis has been laid upon the necessity of so controlling 

 temperature that no condensation of reek occurs upon the 

 upper layers of hops. Two golden rules will serve to prevent 

 this misfortune: a warm oast before drying commences, i.e.. 

 warm walls and roof, and a sufficiently low initial air tempera- 

 ture. The table of temperatures recommended by Hall already 

 referred to still remains the best guide. From this extracts are 

 quoted below : — 



" General rules if draught is moderately r/oor/."' 

 " The temperature at starting should not be higher than 100* Fahrenheit." 

 M For the first three hours the temperature must rise steadily to about 



140°." 



"If the temperature falls at all during this peiiod the colour of the hopa 

 will suffer." 



''For the next five hours the temperature should be kopt pretty steady; 

 it may be allowed to rise a little more but never above 160 Fahrenheit." 



"If the draught is poor the temperature must rise more dowry after 

 starting, and four or even five hours should be taken to gel to 140 



These rules provide an admirable guide for a young dryer, 

 who can scarcely make a mistake if he follows them intelligently. 



