1922.] 



Cultivation of the Hop Ckoi\ 



111 



to 8 to 10 per cent, before the hops are packed. It is thus clear 

 that the amount of water to be evaporated from the hops at the 

 beginning of picking when hops are barely ripe may be very 

 much greater than at the end of the season, and this, of course, 

 coincides with experience that much greater quantities of ripe 

 hops can be dried on the kilns than of green ones. This 

 surplus water is evaporated by causing a current of warm 

 air to pass through the hops whilst they lie upon a horsehair 

 cloth supported upon the drying floor of the kiln. The next 

 point to be considered is the means whereby the current of air 

 or draught is produced. 



Draught. — In some cases kilns are now fitted with fans to 

 produce the necessary current of air through the hops, but in 

 the vast majority of cases draught is produced through the 

 operation of the well-known fact that " hot air rises." 



When the air within a kiln is warmed it rises and passes out 

 of the top through the cowl, whilst cold air enters below to 

 take its place. The draught created is thus proportional to the 

 difference in temperature between the air within and without the 

 kiln, but it is also proportional to another factor, namely, the 

 height of the kiln. Factory chimneys are built high to give 

 better draught, so the higher the kiln the better the draught. 

 The height both below and above the hops is important, and of 

 the two probably that between the fires and the hair cloth 

 below the hops is the more important, because the temperature 

 of the air below the hops is always greater than that above and 

 hence this air is relatively lighter and creates the greater 

 draught. Especially in the early part of drying, the air above 

 the hops is cooled by passing through them and therefore has 

 no great lifting power unless it is warmed again by absorbing 

 heat from the walls and roof above the hops. This re-absorption 

 of heat from the walls of a warm oast is by no means unim- 

 portant and the absence of it may play a serious part with the 

 first load of the season unless the kiln lias previously been 

 well warmed. For this reason the good dryer makes a point 

 of lighting the kiln fires early in the morning of the first day 

 of picking and on each Monday, for the purpose of warming 

 his kiln, though no hops will be ready for drying till perhaps 

 11 a.m. 



Another factor of great importance in the maintenance of a 

 good draught is the sealing of the walls and roof so that no air 

 can enter the kiln at any point above the position of the fire- 

 places, Every such inlet of air weakens the efTec!ivc draught. 



