1 9 io.] Picking, Drying, and Packing Hops. 



93 



of drying, hot air begins to pass upwards through the load 

 of hops spread out upon the "hair-cloth" in the oast. In 

 contact with the bottom layers of hops, the hot air warms 

 the hops and takes up water-vapour from them, and at the 

 same time, by contact with the hops, the air is cooled almost 

 to the temperature of the hops. The air, being thus cooled 

 and nearly saturated with water-vapour, passes through the 

 remainder of the hops without appreciably affecting these, 

 and finally passes away through the top of the oast, carrying 

 with it the water-vapour it has absorbed from the bottom 

 layers of the hops. 



As the bottom layers get dry, the hot air begins to act on 

 those immediately above, and so the drying proceeds through 

 the whole depth of hops, the top layers being the last to 

 get dry. 



At the beginning of drying, the fires are kept low, so that 

 the temperature of the air passing through the hops is also 

 low. Should the temperature of the air become too high, 

 either from too fierce a fire or from too slow a draught, the 

 air absorbs so much water-vapour from the lower layers of 

 hops that, as it is cooled by its passage through the hops, 

 the air becomes supersaturated, and the excess of water is 

 deposited like dew upon the top layers of the hops. This 

 deposition of water upon the top layers of the hops is fatal, 

 and results in the hops becoming "reeked" and spoilt. 



In order to prevent this "reeking," it is essential that a 

 good draught be established within the oast, so that the air 

 may pass rapidly through the hops, and thus, being in con- 

 tact with the fires for a shorter time, the air may not become 

 too hot. As drying proceeds and the hops upon the "hair- 

 cloth" become lighter through loss of water, they offer less 

 resistance to the draught, and consequently the latter con- 

 tinually improves. 



In those oasts in which the draught is artificially produced 

 by means of a fan, such a draught can be readily obtained 

 at the beginning of drying, but this is far from being the 

 case in the common open-fire kilns, in which the dryer is 

 dependent upon the "natural" draught. 



The strength of the draught is dependent upon a variety 

 of factors, which may be classified as follows : — • 



