20 



"yellow" tobacco which is largely used for the manufac- 

 ture of cigarettes : (i) Air-curing is followed for the 

 former, and (2) Flue-curing for the latter kind of tobacco. 



Air-curing 



Tobacco used for the manufacture of cigars is 

 generally air-cured, artificial heat being used only during 

 very wet weather. The curing is controlled simply by 

 opening or closing the ventilators as occasion demands. 

 In considering the changes taking place in the leaf during 

 the curing process, this may be divided into two periods, 

 during the first of which the leaf remains alive, while in 

 the second the changes which occur have no connection 

 with its life activities. 



The principal changes taking place in the first stage 

 of curing are due directly to the activities of the living 

 cells, while they are passing through a period of gradual 

 starvation ; hence the conditions should be such as are 

 most favourable to these activities. These cells are 

 killed by bruising, so that it is important to avoid injury 

 in this way in the harvesting as far as possible. Again, 

 these cells are killed by excessively low or high tempera- 

 tures, and by the rapid loss of water. The life activities 

 of the tobacco plant practically cease at temperatures 

 below 40" F, while they increase as the temperature 

 rises, until at about 125" F the living cells are 

 rapidly killed. These activities are also greatly lessened 

 by loss of water, and cease as soon as the leaf becomes drv 

 In practice, the most lavourable temperatures for curing 

 lie between the limits of ho" F, and 100" F, and 

 the relative humidity should be about Ss per cent. 

 Under these conditions the leaf will 'gradually lose its 



