80 The Fermentation of Cacao 
the leaf) the midrib and (on compressing a 
handful of leaves) the connecting stalks no 
longer break, The leaves are then rolled by 
a mechanical contrivance which causes an 
alternating, heavy and light pressure to be 
brought to bear on them in such a way that 
during the application of the heavy pressure 
the sap of the leaf is forced out and spréad 
over the surface, to be absorbed by the leaf 
again when the pressure is relieved. The 
main object of rolling is to rupture the cells 
of the leaf, or at least to render them more 
permeable to air. The time occupied to do 
this varies between one and one and a half hours 
according to the nature of the leaf. Owing 
to the rolling, the leaves become considerably 
heated and’ simultaneously the amount of acid 
and soluble astringent substances is increased. 
After rolling, the resultant massed leaves are 
passed through a sieve-like contrivance which 
loosens them, and then exposed to oxidation 
in thinner or thicker layers, varying according 
to the temperature conditions. Oxidation then 
proceeds rapidly, as, owing to the rolling, 
access of air to the interior of the leaves is 
facilitated ; the process takes from two to eight 
hours, according to the temperature and nature 
of the leaves. Owing to the oxidation of the 
astringent substances, the green colour of the 
leaves turns yellow or copper-coloured, but 
before this stage is reached, the oxidation should 
be stopped, otherwise the tea becomes over- 
4 
