There are two main processes used in cooking. These are either sulphate or sulphite, each is designed to produce pulp with that meets specific characteristics.
Both processes could be considered basically the same. In both cooking processes, the wood chips are impregnated with cooking liquor, known as known as white liquor. It is then heated under pressure to between 130°C to 170°C and where it is held at the required temperature for a specified period. The pressure and the temperature are then lowered and the pulp is blown or washed out of the digester.
There are two main types of digesters used for cooking. These digesters are known as continuous digesters or batch digesters. The cooking process for both types of digesters can be very similar and while each type will have specific advantages and disadvantages, most new pulp plants world-wide are built using continuous digesters.