Traditionally batch cookers are being used for all types of rendering materials as steam pressure, heat and time can be adjusted and controlled 100%.

Batch cookers are, however, slow and cumbersome to operate, especially when the volume of material increases, and they also have a high steam consumption.

For large capacities, a high number of batch cookers are needed and there was a call for a continuous process to simplify and make the process automated.

In the beginning horizontal tube-type continuous cookers were used and are still in operation, but later the disc type continuous cookers were introduced that had advantages and are easier to operate. Also disc cookers could be made in stainless steel that gave longer life time.

Disc type cookers and disc type dryers are basically the same machines, but the cooker version has better stub shaft seals as the internal is floating in hot tallow (fat/oil) and there is a more sturdy liquid tight outlet bottom screw conveyor system.

The evaporation in a cooker type (fryer) can reach a very high 24 kg water per m2 heating surface while a dryer, processing press or decanter cake normally reach about 8 kg water per m2.

The grax or fatty output from a high temp cooker is normally fed to a high pressure press to squeeze out most of the fat to reach about 12% remaining fat in the final meal.