DRI - WHAT IS IT?

For many years, the preparation of cane has been measured in terms of the ratio of brix in open cells in prepared cane to the total brix in an equivalent sample. The process involves gently washing a fixed mass of sample in a fixed mass of water for a specified time. A second sample is prepared further in a cold digester. The preparation is expressed as the ratio of the brix washed from the prepared cane to the total brix in the sample from the cold digester as a quantity known as preparation index or PI. Although theoretically sound, the process has some practical difficulties, which can cause large errors in the values reported. The causes of these errors include effects such as the washing time and temperature of the water. This, together with the time taken to measure a single sample, has led to the method falling into disfavour. This paper describes an alternative method of expressing preparation as a function of how easily the brix can be extracted from the open cells rather than the fraction of open cells. The concept uses the theory of mass transfer and diffusion through concentration gradients to define the quantity, which has been called the ‘diffusion rate index’ or DRI. DRI is the time constant associated with the process of washing the brix out of a particular preparation. A machine incorporating the theory and several practical innovations has been designed and manufactured. The main focus has been on automation and reducing the inputs required from the operator. Several of these machines have been installed in the South African industry. Some comparisons between DRI and the cane preparation are discussed.