Statistical process control with several variance components in the dairy industry

A typical problem of the application of statistical process control is that of the several variance components of the variable. We can encounter it, for example, in the control of the dry matter content in buttercream. This production is a batch process since the buttercream is mixed in a cutter. The variation of the dry matter content comes from the deviation of the compound, of the sample units and of the measurements of the same sample unit. The variance of the process is estimated from these components and three control charts are presented for monitoring the average, the sample-to-sample variability and the within-sample variability.