An Milp Modelling Approach for Shelf Life Integrated Planning in Yoghurt Production

In the production of perishable products such as dairy, meat, or bakery goods, the consideration of shelf life in production planning is of particular importance. Retail customers with relatively low inventory turns can benefit significantly from longer product shelf life as wastage and out-of-stock rates decrease. However, in today’s production planning and control systems shelf life issues with regard to specific products or customers are seldom taken into account. Therefore the objective of this paper is to pay attention to these issues. The way to do that is by means of optimization models in which shelf life aspects are integrated into operational production planning and scheduling functions. Specifically we make use of so-called Mixed Integer Linear Programming (MILP) models. Our research is based on an industrial case study of yogurt production. Relying on the principle of block planning, an MILP model for weekly production planning is presented that is based on a combination of a discrete and a continuous time representation. Batch sizing and scheduling of numerous recipes and products on several packaging lines are considered in the model. Overnight production and, hence, the necessity for identifying two different shelf life values for the same batch is also included in the model formulation. Numerical experiments show that near-optimal solutions can be obtained within a reasonable computational time. Finally, the proposed MILP model can be adapted to cover specific features arising in other fresh food industries.