Abstract To find systematic ways to justify the design decisions or evaluate alternative and novel solutions for processes for structured products, a conceptual design methodology is being developed. It gives a six-levelled top-down approach similar to the Douglas hierarchical design procedure. The design of a food dressings plant is taken as a pilot to illustrate the application of the methodology. The synthesis, analysis and evaluation procedure at Level-2 is discussed in details. The problem is formulated as a (non-linear) optimisation. Mixed integer problem is avoided by reducing the number of flowsheet alternatives using heuristics. The first results show that significant capacity savings (26%) can be obtained compared to the conventional design. Generally, the findings of this work illustrate that combining the more heuristics oriented hierarchical design approach with numerical optimisation on a refined subset of alternatives works very well in practice without loss of quality of the end results and maintaining insight.