The importance of interfacial and bulk effects in cleaning food process plant

Food process plant becomes rapidly fouled with deposit on the surfaces of process equipment. This can be due to the deposition of thermally unstable components in the fluid: such as the denatured protein that forms when milk is boiled in a saucepan or a food process plant: or from the growth of microorganisms in films on the surface. Fouling deposit endangers both food quality and safety, through the contamination of product that enters the food chain, and the possible presence of pathogens. The problem of fouling is widespread; as a result, cleaning-in-place (CIP) is a common operation within the food industry. Cleaning protocols are however often empirical and are rarely if ever optimised. The long term industrial aims of research into cleaning are: Increased food safety by improving and ensuring cleaning efficiency; minimising environmental impact by reducing the amount and COD of effluent; increased manufacturing efficiency through extension of run length and minimisation of cleaning time. To optimise cleaning requires better understanding of fouling deposits and how they change during processing (ageing) and cleaning. In this project we will study the materials properties of fouling deposits, and how they change. The forces between elements of the deposit, and the forces binding the deposit to the surface, will be measured. A model for the process will be constructed and validated against experiment. This model will then be used to study whether it is possible to change industrial cleaning methods.

Food process plant rapidly becomes contaminated with fouling deposit, formed by the deposition of components of the food onto the surface. Fouling lowers the efficiency of process plant, through increased pressure drop and decreased thermal efficiency, and endangers product safety, through the growth of organisms and the possible presence of allergens (the impossibility of cleaning plant that has once processed nuts leads to the ubiquity of warming notices). These problems necessitate frequent cleaning. CIP processes, in which cleaning chemicals followed by rinsing water are circulated through the plant, are common, but expensive in production time and environmental impact. Previous BBSRC supported work (d13191) has constructed equipment to measure the forces involved in cleaning, and has increased understanding of the materials science of cleaning in terms of the interfacial forces that bind deposits to surfaces and how elements of the deposit bind together. The aim of this work is to carry out an interdisciplinary (process engineering and materials science) of the processes of cleaning. It will use experimental data, obtained on model fouling deposits prepared under realistic conditions and which are relevant to industrial practice, to construct models for the cleaning process that include the evolution of cohesive and adhesive forces during cleaning. Experimental work will first use tomato pastes and milk protein gels as model systems. We will first characterise the materials properties of the deposits, and extract materials parameters by using finite element models created in the commercial software ELFEN. The model will be used to understand the relationship between cohesive and adhesive forces. The ways in which these forces change (i) during processing (`ageing¿) and (ii) cleaning, will be studied experimentally and models developed. Models will then be constructed to describe the cleaning process, which may occur by adhesive failure at the deposit-surface interface or through cohesive failure between elements of the deposit. Once the model has been validated it will be used to study cleaning as a function of different processes, changing flows, temperatures and cleaning agent concentration, to suggest ways in which commercial practice could be improved. The end deliverables will thus be (i) better understanding of this critical food processing problem at the basic level, and (ii) a model which can potentially be used to study real problems.