A process flow diagram is a document that outlines the sequential steps in the production of a product. Its construction forms the foundation for conducting a hazard analysis (principle 1) and therefore must include all process steps and sufficient detail to conduct an effective analysis. The terms of reference will determine the start and end points of the process flow diagram. These usually includes the receipt of raw materials and continues until the product is no longer in the control of the food business operator.
There are two different approaches in the construction of a process flow diagram. The linear approach is product-led and appropriate in an operation where only a few products are made. Whereas the modular approach is process-led and more suitable in a more complex operation where products follow a similar process. The modular approach is divided into an overview of process stages and each module is then supported by a more detailed flow process diagram. Supporting data will be required to help the HACCP team construct the flow process diagram. This information usually includes the following:
- details on raw materials and packaging, and storage conditions;
- time and temperature profiles for all processes and storage/holding conditions;
- significant variations on the processes due to a shift pattern or seasonality;
- intended delays during or between steps, such as sampling
- details on reworking and where waste leaves the flow;
- where water, air and/or steam are used in the process (e.g. washing).
The construction of the flow process diagram, the fourth step in implementing HACCP, should follow some standard conventions. It begins with inputs, such as raw ingredients, labelling and packaging, and concludes with the outputs from a finished product or module at the bottom. Each process module is numbered in the sequence as it occurs and connected by arrows and lines that should not cross. The flow process diagram should state where the product moves from high or low risk areas to a high care area. Temperatures and time durations are highlighted in the detailed process flow modules. Critical control points are also included once they have been identified.
The fifth step in implementing HACCP involves onsite confirmation of the process flow diagram. This is important to make the sure the diagram represents what actually happens in practice. Usually a member of the HACCP team will go into the process area and note any differences to the documented process flow diagram. Factors the HACCP team should consider during validation include the inclusion of all inputs and outputs, and steps in the product flow. For example: water is common ingredient that is not included as an input. Steam and air should also not be forgotten as they are commonly used in processes. The document should be signed and dated by a member of the HACCP team following the validation and any necessary revisions.
Problems do occur in the construction and maintenance of flow diagrams. HACCP team members may not have the relevant onsite experience and knowledge or may be overconfident by assuming they know all the processes and likely variations. It is an easy mistake to make assumptions and miss out critical process steps. The diagram may lack detail or be too complex for users to understand the process. All process, storage, transfer and backward (e.g. reworking) steps must be included. Changes in products and process are likely to occur. The failure to revalidate flow process diagram and other elements in the HACCP plan has led to serious outbreaks of food poisoning. Fortunately verification in the form of a systems audit will confirm the flow process diagram is representative of what is actually happening in practice or highlight deficiencies.
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