Joint production is a production process where the relative amounts of co-products cannot be varied independently. This means that the proportions of the different product outputs are fixed by the technical or biological nature of the production process itself, rather than being adjustable based on market demand or operational choices.
In joint production, multiple products necessarily arise together from a single activity in fixed ratios. Classic examples include the petroleum refining process, which yields petrol, diesel, heating oil, and other products in technically determined proportions, or livestock farming, where meat and hide are produced together in ratios determined by the animal's biology. When one product is produced, the others inevitably follow in their fixed proportions.
This contrasts with combined production, where the relative amounts of co-products can be varied independently through operational adjustments or process modifications. In combined production systems, producers have flexibility to alter output ratios in response to changing market conditions or demand patterns.
The distinction between joint production and combined production has important implications for Life Cycle Assessment modelling, particularly when addressing multi-output processes and determining how to handle co-products. In joint production systems, the fixed technical relationship between outputs means that production decisions for one product automatically determine the quantities of all other products from that activity.
ISO 14040 defines co-products as "any of two or more products coming from the same unit process or product system", and joint production represents a specific technical constraint on how these co-products relate to one another. Understanding whether a process involves joint or combined production helps practitioners select appropriate system modelling approaches and allocation methods when necessary.
