Mass balance

“Mass balance can support a system-level claim; it cannot tell you which bean, fibre or molecule reached the buyer. ”

Mass balance exists because physical segregation can be costly, technically difficult or impossible in some supply chains. Eligible and conventional materials enter the same storage or process, while an accounting system controls how much eligible output can be claimed. The model can accelerate demand for preferred production and also create misunderstanding when the accounting claim is described as physical content.

ISO 22095-2:2026 provides requirements and guidance for the mass-balance chain-of-custody model. It addresses system boundaries, time periods, conversion factors, attribution methods, transparency and claims. The publication is important because mass balance has long been implemented differently across commodities and schemes, making the same term carry different practical meanings.

The core rule is conservation of eligible quantity after legitimate transformation and loss. A company cannot sell more attributed output than its eligible input and accounting rules allow. If one hundred tonnes of eligible material enter a system and processing yields eighty tonnes of output, claims must reflect the conversion rather than treating every input tonne as an output tonne.

Mass balance differs from controlled blending. In controlled blending, a known proportion of the specified material is physically present in the output. In mass balance, eligible and non-eligible material may be mixed, and the claimed quantity is allocated administratively according to the approved method. The particular unit delivered may contain more, less or none of the eligible input.

Two common approaches are a rolling average percentage and a credit method. A percentage approach communicates an attributed share based on input proportions over a period. A credit method creates eligible claim units that can be assigned to output under scheme rules. Both require clear time and product boundaries.

Credits should not migrate across unrelated materials, sites or years unless the programme explicitly permits and justifies it.

Cocoa provides a familiar example. Certified beans may be combined with conventional beans in processing. A chocolate company can buy and retire a corresponding certified quantity under a mass-balance programme, supporting demand for certified production without claiming that the beans in each bar came from certified farms. The model is useful precisely because that physical link is not maintained.

Geography affects meaning. A global mass-balance pool can create demand somewhere while a buyer implies support in a specific sourcing region. Narrower boundaries improve connection and often increase cost. Organisations should state the boundary rather than allow customers to infer one.

Time affects meaning as well. Long reconciliation periods can permit claims to precede eligible purchase or conceal temporary deficits. Shorter periods create tighter connection and operational complexity. Rules should define whether negative balances are prohibited, how carry-over works and when credits expire.

Conversion and co-products create further judgement. A renewable input may produce several outputs with different economic value and physical composition. Attribute allocation should follow defined rules and avoid assigning the same characteristic to multiple products. Transparent conversion factors are part of claim integrity, not back-office detail.

Mass balance can increase producer participation by avoiding separate storage and logistics, but the distribution of value still matters. The premium or certificate payment may be small relative to the downstream claim. A technically correct account does not show whether producers received enough value to change practice or income.

The discipline is to make the non-physical nature of the attribution explicit. Mass balance is not fraudulent segregation; it is a different model with a different claim. Its credibility depends on conserved quantities, controlled boundaries, transparent allocation and wording that tells the buyer what is - and is not - physically in the product.

Practical application

Define eligible material, system boundary, reconciliation period, conversion factors, co-product allocation, accounting method and permitted carry-over. Reconcile purchases, inventory, production and claims, and block duplicate attribution across sites or systems.

Use claim language that states mass balance clearly and does not imply item-level physical content or source. Review geographic and temporal connection, investigate negative balances and disclose material changes in the model. Examine how premiums and system benefits reach producers.

Why it matters

Mass balance can scale demand for specified characteristics where segregation would restrict supply or raise cost. It supports transition at system level, but confidence depends on accounting discipline and honest communication about the missing physical link.

Common misconception

Mass balance is often described either as fully traceable sustainable content or as meaningless paper accounting. Neither is accurate. It is a recognised chain-of-custody model that can support quantity-based claims, but it cannot identify the physical characteristic of an individual item.

Connections

Chain of custody provides the overarching framework. Identity preserved and segregation maintain stronger physical connection, while book and claim separates the attribute further from material flow. Verification can test whether the mass-balance account and claim are truthfully stated.

A question worth asking

Could a reasonable customer read your mass-balance claim and mistakenly believe the specific product physically contains the attributed material?

Selected references

ISO 22095-2:2026. Chain of Custody - Part 2: Requirements and Guidelines for Mass Balance. ISO 22095:2020. Chain of Custody - General Terminology and Models. ISO. 2026. New ISO Standards Bring Clarity to Chain of Custody. ISEAL Alliance. 2016. Effective Chain-of-custody and Traceability Models. Holzapfel, P. et al. 2025. Chain-of-custody Modelling in Carbon Footprinting and Life-cycle Assessment.

International Journal of Life Cycle Assessment.