A practical, 30‑day playbook to choose and implement MSC Mass Balance Chain of Custody in an Indonesian seafood plant. What changes on the floor, which records auditors check, a simple volume calculation, and how buyers view mass balance vs segregation.
If your factory handles both MSC and non-MSC fish, you don’t need a theoretical primer. You need the fastest path to make credible MSC claims without rebuilding your plant. We’ve helped Indonesian processors do exactly that, and mass balance is usually the quickest, lowest-friction route.
Here’s the practical guide we wish we’d had on day one. What changes on the factory floor, the exact records auditors request, a simple mass balance calculation, how retailers actually view it, and a 30‑day prep plan that gets you through the first audit.
Mass balance vs segregation: what really changes day to day?
Mass balance lets you co-mingle certified and non-certified fish of the same species and form on the same line. You don’t physically separate. Instead, you reconcile inputs and outputs so your MSC-claimed sales never exceed your certified inputs for a defined period.
Segregation requires physical separation at all times. That means dedicated storage, clear line-time separation with cleaning, and labeled WIP to ensure every unit labeled MSC is 100 percent certified. It’s clean and strong. It’s also slower to implement if your plant is already busy.
In our experience, mass balance wins when:
- You have mixed supply and can’t dedicate lines or storage.
- You run variable yields and cut types, and you prefer a credit-style system rather than hard segregation.
- You want to start making claims in 30–45 days while you build toward segregation later.
Segregation still makes sense if you need on-pack MSC labels for retail programs that demand it, or if your buyers insist the physical unit itself is certified end to end.
Can I blend MSC and non-MSC lots on the same line?
Yes under mass balance. Co-mingling is allowed for the same species and form. You must maintain lot-level traceability, define your mixing pools, and keep a live volume reconciliation so you don’t oversell MSC claims. Auditors will challenge “silent” mixing across species or forms, so be precise in your definitions.
What auditors actually verify for mass balance
Here’s the thing. Most non-conformities aren’t philosophical. They’re missing or inconsistent records. In Indonesia the last few months, we’ve seen certification bodies tighten three areas: yield validation, subcontractor control, and real-time balances. Expect auditors to test the following.
- Intake records: Purchase orders, delivery notes, and supplier CoC codes for certified lots. For tuna and export whitefish, keep E-docs or catch certificates aligned to lot IDs.
- Defined conversion factors: Approved yields by product form and species. For example, whole round to skinless fillet yield for red snapper, or loin to saku for yellowfin.
- Production records: Batch sheets showing quantities in and out by lot, with rework and trim captured.
- Mass balance ledger: A species-by-form spreadsheet or system log that tracks starting balance, certified inputs, calculated claimable outputs, claims dispatched, and remaining balance. Auditors pick a day and recalc your math.
- Dispatch documents: Invoices and packing lists with correct MSC claim language and your CoC code on lines that carry claims. No claim language on non-claimed lines.
- Subcontractor and cold store controls: Contracts, SOPs, and evidence of oversight or certification (more on this below).
Tip: Keep your ledger at the narrowest practical level. Species plus product form works well. For example, “Red Snapper Skinless Fillet IQF” separate from “Red Snapper Portion 125 g IQF.” Granularity reduces reconciliation arguments.
A simple mass balance calculation you can copy
Say you receive 10,000 kg of MSC-certified whole round red snapper. Your approved yield to skinless fillet is 38 percent. That gives 3,800 kg of claimable MSC fillet credits.
In the same week you process 6,000 kg of non-certified red snapper. Total fillet production is 3,800 kg + 2,280 kg = 6,080 kg. You can sell up to 3,800 kg as MSC. The remaining 2,280 kg must be sold without an MSC claim.
The ledger logic looks like this:
- Starting balance: 0 kg
- Certified input: +10,000 kg WR x 38 percent = +3,800 kg claimable fillet
- Claimed outputs: -2,500 kg shipped as MSC fillet
- Ending balance: 1,300 kg claimable fillet remaining
You can’t issue MSC claims beyond that balance until the next certified intake is posted.
How much certified input do I need before I can sell any MSC-claimed volume?
You need posted certified credits first. Some auditors accept same-day posting before dispatch closes. None will accept negative balances. Don’t pre-sell claims. Keep a positive ledger at all times.
Cold stores, subcontractors, and co-mingled reality in Indonesia
If our processor has MSC CoC but the third-party cold store doesn’t, can we still sell under mass balance?
Yes, but only if the cold store is either MSC CoC certified or formally covered under your certification as a subcontractor with documented controls. That means a signed subcontractor agreement, a risk assessment, clear labeling rules for MSC-eligible stock, and access for your auditor to sample records. If the cold store is neither certified nor under your controlled subcontracting, you can’t maintain Chain of Custody and you can’t claim MSC on those goods.
We generally recommend using certified cold stores for simplicity. But we’ve successfully certified subcontracted storage with tight paperwork and periodic visits.
Can subcontractors be used under mass balance in Indonesia?
Yes. The same rule applies. Either they hold their own CoC, or you include them under your scope with controls. If a subcontractor performs processing that affects yields, include their conversion factors and production records in your ledger checks.
What buyers accept today
Do major retailers accept mass balance claims? For B2B documentation and internal sustainability reporting, many EU and UK buyers accept mass balance, especially for frozen, ingredient, and foodservice lines. For on-pack blue label in retail, a number of programs still want segregation or identity preserved so every unit undeniably contains certified fish. We see growing acceptance of mass balance in private-label ingredient supply, but don’t assume. Ask the buyer up front which claim types they approve. That conversation saves weeks.
If you need a “no-compromise” line while you implement mass balance elsewhere, consider running a small segregated SKU. For instance, a dedicated run of Snapper Fillet (Red Snapper) or Yellowfin Saku (Sushi Grade) with pure certified inputs satisfies strict retail buyers, while mass balance covers the bulk of your mixed production.
The 30‑day prep plan we use to pass a first CoC audit
We’ve found most Indonesian processors can be audit-ready in 30–45 days for mass balance. Here’s a tight plan.
Week 1. Decide the model and define your scope.
- Confirm mass balance eligibility with your key buyers. Align on claim type (on-pack vs off-pack, B2B docs).
- Map products by species and form that will be in scope. Keep it simple at first. One or two forms per species.
- Select conversion factors. Use your last 90 days data or run two controlled trials per form.
Week 2. Build the control system.
- Draft SOPs: intake verification, labeling, production recording, ledger management, dispatch claims, subcontractor control.
- Create your mass balance ledger. Spreadsheet works fine at the start. Lock formulas and restrict manual overrides.
- Set document templates: intake checklist, batch sheet, rework log, dispatch claim language with your CoC code.
Week 3. Train and test on real product.
- Run one live batch per in-scope form. Reconcile inputs/outputs the same day. Fix gaps.
- Stress test co-mingling on the same line. Check that lot IDs survive through WIP to finished goods.
- If you use a third-party cold store, label pallets with claim eligibility flags and test a round trip.
Week 4. Pre-audit and certification body scheduling.
- Do an internal audit with a simple trail: intake to ledger to dispatch for one order. Correct anything that takes more than 10 minutes to explain.
- Book your certification body. Share your scope and confirm they are comfortable auditing subcontractors if needed.
- Prepare your evidence pack: SOPs, two weeks of records, subcontractor files, and yield trials.
Most first audits take one day on site for a single location. If you get minors, they’re usually closed in 1–2 weeks with evidence.
Common mistakes that trigger non-conformities
- Vague yields. “30–40 percent” is not an approved conversion factor. Pin it down by product form and species.
- Ledger at too high a level. Mixing fillets and portions in one pool creates math you can’t defend.
- Claims on invoices for mixed lines. If an invoice has claimed and non-claimed items, label each line correctly. Don’t add generic claim text at the footer.
- Subcontractor blind spots. No signed agreement, no evidence of oversight, and no access for auditors will sink otherwise solid systems.
Fix these and 80 percent of audit friction disappears.
Quick answers to questions we’re asked every week
How long does a first MSC CoC audit take in Indonesia using mass balance?
From kick-off to certificate, 4–8 weeks is normal. Document build and training take 2–3 weeks. Scheduling and the audit itself another 1–2 weeks. Closing minors adds 1–2 weeks.
Do cold stores need MSC CoC for mass balance shipments?
Either the cold store is certified, or you formally control them as a subcontractor under your scope. Otherwise, no claim.
MSC volume reconciliation spreadsheet: what records are mandatory?
Intake with supplier CoC, production batch with yields, rework and trim logs, live ledger with balances, and dispatch docs with claim language. Keep a version-controlled ledger and save it daily.
Can you switch from segregation to mass balance later, or vice versa?
Yes. We’ve moved clients from segregation to mass balance when capacity got tight, and the reverse when a retailer demanded on-pack claims. Just update SOPs, retrain, and inform your auditor.
Bottom line
Mass balance is the fastest credible route to MSC claims for mixed Indonesian supply. Build tight yields, keep a live ledger, control your subcontractors, and agree buyer claim rules before you start. Do that and you can be making verified MSC claims in about a month.
If you’d like our mass balance ledger template and a one-hour walk-through tailored to your species and forms, reach out and we’ll share what we use in our own operations. Need help with your specific situation? Contact us on whatsapp.