A practical, proven spec for CO‑free Indonesian yellowfin saku that holds natural red color 48–72 hours after thaw in retail VSP. What to ask your supplier. Exact cut, freezing, packaging, and handling. And the store‑side playbook to prevent browning in the case or poke bar.
We’ve spent years trialing CO-free Indonesian yellowfin for sushi counters that can’t afford surprises. In our experience, you don’t need carbon monoxide to keep tuna red. You need discipline. We took a client from inconsistent 12–24 hour color to a reliable 48–72 hour market-red program in 90 days using the exact spec below.
The 3 pillars of natural color stability
- Oxygen control from hook to shelf. Brown happens when deoxymyoglobin flips to metmyoglobin. Manage oxygen exposure, not just temperature.
- Speed-to-cold and a hard freeze. The faster you drop core temperature, the less enzymatic and oxidative head-start you give browning.
- The right cut and trim. Short fibers, clean bloodline removal, and consistent block geometry slow edge browning and drip.
Here’s the thing. Most “CO-free doesn’t hold color” stories trace back to sloppy pre-freeze handling or the wrong pack, not the fish.
Week 1–2: Map your case and validate what “red” actually means
Before changing suppliers, define your target. We recommend a simple validation sprint.
- Set your color target. On a portable Lab* meter, aim for a* ≥ 18 on thawed saku centerline, with b* 2–6. If you don’t use instruments, agree on a photo standard under your case lighting.
- Audit your display case. Airflow and light matter. Case deck at -1 to 1 C. No warm spots near fans, and LED lighting with minimal UV. Record temperature every 15 minutes for two full days.
- Thaw test with your current product. Keep saku vacuum-sealed during thaw at 0–2 C. Don’t open early. Log time-to-edge browning and drip. You’ll see where you’re losing color.
Practical takeaway: decide what “market-red” is for your team and document the temperature and lighting you’ll hold it at. Everything else flows from that.
Week 3–6: Build the MVP spec and run controlled trials
This is the CO-free Indonesian yellowfin saku spec we use when color stability is the KPI. It’s designed around one-by-one handline fish and tight oxygen management.
Supplier and raw material
- Species and size: Yellowfin tuna (Thunnus albacares), 30–60 kg GW. Larger fish tend to carry more stable color.
- Capture: Handline only. Fish spiked or brain-stunned on retrieval, gill-bled 3–5 minutes, then immediately placed in ice slurry.
- Onboard chilling: Ice slurry at -1 to 0 C within 30 minutes of capture. Core to ≤2 C within 2 hours. No deck exposure.
Cut and trim
- Saku geometry: 2.5–3.0 cm thick, 5–6 cm wide, 12–16 cm long. Target 180–220 g per block for retail, 250–350 g for foodservice.
- Trim: Bloodline fully removed. No silver skin. Exclude oxidized edges. Grain aligned for sushi slicing.
- Pre-freeze rinse: 0.5% chilled saline dip (0–1 C) for 30–45 seconds to reduce surface purge and improve hue on thaw.
Freezing
- Blast freeze tunnel setpoint: -45 C or colder with high air velocity. Rack spacing to avoid shadowing.
- Core targets: ≤ -20 C within 2.5 hours, ≤ -35 C within 6 hours. Hold at ≤ -40 C for 6–8 hours to stabilize color before packing.
- Storage and shipping: Maintain -35 to -45 C storage. Ship at -20 C or colder.
Packaging
- Primary: Vacuum skin pack (VSP) on a high-barrier board. Oxygen transmission rate ≤ 5 cc/m²/day at 23 C, 0% RH. Residual headspace O2 ≤ 0.5%.
- Alternative: IVP bag with oxygen scavenger in the outer carton. Check local rules for scavenger use. No MAP with CO, wood smoke, or “filtered smoke.”
- Labeling: “CO-free” and “No color stabilizers used” where permitted.
Thawing protocol (in-pack)
- Keep VSP sealed. Thaw at 0–2 C for 12–18 hours. Target core -1 to 0 C.
- Post-thaw hold: If unopened, you have 48–72 hours of market-red in VSP at 0–2 C.
Trial design
- Run A/B with two pack films of different OTRs. Measure a* at 0, 24, 48, 72 hours post-thaw without opening. Only open to slice when you plan to sell.
Looking for a model spec or a quick review of your current setup? Need a sanity check on your film choice? You can Contact us on whatsapp. We’re happy to share sample CO-free specs and run through your constraints.
Week 7–12: Scale, train, and tweak for your store realities
What’s interesting is how much performance improves once store teams change two habits: opening packs too early and overexposing to air in the case.
- Open-to-slice timing. Keep saku in VSP until the hour you’ll cut. After opening, work in 30–60 minute batches rather than opening the day’s full volume.
- Case handling. Place sliced tuna on cold plates or over crushed ice shields at -1 to 1 C. Lightly cover with low-OTR film between rushes to limit oxygen.
- Poke workflow. Hold cubes in covered hotel pans on ice. Dress to order. Acidic marinades accelerate browning. Pre-marinated holds 4–6 hours max at 0–2 C.
- Night routine. Rewrap any unsold cut pieces tight in low-OTR film or return to a clean vacuum pouch, purge air gently, and refrigerate at 0–1 C.
- Data loop. Have the team snap a photo at 24, 48, 72 hours under consistent light. If edges brown early, check case airflow and opening cadence first.
If you need CO-free options beyond saku for the same program, our Yellowfin Saku (Sushi Grade) pairs well with Yellowfin Cube (IQF) for poke and Yellowfin Steak for grill features. You can also browse everything in one place here: View our products.
The 5 mistakes that kill CO-free color programs
- Opening packs to “let it bloom.” Tuna isn’t beef. Oxygen triggers brown. Keep it sealed until slicing.
- Thawing warm. A 5–7 C walk-in will burn 12–24 hours of color. Thaw at 0–2 C.
- Over-trimmed, thin sakus. Thin edges brown faster. Stick to 2.5–3.0 cm thickness.
- High-OTR film. If your film breathes, your tuna browns. Specify OTR ≤ 5 cc/m²/day and verify with the converter.
- Slow freezing. If core doesn’t hit -35 C fast, you’ll chase color all week. Ask for freezing curves on your lots.
Quick answers to what buyers ask us most
Is CO-treated tuna legal in the EU and why do retailers avoid it?
As of 2025, the EU hasn’t authorized carbon monoxide for stabilizing the color of fresh or thawed fish. That makes CO-treated tuna effectively non-compliant in the EU. Many UK/EU retailers run zero-tolerance policies for both legal risk and consumer trust reasons. Even in markets where CO is allowed, retailers avoid “permanent cherry red” fish because it can mask age.
How do I spec CO-free yellowfin saku so it holds color on shelf?
Use the spec above. The short version: handline Indonesian yellowfin, fast bleed and slurry, 2.5–3.0 cm saku, -45 C blast with core ≤ -35 C, high-barrier VSP with residual O2 ≤ 0.5%, thaw sealed at 0–2 C. That consistently yields 48–72 hours of natural red in-pack.
How long will CO-free Indonesian yellowfin stay red in vacuum skin pack after thaw?
Our benchmarks: 48–72 hours at 0–2 C when left unopened. Once opened, you have 12–18 hours of prime appearance if you minimize air exposure and keep -1 to 1 C. Pre-marinated poke holds visual quality for 4–6 hours.
What handling steps keep CO-free tuna from browning in a poke or sushi case?
- Keep cubes covered and on ice. Dress to order.
- Use shallow pans to maximize cold contact. Avoid stacking.
- If you must pre-dress, use minimal acid and keep at 0–2 C, sell within 4–6 hours.
- Between service, tent with low-OTR film to limit oxygen. Replace any piece that shows grey edges.
Can I tell if tuna was CO-treated just by looking at it?
Not with certainty. CO-treated tuna tends to be uniformly cherry red, almost bubble-gum, with no edge browning even after days. Natural CO-free yellowfin is red but shows a gentle gradient at edges after 24–48 hours. When in doubt, rely on documentation and testing. Request CO-free declarations and, for audits, a lab check for carboxymyoglobin via spectrophotometry or GC.
Do Indonesian handline fish produce better natural color than longline fish?
Generally yes. One-by-one handline fish are landed alive, bled, and chilled within minutes. Longline soak times mean many fish die on the line. That stress and delay to cold lead to faster browning and higher drip. We see tighter color and texture from Indonesian handline supply, batch after batch.
What PO wording guarantees a CO-free supply and testing back-up?
You don’t need novel legalese. Be specific and testable.
- “Product must be CO-free. No carbon monoxide or filtered/wood smoke used at any stage including harvest, transport, processing, freezing, or packing.”
- “Supplier to provide batch-level CO-free declaration and freezing curve showing core ≤ -35 C before packing.”
- “Packaging must be high-barrier VSP. OTR ≤ 5 cc/m²/day. Residual O2 ≤ 0.5% at pack.”
- “Buyer reserves right to test lots for carboxymyoglobin/CO. Non-conformance is grounds for rejection at supplier cost.”
- “Capture method: handline. Onboard bleed and ice slurry within 30 minutes of capture.”
The reality is that when the PO matches the processing floor SOP, color stability becomes repeatable.
Resources and next steps
If you’re building or fixing a CO-free program, start with two moves this week. Tighten your thaw protocol to 0–2 C while keeping VSP sealed, and confirm your film’s OTR is ≤ 5. Those two steps alone extend shelf appearance by a day in most stores. Want us to sanity check your spec against your case conditions or send a test lot of Indonesian handline saku? Contact us on whatsapp.