Ethylene Scrubber & Hold the Store Below the Ripening Line
Sizes the KMnO₄ bed
A cold store fills with the ripening hormone ethylene until production balances removal — enter your commodity, mass, temperature and room to get the steady-state ppm, the KMnO₄ media mass needed to hold it below the sensitivity threshold, and the shelf-life gained.
Size the cold-store scrubber
Next: at 2°C with 0.3 air changes/h the room settles to 0.007 ppm, already under the 0.1 ppm limit for Kiwifruit. No scrubber is required — but verify with an ethylene sensor, and keep high producers out of the same room.
Steady-state mass balance: at equilibrium the produce's ethylene production equals the rate removed by air exchange plus the KMnO₄ bed. Production scales with temperature (Q10≈2.7), so dropping the store 5 °C roughly halves the ethylene load — the cheapest control. KMnO₄ media saturate and must be replaced. Sources: UC-Davis Postharvest Technology Center; Kader & Mitchell; Saltveit 1999; scrubber-media datasheets.
Ethylene scrubbing — key facts
- Room ppm
- ethylene generated ÷ (1000 × airflow)
- Airflow
- room volume × air changes/h
- Required removal
- generated − threshold × 1000 × airflow
- Media mass
- required removal ÷ media rate
- Q10 (ethylene)
- ≈ 2.7 per 10 °C
- Sensitive threshold
- kiwi/lettuce/flowers ≈ 0.05–0.1 ppm
- KMnO₄ rate
- ≈ 2,200–2,600 µL/h per kg
- Privacy
- Runs in your browser; nothing uploaded
Commodity ethylene production & sensitivity
Production at 20 °C (scales ≈ ×2.7 per 10 °C). The sensitivity threshold is the room ppm above which damage begins — the scrubber must hold the room below it. Source: UC-Davis Postharvest Technology Center; Kader & Mitchell; Saltveit 1999.
| Commodity | Group | Production class | µL/kg·h @20°C | Threshold ppm |
|---|---|---|---|---|
| Apple | Fruit | high | 30 | 1 |
| Apricot | Fruit | high | 12 | 1 |
| Avocado | Fruit | high | 60 | 1 |
| Banana (ripening) | Fruit | high | 20 | 0.1 |
| Passion fruit | Fruit | very-high | 120 | 1 |
| Cherimoya | Fruit | very-high | 150 | 1 |
| Mango | Fruit | moderate | 5 | 1 |
| Papaya | Fruit | moderate | 7 | 1 |
| Peach / Nectarine | Fruit | moderate | 5 | 1 |
| Pear (European) | Fruit | high | 25 | 1 |
| Plum | Fruit | moderate | 4 | 1 |
| Tomato (ripe) | Fruit | high | 10 | 0.5 |
| Cantaloupe melon | Fruit | high | 30 | 1 |
| Fig | Fruit | moderate | 8 | 1 |
| Kiwifruit | Fruit | low | 1 | 0.1 |
| Lettuce | Vegetable | very-low | 0.1 | 0.1 |
| Broccoli | Vegetable | very-low | 0.1 | 0.1 |
| Carrot | Vegetable | very-low | 0.1 | 0.1 |
| Cucumber | Vegetable | low | 0.4 | 0.5 |
| Leafy greens (spinach/chard) | Vegetable | very-low | 0.1 | 0.1 |
| Potato | Vegetable | low | 0.5 | 1 |
| Cabbage | Vegetable | very-low | 0.1 | 0.5 |
| Asparagus | Vegetable | low | 0.4 | 0.5 |
| Pepper (bell) | Vegetable | low | 0.3 | 1 |
| Watermelon | Fruit | low | 0.5 | 0.5 |
| Carnation (cut flower) | Flower | low | 1 | 0.05 |
| Orchid (cut flower) | Flower | low | 0.5 | 0.05 |
| Citrus (orange) | Fruit | very-low | 0.2 | 1 |
Scrubber media
| Media | Working rate µL/h·kg | Lifetime µL/kg | Note |
|---|---|---|---|
| KMnO₄-on-alumina pellets | 2,200 | 90,000 | Bulk media for recirculated cold-store scrubbers; turns brown when spent. |
| KMnO₄-on-zeolite | 2,600 | 110,000 | Higher surface area; common in produce scrubbers. |
| KMnO₄-on-vermiculite sachets | 1,400 | 60,000 | Sachets/blankets for cartons & reefers; passive. |
| Activated carbon (impregnated) | 900 | 40,000 | Adsorptive; lower rate, needs regeneration. |
| Catalytic / Pt heated (non-KMnO₄) | 5,200 | 9,000,000 | Catalytic converter style; very high capacity, powered. |
What an ethylene scrubber does — and why size it
Ethylene is the gaseous ripening hormone. Stored produce keeps making it, and in a sealed cold room the concentration climbs until production is balanced by removal — through air exchange and, if fitted, a potassium-permanganate scrubber that oxidises ethylene to carbon dioxide and water. The room settles at a steady-state ppm. If that plateau sits above the most sensitive crop's threshold, the crop ripens, yellows or is injured. A scrubber sized too small fails silently; too large wastes media. This tool finds the mass that just clears the line.
It reports the ethylene generated, the room ppm with and without scrubbing, the media mass to hold the threshold, the media lifetime and the shelf-life gained. Because production follows a Q10 near 2.7, the calculator also makes the case for the cheapest control of all — a colder store. Pair it with the Controlled-Atmosphere Storage Gas, CA-Store Nitrogen Flush and Cold Storage Shelf-Life tools for a full storage plan.
Stop silent ripening
Hold the room below the crop's ethylene threshold.
Buy the right media
Size KMnO₄ to the load — no guesswork, no waste.
Value a colder store
See how cooling slashes the ethylene load (Q10≈2.7).
Plan replacements
Know the days until the media is spent.
Frequently Asked Questions
How much KMnO₄ scrubber media do I actually need?+
The tool sizes it from a steady-state mass balance: the media must remove the ethylene generated minus what air exchange already carries out. Required removal = ethylene generated − (threshold ppm × 1000 × airflow m³/h); divide that by the media's working rate (about 2,200–2,600 µL/h per kg for KMnO₄-on-alumina or zeolite) to get the kilograms. For a few tonnes of a high producer in a tightly sealed room that is typically a handful to a few dozen kilograms of media.
What is an ethylene sensitivity threshold?+
It is the room ethylene concentration, in parts per million, above which a crop starts to ripen, yellow, soften or show injury. Very sensitive crops like kiwifruit, lettuce, broccoli and cut carnations react at about 0.05–0.1 ppm, while many fruits tolerate around 1 ppm. The scrubber's job is to hold the room below this number for the most sensitive item present.
How does temperature change the ethylene load?+
Ethylene production rises steeply with temperature — roughly following a Q10 of about 2.7, meaning every 10 °C warmer multiplies production by about 2.7×. Dropping the store from 10 °C to 0 °C cuts the ethylene load to well under half. Cooling is therefore the cheapest ethylene control; the scrubber handles the residual.
What is the steady-state room ppm without scrubbing?+
At equilibrium the ethylene produced equals the ethylene removed by air exchange, so room ppm = ethylene generated (µL/h) ÷ (1000 × airflow m³/h), where airflow = room volume × air changes per hour. A sealed controlled-atmosphere room with very low air exchange lets ethylene build to a high plateau, which is exactly when a scrubber matters most.
Which crops are the worst ethylene producers?+
Cherimoya, passion fruit, avocado, ripening pears and apples are among the highest, producing tens to over a hundred µL per kg per hour at 20 °C. Storing these alongside sensitive crops like kiwifruit, leafy greens or cut flowers is the classic mistake — the producers gas the sensitive ones, which is what a scrubber, or simply separating them, prevents.
How long does the scrubber media last?+
KMnO₄ media have a lifetime capacity of roughly 60,000–110,000 µL of ethylene per kilogram before they are spent — the pellets brown as the permanganate is consumed. The tool estimates the days to exhaustion at your load. Replace the media on schedule; an exhausted bed silently stops working while the room re-gasses.
Is a scrubber better than ventilation?+
They work together. Fresh-air exchange dilutes ethylene but also brings in heat and humidity and costs refrigeration energy, and sealed CA rooms deliberately minimise it. A KMnO₄ scrubber removes ethylene without venting the controlled atmosphere, so it is the tool of choice for sealed and CA storage; ventilation is the backup for leaky rooms.
Will scrubbing really extend shelf life?+
For ethylene-sensitive crops held above their threshold, yes — keeping the room below the threshold can extend marketable life by anywhere from a few days to roughly doubling it, depending on how far over the threshold the room would otherwise sit. The tool shows a relative shelf-life factor so you can see the payoff for your specific load.
Does the scrubber remove ethylene from the fruit itself?+
No — it lowers the ethylene concentration in the room air around the fruit. Because ethylene acts as a gas-phase signal, reducing the surrounding concentration slows the ripening response. It cannot reverse ripening already triggered, so size and run the scrubber from the day the room is loaded.
Can one scrubber protect a mixed cold store?+
It can, but size it for the most sensitive crop's threshold and the total ethylene generated by every item in the room, including the producers. The safest practice is still to keep high producers out of a room holding sensitive crops; where that is impossible, the scrubber must be sized for the combined load, which this calculator does.
What air-change rate should I enter for a CA room?+
Sealed controlled-atmosphere and gas-tight cold rooms run very low air exchange, often 0.1–0.5 air changes per hour, precisely to hold the modified atmosphere. Conventional cold rooms with door traffic and some ventilation may be 0.5–2 per hour. Enter the figure for your room; lower exchange means a larger scrubber is needed.
Is 0.5 ppm safe for my store?+
It depends entirely on the crop. For most fruits 0.5 ppm is acceptable, but for kiwifruit, leafy greens or cut carnations 0.5 ppm is several times their 0.05–0.1 ppm threshold and will cause damage. Always judge the room ppm against the threshold of the most sensitive item — which the tool plots as a red line on the curve.