Atmosphere Setpoints & Extend Storage Without Injury

The classic recommendation for apples is about 2% oxygen and 3% carbon dioxide, with O2 kept in the 1–3% band and CO2 in 1–5%. Held there at the right temperature, apples can store roughly 2.5× longer than in air — often six to twelve months. Drop O2 below ~0.8% and the fruit ferments; push CO2 above ~6% and you risk internal browning.

It depends on the commodity. At its recommended setpoint, apple reaches about 2.5× air, cabbage about 2.4×, kiwifruit about 2.2×, banana and avocado about 2×, and high-respiring leafy greens about 1.8×. The tool shows a storage-life multiplier that grows as your O2/CO2 dot moves into the green optimum box and falls toward 1× (air) as it drifts away.

Pulling a room from 20.9% O2 down to a target follows exponential dilution: the number of well-mixed air changes ≈ ln(20.9 ÷ target O2). Multiplying by the room's free volume gives the nitrogen needed; dividing by your N2 supply rate gives the flush time. To reach 2% O2 you need about ln(20.9/2) ≈ 2.3 air changes, plus a margin for imperfect mixing.

If oxygen falls below the commodity's lower limit, the produce switches to anaerobic respiration and makes ethanol and acetaldehyde, causing off-flavours, off-odours and tissue breakdown. The limit is commodity-specific — about 0.8% for apple, 2% for mango and tomato, and as low as 0.5% for broccoli. The calculator flags a red fermentation zone whenever your O2 setpoint is below that limit.

Too much carbon dioxide damages tissue — brown stain in lettuce, core browning in pears, internal browning in apples. Each commodity has a CO2 ceiling: about 2% for lettuce and pear, 5–6% for apple and tomato, but 20–25% for strawberry and blueberry, which actually use high CO2 to suppress decay. The tool marks a red CO2-injury band above each commodity's limit.

Tolerance is commodity-specific. Strawberries and blueberries benefit from very high CO2 (15–20%) because it strongly suppresses Botrytis and other decay without harming the fruit. Crisphead lettuce, by contrast, develops brown stain above about 2% CO2. That is why a single 'good' atmosphere doesn't exist — the calculator loads each commodity's own safe window.

For apples and several pome and stone fruits, yes — it sits in the recommended optimum and delivers most of the achievable storage-life extension. For a high-CO2 fruit like strawberry or a CO2-sensitive one like lettuce it would be wrong. Select your commodity first; the green box on the map then shows whether 2/3 is inside its recommended window.

Controlled atmosphere (CA) actively holds set O2 and CO2 in a sealed room with gas generators and scrubbers. Modified atmosphere packaging (MAP) is passive: the produce's own respiration draws down O2 and raises CO2 inside a sealed film pack, and the film's permeability is chosen so the pack settles near the target. The calculator gives the setpoints for both and a film-permeability band for MAP.

Match the film's gas transmission to the produce's respiration so the pack equilibrates at the target O2 instead of going anaerobic. High-respiring items (leafy greens, broccoli, strawberry) need a high-permeability film; low-respiring items (apple, pear, cabbage) need a low-permeability film. The tool suggests a permeability band from the commodity's respiration class.

No — CA works alongside cold storage, not instead of it. Low temperature does most of the work of slowing respiration; CA adds a further slowing on top and is especially valuable for long-term holding (apples, pears, kiwifruit, cabbage). For chilling-sensitive tropicals like mango, CA can extend life at a safe, non-chilling temperature.

The initial flush establishes the low-O2 atmosphere; after that the produce's respiration keeps consuming O2 and producing CO2. You top up nitrogen to replace leakage and to hold O2 at setpoint, and you scrub or vent CO2 to keep it from climbing past the injury limit. The big nitrogen demand the tool shows is the first pull-down; maintenance volumes are smaller.

They are drawn from USDA Agriculture Handbook 66 (The Commercial Storage of Fruits, Vegetables and Florist & Nursery Stocks) and the UC-Davis Postharvest Technology Center CA/MA recommendation tables compiled by Kader and colleagues. These are the standard references the industry uses to set CA room and MAP targets.