Table Grape Storage | MAP Bag + SO2 Pad Guide

Unlike most fruit, table grapes are non-climacteric and harvested fully ripe — they don’t continue ripening in storage the way stone fruit or avocado does. That removes one variable, but it doesn’t make grapes easy to store. The overwhelming cause of loss is a single fungal threat: Botrytis cinerea, grey mould, which can spread rapidly through a carton once it takes hold.

Why MAP Alone Isn’t the Whole Answer

A modified atmosphere liner does real work for grapes — it holds relative humidity at the right level, inhibits desiccation and browning of the pedicels and rachis (the stems and stalk structure buyers judge freshness by), and its antimicrobial properties help resist decay-causing organisms generally. But Botrytis is aggressive enough that most commercial grape storage programs pair MAP with a second, purpose-built line of defence: an SO2 pad.

How SO2 Pads Actually Work

An SO2 pad contains sodium metabisulphite, which reacts with ambient moisture to release sulfur dioxide gas. That SO2 directly inhibits the development of Botrytis cinerea within the sealed carton, allowing significantly longer storage and transport than MAP alone can achieve. Combined, MAP + SO2 pad can extend table grape storage to 12–14 weeks, depending on cultivar — a substantial jump from what atmosphere control by itself provides.

Not all SO2 pads behave the same way. A laminated design — two sheets of co-extruded polyethylene bonded together with the active ingredient between them — gives much finer control over the release rate: an initial fast release at a higher SO2 level, tapering to a slow, low-level release for the remainder of storage. This matters because low-emission, controlled release also reduces the risk of bleaching — visible damage to the fruit — during any break in the cold chain, where a poorly controlled pad can release too much SO2 too quickly.

Real Trial Evidence: MAP + SO2 vs. SO2 Alone

Side-by-side trials across three major table grape varieties — Crimson, Red Globe, and Thompson Seedless — compared fruit stored in a Lifepack® MAP bag with an SO2 pad against fruit stored with an SO2 pad alone (no MAP liner). The visual difference was clear and consistent across all three varieties: the MAP + SO2 combination produced tight, vibrant clusters with intact colour, while the SO2-only control showed visible mould growth, browning, and shrivelling over the same storage period.

This lines up with the underlying logic — SO2 handles the fungal threat directly, but it’s the MAP liner’s humidity and atmosphere control that protects against the desiccation, browning, and general quality decline that SO2 alone was never designed to address.

Matching the System to the Storage Length

Not every grape shipment needs the full 12–14 week system. Shorter programs — 3 to 4 weeks, typically domestic market or short-haul export, including organic grapes — can rely on MAP’s own elevated CO2 atmosphere for Botrytis suppression without an SO2 pad at all, since SO2 treatment isn’t organic-approved. Longer programs — 10 to 12+ weeks, typically long-haul export to Asian markets or extended cold storage on conventional (non-organic) grapes — call for the combined MAP + SO2 pad system.

One further point worth flagging for growers managing multiple varieties: Crimson, Thompson Seedless, Red Globe, Autumn Crisp and others each have different respiration rates and postharvest requirements. A single generic bag can’t correctly serve all of them — the liner needs to be specified to the variety and the storage program, not treated as one-size-fits-all.

What This Means for Packaging

A Lifepack® MAP bag engineered for table grape’s specific respiration rate holds humidity, protects pedicel and rachis colour, and provides baseline antimicrobial resistance. For programs needing longer storage or facing Botrytis pressure, pairing it with a properly controlled SO2 pad — ideally a laminated, dual-release design that limits bleaching risk — is what gets a shipment reliably past the 8–10 week mark that MAP alone typically can’t sustain.

The Practical Takeaway

Grapes don’t face the ripening-and-ethylene battle other fruit does, but Botrytis fills that gap as the dominant threat. The trial evidence across three major varieties is consistent: MAP alone helps, but MAP paired with a properly engineered SO2 pad is what actually delivers the extended storage windows long-haul export demands.

Table Grapes Have One Real Enemy, and It’s Not Ripening