Defect and tolerance
Sour rot, and the box it works its way through
Most citrus rots arrive as a count of affected fruit. This one arrives as a process. A whitish mycelium produces an exudate that breaks down skin and flesh and infects whatever is touching it, so a single soft orange inside a closed package is the beginning of something rather than a number on a report.
The figures
| The fungus | Geotrichum citri-aurantii |
|---|---|
| Rank among post-harvest citrus rots | Third, after the green and blue moulds caused by Penicillium |
| What it smells and feels like | A soft rot with a sour smell recalling vinegar, under a whitish layer of mycelial growth |
| How it moves inside a package | The exudate disintegrates the skin and the flesh and infects adjacent fruit |
| How it gets in | Through micro and macro wounds on the surface of the fruit. Insects act as potential vectors |
| Growth range | 5 °C to 35 °C, optimum 25 °C to 30 °C, favoured above all by high humidity |
| Recommended holding for oranges | 3 to 8 °C at 90 to 95 % relative humidity |
| Post-harvest treatment on our fruit | Not confirmed by the grower |
What it changes on an order
You break pallets and hold part of the load
A package carrying one affected fruit is not a package carrying one defect, because the thing spreads by contact under the lid. Separating early costs a few minutes and separating late costs the package.
You are relying on the cold room
The lower end of its growth range sits under the temperature oranges are held at, so refrigeration is slowing this down rather than stopping it. That makes time, not temperature, the variable you actually control.
You buy from a week that had rain in it
Picking in very high humidity, picking after rain and picking over-ripe fruit are the three practices the reference manual warns about. Asking what the weather did during a picking week is asking about this.
What this note does not settle
- The manual gives a lower limit of observed growth, not a temperature at which the fungus stops. Treating that figure as a switch reads more into it than the source says.
- Sources name the organism differently. The Spanish manual has Geotrichum citri-aurantii and the Californian orange sheet has Geotrichum candidum for sour rot. Both are reported here rather than one being chosen.
- Telling one citrus rot from another by eye is unreliable, and the smell people describe is easier to recognise once it is already advanced. Where the distinction changes what you do next, it takes a laboratory.
- We have no post-harvest treatment confirmed, no drencher practice documented and no line hygiene record. Nothing we could say about how our own fruit behaves here would be verified.
Source: IRTA, Manual descriptivo de podredumbres y fisiopatías en naranjas y mandarinas, UC Davis Postharvest Technology Center, Orange produce facts
The rot that uses the packaging
Put a decayed orange into a box and most fungi leave the neighbours alone. Not this one. The white growth on the surface produces an exudate, the exudate breaks down skin and flesh, and whatever it touches next it infects. A package is a small closed space where everything touches something. For this mechanism that is close to ideal conditions.
So the arithmetic of an ordinary defect count stops working. One affected fruit found on a Monday is not one affected fruit by Thursday, and whether you find it early comes down to whether anybody opened the box. Buyers who break pallets and hold part of a load are the ones this catches, because holding is where the time comes from.
Cold slows it without stopping it
Oranges travel and sit in a narrow band of temperature, and the lower end of this fungus's observed growth range reaches under that band. Its optimum is far warmer, so a cold room is doing real work. It is doing less work than people assume, and what it leaves you to manage is time rather than degrees.
Upstream, everything that matters is about wounds and about water. Rough harvesting, picking in high humidity, picking after rain, picking fruit already over-ripe, unwashed line surfaces and recirculated treatment water are all named in the reference manual. None of it is documented for our fruit. What we can give you is the list of questions that gets a real answer out of a packhouse.
Talk to the grower
Tell us the variety, the sizes and the delivery week you need. You get a delivered price and what we can commit to in writing, from the person who picks the fruit.
The grower handles enquiries. Response times are still to be confirmed.