Fig Souring (Internal Fermentation): Causes & Prevention

Quick Answer

Souring is internal fermentation of a ripening fig. Yeasts and bacteria, usually carried in by fruit flies and small beetles, get through the fig’s eye (the ostiole) and ferment the flesh, so the fruit looks fine outside but is watery, sour, and sometimes oozing inside. Prevent it by harvesting promptly, removing dropped and rotting figs immediately, keeping water off the fruit, and reducing fruit fly pressure. Open-eyed varieties sour the most, so closed-eye cultivars are a big advantage.

Few things sting like slicing into a perfect-looking fig and finding a fermented, watery mess. Souring is one of the most common fruit disorders in fig growing, especially in humid climates, but it is largely preventable once you understand that it is really a hygiene and timing problem more than a disease.

What Souring Looks Like

The frustrating thing is that souring hides. From the outside, an affected fig often looks normal or only slightly soft. The signs are: figs that smell sour, fermented, or rotten when cut open, interior flesh that is watery, discoloured, or full of liquid, and often oozing or weeping from the base of the fig at the eye. You will frequently see small fruit flies (Drosophila) hovering around the ripening fruit, which is both a warning sign and part of the cause.

What Causes It

As a fig ripens it softens and its eye opens slightly. That opening is a doorway. Yeasts and bacteria ride in on fruit flies and small sap and driedfruit beetles, and once inside the warm, sugary interior they ferment rapidly. Wet weather and overhead watering make it worse by keeping the fruit and eye moist, and overripe fruit left on the tree is the perfect incubator. Varieties with a large, open eye are dramatically more susceptible than those with a tight, closed eye.

Is It Serious?

It will not harm the tree, but it can ruin a large share of your harvest if left unchecked, because each soured fig feeds the fruit fly population that goes on to infect the next wave of ripening fruit. Souring is a cycle, and a few neglected fruits can seed a serious problem. The good news is that breaking the cycle is entirely within your control.

My Prevention Plan

Harvest promptly. Pick figs as they hit peak ripeness and never leave them to go overripe on the tree.
Remove and bin dropped or rotting figs immediately. Fallen fermenting fruit is the breeding ground for the flies that spread souring.
Keep water off the fruit. Reduce overhead irrigation and water at the base to keep the eye dry.
Monitor fruit fly pressure with yellow sticky traps so you know when to be vigilant.
Bag vulnerable clusters with fine mesh or organza bags if souring is a persistent problem on open-eyed varieties.

⚠️ Break the cycle

Never leave soured or dropped figs lying under the tree. Each one is a fruit fly nursery that reinfects your ripening crop. Clean fallen fruit up daily during peak season and the whole problem shrinks fast.

Choosing Around the Problem

If souring plagues you every year, variety choice is your strongest lever. Closed-eye cultivars such as Celeste and Chicago Hardy have tight ostioles that physically block the organisms and insects responsible, and they hold up far better in humid, fruit-fly-heavy conditions. When you are picking new trees, eye type is worth weighing alongside flavour and hardiness. My Fig Variety Selector can help you match a variety to your climate and priorities.

Not sure it’s souring? Internal spoilage overlaps with insect damage from beetles and stink bugs. Check your tree’s symptoms against all 18 conditions with the free interactive tool.

Run the Symptom Checker

Frequently Asked Questions

What causes figs to sour on the tree?

Souring is internal fermentation. Yeasts and bacteria, usually carried in by fruit flies (Drosophila) and small beetles, enter through the fig's eye (the ostiole) as the fruit ripens and softens. Inside, they ferment the sugars, turning the flesh watery and sour. Varieties with a large open eye are far more prone to it.

Can you eat a soured fig?

No. A soured fig is fermenting: the interior is watery, off-smelling, and often oozing, and it will taste sour or alcoholic. It is not dangerous in the way a toxic food is, but it is spoiled and unpleasant. Cut figs open if you are unsure; a healthy ripe fig smells sweet and jammy, a soured one smells sharp and fermented.

How do I stop my figs from souring?

Harvest promptly as figs ripen and never leave overripe fruit on the tree, remove and bin any dropped or rotting figs right away, keep water off the fruit, and reduce fruit fly pressure with monitoring traps. For varieties that sour badly, choosing closed-eye cultivars or bagging individual fruit clusters is the most reliable fix.

Why are there fruit flies around my figs?

Fruit flies are drawn to ripening and fermenting figs, and they are both a symptom and a cause of souring. They feed on split or overripe fruit and carry souring yeasts from one fig to the next. A cloud of small flies around your figs is a signal to harvest promptly and clear away any spoiled fruit.

Do closed-eye figs sour less?

Yes, significantly. The ostiole (eye) is the doorway souring organisms and insects use to get inside. Varieties with a tight, closed, or sealed eye, such as Celeste and Chicago Hardy, resist souring far better than open-eyed varieties, which is a real advantage in humid climates with heavy fruit fly pressure.