Bottle bombs
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A glass bottle failing under internal pressure is not a leak. It is fragments at speed, and it is the one failure in this estate that can seriously injure a customer.
The most dangerous failure in this estate
Pressure builds gradually and silently and the failure is instantaneous.
It happens in a fridge, in a bag, in a shop, on a shelf above somebody, and when a person is opening the bottle with their face over it.
Which is why this page exists and why the pressure rating of the container is a safety decision rather than a cost one.
Why it happens
Fermentation continuing in the bottle, producing carbon dioxide from residual sugar. The usual cause in a live product.
Over-carbonation at filling.
Temperature. Pressure rises steeply with it, so a bottle that was safe at 4 degrees can be at several times that pressure at 30.
An unrated container. A decorative bottle, a swing-top intended for still liquids, a jar, none of them is specified for internal pressure, and they may hold for months before failing.
Infection. A wild organism that ferments sugars the intended culture leaves alone can produce far more gas than the process predicted.
Where it happens
Almost always warm: a van, a stockroom, a windowsill, a car.
And usually late: weeks after filling, when enough sugar has been converted.
Which means the bottle that fails is one you shipped and forgot about, and by the time it happens the batch is distributed.
Preventing it
Use a pressure-rated container, specified as such by the supplier, and consider PET, which deforms before it bursts and gives a warning.
Reduce the fuel: ferment drier, or stabilize, or sweeten with something non-fermentable.
Hold the cold chain, and label the requirement clearly.
Test the worst case: bottles from every batch held at the warmest realistic temperature for the full shelf life, behind a screen, and opened.
And set a shelf life you have tested rather than one you hope for. A best-before on a live product is a pressure statement as much as a flavor one.