What it actually is
A gel is a network holding water in its spaces. Networks are not static: over time the junctions between chains tighten and multiply, the network contracts, and the water it was holding has nowhere to go but out. Nothing has spoiled and nothing has been lost; the structure has simply squeezed.
Why it matters
It is usually the first defect a consumer sees, and it reads as a product that has gone wrong even when it is entirely safe. In chilled dairy it is the most common single cause of complaint.
What changes it
The gelling system chosen, acidity, calcium, temperature cycling in distribution, and mechanical damage to the set gel. A gel that is cut, stirred or jolted after setting will weep where an undisturbed one will not.
