The fruit shriveled

What is happening

Shrivelling is osmosis doing exactly what it should, faster than the fruit can cope with. Sugar outside the fruit pulls water out of it, and if the gradient is steep enough the piece collapses rather than equilibrating.

A heavy syrup pulls water out of the fruit. If that happens faster than sugar moves in, the piece loses volume and does not get it back. The result is a preserve with the right flavor and the wrong appearance, which in a clear jar is most of the product.

The handling that avoids it

The fix is gradient rather than temperature or time: let the sugar arrive slowly enough that water can move both ways. In a kitchen that means an overnight step rather than a technique.

Start lighter and build. The published causes for tough fruit name the same mistake from the other side: starting the cooking in syrup that is too heavy, and not plumping the fruit properly. Both say the fruit needs time in a weaker syrup before the concentration comes up.

Why this is a preserve problem and not a jam one

It only matters where the fruit is supposed to keep its shape, which is why it shows up as a complaint about preserves and never about a crushed-fruit jam. If the fruit is going to be crushed anyway, none of this is worth the extra step.

A jam is crushed, so there is no piece to shrivel. A preserve is defined by the fruit holding its shape, which is exactly the property this failure destroys.

References