Yet again I've followed a simple sauce reduction recipe (juniper berries, stock, wine, butter) and ended up with something that basically hasn't thickened at all. All these recipes read like the reducing step also thickens, but when it's just wine and stock, all that happens is I get less liquid - it stays the same consistency. The butter was supposed to thicken it, I suppose, but it didn't really seem to.

What can I be doing wrong?