Mountain ash berries develop their sugar content only after the first frost or by freezing. Now gently roll the berries in a little water for 20 minutes and strain through a sieve. Measure 500 g of the puree. Mix with the pear cubes, the vanilla pulp, the lemon zest and the preserving sugar. Make bubbling with stirring for at least 3 min and empty on the spot into hot rinsed jars.