Step 1: Put a small plate in the freezer.
Step 2: Put the loquats in a sauce pan, and add enough water to simply cover them. Bring them to a boil and simmer them until a third of the water has evaporated and the flesh is soft and pulpy- 25 minutes.
Step 3: Strain through a fine sieve and press on the flesh a little to extract as much juice as possible.
Step 4: Place your liquid, sugar, glucose and pectin sugar mix into a large pot. Check for acidity, and add the lemon juice if you like, give a stir to combine all ingredients.
Step 5: Place the pot back on the stove and bring the mixture back to a boil, heat until it reaches 105C, which is jam setting temperature. You can test if the jelly has set by spooning some on the cold plate. It will cool quickly, and will wrinkle when you push your finger across if it has set.
Step 6: Pour into sterilised jars and store, consume once cold and set.