1. Rinse the fruit and place in a preserving pan, cover with water and mush the guavas up a bit with a potato masher.
2. Bring to the boil then simmer for around 20 minutes.
3. Line a colander with muslin (or similar - I used baby gauze doubled up) and place inside a stockpot or similar. Pour in the fruit. Leave it for 10-20 minutes until the juice has dripped through - don't be tempted to push the fruit down!
4. Lift out the colander and discard fruit.
5. Measure out how much juice you have return to preserving pan with an equal amount of sugar (i.e. 5 c juice plus 5 c sugar). Bring to boil then simmer 25 or more minutes until it starts to coat the back of the spoon and go thick.
6. Pour into sterilised jars and seal.