30-34small/medium feijoas (less if the feijoas are large)
Sterilise the jars you will be using. I used proper Agee preserving jars but you may also use pasta sauce or jam jars. Sterilise them by running them through the dishwasher or washing them thoroughly in hot soapy water. Making sure that the jars are sterilised is very important to ensure that they are free from bacteria and lingering smells that could taint the fruit. Keep the jars full of hot water until you are ready to use them as this keeps the jars warm and ready for you to put boiling liquid into.
Put the water and sugar in a saucepan and bring to the boil. In a separate saucepan cover the seals and screw top bands for the jars in water and bring to the boil. This ensures that they are clean and sterile when it comes to putting them on the jars.
Cut the feijoas in half and scoop out the flesh. Discard the skins. When you have enough fruit, pack it into a jar until it reaches the top.
Using a ladle, fill the jars with the sugar syrup until almost to the top. Place the jar in the microwave and cook on high for 50-60 seconds for a small (500ml) jar, or 90 seconds for a big (1L) jar. (If you are using regular glass jars you can skip this step as they will not tolerate the microwave). (See recipe notes for alternative method)
Remove from the microwave and run a butter knife around the inside of the jar to ensure there are no air bubbles in the liquid. Top up the jars with more liquid until they are just overflowing. Using tongs remove a seal (or the lid) from the boiling water, and making sure that there is no fruit underneath the seal, place it on top of the jar. Now take a screw band (still using tongs) and at the same time and you press down the seal onto the jar, screw the band on tightly. You may need to use a tea towel as the jars will be very hot.
Wipe down the jar and leave sitting on the bench for about 24 hours. Remove the screw band and check that the jars have sealed. If the jar hasn't sealed properly you will be able to lift off the seal. If you can't then you're good to go! Store in a cool dark place. If they don't seal, put them in the fridge and eat within a few days or put in a ziplock bag and freeze.
Sealed jars will store in the pantry for at least 1 year.
UPDATED 2018 - I have recently started adding the feijoas to the sugar syrup on the stove, bringing to the boil and cooking for 2 or 3 minutes and then adding the fruit and the syrup to the jars. This removes the need to use the microwave which I like. Once you have filled the jar up with fruit and sugar syrup, continue from step 5