Wash and wipe the guavas till dry. Cut them into small pieces.
Place the guava pieces in a pressure cooker and add water just enough to cover the fruit. Cook till two whistles. Turn off the heat. Leave it to cool.
Take a big size bowl or vessel. Place a strainer that sits well on the mouth of the bowl. Spread a muslin cloth on the strainer. Invert fruit onto the cloth. Hold the corners of the muslin cloth and tie them.
The juice should drip through the muslin bag and strainer into the bowl. Hang the bag and keep squeezing lightly till you feel you have collected all the juice.
Discard the pulp. Measure the liquid and transfer it to a thick bottom steel wok.
For every cup of liquid, add one cup of sugar and one tablespoon of lemon juice.
Cook this mixture over medium flame. Once it starts boiling, cook it on low flame stirring constantly.
Cook till the liquid thickens and starts coating the ladle thickly. When poured from the ladle, it should flow thickly and in the end, drops should drip in jointed fashion. Turn off the heat.
In the meantime, sterilize the jars. Place the washed and dried bottles with the lids in the oven. Set the temperature to 100 degrees and set the timer to 10 minutes. Remove the bottles and their lids from the oven.
Ladle hot jelly into the jars leaving ¼ inch headspace. Secure the lids tightly.