Clean the guavas, removing the end flaps and washing off bugs if organic.
Cut ends off, peel skins, cut into halves (or smaller for large guavas), and place in blender.
Place mesh strainer on top of large measuring cup, and strain out seeds from guava puree. Stir and shake strainer as necessary.
For every cup of guava puree, measure 1 cup of sugar, set aside in mixing bowl.
For every cup of guava puree, measure 1 tblspn. lime juice and set aside.
Pour guava puree into medium-sized saucepan and add sugar and lime juice.
Bring to low boil, stirring constantly with wooden spoon. Reduce heat if it begins to spit.
Add food coloring if desired, approx. 2-3 drops per cup guava.
Continue cooking and stirring for about 20 minutes, or until liquid has decreased by half.
To check for done-ness, place a drop on the frozen plate and return plate to freezer. Time for one minute, then check to see that the preserves are setting up. If not, cook a few more minutes, but do not over do it or jam will be hard to spread.
Remove from heat.
Carefully reheat the jars to bring temperature up so they will not crack upon sealing in the boiler.
Pour guava jam into jar, leaving 1/4" headspace.
Clean off rim for proper seal, and place lid on jar, tightening to hand tight. Place jar into water for 5 minutes. I keep the tongs on and hold it to ensure jar does not touch bottom.
Repeat with next jar, and remainder can be used unpreserved.