There really are only two things to remember when harvesting Aloe Vera gel:
- Let the yellowish (or reddish, depending on the kind of Aloe) moist drip out of the plant for 15 minutes or so.
- You want the white, translucent inside of the leaf, not the green.
In order to do this, you take the fattest leaf at the bottom of the plant. Cut it off with a sharp knife. Using a blunt blade will wound the plant unnecessarily. Let the leaf stand with the cut down for 15 minutes to let the unwanted sap get out.
Then use a knife to cut the green apart from the inside. There are several methods to do this, but the main thing is really just this: cut close to the rim, so as to not lose any of the gel. Don’t keep any of the green in: it’s not good for you.
Use a bit for cuts and bruises you have at that moment, put away the rest in a refrigerator and keep it cool. Like with fruit, the way to keep it from turning brown is to add a bit of acid, like citrus to the can. Since this is an oxidizing effect, make sure the aloe gel is in a closed container.