First, you will need to harvest the basil leaves. The best time to do this is mid-morning, after any morning dew has burned off and before it gets hot and the leaves start to wilt. When you go to collect the leaves, take as much from the plant as you desire. However, if you want to encourage new growth after harvesting basil, make sure to cut each of the stems of the herb directly above a leaf node.
Second, you will need to prepare the leaves for drying. Removed any noticeably damaged or diseased leaves at this time. Shake the stems of each bunch vigorously to make sure any resident insects are thrown from the basil. Rinse the herb under a gentle stream of cold water and remove any soil that may remain. Dry any excess moisture from the leaves. This can easily be accomplished by layering the leaves between sheets of paper towels and applying a gentle dabbing pressure until the leaves are mostly dry.
Now that the preparations are complete, there are various methods that can be used to dry basil. This herb has a relatively high water content compared to other herbs, weighing in at 91% water by weight. This means that it is not the best candidate for drying naturally and so dehydrator drying or oven drying is your best way to go. If the herb stays wet for too long it is susceptible to mold. Any leaves that grow mold during the drying process should be thrown out. Here are some methods for how to dry basil leaves.
This is the easiest method, but you need to have a food dehydrator. Simply dry basil leaves at approximately 95 degrees for 1 to 3 hours. Remove the stems once the herb is dried. It is my understanding that this Nesco Food Dehydrator is the bees knees.
Even though high temps will dry basil faster many people say that it damages the essential oils, so I recommend using relatively low temperatures in an oven. Turn your oven on to the lowest possible setting (usually around 140° F) and get it warm. Place your basil on a cookie sheet. Now turn the oven off and place the basil in the oven. After an hour of drying you can turn the oven back onto the lowest setting for ten to fifteen minutes. You can repeat this every hour until the herb is brittle, which means it is dry.
One method for drying leaves is to hang bunches, upside-down by the stem, in a warm, dry, well-ventilated room for a week or more. You can run a sort of “clothesline” in a quiet, undisturbed part of your home from which basil can be hung. Use twisty-ties or twine to hang the basil herb upside-down from the clothesline by the stem. Once the basil is brittle to the touch it is dried.
Regardless of the method you use to dry your basil, once the herb is dried strip the leaves away from the stems and store the leaves in airtight containers away from sources of light and heat. If properly dried and stored, basil will keep for about a year. Now that you’ve taken all that care growing basil, you can enjoy it all year long!