To store Thai basil for the longest shelf life, the best method is to treat it like cut flowers. Trim the stems, place them in a jar or glass with an inch of water, and loosely cover the leaves with a plastic bag to create a greenhouse effect. Store at room temperature for up to a week, changing the water and trimming stems every few days. Alternatively, you can freeze it by blanching, then freezing the leaves on a baking sheet before storing in an airtight container.
Here's a more detailed breakdown:

1. Room Temperature Storage (Best for short-term freshness):
Trim and hydrate:
Cut about 1/2 to 1 inch off the bottom of the stems and remove any damaged leaves.

Water bath:
Place the basil in a jar or glass with about an inch of water, similar to how you'd store cut flowers.
Create a humid environment:
Cover the basil leaves loosely with a plastic bag to help retain moisture and prevent wilting.
Refrigerate (if necessary, but not ideal):
If you need to refrigerate, keep the basil in the water-filled jar, covered with the plastic bag, and place it on the refrigerator door (avoiding the coldest parts). Change the water every couple of days.
Avoid the fridge if possible:
Storing basil in the fridge can cause it to turn brown and die, as basil prefers warmer temperatures.
2. Freezing (For longer-term storage):
Blanching (optional but recommended):
Blanch the basil leaves by dipping them in boiling water for a few seconds, then immediately transferring them to ice water to stop the cooking process.
Dry and freeze:
Spread the blanched (or fresh, if not blanching) basil leaves in a single layer on a baking sheet and freeze until solid.
Store in freezer-safe containers:
Once frozen, transfer the leaves to a freezer-safe bag or container for long-term storage.
3. Other Tips:
Don't wash before storing:
Unless you're immediately freezing it, avoid washing the basil until you're ready to use it.
Change water regularly:
When storing in water, changing the water every few days and trimming the stems will help prevent bacterial growth and keep the basil fresher longer.
Be mindful of space:
If using the water method, choose a jar or container that fits comfortably in your refrigerator.