Process the sansho peppercorns as soon as you can after bringing them home! If you leave them they'll become discolored.
Wash them on the branches, and rinse off any dirt or insects (there was one this time!). If you prefer, you can remove the peppercorns from the branches at this stage; but it's a lot of work.
Boil the peppercorns on their branches for 4 to 5 minutes over medium heat without bringing it to a rolling boil. The peppercorns should become tender enough to crush between your fingers.
Once the peppercorns are boiled, cool them in cold water, and let them soak for about an hour. Taste one, and if it's strongly bitter, soak them for a while longer. Refresh the water several times.
Once the bitterness is gone, drain them in a colander or sieve. If you want to take the branches off before freezing them, do so now. This is very easy to do at this stage.
You don't have to remove the little stems from the peppercorns. They can be eaten; however, if you prefer, you may remove them completely.
Pat them completely dry, and wrap single-use portions in plastic wrap. Put the wrapped portions in a freezer bag, and freeze!
You can enjoy the peppercorns all year round this way. Freeze them on the branches, and pop them off very easily when using.
I made furikake using these sansho peppercorns and the contents of a used dashi stock pack (containing bonito flakes and so on). See (Recipe ID: 2254423) "Furikake from Leftover Dashi Stock Packs".
I also made chirimen sansho! "Chirimen sansho to go with rice" (Recipe ID: 2271507).
Story Behind this Recipe
Several years ago, a trustworthy greengrocer taught me how to prepare sansho peppercorns for freezer stock. Ever since, then I've been processing them whenever I find them on sale at the supermarket, and freeze stocking. That way, I can enjoy their refreshing fragrance and zing all year round.
Important! I often see recipes that say "take the peppercorns off the branches...", but...you actually don't need to do that. It's much easier if you boil them on the branches; they come off much easier afterwards. I often just boil them and freeze them still on the branches. They pop right off the branches that way.