John Ash on shiso leaves and ways to cook with them

If you've ever had a tray of sushi or a Japanese bento box and noticed those strips of fake plastic grass separating the items, there’s a backstory to them that has become somewhat lost in translation.

That imitation greenery is supposed to replicate shiso leaves, with the plastic trimmed to represent the shiso’s characteristic ruffled, saw-toothed edges.

Shiso leaves are an aromatic herb from the same botanical family as mint.

It traditionally accompanies sushi and sashimi and is used to divide the items in a tray or platter to keep the flavors separate. It is meant to be eaten along with the main item on the plate.

The leaves are also credited with antibacterial properties and contain compounds called phytoncides, which are believed to help prevent the spoilage of food that is wrapped in the leaves. For centuries, the Japanese have used shiso leaves to help slow the spoilage of raw fish and seafood.

Depending on your location, shiso can be a bit hard to find fresh and can be slightly more expensive than other fresh herbs. It is sometimes available frozen or as a dried herb.

Shiso leaf uses

Shiso leaves, however, are more than just a divider or an edible garnish — they are often included as an ingredient in the sushi itself.

The herb pairs well with fatty fish like salmon, yellowtail, and tuna, and can be enjoyed by wrapping a whole leaf around a piece of sashimi and dipping it in soy sauce.

Shiso also complements vegetables and fruits. Julienned shiso leaves are often mixed with salads to add a fresh, citrusy flavor. Whole shiso leaves are made into tempura by dipping them in a light batter and frying until crispy and puffy. It's a popular ingredient in Vietnamese summer rolls.

Shiso is also a popular ingredient in drinks and desserts, including granita, mojito cocktails, infused water and teas and for making simple syrup. It is also dried and ground and used as a seasoning and sprinkled on rice, omelets, tofu and soups, (use your imagination) much like dried nori.

Green vs. red

In addition to the green shiso leaves, which are by far more common, there is also a red variety. Red shiso leaves are mostly used for dyeing foods a red color, such as pickled plums, known as umeboshi, and pickled ginger.

Red shiso leaves are also the main ingredient in a refreshing beverage called shiso juice.

Shiso juice is prepared by simmering red shiso leaves, then straining and reducing the liquid along with sugar and mild vinegar to form a syrup. This syrup is then combined with sparkling water and served over ice. The resulting drink has a vivid red color like that of cranberry juice.

What does it taste like?

Shiso leaves have a fresh, citrusy flavor and aroma with hints of cinnamon, cloves, basil and mint.

They are somewhat astringent with a bitter finish, particularly the red shiso leaves. The flavor of dried leaves is more subdued.

Shiso is similar in texture to fresh mint, and can be used like mint in cocktails, desserts, and syrups for a different flavor. Serve with fresh sushi for a classic presentation.

Where do I buy?

You can buy shiso leaves at most Asian grocery stores, especially Japanese. In addition to fresh leaves, shiso is also available frozen, packed in sesame oil and dried and ground. Fresh they are generally sold by the bunch along with other fresh herbs. In Sonoma County you can also source shiso from Radical Family Farms in Sebastopol, which sells fresh in season and dried all year round every Sunday at the Sebastopol Farmers’ Market.

Storage

Fresh shiso leaves need to be kept in the refrigerator in the crisper. They dry out easily, so when you're working with them, it helps to keep them covered with a damp cloth or paper towel. Fresh shisho can last a few days but use as soon as possible for best results. Dried shiso should be stored the same as other dried herbs (in an airtight container in a cool, dark, place) and frozen shiso should be kept fully frozen until used.

Grow you own

Shiso, also sometimes called perilla, is an annual and best grown from seed and raised as seedlings. Soak the seeds overnight before sowing to accelerate germination. Sow 1 mm deep in spring when temperatures reach above freezing as they need some heat to germinate. Don’t cover them with too much soil as they need light to germinate. If your area is susceptible to frost, wait until the last frost date before sowing.

Germination can be slow and can take anywhere from 7 to 21 days. Once the seedlings have their first or second true leaves, they can be transplanted to their permanent position. Space the seedlings 6 inches apart and plant in moist soil, in full sun though they can tolerate part shade. Shiso grows to a height of 3 feet and takes approximately 70 days for mature leaves to form.

Shiso can be grown successfully in containers as well as a raised garden bed. Pinch the top to encourage more bushy growth and to provide micro greens. Once established they’ll reseed themselves in temperate climates.