The seaweed that wraps sushi is known as nori. Preparing these dark, paper-like sheets for rolling requires little other than proper selection and storage. The moisture of the rice and fillings makes them pliable enough to roll into the familiar cylinder that you then chop into smaller sections.
Many grocery stores carry nori in the Asian section, or you can acquire it at a specialty store. The primary locations from which nori comes are Kobe Bay, Ariake Bay and Tokyo Bay. Nori's place of origin influences its qualities: Kobe Bay nori tends to be thicker, while Ariake Bay provides sushi that was made from more delicate leaves. For large rolls, known as futomaki, select thicker sheets; if the sushi is delicate or decorative and contains several sheets of nori for effect, go for the thinner type.
In general, nori should be of uniform thickness and crisp, rather than soggy. The sheen on the seaweed should be bright and smell good and clean. A batch of nori sheets that have holes or no odor is not of the best quality.
Store nori in a cool, dark place and sealed in packaging until you plan to use it. It deteriorates in quality when exposed to light.
Use a bamboo sushi roller to begin. This roller consists of bamboo skewers woven together into a mat that is flexible in just one direction and is a critical tool if you want to make tightly packed rolls.
Place the mat flat-side up and place the nori on it, shiny-side down. No special treatment of the nori is required before rolling it. Just line up the short side of the nori sheet with the bottom of the mat.
Top the nori with the rice and lay down any fillings you plan to add in the center. When you do add the rice, pack it to the edges of the nori, but leave a 1-inch gap at the very top of the square so that you have area for sealing.
Press against the filling with your fingers as you begin to roll the mat using your thumbs. Use firm pressure as you guide the roll with the mat. Pull up the edges of the mat as the roll forms so that it doesn't end up as part of the sushi.
Once rolled, cut the cylinder into about eight pieces. Use a sharp knife and dip it into water before making each slice to ensure smooth lines.