What makes rainbow roll harder than regular rolls like California is that a chef needs to slice a few pieces of fish before start making the roll.
Rainbow roll, like Caterpillar Roll is one of so-called Special Rolls. It’s special because it has double layers of fish: both inside and outside.
A California Roll must have both crab and avocado, while, there is not set rule as to which fish a Rainbow Roll needs to have to be called Rainbow.
For one, the inside of a rainbow can be anything, as long as the outside is colorful. The two standards, as far as the inside goes, are California and Spicy Tuna.
No one seems to know who invented the Rainbow Roll, and I am guessing one the reason for inventing the Rainbow was to use unwanted slices of fish.
Unwanted, not meaning, not fresh nor gone bad fish: when we slice blocks of saku fish, there always will be some end pieces which we will not be able to use for nigiri or sashimi.
One way to utilize those pieces are to mix into spicy tuna or put several pieces together and make a “special roll” and call it something like “Everything roll.”
Because everything roll could have multiple fish – tuna, salmon, hamachi, Hirame -all in one roll, it could become a nice roll.
In fact, I’ve made a roll like that and all of the customers loved it – especially when I told them that it had virtually all the fish we had at the sushi bar.
Perhaps, someone thought of a creative way to utilize those end pieces and made a Rainbow Roll instead.
At Rock and Hollywood Sushi, a standard rainbow roll had tuna, white fish, salmon, shrimp and avocados on top. The inside can be either California or Spicy Tuna and it was up to the customers to choose.
Back then, Tuna was expensive and so was Hamachi. Hamachi was farm raised and air shipped from Japan. Salmon was extremely inexpensive, going for less than $5/lbs.
So we put just one piece of tuna for color and used white fish and salmon. Adding more pieces of avocado was also welcomed to save the food cost.
“First, you cut the fish. One piece of tuna, two pieces of white fish, two salmon and shrimp,” Toshi explained to me.
Until then, I never made sashimi or sliced raw fish for a roll or nigiri, so I was anxious and nervous at the same time.
“You pull your knife backward when slicing the fish and never to press down the knife too hard. When you apply too much pressure, you will break the soft flesh of the fish and its tissue.”
The flavor of the raw fish, is stored in the tissue in the from of liquid, or more precisely, an amino acid. When you break the tissues, it will release the delicate flavor. To minimize the loss of umami, a sushi chef must develop a superb slicing skill.
“You also need to do is gentle with as little force as possible. You see that we tend to use more force when we have difficulty slicing, but that’s the opposite of what we should be doing. What we need to do is to let the knife “run” – use the weight and sharpness of the knife and slide through the fish, applying just a small amount of pressure. Let the knife do the work. The harder you try, more damage you will make to the fish.”