I wanted to know if sushi could be prepared on shabbos and found, what seems to me to be conflicting responses on this site. In the English site dinonline.org it seems to say that it is permitted to make a sushi roll on shabbos as long as the rice is not too hot. But on the Hebrew site, din.org.il, it seems to say that there are a number of problems, including boneh as a result of shaping the rice, similar to making shapes with egg salad, along with tofer possibly, and maybe even makke bepatish. Are you able to help me out with understanding the two seemingly different responses, and most important, is there a clear issur or heter?
There are a number of different Rabbanim answering questions, over the years there are also new Rabbanim, as such you may find different opinions, hopefully all valid opinions!
Careful study of the potential problems seems to lead to the conclusion that in fact there is no problem of making sushi on Shabbos, as long as cooking is avoided.
Boneh: The comparison to Megaben, cheese making which is forbidden because of Boneh is difficult. Cheese making creates an entirely new entity from it’s ingredients, merely shaping or clumping food together is much less significant as nothing new was made. The Kitzur Shlchan Aruch does prohibit something similar. His source is the Magen Avraham 340:17 who questions why making date cakes or stringing figs is a problem of Meamer and not Boneh. To this he answers boneh would only be when it is done to beautify the final product. A careful reading of the Magen Avraham reveals he was only bothered by the stringing of figs which to an extent is a new creation, not making date cakes. Sushi would seem to be most similar to date cakes , clumping and slightly molding into a shape which is explicit in Shulachan Aruch that there is no problem of Boneh. This is not done for beauty per say, rather this is the shape of the food and the way to get the ingredients together.
Makeh Bpatish: there is a debate in the achronim if this prohibition exists by food, the opinion of the 318:4 is that it does not. Even according to the Pri Megadim this prohibition is only when something is done to food that was otherwise unfit for consumption, such as rinsing off salty meat even with cold water. Sushi is perfectly edible before it is all rolled together.
Tofer: The melacha of Tofer is not applicable to sushi. There is no binding agent used, moistness creates a slight stickiness which holds the food together in a loose way which is not intended to last for more than a short time. See Rama 317:3 that there is no problem of tefira in such a manner.