Hmm... it's art of sushi-making!

Literally, ほぐし具合　is how easily something breaks up, and the word ほぐす is translated into gazillions ways depending of what the subject/context is. For cooked rice, the action of ほぐす is to "fluff up" and it a "must-do" step after the rice is done cooking.

With nigiri-sushi and makizushi, it must maintain a just right level of airiness and fluffiness instead of rice being packed tight, and at the same time keep a shape so that it doesn't fall apart when you pick it up with your fingers. This balance is the big difference between おにぎり and にぎり鮨.

A similar discussion is tenderness for sirloin steaks and flakiness for pie crusts, but neither one is translated into ほぐす...

It's something like "not crumbly but not firm, just delicate enough to melt in your mouth... "

To perfect your translation, やっぱりお鮨を食べに行かないと！