It's important to note that in "The Su Yuan Food List," sea cucumber is described as a tasteless ingredient, sandy and fishy.
Qin Huai is self-aware. Before practicing Crab Dumplings, he wasn't familiar with crab as an ingredient and spent a lot of time getting to know it.
Similarly, Qin Huai isn't very familiar with sea cucumber either. In his previous pastry-making endeavors, he used sea cucumber very sparingly, mostly in the Five Fillings Bun, but in that dish, sea cucumber is a definite supporting player, primarily serving a nourishing role.
Not knowing the ingredient well and the flavoring being very challenging, Qin Huai feels that at his current level, even with hard practice, he might not be able to make Double Crab Bun.
Qin Huai thinks he might need to wait until his seasoning skills reach a Master Level before he can try to learn how to make it.
Wang Gen Sheng is in great status, and the side quests aren't urgent, but there is one side quest that's actually urgent.
