fermented beans
豉 centers on fermented beans, specifically a type of savory fermented soybean product. The meaning is narrow and concrete, without broad abstract extensions.
豉 combines 豆 (bean) with 支, which likely contributes a phonetic element. The character is specifically associated with fermented bean products.
The left side 豆 is a bean, and the right side 支 looks like a hand holding a tool. Picture a hand stirring a pot of beans to ferment them into a savory paste.
For シ, imagine a sheaf of fermented beans: sheaf -> シ, and the beans are bundled together after fermenting.
Chinese fermented black beans