yeast, leaven
麯 centers on a fermenting agent used in food production: yeast or leaven that causes dough or grains to rise and develop flavor.
麯 combines 麥 (wheat) with 曲, which likely contributes the sound and may suggest the curved shape of fermenting molds or the process of bending grain into leaven.
Wheat (麥) bent or curved (曲) by fermentation becomes yeast or leaven, transforming simple grain into something that rises.
For キク, imagine a baker kicking a batch of dough to wake up the yeast: kick -> キク, and the leaven starts to work.