Yeast
Leaven
noun
The mother of good fermentation is yeast! If you want to bake a pie or bread you have to have the best. And if you don't have any, maybe your neighbor has some extra that you can borrow?
こうぼ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
自作酵母を使ってパンを作っています。
I’m using my own yeast to make bread.