Usage patterns
〈物〉に酵母を加えるto add yeast to something
Add yeast to the dough and mix well.
酵母で発酵させるto ferment (something) using yeast
This bread is fermented using natural yeast.
酵母が働くfor yeast to act/be active (during fermentation)
If the temperature is too low, the yeast doesn't work well.