Jesus uses this question to rebuke the disciples. Alternate translation: "You should have understood that I was not really speaking about bread." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "yeast" represents evil ideas and wrong teaching. Translate as "yeast" and do not explain the meaning in your translation. In 16:12 the disciples will understand the meaning. (See: [[rc://en/ta/man/translate/figs-metaphor]])