In traditional Jain view, yeast is not considered Jain-friendly.

Simple explanation:

• Yeast is a living organism (a type of fungus, one-sensed life).
• Using yeast means intentionally cultivating and then killing countless tiny living beings, especially in baking, brewing, and other fermentations.
• Because Jain dharma teaches ahimsa toward even the smallest life forms, many Jains:

- Avoid yeast itself (nutritional yeast, baker’s yeast, brewer’s yeast, etc.). - Avoid yeast-based breads and other yeast‑fermented foods in daily life, and especially during Paryushan/Das Lakshan. ( jainknowledge.com)

Both Śvetāmbara and Digambar traditions agree in principle on avoiding unnecessary harm to micro‑organisms. Practice can vary by family and region, but from a strict Jain standpoint, yeast is not accepted.

So:

• If you are trying to follow stricter Jain food rules, you should treat yeast and yeast-based products as non-Jain and avoid them.