Short answer
Yes. Yeast is a single-celled fungus, so baker's yeast, nutritional yeast and yeast extract are halal. Bread and sourdough are halal too: the small amount of alcohol that forms while the dough rises mostly bakes off and cannot intoxicate. Brewer's yeast recovered from beer making is a separate question.
Yeast is pure and halal. Natural traces of alcohol produced by fermentation in bread and similar foods, which cannot intoxicate, do not affect the ruling.
The four schools agree on this.
Explanation
Yeast is a living micro-organism, a kind of fungus. In dough it feeds on sugars and releases carbon dioxide, which makes bread rise, along with a little alcohol. Most of that alcohol evaporates in the oven, and none of it could ever make anyone drunk. The four schools agree that bread is halal.
- Baker's yeast (fresh, dried or instant): halal.
- Sourdough starter: wild yeast and bacteria grown in flour and water. Halal.
- Nutritional yeast: deactivated yeast grown on molasses or sugar. Halal.
- Yeast extract: in spreads, stock cubes and crisps. Halal, though check the product for other ingredients.
- Brewer's yeast supplements: some are grown for the purpose and are halal; some are recovered from beer making. Many muftis advise choosing ones that are grown for supplements or certified halal.
The general rule is that a natural trace of alcohol from fermentation, in food that cannot intoxicate, is not counted (see how much alcohol is haram). That is why bread, yoghurt, ripe fruit and kefir are all halal.
What can make a baked product doubtful is not the yeast but other ingredients: lard, butter flavourings with alcohol, L-cysteine from non-halal sources, or glazes made with gelatin. Check the label or use the halal food checker.
The evidence
Quran, Surah Al-Baqara 2:168
يَٰٓأَيُّهَا ٱلنَّاسُ كُلُوا۟ مِمَّا فِى ٱلْأَرْضِ حَلَٰلًۭا طَيِّبًۭا وَلَا تَتَّبِعُوا۟ خُطُوَٰتِ ٱلشَّيْطَٰنِ ۚ إِنَّهُۥ لَكُمْ عَدُوٌّۭ مُّبِينٌ ﴿١٦٨﴾
O mankind, eat from whatever is on earth [that is] lawful and good and do not follow the footsteps of Satan. Indeed, he is to you a clear enemy.
Lawful, wholesome food is to be eaten.
Where the ruling is recorded
- al-Hidaya, Kitab al-Ashriba. What is forbidden is what intoxicates; foods that cannot intoxicate are not included.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Hazr wa al-Ibaha. Things are permitted by default unless evidence shows otherwise.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.