# Brewer’s yeast (Saccharomyces cerevisiae)

**Saccharomyces cerevisiae**

**Known today as.** The single-celled fungus of bread, beer, and wine.

Kind: Fungus

## What was it used for?

Leavening, fermentation, and in old medicine a poultice for sloughing ulcers.

## What does modern science say?

A source of B vitamins, and the workhorse of genetics and of modern drug manufacture, including insulin.

## Pharmacognosy and toxicology

- **B vitamins**: 
- **beta-glucan**: 

**Mechanism.** Very rich in the B vitamins, except B12; the live yeast *Saccharomyces boulardii*, a strain of it, prevents antibiotic-associated and travellers’ diarrhoea in trials and is used against acute diarrhoea.

**Dose.** Fungaemia in the gravely ill given the live yeast.

**Standing.** *S. boulardii* is made industrially and used clinically as a medicine.

## What lore surrounds it?

Louis Pasteur showed in the 1850s that alcoholic fermentation was the work of living yeasts; in 1876 he wrote of the “organised and living ferments” found in the previous twenty years.

## Sources

- Pasteur, L. (1876). *Études sur la bière*.
- Wikipedia, “Saccharomyces cerevisiae,” en.wikipedia.org (read 2 October 2026).
- Wikipedia, “Yeast,” en.wikipedia.org (read 2 October 2026).
- Wikipedia, “Louis Pasteur,” en.wikipedia.org (read 2 October 2026).
- Felter, H. W., and Lloyd, J. U. (1898). *King’s American Dispensatory*, “Cerevisiae Fermentum.—Beer Yeast.” Ohio Valley Co.
- Wikipedia, “Beta-glucan,” en.wikipedia.org (read 2 October 2026).
- McFarland, L. V. (2010). “Systematic review and meta-analysis of *Saccharomyces boulardii* in adult patients.” *World Journal of Gastroenterology* 16.

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*Brewer’s yeast.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-03. The Thinking Press. https://thethinkingpress.org/materia-medica/brewers-yeast

Historical description, not medical advice.