Yeast

Yeast is a single-celled microorganism classified as a member of the fungus kingdom. The most common species, Saccharomyces cerevisiae, is essential for baking and brewing.

Description of what it is like

Individually microscopic, yeast colonies appear as a creamy, beige, or off-white paste or powder. It has a distinctive, slightly sour or bready smell.

Origin and where to find it

• Environments: Naturally occurs on the skins of sugar-rich fruits (grapes, apples), berries, and in the soil.
• Signs: Whitish bloom on fruits; spontaneous fermentation of sugary liquids.
• It is a natural material.

Minimum processing required

• Collection: Harvesting from fruit skins or established cultures (sourdough starter).
• Cultivation: Feeding with flour and water or sugar water to increase biomass.
• Drying: For long-term storage (dormancy).

Tools needed to work on it

• Containers: Jars or bowls for culturing.
• Cloth: To cover cultures while allowing airflow but keeping bugs out.
• Warmth: Requires moderate temperatures (20-30°C) to thrive.

Common forms of use

• Leavening Agent: In bread making, it produces CO2 which makes the dough rise.
• Fermentation Starter: In brewing and winemaking, it converts sugars into alcohol.
• Nutritional Yeast: Deactivated yeast used as a food supplement (rich in B vitamins).

Possible substitutes

• Chemical Leaveners: Baking soda and acid (for baking).
• Wild Fermentation: Relying on airborne yeast (less predictable).

Limitations and common failures

• Temperature Sensitivity: Dies at high temperatures (>50-60°C); dormant at low temperatures.
• Contamination: Vulnerable to mold or bacteria if not maintained properly.
• Food Source: Requires sugar/starch to survive.

Risks and safety

• Spoilage: Can spoil food if unwanted fermentation occurs.
• Allergies: Some people are sensitive to yeast.
• CO2 Production: Produces gas which can build pressure in sealed containers.

Related materials

• Sugar: Primary food source for yeast.
• Water: Medium for yeast activity.
• Alcohol: Metabolic byproduct of yeast.