The Science Behind Yeast Harvesting: Strain, Storage, and Optimal Conditions

Yeast, a microscopic fungus, plays a crucial role in the food and beverage industry, particularly in baking and brewing. The process of yeast harvesting, which involves the collection, storage, and propagation of yeast, is a fascinating blend of biology and technology. This article delves into the science behind yeast harvesting, exploring the strains commonly used, the optimal conditions for storage, and the length of time yeast can be kept in a petri dish.

Yeast Strains

There are hundreds of yeast strains, each with unique characteristics and applications. However, the most commonly harvested strain is Saccharomyces cerevisiae, used in baking, brewing, and winemaking. This strain is favored for its ability to ferment sugars quickly and efficiently, producing carbon dioxide and alcohol in the process.

Harvesting Process

Yeast harvesting begins with propagation, where a small amount of yeast is grown in a nutrient-rich medium. This is typically done in a laboratory setting under sterile conditions to prevent contamination. The yeast is then transferred to a larger vessel where it continues to grow and multiply. Once the yeast reaches the desired density, it is harvested. This is usually done by centrifugation, a process that separates the yeast cells from the liquid medium.

Storage Conditions

Once harvested, yeast must be stored under specific conditions to maintain its viability. The optimal storage temperature for yeast is 4°C (39.2°F), which slows down metabolic activity and prolongs the yeast’s lifespan. It’s also crucial to store yeast in a medium that provides the necessary nutrients and maintains an appropriate pH level. This often involves suspending the yeast in a solution of water and glycerol.

Yeast in a Petri Dish

Yeast can be stored in a petri dish, typically on a solid agar medium. Under optimal conditions, yeast can survive in a petri dish for several weeks. However, for long-term storage, it’s better to store yeast in a glycerol solution at -80°C (-112°F). This method, known as cryopreservation, can preserve yeast for years without significant loss of viability.


The science behind yeast harvesting is a complex yet fascinating field, combining elements of microbiology, chemistry, and technology. Understanding this process is crucial for industries that rely on yeast, such as baking and brewing. By maintaining optimal conditions and using appropriate storage methods, yeast can be harvested and preserved effectively, ensuring a consistent supply for various applications.