Why does the traditional yeast you buy in store for making bread say to refrigerate after opening?

Traditional yeast, also known as active dry yeast, needs to be refrigerated after opening for several reasons:

* To slow down yeast activity: Yeast is a living organism, and it continues to metabolize and reproduce even after you purchase it. Refrigeration slows down these processes significantly, extending the yeast's lifespan.

* To prevent moisture absorption: Yeast is sensitive to moisture, and exposure to air can cause it to absorb moisture and become inactive. Refrigeration helps to minimize moisture absorption and keep the yeast dry.

* To protect against contamination: Refrigeration creates a cold environment that is less hospitable to bacteria and other microorganisms that could contaminate the yeast.

* To ensure consistent performance: Refrigerated yeast remains more stable and consistent in its performance, making it more reliable for baking.

However, some types of yeast don't need refrigeration:

* Instant yeast: This type of yeast is designed to be used directly from the packet and doesn't require rehydration. It's usually more tolerant of warmer temperatures and doesn't need to be refrigerated.

* Active dry yeast in a vacuum-sealed package: This type of yeast is sealed in a protective environment that prevents moisture and contamination. It can typically be stored at room temperature for a longer time.

In summary: Refrigerating traditional active dry yeast after opening is essential to maintain its quality, prevent moisture absorption and contamination, and ensure its consistent performance.