Storage conditions greatly influence the viability of active dry yeast products, according to research at Kansas State University.
In sampling products, they found highly variable concentrations of viable cells within and across products. And, high-temperature storage was a particular problem.
"Even when samples were stored in an airtight, ambient-humidity environment, the high-temperature storage condition (40 degrees C or 104 degrees F) decreased viable cell counts of (active dry yeast) products by approximately 90 percent per month," they wrote.
In this month's edition of the Journal of Dairy Science, researchers suggest storing these products at cool temperatures and using them as quickly as possible.