Yeast that has been packaged for storage in a refrigerator is typically not stored with any food for the yeast because it is intended to stay dormant. When the yeast warms up to room temperature it will become active, and during this time the cell population will increase slightly, however it quickly runs out of energy reserves. The bacteria, on the other hand, will feed on the dead yeast cells, and continue to propagate even after the yeast have stopped growing.
During a test of two strains of yeast, WLP004 and WLP566 It was noted that within the first 12 hours both strains grew in population. Initial inspection of the yeast when it was removed for the refrigerator showed no signs of bacteriological activity, but after only 12 hours pairs of bacteria were observed indicating cell growth.