What two things would make the yeast stop working properly?

Two factors that can inhibit yeast activity are temperature and the presence of high concentrations of sugar. Yeast thrives within a specific temperature range, typically between 70°F and 100°F (21°C to 38°C); temperatures outside this range can slow down or kill the yeast. Additionally, excessive sugar can create an osmotic pressure that dehydrates yeast cells, preventing them from fermenting effectively.