To deactivate dry yeast, there are a few methods you can use. One method is to dissolve the yeast in water and then subject it to heat. This can be done by first dissolving the yeast in four times its weight of water. For example, if you have 1 gram of yeast, you would dissolve it in 4 grams of water.
Once the yeast is dissolved in water, let it sit for about 10 minutes or so. This allows the yeast to fully hydrate and become active. During this time, you can gently stir the mixture to ensure all the yeast is fully dissolved.
After the hydration period, you can choose to either microwave the yeast or mix it with additional boiling water. The objective here is to bring the mixture above the temperature that would kill the yeast, thus breaking its cell walls and deactivating it.
If you choose to microwave the yeast, transfer the yeast-water mixture to a microwave-safe container. Place the container in the microwave and heat it on high for a short burst, around 10-15 seconds. Check the temperature of the mixture after each burst to ensure it doesn't exceed the yeast's tolerance level. Repeat this process until the temperature of the mixture reaches around 140°F (60°C). This temperature is generally considered to be sufficient in deactivating the yeast.
Alternatively, you can mix the yeast-water mixture with additional boiling water. This method is especially useful if you don't have access to a microwave. Simply add boiling water to the yeast-water mixture, stirring gently to combine. Continue adding boiling water until the temperature reaches around 140°F (60°C).
It's important to note that the exact temperature and time required to deactivate the yeast may vary depending on the specific strain of yeast used. Some yeast strains may be more heat-resistant than others. Therefore, it's a good idea to consult the manufacturer's instructions or do some research to determine the optimal deactivation conditions for your specific yeast strain.
In my personal experience as a brewer, I have found that deactivating dry yeast is an essential step when reusing yeast from previous batches. By deactivating the yeast, you can ensure that any remaining viable yeast cells are rendered inactive, preventing them from fermenting any new batches of beer unintentionally.
Deactivating dry yeast can be achieved by dissolving the yeast in water and subjecting it to heat. Whether through microwave or boiling water, the goal is to bring the mixture above the yeast's tolerance temperature to break its cell walls and deactivate it. Remember to adjust the temperature and time based on the specific yeast strain being used.