One important component of bread is yeast. Yeast is a tiny, one-celled organism whose only job is to eat sugars (carbohydrates) and produce carbon dioxide gas along with alcohol. It is the carbon dioxide gas that yeast produces that causes bread to rise. If you intend to make bread, you have to keep yeast. The best way to keep yeast cells alive between acquiring them and baking your bread depends on what kind of yeast you have.
Store yeast at room temperature. Active dry yeast can be stored at room temperature for up to four months after being opened, or until the expiration date stamped on the package, whichever comes first. You can also store bread machine yeast and instant yeast this way.
Store yeast in the refrigerator. Some yeasts, such as fresh yeast (not dried), survive longer if they are kept in the fridge. Fresh yeast will survive for up to four months in the fridge, though it will lose its potency over time.
Grow your own starter yeast. A yeast starter is a mixture of yeast, flour and water kept in the fridge. Make starter yeast by mixing your yeast with warm water and flour, then storing it in an airtight container in the fridge. Leave room in the container for the gas that will be released by your feeding yeast.
Once a week, take your starter out of the fridge and allow it to warm to room temperature. Once it has warmed up, remove about 75 per cent of your mixture from the container (you can use this yeast in a recipe if you are prepared to or just toss it). Then replace what you took out with equal parts warm water and flour.
You must allow the starter yeast mixture to come to room temperature before adding the warm water because adding warm water directly onto cold yeast might shock and kill your starter. Once you have mixed it all together, put it back in the fridge for another week.
You can repeat these steps to keep your yeast alive indefinitely.
Unless you are doing a starter, keep your yeast dry until you are ready to use it.
Yeast starters can go bad. If you notice a nasty smell or pink/orange colour to your starter, do not use it. Throw the whole batch out and start over because your starter has either died or is contaminated. Do not eat uncooked bread yeast.