Yeast Likes and Dislikes

Being a living thing, yeast has needs if it’s going to survive in the kitchen or anywhere else. Obviously it needs food (simple sugars) and water. Beyond that it has temperature requirements.

Yeast grows and produces CO2 most prodigiously at about 92 degrees Fahrenheit. It slows to the point of dormancy at 40 degrees and goes completely dormant below the freezing point of water. If it’s frozen for long, some of its population dies, about 10% per month. Similarly, yeast activity starts to slow down when the temperature gets over about 100 degrees Fahrenheit and stops completely at 135 degrees, at which point it dies.

Being made up of microbes yeast is also sensitive to, shall we say, “pollutants” in its environment. It likes — and indeed grows best in — environments containing small amounts of sugar and salt. Too much of either one of those will kill it, however. Sugar because it binds up water and starves it, salt because it extracts moisture directly from it via osmosis. Yeast has similar relationships with alcohol and acid.

Knowing these basic rules is handy for the baker, as it allows him or her to manipulate yeast to create a variety of interesting and delicious effects.