Yeast, a fungus, is one of the most crucial ingredients in the baking world; without it, it would be impossible to make breads and a variety of other pastries. There are two types of yeast, fresh and dry. Fresh yeast is especially finicky, in that it requires very specific conditions to grow. Under the right conditions though, yeast can multiply very quickly.
Yeast requires a very specific temperature to multiply. Ideally, yeast should be exposed to an environment that is between 25.6 and 26.7 degrees Celsius. Depending on whether the temperature of the water that the yeast is placed in is higher or lower, the growth of the yeast will be faster or slower. Yeast will not grow at 40 degrees and grows very slowly in the 50 degree range. In water that is warmer than 120 degrees, the yeast will not grow at all, because it will be accidentally killed.
Moisture is the main component necessary for the growth of yeast. The more moist the environment, the better and faster the multiplying of the yeast will be. In the case of baking bread, you start out placing the yeast in warm water. This is because the wetness of the environment will very quickly trigger the growth of the yeast. This is necessary, as a bread dough that is too dry will take a very long time to rise, since the yeast did not multiply as quickly or as well.
Yeast, being a living microorganism, requires food. When in a moist, warm environment, yeast feeds on sugar and then multiplies. Yeast may also convert starch to sugar for its food. This latter process is necessary for sugar-free breads, such as French bread. To make yeast multiply more quickly, add sugar. This is why the first step of baking most bread is to add a teaspoon of sugar into the warm water in which the yeast is placed. Conversely, salt slows down the growth of yeast.
The Process of Multiplying
The multiplying of yeast is a very specific process. It starts off with one healthy yeast cell. When this vigorous yeast cell is placed in an environment of the right conditions, it will reproduce by multiplying itself. Then, these new yeast cells reproduce and continue the process. Yeast can start off as a single cell and ultimately grow into tons of yeast. By the end of the process, it will have multiplied 5 to 8 times, creating over three generations and around 60,000 gallons of yeast.