Yeast: The Effect of Temperature and Ingredients
This video was so fun to make! One of my dear friends has a microscope that she can take pictures with. She also happens to be an amazing photographer! Check her out on instagram at @themechanicalstage.
There are a few pictures under the microscope at the beginning of the video that show a lot about how yeast works.
The first picture shows yeast right after it has gotten hydrated.
The next few pictures are of the dried yeast. Dry yeast is dried in a variety of ways that allow it to become active at different rates. When it is dried more quickly, the yeast takes a longer time to activate. When it is dried more gently, it activates the yeast more quickly. This is because the yeast granules are dormant yeast that can be activated surrounded by a shell of dead yeasts. The more harshly the yeast is dried, the more dead yeast there are surrounding it. Also, the longer dried yeast sits around, the more dead yeast there are. If your yeast is old, I recommend testing it before going through the process of making bread. Making bread is a 3 hour process, but in about 15 minutes, yeast in warm water with sugar will start bubbling, which lets you know it is ready to go. If it is slow to activate, you can add more yeast, or your bread will take longer to rise, which may or may not be a problem for your schedule.
The final microscope picture shows the air bubbles created by the yeast as it works. These bubbles, in yeast breads, allow for rise. But since the yeast is living, it needs to rise before it goes in the oven or the yeast dies before the rise happens. This is why you need yeast breads to proof in their pan for a bit. There is a bit of rise that happens in the oven before the temperature is too extreme for the yeast. This is called oven spring.
Yeast is a super cool food. It allows you to perform science in your kitchen. This video is an adaptation of an experiment that I have done with my students many times, and it shows some properties of yeast so well. I started with 5 jars and labeled them using my label maker (because label makers are life) The contents of each jar are:
Warm water (about 110°F)+Yeast
Warm water+yeast+sugar
Warm water +yeast+salt
Cold water + yeast
Boiling water +yeast
As the teacher, I knew exactly what would happen with this experiment, but it was so cool watching kids get excited about the blob that would form.
The first jar: warm water and yeast, would move a bit, kind of like me before I’ve had my coffee. Yeast requires warm water because it needs to both rehydrate and also have a warm temperature to begin moving around. Yeast is a living organism, after all. It doesn’t, however, have anything to eat, hence the coffee reference. It can move, but the reaction that you are looking for in yeast, rise, will not happen without food.
The Second jar: warm water, yeast, and sugar, is the sweet spot for yeast. It has water to activate, but also some food. This combo allows a process called fermentation . Fermentation happens when yeast eats food (sugar) and expels carbon dioxide and alcohol. The alcohol is what creates that “yeast roll” smell we all know and love .
The Third Jar: warm water, yeast, and salt shows another ingredient function, salt is needed in yeast breads to control yeasts growth a bit. Without it, your bread will rise so much that it can collapse and not be stable. You can, however, have too much salt. I always bloom my yeast by warming the water to about 110°F and adding all the yeast and sugar called for. I let that sit for a bit, add most of the flour to the kitchenaid bowl and then add salt on top of the flour. Salt will kill yeast if it comes in direct contact, but it just slows it if added to the recipe as a whole. You can’t leave salt out of yeast breads because your bread will end up tasting something like that putty you put posters on the wall with and your dough will rise out of control.
The Fourth Jar: cold water and yeast. This jar demonstrates the importance of water being warm. Think of those cold mornings when you don’t warm your car up and that is pretty much the way yeast reacts to water. It’s alive, but it has no motivation to do anything until it warms up.
The final jar is boiling water and yeast. This one seems obvious, but if you pour boiling water on any living thing, it is not going to do very well. Boiling water in this case kills yeast before it has a chance to do anything. While most of the time, we will not be using boiling water, it is a severe representation of how extreme temperatures can affect living organisms.
I have 2 methods for temperature when working with yeast.
I usually mix it with the warm water (About 110°F-120°F) and sugar before adding flour to give it a little jump start. I even do this when using my bread machine. This makes sure the yeast has a fighting chance of waking up and thriving to make the best bread possible.
If I add the yeast directly to flour, I use warmer water (about 130°) because the flour will cool the water down a bit. I try to avoid adding dry yeast to dry flour when at all possible.
Yeast breads can be tough to make, but the final product is so good that you will feel very accomplished when you finish. It is relaxing and useful, and I love things that are both relaxing and useful!