Can you name a type of fungus that is important in the diet of humans? No! I am not talking about Mushrooms. However, there is a fungus that is arguably more common in human food and that’s known as Yeast.
Yeast
Yeast is a type of fungus. Like all living things, it respires. Yeast can respire anaerobically. So without oxygen another word for this is fermentation.
Anaerobic Respiration of Yeast/ Fermentation
When yeast respires anaerobically, this is what happens, the yeast uses glucose as a fuel to produce carbon dioxide, ethanol or alcohol and energy. The energy that is produced by fermentation is useful to the yeast, as the yeast then uses this for metabolic processes such as growth.
However, the carbon dioxide and ethanol are waste products for the yeast but useful products for humans. One way humans use the fact that yeast fermentation produces carbon dioxide is in bread making.
Process
Yeast is mixed with flour, sugar, salt and water to make dough. The yeast then respires anaerobically producing carbon dioxide. Bubble of carbon dioxide are trapped in the dough of the bread. This makes the bread rise, resulting in a lovely soft bouncy loaf of bread yum.
Why do you think sugar is added to the dough?
Sugar is added because it is the fuel for respiration. No sugar would mean, the yeast is unable to respire. Respiring yeast, produces alcohol.
So why don't people get drunk when eaten bread?
When the bread is baked, the yeast is killed and the ethanol evaporates.
Can evaporating ethanol help you think of another use for yeast?
Yeast is also used in the production of beers and wines. This time useful waste material is "ethanol" to make beer. Barley grains are soaked in water to cause them to germinate, this is known as malting. The malted grain is ground, which activates enzymes that turn the starches in the grain into sugars. The mashed barley is then boiled and hops are added to give flavor. As the mixture cools, yeast is added. The yeast fungus consumes the sugars from the grains and starts to produce carbon dioxide and alcohol. The beer is usually filtered and the yeast is recycled to make more beer.
So we've had yeast to make bread and barley hops and yeast to making beer and what about wine?
Why do you think bubbles are visible? why do you think there is an airlock in the neck of the Demijohn?
The bubbles show that carbon dioxide is being produced as the yeast respires anaerobically. The airlock has two purposes, it allows the carbon dioxide out of the demijohn so that it doesn't explode. It also prevents air from entering the demijohn ensuring the yeast continues to respire anaerobically and is not contaminated by other microorganisms.
Hopefully, you now agree that yeast is a humans have learnt to
use to our advantage not only is mushrooms on our pizzas but for making bread
beer and wine.