Meet the Microbes
What are the three main types of microorganisms discussed in our fermentation lesson?
Bacteria, yeast, and mold
What two basic ingredients are combined to begin making a sourdough starter?
Flour and water.
What gas produced by yeast causes bread dough to rise?
Carbon dioxide (CO₂)
What fermented dairy food is made when bacteria convert milk sugar into lactic acid?
Yogurt
What is one thing microbial cells need to grow and reproduce?
Nutrients, available water, or suitable environmental conditions such as temperature and acidity.
Which two types of microorganisms are classified as fungi?
Yeast and mold
What two types of microorganisms work together in a sourdough starter?
Wild yeast and lactic acid bacteria.
What do yeast cells consume to obtain energy during fermentation?
Sugars, such as glucose.
What substance produced by bacteria gives yogurt its tangy flavor?
Lactic acid
Why does a sourdough starter need to be fed regularly?
Feeding provides new nutrients that help sustain the yeast and bacteria living in the starter.
What is the main difference between bacterial cells and yeast cells?
Bacteria are prokaryotic and do not have a membrane-bound nucleus. Yeast cells are eukaryotic and have a nucleus.
What does SCOBY stand for?
Symbiotic Culture of Bacteria and Yeast.
What is the name of the enzyme in flour that helps break starch into smaller sugars?
Amylase
What fermented beverage is made from sweetened tea using a culture of bacteria and yeast?
Kombucha
Why does sourdough bread have a tangier flavor than ordinary bread made with commercial yeast?
Lactic acid bacteria produce acids during fermentation that contribute to sourdough's distinctive tangy flavor.
What are the branching, thread-like structures that make up mold called?
Hyphae
Where do the wild yeast and bacteria in a sourdough starter come from if we do not add store-bought yeast?
They occur naturally on grains and in flour, with microorganisms from the surrounding environment also potentially contributing.
During alcoholic fermentation, yeast converts glucose into which two main chemical products?
Ethanol and carbon dioxide.
What causes the holes found in Swiss cheese?
Carbon dioxide gas produced by bacteria called Propionibacteria during fermentation.
In our bread experiment, why might bread begin to taste sweeter after chewing it for a while?
Saliva contains the enzyme salivary amylase, which breaks starch into smaller sugars, including maltose.
Why is it important to know which microorganisms are present in food rather than simply knowing that microorganisms are present?
Different microorganisms have different effects. Some help produce fermented foods, some cause spoilage, and others can cause illness. We need to know which microorganisms are present and whether conditions favor their growth.
Why is a sourdough starter considered a living ecosystem rather than just a mixture of ingredients?
Because it contains multiple populations of living microorganisms, including yeast and bacteria, that interact with one another and their environment. They consume nutrients, produce substances, and sometimes benefit from one another's activities.
Why must the number of carbon, hydrogen, and oxygen atoms be the same before and after the fermentation reaction?
Because of the law of conservation of mass. Atoms cannot be created or destroyed in a chemical reaction; they are rearranged into new molecules.
Why is the mold used to make cheeses such as Brie or blue cheese different from mold that unexpectedly grows on ordinary food?
Cheesemakers intentionally use selected molds under controlled conditions to develop specific flavors and textures. Unexpected mold on ordinary food has not been selected or controlled and should not be assumed safe.
Both food spoilage and fermentation involve microorganisms. What is the important difference between them?
During controlled fermentation, we encourage selected microorganisms to grow and produce desired changes in food, such as acids, flavors, or gases. During spoilage, unwanted microorganisms cause food to deteriorate.