Industrial fermentation (baker's yeast): The manufacture of baker's yeast for leavening bread primarily involves which microorganism?

Introduction / Context:
Baker's yeast is the cornerstone of bread making and many leavened baked goods. The organism used must produce carbon dioxide efficiently, be safe for food use, and withstand industrial propagation, harvesting, and storage. This question tests recognition of the correct species employed worldwide in bakeries and yeast factories.

Given Data / Assumptions:

• The target product is baker's yeast used to leaven dough via CO2 production from sugars.
• Options include yeasts and non-yeast microbes, some of which are used in other foods.
• Focus is on the organism predominantly propagated at industrial scale for bread.

Concept / Approach:
Saccharomyces cerevisiae is the standard organism for baker's yeast. It rapidly metabolizes fermentable sugars (glucose, fructose, maltose) via glycolysis and fermentation, producing CO2 that expands dough. It also imparts desirable aroma compounds. Industrial strains are selected for high biomass yield in aerobic fed-batch culture and robust performance in dough.

Step-by-Step Solution:
Match the product (baker's yeast) with the conventional production organism. Note that S. cerevisiae is optimized for CO2 generation and baking functionality. Exclude organisms mainly used for yogurt starters (Streptococcus thermophilus) or spoilage/enzymes (Bacillus subtilis). Select Saccharomyces cerevisiae as the correct answer.

Verification / Alternative check:
Commercial yeast packages and technical datasheets list S. cerevisiae for instant, active dry, and compressed forms. Brewing and wine strains are also S. cerevisiae variants, underscoring its food safety and performance record.

Why Other Options Are Wrong:

• Streptococcus thermophilus: Dairy starter bacterium for yogurt; not a leavening yeast.
• Bacillus subtilis: Produces enzymes; certain strains cause rope spoilage in bread.
• None of these: Incorrect because S. cerevisiae is correct.
• Candida utilis: Used for SCP/biomass and flavor enhancers, not standard baker's yeast.

Common Pitfalls:
Confusing general "yeast" with any fungus; only specific Saccharomyces strains give reliable baking performance and gas production.

Final Answer:
Saccharomyces cerevisiae is the organism used to manufacture baker's yeast.