Baker's yeast propagation medium: The most commonly used medium for culture build-up and production of baker's yeast consists of which components?

Introduction / Context:
Industrial production of baker's yeast uses large aerobic fermenters and economical substrates. Media design must support high cell yields, maintain vitality, and control by-products such as ethanol. Understanding the standard formulation is fundamental in food and industrial microbiology.

Given Data / Assumptions:

• Feedstocks should be low-cost and rich in fermentable sugars.
• Trace minerals and salts are required for enzyme cofactors and osmotic balance.
• The question seeks the broad component list used worldwide.

Concept / Approach:
Cane or beet molasses provides sucrose, minerals, vitamins, and growth factors, making it the dominant carbon source. However, additional minerals (e.g., magnesium, phosphate) and salts (e.g., ammonium sulfate as nitrogen, phosphate buffers) are supplemented to optimize biomass yield and prevent nutrient limitations during fed-batch growth.

Step-by-Step Solution:
Identify molasses as the economical sugar source for yeast biomass. Recognize the need for mineral and salt supplementation for balanced growth. Reject options lacking supplements or substituting lactose (S. cerevisiae lacks efficient lactose use). Choose “Molasses, minerals, and salts.”

Verification / Alternative check:
Process manuals describe molasses with ammonium salts, phosphates, magnesium, and vitamins, plus antifoam and pH control, as the standard recipe for baker's yeast propagation.

Why Other Options Are Wrong:

• Molasses only / Molasses and minerals: Incomplete without proper salts and nitrogen sources.
• Molasses and lactose: Lactose metabolism is poor in typical baker's yeast strains.
• Refined sucrose without minerals: More costly and nutritionally incomplete.

Common Pitfalls:
Assuming molasses composition alone suffices; variability in molasses requires precise mineral and nitrogen supplementation.

Final Answer:
Molasses, minerals, and salts form the common production medium.