Beer styles and yeast behavior — what yeast type defines ale fermentation? Ales are produced by fermentation led primarily by which yeast behavior/class at warmer temperatures?

Introduction / Context:
Ale and lager differentiation hinges on yeast physiology and fermentation temperature. These factors influence ester formation, flavor intensity, and maturation requirements.

Given Data / Assumptions:

• Ale fermentation typically occurs at approximately 18–22°C.
• Yeast tends to rise and collect as a foam “krausen.”
• Style goal: expressive esters and fuller body in many ale types.

Concept / Approach:

Top-fermenting strains, primarily Saccharomyces cerevisiae, dominate ale production. Their buoyant flocculation and metabolic profile at warmer temperatures result in characteristic aroma compounds that define ale styles from pale ales to stouts.

Step-by-Step Solution:

Verification / Alternative check:

Brewing references and yeast producer datasheets list ale strains as top-fermenting S. cerevisiae with suitable temperature ranges and flavor profiles.

Why Other Options Are Wrong:

Bottom yeast (option b) defines lagers. “Either” (option c) obscures the style-defining distinction. “Middle yeast” (option d) is not standard terminology. Acetobacter (option e) is spoilage bacteria producing acetic acid.

Common Pitfalls:

Assuming all beers use the same yeast—strain selection is the backbone of style creation.

Final Answer:

Top yeast