Which of the following is known as bottom fermenting yeast?

• A. Saccharomyces cerevisiae
• B. Saccharomyces boulardii
• C. Saccharomyces carlsbergensis
• D. Saccharomyces pastorianus

Answer: (C)

Bottom-fermenting yeast are the lager yeasts that work best at cooler temperatures and tend to settle to the bottom as fermentation progresses, yielding the clean, crisp character typical of lagers. Saccharomyces carlsbergensis has historically been identified as this bottom-fermenting lager yeast, commonly associated with cooler fermentation and the bottom‑settling behavior. By contrast, Saccharomyces cerevisiae is the classic top-fermenting ale yeast, which ferments warmer and tends to rise to the surface. Saccharomyces boulardii is a probiotic yeast not used in brewing, and Saccharomyces pastorianus is the modern name used for lager yeast in many texts (a related bottom-fermenting yeast). The option that matches the bottom-fermenting description, given the traditional labeling, is Saccharomyces carlsbergensis.