Brewing microbiology — “Sarcina sickness” (ropey, turbid, sour beer defect) is caused by which organism historically known as a sarcina-former?

Introduction / Context:
Beer spoilage can arise from wild yeasts and lactic acid bacteria. One classic defect is “Sarcina sickness,” historically associated with micrococci or tetrad-forming lactic bacteria that produce turbidity, viscosity (ropiness), and acidity changes in beer. Correctly identifying the culprit aids in hygiene control and pasteurization decisions.

Given Data / Assumptions:

• The term “Sarcina” reflects cell arrangement (packets/tetrads).
• We are dealing with a beer defect (not primary fermentation).
• Organisms listed include brewing yeasts and bacteria.

Concept / Approach:
Pediococcus cerevisiae (often spelled Pediococcus) is a tetrad-forming lactic acid bacterium historically implicated in Sarcina sickness. It produces diacetyl and exopolysaccharides leading to buttery off-flavor and ropey textures. Saccharomyces yeasts listed here are normal brewers’ yeasts, not the typical cause of Sarcina sickness, while the “Zygomonas” distractor (properly Zymomonas) is more relevant to other carbohydrate fermentations.

Step-by-Step Solution:

Verification / Alternative check:
Brewery QA manuals note Pediococcus and Lactobacillus as key beer spoilers; Pediococcus is explicitly linked to ropiness and diacetyl faults characteristic of “Sarcina sickness.”

Why Other Options Are Wrong:

• S. cerevisiae and S. carlsbergensis: primary fermenters; not the usual cause of Sarcina defect.
• “Zygomonas anaeroium”: spelling aside, Zymomonas is not the classic agent of this beer defect.

Common Pitfalls:
Relying on final pH alone; diacetyl and rope formation are better indicators of Pediococcus-related spoilage.

Final Answer:
Pedicoccus cerevisiae